JOURNAL OF
MECHANICAL ENGINEERING
STROJNIŠKI VESTNIK
Strojniški vestnik - Journal of Mechanical Engineering ISSN 0039-2480
Editorial Office
University of Ljubljana Faculty of Mechanical Engineering Journal of Mechanical Engineering Aškerčeva 6
SI-1000 Ljubljana, Slovenia Phone: 386-(0)l-4771 137 Fax: 386-(0)l-2518 567 E-mail: info@sv-jme.eu http://www.sv-jme.eu
Founders and Publishers
University of Ljubljana
-	Faculty of Mechanical Engineering University of Maribor
-	Faculty of Mechanical Engineering Association of Mechanical Engineers of Slovenia Chamber of Commerce and Industry of Slovenia
-	Metal Processing Association
Editor
Andro Alujevič
University of Maribor, Faculty of Mechanical Engineering
Smetanova 17, SI-2000 Maribor, Slovenia
Phone: +386(0)2-220 7790, E-mail: andro.alujevic@uni-mb.si
Publishing Council
Jože Duhovnik, chairman
Niko Samec, vice chairman
Ivan Bajsić
Jože Balič
Iztok Golobic
Mitjan Kalin
Aleš Mihelič
Janja Petkovšek
Zoran Ren
Stanko Stepišnik
International Advisory Board
Imre Felde, Bay Zoltan Inst, for Materials Science and Techn.
Bernard Franković, Faculty of Engineering Rijeka
Imre Horvath, Delft University of Technology
Julius Kaplunov, Brunei University, West London
Milan Kljajin, J.J. Strossmayer University of Osijek
Thomas Lübben, University of Bremen
Miroslav Plančak, University of Novi Sad
Bernd Sauer, University of Kaiserlautern
George E. Totten, Portland State University
Nikos C. Tsourveloudis, Technical University of Crete
Toma Udiljak, University of Zagreb
Arkady Voloshin, Lehigh University, Bethlehem
Deputy Editor	Editorial Board
Vincenc Butala	Anton Bergant
University of Ljublj ana, Faculty of Mechanical Engineering	Franci Cuš
Aškerčeva 6, SI-1000 Ljubljana, Slovenia	Matija Fajdiga
Phone: +386(0)1-4771 421, E-mail: vincenc.butala@fs.uni-lj.si	Jože Flašker
Janez Grum
Technical Editor	Janez Kopač
Darko Švetak	Franc Kosel
University of Ljublj ana, Faculty of Mechanical Engineering	Janez Možina
Aškerčeva 6, SI-1000 Ljubljana, Slovenia	Brane Širok
Phone: +386(0)1-4771 137, E-mail: info@sv-jme.eu	Leopold Škerget
Cover plate: The Zoller tool manager system is a system for managing tool components, tool assemblies, machine setup sheets, tool graphics and tool supplier informations. Zoller »smile« is available with Pilot 3.0 software in five different measuring ranges depending on tool length. Compact and easy to operate it may be used for any purpose: machining centers, transfer machines, boring mills, CNC -controlled lathes and for measuring grinding wheels and tools.
Image courtesy of: Cutting conditions laboratory, UM, FME.
Print
Littera Picta, Medvode, printed in 600 copies
Yearly subscription
companies individuals students abroad single issue
100,00 EUR 25,00 EUR 10,00 EUR 100,00 EUR 5,00 EUR
© 2008 Journal of Mechanical Engineering. All rights reserved. SV-JME is indexed in SCI-Expanded, Compendex and Inspec. The journal is subsidized by the Slovenian Research Agency.
Strojniški vestnik - Journal of Mechanical Engineering is also available on http://www.sv-jme.eu, where you access also to papers' supplements, such as simulations, etc.
Contents
Strojniški vestnik - Journal of Mechanical Engineering volume 54, (2008), number 11 Ljubljana, November 2008 ISSN 0039-2480
Published monthly
Papers
Kostanjevec T. Polajnar, A., Sarjaš A.: Product Development Through Multi-Criteria
Analysis	739
Župerl U., Cuš F.: Machining Process Optimization By Colony Based Cooperative Search
Technique	751
Ostojić G., Lazarević M., Stankovski S., Cosić I., Radosavljavić Z: Radio Frequency
Identification Technology Application in Disassembly Systems	759
Maksimović R., Lalić B.: Flexibility and Complexity of Effective Enterprises	768
Brumnik R., Balantič Z.: Reliability and Efficacy of Identification Systems and Supply Chain
Management	783
Ozel K., Sahin M., Akdogan A.: Mechanical and Metallurgical Properties of Aluminium and
Copper Sheets Joined by Cold Pressure Welding	796
Burzić M., Prokić-Cvetković R., Grujić B., Atanasovska I., Adamović Ž.: Safe Operation of
Welded Structure with Cracks at Elevated Temperature	807
Instructions for Authors	817
Paper received: 19.06.2008 Paper accepted: 25.09.2008
Product Development Through Multi-Criteria Analysis
Tomaž Kostanjevec1, , Andrej Polajnar1, Andrej Sarjaš2 1 Faculty of Mechanical Engineering, University of Maribor, 2 Faculty of Electrical Engineering and Computer Science, University of Maribor
The trend regarding the development of sanitary fittings is forecasted by the use of a developed model of multi-criteria analysis. In this analysis a multi-dimensional space is used, which enables the establishment of a time argument in comparison to product parameters. The establishment of product parameters is achieved by means of internal company information and market needs. In this way it is possible to establish an innovative environment for the development of new products.
This paper indicates various ways of dealing with product development, on the basis of which the method of multi-criteria analysis for establishing future trends in product development is acquired. © 2008 Journal of Mechanical Engineering. All rights reserved.
Keywords: sanitary fittings, product development, multi criteria analysis, multi-dimensional space
0 INTRODUCTION
The key moment of any company's strengths lies within essential and sustainable continuous development. Modern companies require constant investment into development. The development of the equipment for product development is also very wide, while the use of such equipment is still not as widespread as it should be [1]. As a line of business, product development has played an important role in production engineering by researches within the global industry experience[2], design and analysis [3] and [4], product design [5] to [8] and creativity used in product development [9].
On the other hand, product development also includes research within the market with regard to customer needs [10], [6] and [11], product positioning and segmentation [7] and [12], product forecasting [13] to [15] and test marketing [16]. A number of applications, marked by different views, led to a deeper understanding of how to join and use the information regarding customers and product engineering in designing, testing, starting and managing new products. To further disclose the contents, methods and applications of the above, more integrative views and papers on the topic of product development were published [17]. The production and engineering precision, combined with the marketing approach, both of which were focused on customer needs and production capability, proved very successful. In parallel with the development of established equipment, researchers discovered the correlation of new product success by establishing the
communication between marketing and production engineering as the most important elements necessary for success [2], [5], [10], [19] and [20]. Organisation processing equipment as are, for example, teams functioning via network [14], quality function development (QFD) and distribution [21], were all developed with the purpose of establishing a closer link between production engineering decision-making and customer needs [22]. New challenges and opportunities are reflected in global markets, global competitiveness, the global spread of engineering knowledge and with communication technologies. The use of multi-criteria analysis with product development represents a new challenge and an opportunity in design research and new product forecasting [23] and [24].
1 THEORETICAL BACKGROUND
In the last decade companies were focused on new product development on the basis of satisfying customer needs. Researchers in the field of marketing were convinced that understanding customer needs and improving the transfer of these needs to product manufacturers was the key to success.
The Kaizen method for continuous improvement helped enhance the understanding of quality in product development with improved reliability [25], with statistical-qualitative control [26], modified experimental design [20] and design for production [27] to [29]. Engineers were certain that a product of higher quality was the key to success [30].
*Corr. Author's Address: Faculty of Mechanical Engineering, Smetanova 17, Maribor, Slovenia, tomaz.kostanjevec@uni-mb.si
Both marketing and production engineering recognised that the time from conception to implementation was of key importance. The awards for the early entrants were excellent, while production engineering went through great losses by working overtime and delays. Customer satisfaction and the time from conception to marketing became the warranty for success and profit.
Both the economic and academic worlds realised that successful product development is a closely related process, which can bypass many compromises. Customer satisfaction, the time from conception to marketing and cost reduction through complete control and quality management are also important factors. However, none of them has been recognised as a warranty for success.
Fig. 1. Alternatives and connections in new product development [16]
Under unchanged conditions a product will prove profitable if it supplies customers with greater satisfaction, is among the leading products in the market, and has low production and development costs. Fig. 1 puts forward researches carried out in the field of equipment and product development methods. These researches should ensure that companies are directed towards new fields by taking into account all the strategic aims presented in Fig. 1. The concept of joint or common dealing of product parameters is included in the conjoint product analysis [13] and
[31].
Researches must prove that various perspectives with all the effective new fields of development are of key importance. If a closer look is taken at only two of the numerous aims in the development of a new product, effectiveness
proves the most essential. QFD can represent the most effective way of supplying customer satisfaction by means of improved communication and coordinating the efforts of the various parties involved in the process of product development. At the same time it is necessary to stress that certain equipment might prove inefficient in saving time in the process from conception to implementation and thus increase development costs.
Most companies see product development as a process of conception and implementation and connect it with production engineering, marketing, production and organisation development. Fig. 2 shows the process that takes place from conception to implementation [16]. It is a set of strengths that influence product development and shed light on opportunities for researches regarding product development.
Fig. 2. Product development: from cognition to implementation
Instead of choosing a 3-year planning cycle it is advisable for companies to adopt a development plan which is checked on a monthly or even weekly basis. For example, a company should have a strategy for dealing with technology and with implementing methods for understanding opportunities that are to be offered to customers by means of offered products, as well as with recognising where demands and expectations are not being fulfilled. Here it is just as important to know how the competition will respond, while the supplier's chain helps and is
involved in the development in order to fulfil customer demands.
Perspectives of marketing, production engineering, designing and manufacturing must be integrated for the needs of product development and show themselves as the basic network of a functional team that supports an effective organisation.
Human resources are important for the inclusion of needs for context and culture organisation understanding, as well as the need for developing human capabilities through training, information technology, and communication on the part of practice. Marketing, engineering and processing equipment enable the process of development from its conception to its implementation and support this process in being effective.
Product development, as shown at the funnel neck in Fig. 2, shows a normal - traditional view, according to which product development generates itself through idea conception and develops further into a number of potential products that are potentially realised. Within the neck presented in Fig. 2a method is adopted -steps of opportunities, identification and idea formation, concept development and choice, detailed selection of design and engineering, testing and implementation [8]. Although the context and individual companies use a slightly different description of the steps, the description of product development in the form of development steps remains more or less the same.
The basic idea of management is that it is less expensive to establish product suitability in the early rather than in later steps, and that every following step might improve the product and its positioning and thus increase its success in the market. Mathematic examples show that such a step process, which is best presented in the form of key steps, proves to be the most efficient in decreasing costs [1].
The neck in Fig. 2 also tries to show the concept of management flow by means of parallel projects that are moving through the funnel neck. However, in the steps, and in the assessment of the work carried out in each step, there is no connection between individual steps, which remains one of the greatest weaknesses of the step process. On the other hand, in the process of continuing product development in the multi-
dimensional method this moment of weakness is smaller.
Often the best strategy for companies is to have a suitable number of parallel projects, since it is in this way possible to implement the project that shows the most profitable future. Fig.2 does not show clearly enough the importance of the real product development process characteristics, since certain steps are often expedited and left out.
For example, with advanced methods, as are user's and same-time design, it is possible to test the design concept already in the early steps of designing and engineering, or to, for example, present ideas already in the concept phase more effectively. Moreover, Fig. 2 does not explicitly include (co-)circumstances of the nature of the whole process [32]. Nowadays many companies use a spiral instead of line development process, since in the former products or concepts move through numerous narrower and narrower steps.
The essential difference between the neck and spiral processes is that the latter is more suitable for higher expectations in the form of a repeating return in the parallel direction through the neck of the shown funnel and leads to improvement. An interesting challenge for research would be to make a comparison of input data in the spiral and the funnel form of the process. Here could be compared which circumstances influence one or the other form of development and which is more suitable.
The process of multi-criteria product analysis also includes product platforms. It has been recognised in numerous industry branches and companies that it is far more effective to develop products in platforms. In the field of sanitary fittings a platform carries a very specific name - family. From the point of view of customers these platforms supply companies with the possibility of adapting to customer demands and market needs [4], [17], [27] and [33].
On the right side of Fig. 2, where the process from conception to implementation is presented, an increasing trend in the direction of conventional product development is shown. When the process is exposed to various circumstances, as are functionality, teams and suppliers, the process itself becomes more dispersed and the product involved consequently more complex. This then leads to a greater need for balancing in the controlling of top
management by means of their increased and stressed own engagements in the role of connecting within functional teams. To achieve such balance companies turn to a metrical approach, in which teams are measured on the basis of strategic indicators, as are customer satisfaction and the time needed for implementation, as well as production and development costs. The enumerated parameters are followed-up in the analysis covered within this article. If the ratio of these parameters is correct, then these teams can perform in the best possible way and with the greatest short- and long-term enthusiasm, and it is only in this way that the accepted decisions will lead to the best short- and long-term profits [34].
2 METHODOLOGY
The conceptual model with data capture and information flow is shown in Fig. 3. The data are collected from the market with a data collecting form and the data flows into the data collector together with the technological company capabilities (internal data). The combined data are processed in the model, and in this way the model
anticipates trends on the basis of individual parameters as well as the common trend. The possibility of development determination also depends on the body's centre of gravity which is time-dependent. Possible feedback connections are also shown on the conceptual Fig. 3 and serve as corrections or modifications to the model.
3 MODEL OF MULTI-CRITERIA ANALYSIS FOR PRODUCT DEVELOPMENT ASSISTANCE
The idea about multi-dimensional analysis of product acceptability in the market was born from watching two-dimensional graphs showing the dependence of the dependent variable from the independent one. The independent variable represents time, the dependent one is derived from the observed and most representative parameters - e.g. prices, sale quantities, input into development on individual product, costs of manufacturing. Because of the incapability of demonstrating individual parameters on one graph the concept or model is presented, which could eliminate that weakness.
Fig. 3. Conceptual scheme of product development
Due to longer non-changeability of products and technology in the branch most of the products observed remained the same in that time or changed minimally (e.g. sanitary fittings, handles of sanitary armatures and packaging changed [35]), which is an additional confirmation of the models results. The calculated trend on the basis of the gravity centre is represented graphically and mathematically and applies for future years.
The transition from Cartesian coordinates to polar coordinates is given by the following Equations (1), (2) and (3). In Equation (4) we calculate the uniform distribution of the horizontal axes of observed parameters around time - central axis. This uniform way of distribution of product parameters does not emphasise only one parameter but that all parameters are equivalent Equation (6).
The representative parameters acquired from the company are evenly distributed on the circle arch of 360° with the centre in coordinate origin. The angle according to Equation (1) belongs to each parameter; parameter n means the number of representative parameters.
V = 360/
Fig. 4. Outline scheme of the model
xk (%) = Park (%)cosVk
•(n - k) ; k = 0,1,2 ....n-1
(1)
The percentage value of an individual parameter with belonging angle (Equation (1)) is converted to Cartesian coordinates upon Equations (2) and (3). On the coordinate axis "z" an independent variable time is shown or the period of watching (e.g. from 1997 to 2007).
(2)
yk (%) = Park (%) sinV	(3)
Each parameter is represented in the form of a point, with three parameters used for representation of the results in three-dimensional space, where parameter m is the number of years observed.
(%) = (
Pan
' yk >
(4)
Presentation of results with a polar way of data demonstration is improved since it shows the trend and not just information. The centre of gravity of the surface shape enclosed by polar coordinates of observed parameters is calculated upon Equations (5) to (9). The shape contains a set of n-triangles and the sum of the n-centers of the mass of those triangles is the mass centre of one observed time parameter [35].
S =
x„ =
xk	yk 1
xk+1	yk+1 1
x0	y0 1
n ,n—1 X	Sx
=1,k=0	
(0, У0 ) = (0,0)
(5)
m	n
X Si
(6)
Уп,
t Styk
!=1, k-0 n
(7)
An algorithm draws and calculates polar coordinates for individual periods between the year m-1 and the adjacent variable, and the year m+1 and the adjacent variable. The year is selected as a time argument typical for the branch since the product and technology changes are relatively slow.
The representation of the centre of mass in a polar way Equation (8) to (10) provides complete information related to an individual time period.
T>_ =Pmj
Pm
=4
2 , 2 X~ + У m
Гт = g1 f ym
(8) (9)
(10)
Time as the only independent variable is represented by the central axis in the graph, which is the result of model visualization. The displacement of dependent variables on time shows their importance and development upon time parameter.
There is an arbitrary number of dependent variables in the model. They are configured in the circle around time in the form of uniform distribution. For the purpose of this investigation a model is prepared where data is uniformly distributed.
In the observed changing of the trend it has been ascertained that linear accommodation is inaccurate.
These are higher order curves that are genomically imposed and on the bases of polynomial curves and Fourier rows (harmonic analysis) in Equation (11) they form a trend for each parameter separately (curve accommodation is higher than 95%)
. . a0	2m	. 2m an 2m.
s (x) = —00 + a, cos--V a2 cos2--V... + —- cosn--V...
n 2 1 T	T 2 T
2mx	2mx	2mx
V b1 sin^- + b2 sm^— +... + bn_1 sin(n
(11)
3.1 The Use of a model in the Example of Sanitary Fittings
There is practically no research to be found on the topic of development of sanitary fittings products. The field of survey is from the production engineering point of view, which is interesting due to the complexity of the product. It is pre-supposed that sanitary fittings represent generic products which are intended for a wider range of users.
The sample on which the first model of multi-dimensional analysis is prepared with the intention of product development covers eight time-dependent variables of sanitary fittings. The products observed were sanitary fittings of middle-price range in Slovenia. The price and quality range was assumed on the basis of expert opinions from the branch of sanitary fittings production and from the branch of sanitary fittings suppliers. The number of the chosen sanitary fittings representatives comprises 95% of the observed range, that is the sixteen most representative products of the middle-priced range of recognised European trade marks that were, and still are, present in the Slovenian market. The price range of up to 110 EUR, for which certain marketing and production rules are applicable, is a so-called premium range. The characteristics that were observed in the chosen sanitary fittings were the following: price, shape, packaging, service, production costs, capacity, design complexity, and unclear influences given under the column other.
The questionnaire that was carried out in the market and among the Slovenian producers of sanitary fittings showed the information represented in Table 1. The key moment belongs to 'product' and 'product characteristics'. On the basis of this key moment the carrying out of the analysis covered the most important parameters of the product in each time period for the observed group of sanitary fittings (herein parameters). These parameters do not change through time intervals. The concept of the information analysis is based on the observation of the product in each of the given time periods. However, trend forecasting for future time intervals is based on statistical analysis by means of an approximate function that is designed as development simulation. The information that was not gained empirically is subject to the joint
evaluation of experts in the field of sanitary fittings. In 1997 the characteristics of the product in the market were the following: 30% of its value was represented by price, 10% of the overall product was represented by the importance of its design, 5% was represented by its packaging, 5% by service, 20% by production costs, 10% by capacity, 10% by design complexity and 10% by other characteristics. The total of the observed and covered parameters lies in the centre of a polygonal form of the observed characteristics.
In 1998 the same market and the same product were analysed. However, the latter included new characteristics this time. This paper represents the same number of variables for each year, with the intention of showing the functionality of the system.
The established algorithm was modelled in the Matlab programme version 7.6.0.324. This programme enables easy and transparent recording of algorithms. By means of Matlab computing language, which contains a number of other functions for three-dimensional presentations of objects, three-dimensional programming was also performed.
4 RESULTS AND PREPARATION
The established model has eleven years' worth of recognised parameters (Table 1), which develop partly independently from one another. Even though the reviewed parameters do not have
much in common, they represent one product and development path within one time determinant. The combination of market data and strategic know-how of the company are thus presented in a graphically simple, transparent manner and within a mathematically ascertainable system. Polynomial interpolation and extrapolation allow the adjusted trend to offer values of individual monitored parameters based on a set time-frame. In polynomial interpolation, we find the polynomial which corresponds to function f at given points.
If we are presented with N points, we require a polynomial at N-1, so that the set polynomial is uniform. Some functions may be interpolated well by using polynomials, while others pose more difficulty. Calculation of polynomial interpolation is carried out by using Neville's algorithm. The trend determined in such a way will confirm future parameter values with a probability higher than 2 sigma. These values, moreover, represent changes in product development throughout future time-frames.
There is an indication of which way the product will lean towards and which parameters will be emphasised. This will give designers of new products in the company guidelines for development, which will not be limited solely by the market, but also by the company. The combination of the company's internal -economic arguments and external data obtained from the market, is presented as key in the literature [6], [10], [27] and [35].
Table 1. Information gathered from the market and company
Time (years)	Observed parameters								
	Market information				Manufacturer information				
	Price	Shape	Packaging	Service	Production costs	Capacity	Design complexity	Other	Total
1997	30	10	5	5	20	10	10	10	100
1998	30	11	6	7	17	8	6	15	100
1999	31	12	6	6	15	8	7	15	100
2000	33	12	6	7	15	8	8	11	100
2001	34	14	7	8	13	9	9	6	100
2002	32	15	6	7	14	7	8	11	100
2003	34	16	4	6	12	8	9	11	100
2004	36	18	4	4	11	7	10	10	100
2005	37	19	3	3	11	7	7	13	100
2006	38	19	2	3	10	8	6	14	100
2007	43	17	2	2	12	8	8	8	100
The observed model shows the aggregate variable to be the centre of gravity. Analysis of data in the future allows linear review or quadratic review of the trend, including an arbitrary form of establishing a trend based on lines of respective independent variables.
The common trend of spatial lines allows for analysis of a common product development trend. It depends on the respective field whether data from the market or from the company is more important. When the model is ideal, all dependent variables may be presented arbitrarily at optional angles, and further broken down into their dependent variables. When reviewing independent variables this may be done in a classical circle diagram.
The system is limited by the values of the dependent parameters of the product, which
represent the limit value. This limit value is the limit which the company is not allowed to surpass in a respective product development in considering the model, as doing so would impair its competitiveness, which must be monitored with regard to all parameters of the product. In this part the model looks to the finite elements analysis, where outer limits are recommended for development and establishment of individual product parameters - summarised according to [22].
Fig. 5 shows the "skeleton" multidimensional graph of product development. Limits to the system are set uniformly with boundary lines of observed parameters. The central axis is represented by the centre of gravity, which is the aggregate variable, and indicates a trend, which is presented in greater detail in Fig. 6 and Fig. 7.
CEKTBÉC* SSÌVtCE	GRAVJTf
PACWGIHG
PfiCOUCTCW COSTS
-О' CAPACITY	DESIGN
CMHflON
Fig. 5. Overview of links between individual product parameters and the aggregate variable - the centre
of gravity
Fig. 6. The ground plan of the graph shows deviation of the centre ofgravity to the desired product
parameters
Fig. 6 shows a view of the polar graph through various time-frames. The centre of the graph is the point of time with coordinates T (0, 0, 1997). The whole display otherwise presents the development of individual product parameters and their mathematically ascertained trend.
The polar diagram shows shifts in the gravitational centre from 1997 until 2010 - Fig. 6 and 7. The path travelled by the aggregate parameter, comes from the direction of different characteristics, which substantially mean unchartered territory for the product in the direction of the product design. These data are appropriate and also logical considering that the industry is an unknown variable. Development departments in the company will thus have a goal to design an armature that will be interesting and demanding from a design point of view. The direction of development would be further improved by conducting an analysis of the sense of design and thus obtain the desired values. It is presumed that the product design in the observed class will summarise the features of design in the higher class, which generally dictate the direction of development of lower and less demanding products in terms of quality. They would also discover whether they are able to achieve the desired market design with the given technology and production costs, which would give the
model a moment of strategic decision-making with regard to product development.
Fig. 8 gives us the opportunity to observe a multidimensional curve, which is defined by the absolute value of the angle of aggregate indicator of the trend of the centre. These curves show a linear trend which, in the coming years, moves the centre of the observed products towards the importance of product design.
5 CONCLUSION
Life cycles of technologies, products and processes are becoming ever shorter, so technological foresight is a very important aspect of their planning. In a time when foretelling the development of products is difficult and the price of error as steep as it is, the article offers a solution for the development of products through multidimensional analysis. An alternative manner of product development, it is based on a simple premise that an individual product in a certain time consists of separate parameters, which make a whole.
The presented concept can be developed and adjusted towards all dimensions of modern forecasting of the development of middle range sanitary faucet products, which will, through time, show a deviation from the orientation towards unexplored elements towards product design.
Fig. 7. Polar graph of the movement of the centre in the observed years
Fig. 8. Variation of the absolute value and angle of the centre in the observed time interval
are
Advanced options of the defined model
The introduction of virtual reality into strategic product development, which would allow a multilayered and even spatial analysis of the outer limits of the system, which delineate the logical scope of development of a single product.
A comparison of the development of two competing products through time, which would show the differences and similarities of products and highlight the advantages and disadvantages of an individual product through an analysis of 10 parameters. An opportunity to improve the visualization of the advantages and disadvantages in the business area the product is placed in. An opportunity to link the model directly with production and computer prototyping. Trend forecasting on the basis of extensive experience.
An opportunity to analyse the internal characteristics of the company and gathered external data. The internal data gathered within a company and market research data allow simple and straightforward development of a concept of further company development, and enable the assessment of separate parameters through simulation. This is very important considering the fact that the limitations of production are equally or more important than market demand (high tech products), which enables us to enforce the claim calling for a technology "push" and marketing "pull".
Computer models include a data entry
interface which allows entry of data for instantaneous analysis in the model, thus effectively simulating whether further improvements remain reasonable [36].
•	Analysis of separate parameters with the aid of approximation of existing movement by the movement of the aggregate central variable; a joint concept would provide more detailed data about product development as it would allow double simulation.
•	An opportunity to analyse the shift of the aggregate variable of the body centre and its deviation towards individual dependent variables represents the quality of such an analysis.
•	Another option is the representation of the "onion" product strategy - on a model where the basic demand for the product is fulfilled and its transfer into higher levels improves the product.
•	Choosing shorter periods of time would not allow for such detailed data. The line between both time intervals can be an approximated value, which would indicate seasonal movement of product parameters.
The developed model of product design through multi-criteria analysis can be used in the development of virtually any mass produced product.
6 REFERENCES
[1]	Cooper, R. G. New product strategies: what distinguishes the top performers? Journal of product innovation management, September 1984, vol. 1, no. 3, p. 151-164.
[2]	Dougherty, D. Interpretive Barriers to
Successful Product Innovation in Large Firms. Organization Science, May 1992, vol. 3, no. 2, p. 179-202.
[3]	The PDMA Handbook of new product development. 2nd ed. Hoboken (N. Y.): Wiley, cop. 2005. XIII, 625 p. ISBN 0-47148524-1
[4]	Ulrich, K. T., Eppinger, S. D. Product design and development. 2nd ed. Boston: Irwin/McGraw-Hill, 2000. XXVI, 358 p. ISBN 0-07-229647-X
[5]	Clark, K. B., Wheelwright, S. C. Managing new product and process development: text and cases. New York [etc.]: The free press: Simon & Schuster, 1993. XV, 896 p. ISBN 0-02-905517-2
[6]	Crawford, C. M., Di Benedetto, C. A. New products management. 9th ed. Boston [etc.]: McGraw-Hill/Irwin, 2008. XVIII, 558 p. ISBN-13 978-0-07-352988-2
[7]	Green, P. E., Krieger, A. M., Zelnio, R. N. A componential segmentation model with optimal product design features. Decision science, June 1989, vol. 20, no. 2, p. 221238.
[8]	Urban, G. L., Hauser, J. R. Design and marketing of new products. 2nd ed. Englewood Cliffs (New Jersey): Prentice hall, London [etc.]: Prentice hall international, cop. 1993. XXVII, 701 p. ISBN 0-13-201567-6
[9]	Goldenberg, J., Mazursky, D. Creativity in product innovation. 3rd printing. Cambridge (U. K.) [etc.]: Cambridge university press, 2004. XIII, 224 p. ISBN 0-521-80089-7
[10]	Cooper, R. G. Winning at new products: accelerating the process from idea to launch. 3rd ed. Reading (Mass.): Perseus, 2001. XIII, 425 p. ISBN-13 978-0-7382-0463-5
[11]	Griffin, A. J., Hauser J. R. Integrating R&D and marketing: a review and analysis of the literature. Journal of product innovation management, May 1996, vol. 13, no. 3, p. 191-215.
[12]	Currim, I. S. Using segmentation approaches for better prediction and understanding from consumer mode choice models. Journal of marketing research, August 1981, vol. 18, no. 3, p. 301-309.
[13]	Chul-Yong, L., Jeong-Dong, L., Yeonbae, K. Demand forecasting for new technology with a short history in a competitive environment:
the case of the home networking market in South Korea. Technological forecasting & social change, January 2008, vol. 75, no. 1, 91-106.
[14]	Jamieson, L. F., Bass, F. M. Adjusting stated intention measures to predict trial purchase of new products: a comparison of models and methods. Journal of marketing research, August 1989, vol. 26, no. 3, p. 336-345.
[15]	Morrison, D. G. Purchase intentions and purchase behaviour. Journal of marketing, spring 1979, vol. 43, No. 2, p. 65-74.
[16]	Handbook of marketing. Weitz, B. A. (ed.), Wensley, R. (ed.). London, Thousand Oaks, New Delhi: Sage, 2002. XIX, 582 p. ISBN 978-0-7619-5682-2
[17]	Kmetovicz, R. E. New product development: design and analysis. New York: Wiley, cop. 1992. XIII, 334 p. ISBN 0-471-55536-3
[18]	Jamieson, L. F., Bass, F. M. Adjusting stated intention measures to predict trial purchase of new products: a comparison of models and methods. Journal of marketing research, August 1989, vol. 26, No. 3, p. 336-345.
[19]	Cooper, R. G. (1984). How new product strategies impact on performance. Journal of product innovation management, January 1984, vol. 1, no. 1, p. 5-18.
[20]	Smith, P. G., Reinertsen D. G. Developing products in half the time. 2nd ed. New York: Wiley, 1998. XIX, 298 p. ISBN 0-47129252-4
[21]	Allen, T. J. Managing the flow of technology: technology transfer and the dissemination of technological information within the R&D organization. 1st pbk. print. Cambridge (Mass.), London: MIT Press, 1984. XIV, 320 p. ISBN 0-262-51027-8
[22]	Palčič, I., Polajnar, A., Pandža, K. A model for the effective management of order-based production, Journal of Mechanical engineering, 2003, vol. 49, no. 7/8, p. 398412.
[23]	Cancer V. (2007). Frame procedure for multi-criteria decision making (in Slovenian). Organization, 2007, vol. 40, no. 5, p. A160-A167.
[24]	Glavač, M., Ren, Z. = Multicriterial optimization of a car structure using a finite element method, Journal of Mechanical engineering, October 2007, vol. 53, no. 10, p. 657-666.
[25]	Imai, M. Ky'zen: the key to Japan's competitive success. New York [etc.]: McGraw-Hill, 1986. XXXIII, 259 p. ISBN 0-07-554332-X
[26]	Deming, W. E. Out of the crisis. 1st MIT Press ed. Cambridge (Mass.): MIT Press, 2002. XIII, 507 p. ISBN 0-262-54115-7
[27]	Schäppi, B., Andreasen, M. M., Kirchgeorg, M., Radermacher, F. J. Handbuch Produktentwicklung. Müchen [etc.]: C. Hanser, cop. 2005. XXVI, 838 p. ISBN 3446-22838-1
[28]	Buchmeister, B., Kremljak, Z., Pandža, K., Polajnar, A. Simulation study on the performance analysis of various sequencing rules. International journal of simulation modelling, June/September 2004, vol. 3, no. 2-3, p. 80-89
[29]	Mitrouchev, P., Brun-Picard, D. A new model for synchronous multi agents production amongst clients and subcontractors. International journal of simulation modelling, September 2007, vol. 6, no. 3, p. 141-153.
[30]	Vujica-Herzog, N., Polajnar, A., Tonchia, S. Development and validation of business process reengineering (BPR) variables: a survey research in Slovenian companies. International Journal of Production Research, December 2007, vol. 45, no. 24, p. 5811-5834.
[31]	Baumgartner, B., Steiner, W. J. Are consumers heterogeneous in their preferences for odd and even prices? Findings from a choice-based conjoint study.
International journal of research in marketing, December 2007, vol. 24, no. 4, p. 312-323.
[32]	Baker, G., Gibbons R., Murphy, K. J. Relational contracts and the theory of the firm. The quarterly journal of economics, February 2002, vol. 117, no. 1, p. 39-84.
[33]	Gilmore, J. H. and Pine, J. 2nd. The four faces of mass customization. Harvard business review, January-February 1997, vol. 75, no. 1, p. 91-101.
[34]	Baker, G., Gibbons R., Murphy, K. J. Informal Authority in Organizations. Journal of law, economics, and organization, March 1999, vol. 15, no. 1, p. 56-73.
[35]	Market research for PE Armal: internal literature (in Slovenian). Maribor: Maribor Foundry Company, 2006.
[36]	Bronstejn I. N., Semendjajev K. A. Mathematics handbook for engineers and students of technical colleges (in Slovenian). 5th edition. Ljubljana: Technical Publisher of Slovenia, 1978. p.699
[37]	Polajnar, A. [etc.]. Management of production systems - contemporary concepts (in Slovenian). Maribor: Faculty of Mechanical Engineering 2004. VII, 506 p. ISBN 86-435-0666
[38]	Buchmeister, B. Investigation of the Bullwhip effect using spreadsheet simulation. International journal of simulation modelling, March 2008, vol. 7, no. 1, p. 29-41.
Paper received: 04.09.2008 Paper accepted: 25.09.2008
Machining Process Optimization BY Colony Based Cooperative Search Technique
Uroš Župerl* - Franci Čuš University of Maribor, Faculty of Mechanical Engineering Maribor, Slovenia
Research of economics of multi-pass machining operations has significant practical importance. Non-traditional optimization techniques such genetic algorithms, neural networks and PSO optimization are increasingly used to solve optimization problems. This paper presents a new multi-objective optimization technique, based on ant colony optimization algorithm (ACO), to optimize the machining parameters in turning processes. Three conflicting objectives, production cost, operation time and cutting quality are simultaneously optimized. An objective function based on maximum profit in operation has been used. The proposed approach uses adaptive neuro-fuzzy inference system (ANFIS) system to represent the manufacturer objective function and an ant colony optimization algorithm (ACO) to obtain the optimal objective value. New evolutionary ACO is explained in detail. Also a comprehensive user-friendly software package has been developed to obtain the optimal cutting parameters using the proposed algorithm. An example has been presented to give a clear picture from the application of the system and its efficiency. The results are compared and analysed using methods of other researchers and handbook recommendations. The results indicate that the proposed ant colony paradigm is effective compared to other techniques carried out by other researchers. © 2008 Journal of Mechanical Engineering. All rights reserved. Keywords: machining, turning, optimization, cutting parameters
0 INTRODUCTION
The selection of optimum cutting parameters is a very important issue for every machining process in order to enhance the quality of machining products, to reduce the machining costs and to increase the production rate. Due to machining costs of Numerical Control (NC) machines, there is an economic need to operate NC machines as efficiently as possible in order to obtain the required pay back. In workshop practice, cutting parameters are selected from machining databases or specialized handbooks, but they do not consider economic aspects of machining. The cutting conditions set by such practices are too far from optimum. Therefore, a mathematical approach has received much attention as a method for obtaining optimised machining parameters. For the optimisation of a machining process, either the minimum production time or the maximum profit rate is used as the objective function subject to the constraints. Optimization of cutting parameters is a difficult task [1], where the following aspects are required: knowledge of machining; empirical equations relating the tool life, forces, power,
surface finish, etc., to develop realistic constrains; specification of machine tool capabilities; development of an effective optimization criterion; and knowledge of mathematical and numerical optimization techniques.
Optimization of machining parameters is complicated when a lot of constraints are included, so it is difficult for the non-deterministic methods to solve this problem. Conventional optimization techniques are useful for specific optimization problems and leaned to find local optimum solution. Consequently, non-traditional techniques were used in the optimization problem. Researchers [2] have done comparative analysis of conventional and non-conventional optimization techniques for CNC turning process. The optimization problem in turning has been solved by genetic Algorithms (GA), Tabu search (TS), simulated annealing (SA) and particle swarm optimisation (PSO) to obtain more accurate results [3]. Milfelner et al. [4] have described the multi objective technique of optimization of cutting conditions for turning process by means of the neural networks and particle swarm optimization (PSO) [5], taking into consideration the technological, economic
*Corr. Author's Address: University of Maribor, Faculty of Mechanical Engineering, Smetanova 17, Maribor, Slovenia, uros.zuperl@uni-mb.si
and organization limitations. Further genetic GA and simulated annealing techniques have been applied to solve the continuous machining profile problem by [6]. They have shown that GA approach outperforms the simulated annealing based approach.
In this paper, a multi-objective optimization method, based on combination of ANFIS and ACO evolutionary algorithms, is proposed to obtain the optimum parameters in turning processes. The advantage with this approach is that it can be used for solving a diverse spectre of complex optimisation problems [7] and [8]. This paper also compares the results of ANFIS-ant colony algorithm with the GA and simulated annealing (SA). The results exhibit the efficiency of the ACO over other methods.
1 THE HYBRID ANFIS-ANTS APPROACH
The proposed approach consists of two main steps.
Step 1
Step 2
Fig. 1. Scheme of the proposed approach
First, experimental data are prepared to train and test ANFIS system to represent the objective function (y). Finally, an ACO algorithm is utilized to obtain the optimum objective value. Figure 1 shows the flowchart of the approach.
Detail steps for optimization of cutting parameters by ANFIS-ants approach:
1.	Entering of input data.
2.	Generation of random cutting conditions-initial solutions.
3.	Calculation of other values (P; F; MRR; Cp; T; Ra; Tp; y).
4.	Preparation of data for training and testing of ANFIS.
5.	Use of ANFIS model: The purpose of ANFIS is to predict the manufacturer's value function (y) in case of randomly selected cutting conditions.
6.	Training and testing of ANFIS.
7.	Optimization process: The cutting conditions where the function (y) has the maximum are the optimum cutting conditions. The extreme of the function (y). Since the function (y) is expressed with ANFIS, it means that the extreme of ANFIS is searched for.
8.	Survey of optimum cutting conditions and the variables relevant to them.
9.	Graphic representation of results and optimization statistic.
1.1. Machining Model Formulation
In CNC machine tools, the finished component is obtained through a number of rough passes and finish passes. The roughing operation is carried out to machine the part to a size that is slightly more than its desired size in preparation for the finish cut. The finish cut is called single-pass contour machining, which is machined along the profile contour. In this paper one roughing stage, and a finished stage are considered to machine the component from the bar stock.
The objective of this optimization is to determine the optimum machining parameters including cutting speed, feed rate and depth of cut in order to minimize the production cost (Cp) and to maximize production rate (represented by manufacturing time (Tp)) and cutting quality (Ra). The operation of turning is defined as a multi-objective optimization problem with limitation non-equations and with three conflicting objectives (production rate, operation cost,
quality of machining). All the above-mentioned objectives are represented as a function of the cutting speed, feed rate and depth of cutting.
1.1.1 Production rate [9]
The production rate is measured as the entire time necessary for the manufacture of a product (Tp). It is the function of the metal removal rate (MRR) and of the tool life (T) [10];
Zp = Ts + V(1 + T )/mrr + T (1)
where Ts, Tc, Ti and V are the tool set-up time, the tool change time, the time during which the tool does not cut and the volume of the removed metal. In some operations the Ts, Tc, Ti and V are constants so that Tp is the function of MRR and T. The metal removal rate is expressed as:
MRR = 1000 ■ v ■ f ■ a
1.1.2 The Cost function [9]
(2)
The unit production cost, Cp, for turning operations can be divided into three basic cost elements: the tool cost and tool replacement cost (Ct), cutting cost by actual time in cut (Cl) and overhead cost C0, T is tool life.
The formula for calculating the above cost is used as given by [9].
Finally, by using the above mathematical manipulations, the unit production cost ($/piece) can be obtained as:
Cp = Tp —t + C + C0 )
1.1.3 Cutting quality [9]
(3)
Parameter bounds. The available range of cutting speed, feed rate and depth of cut are expressed in terms of lower and upper bounds. The bounds on feed rate and depth of cut is setup for the safety of the operator. The parameter bound values and constants are: vmin < v < vmax ,
fmin < f < fmax, amin < a < amax .
Tool-life constraint. The constraint on the tool life is taken as Tmin < T <Tmax.
Power constraint. The power required during the cutting operation should not exceed the available power of the machine tool. The power is given as:
к f и dv v
P = fA r r ,	(5)
6120ц
where kf , / and v are the constants pertaining to specific tool-work piece combination and ^ is the power efficiency. The limitations of the power and cutting force are equal to: P(v, f, a) < Pmax
In order to ensure the evaluation of mutual influences and the effects between the objectives and to be able to obtain an overall survey of the manufacturer's value system the multi-attribute function of the manufacturer (y) is determined. The cutting parameter optimization problem is formulated as the following multi-objective optimization problem: min Tp (v, f, a), min Cp (v, f, a), min Ra (v, f, a).
y = 0.42e(-°-22Tp) + 0.17el--°,26Ra) +-
0.05
1 + 1.22TpCp Ra
(6)
A multiattribute value function is defined as a real-valued function that assigns a real value to each multiattribute alternative, such that more preferable alternative is associated with a larger value index than less preferable alternative.
The most important criterion for the assessment of the surface quality is roughness calculated according to:
Ra = к vX1 fX2 ax	(4)
where x1, x2, x3 and k are the constants relevant to a specific tool-workpiece combination.
1.1.4 Cutting condition constraints
The practical constraints imposed during the roughing and finishing operations are stated as follows [9].
1.2 Objective Function Modelling
First step uses an ANFIS to model the response (manufacturer's implicit multiattribute) function (y). The variables of this problem are velocity, feed rate and depth of cut, which can have any continuous value subject to the limits available. The ANFIS system needs three inputs for three parameters: cutting speed (v), feedrate (f) and depth of cutting (a). The output from the system is a real value (y). The relationship between the cutting parameters and manufacturer objective function is first captured via a neural network and is subsequently reflected in linguistic
form with the help of a fuzzy logic based algorithm. Algorithm uses training examples as input and constructs the fuzzy if-then rules and the membership functions of the fuzzy sets involved in these rules as output.
Figure 2 shows the fuzzy rule architecture of ANFIS when triangular membership function is adopted. The architectures shown in Figure 2 consist of 32 fuzzy rules. During training in ANFIS, 140 sets of experimental data were used to conduct 400 cycles of training. ANFIS has proved to be an excellent universal approximator of non-linear functions. If it is capable to represent the manufacturer's implicit multiattribute function.
Fig. 2. Fuzzy rule architecture of the triangular membership function
Using a given input/output data set, the ANFIS method constructs a fuzzy inference system (FIS) whose membership function parameters are tuned using either a backpropagation algorithm alone, or in combination with a least squares type of method. This allows fuzzy systems to learn from the data they are modeling. FIS structure is a network-type structure similar to that of a neural network, which maps inputs through input membership functions and associated parameters, and then through output membership functions and associated parameters to outputs. ANFIS applies two techniques in updating parameters. For premise parameters that define membership functions, ANFIS employs gradient descent to fine-tune them. For consequent parameters that define the coefficients of each output equations, ANFIS uses the least-squares method to identify them. This approach is thus called Hybrid
Learning method since it combines the gradient descent method and the least-squares method.
ANFIS modeling process starts by:
1.	Obtaining a data set (input-output data pairs) and dividing it into training and checking data sets.
2.	Finding the initial premise parameters for the membership functions by equally spacing each of the membership functions
3.	Determining a threshold value for the error between the actual and desired output.
4.	Finding the consequent parameters by using the least-squares method.
5.	Calculating an error for each data pair. If this error is larger than the threshold value, update the premise parameters using the gradient decent method as the following (Qnext=Qnov+7d, where Q is a parameter that minimizes the error, j the learning rate, and d is a direction vector).
6.	The process is terminated when the error becomes less than the threshold value. Then the checking data set is used to compare the model with actual system. A lower threshold value is used if the model does not represent the system.
After training the estimator, its performance was tested under various cutting conditions. Test data sets collected from a wide range of cutting conditions in turning were applied to the estimator for evaluating objective function (y). The performance of this method turned out to be satisfactory for estimating of objective function (y), within a 2% mean error.
Once a multi-attribute value function is assessed and validated the ANFIS is used to decipher the manufacturer's overall preference and the multi-objective optimization problem will be reduced to a single objective maximization problem as follows:
maxv,f,a y [Tp (v, f, a), Cp (v, f, a), R (v, f, a)] (7)
2 ANT COLONY OPTIMIZATION-ACO
ACO is a non-traditional optimization technique in which the main idea underlying it is that of a parallelizing search over several constructive computational threads, all based on a dynamic memory structure incorporating information on the effectiveness of previously obtained results and in which the behavior of each
single agent is inspired by the behaviour of real ants.
Special insects like ants, termites, and bees that live in a colony are capable of solving their daily complex life problems. These behaviours which are seen in a special group of insects are called swarm intelligence. Swarm intelligence techniques focus on the group's behaviour and study the decartelized reactions of group agents with each other and with the environment. The swarm intelligence system includes a mixture of simple local behaviours for creating a complicated general behaviour and there is no central control in it. Ants have the ability to deposit pheromone on the ground and to follow, in probability, pheromone previously deposited by other ants. By depositing this chemical substance, the ants leave a trace on their paths. By detecting this trace, the other ants of the colony can follow the path discovered by other ants to find food. For finding the shortest way to get food, these ants can always follow the pheromone trails. This cooperative search behaviour of real ants inspired the new computational paradigm for optimizing real life systems and it is suited for solving large scale optimization problem.
The first ACO algorithm, called ant system (AS) has been applied to the travelling salesman problem (TSP). Dorigo [7] proposed an ACO methodology for machining parameters optimization in a multi-pass turning model, which originally was developed by [8]. Recently, a modified ACO was presented as an effective global optimization procedure by introducing bilevel search procedure called local and global search. The important aspect in ACO is that the artificial ants select the solution.
2.1 ACO Algorithm of Process Optimization
The proposed continuous ACO for optimization of cutting conditions in multi-pass turning is shown as scheme in Figure 3. The distribution of ants is shown in Figure 4.
Initial solution. An initial solution of N will consist of 160 randomly generated solutions, with values that lie in the range of allowable cutting speed, depth of cut and feedrate. The 160 solutions are then sorted in ascending order with respect to the objective function.
The regions pertaining to minimum production cost are referred to as superior
solutions, while regions pertaining to the maximum production cost are referred to as inferior solutions.
Distribution of ants. The total numbers of ants, A, is 80, which is half of N and is distributed as 72 for global (G) and 8 for local search (L).
An ACO utilizes bi-level procedures which include local and global searches.
Local search: With a local search, the L local ants select L regions from N regions and move in search of better fitness. Here L is 6, and L solutions are selected as per the current pheromone trail value. Local search ants select a region L with a probability p (t) =ri(t)J ^Vk(t),
where i is the region index and ti(k) is the pheromone trail on region i at time t. After selecting the destination the ant moves through a short distance (finite random increment 0.005).
Updating the pheromone trail value of new solution in local search. If the fitness is improved, the new solutions are updated to the current region. Correspondingly the regions position vector is updated. The variables of this problem are cutting speed, feedrate, depth of cut, all of which can have any continuous value subject to the limits imposed. The objective functions are calculated for each solution. In the continuous algorithm, the pheromone values are decreased after each iteration by:
T.(t +1) = p-ri(t)	(8)
where p is the evaporation rate which is assumed to be 0.2 on a trial basis and q(t) is the trail associated with solution at time t.
Global search. Using global search, global ants create G new regions by replacing the inferior solutions of the existing solutions.
The following three operations are performed on the randomly generated initial solution: (a) Random walk or cross over -90% of the solutions (randomly chosen) in the inferior solutions are replaced with randomly selected superior solutions; (b) Mutation - the process where by randomly adding or subtracting a value is done to each variable of the newly created solutions in the inferior region with a mutation probability; and (c) Trial diffusion - applied to inferior solutions that were not considered during random walk and mutation stages.
A global search is done sequentially by crossover, mutation and trial diffusion operations. The subsequent values of the variables of the
child are set to the corresponding value of a randomly chosen parent with a crossover probability (0.75). Mutation operation adds or subtracts a value to/from each variable with mutation probability. The mutation step size is the same as the above distance A(T, R). After selecting the destination, the ant moves through a short distance ( A(T,R) = R(1 - r10(1-T)), where R is maximum search radius, r is a random number from [0,1], T is the total number of iterations of the algorithm.
Performing an ACO, ants are repeatedly sent to trail solutions in order to optimize the objective value. The total number of ants (denoted by A) is set as half the total number of trail solutions (denoted by S).
Trail diffusion. Here, two parents are selected at random from the parents region. The child can have:
1.	the value of the corresponding variable of the first parent;
2.	the value of the corresponding variable of the second parent; or
3.	a combination arrived from the weighted average of the above X(child) =a x(parent 1)+[1-a]x (parent 2), where a is a uniform random number in the range [0,1]. The probability of selecting the 3rd option is set equal to the mutation probability 0.75, and the probability of selecting the 1st and 2nd options is allotted a probability of 0.2.
Updating of pheromone trail value of new solution in global search. After the global search, the pheromone trail value of the new solutions is updated proportionally to the improvement in the objective value.
Sort the regions according to the function value. New solutions will be obtained after the global and local search. The solutions will also have the new pheromone trail values. The solutions are sorted in ascending order of the objective values and the best objective value is stored. The process is repeated for a specified number of iterations.
The ACO algorithm: Step 1. Set parameter values including: S, A, p, r0, Pc, Pm, T, R, and bounds of each control factor.
Step 2. Create S trail solutions (v, f, a). Estimate the objective value of the trail solutions through the ANFIS model (y).
Step 3. Set the initial pheromone value of all trails.
Step 4. Repeat steps 6 to 8 until the stopping criteria has reached.
Step 5. Send L ants to the selected trail solutions for local search.
Step 6. If the solution is improved, move the ants to the new solution and update the pheromone value.
Step 7. Send G ants to global trails and generate their offspring by crossover and mutation.
Step 8. Evaporate pheromone for all trails.
Fig. 3. Scheme of the ACO algorithm
Total no. of ants: 60
(1 / 2 of the initial solutions)
V	--_у
Fig. 4. Distribution of search points (ants) in ACO algorithm
3 COMPUTATIONAL RESULTS AND DISCUSSION
The ant colony optimization method combined with ANFIS prediction system was tested on the CNC lathe GF02. The work piece material is mild steel (Ck45) and the tool material has a carbide tip. The task is to find optimum cutting conditions for the process of turning with minimum costs.
Proposed ACO approach was compared with three non-traditional techniques (GA, SA and PSO). The results obtained from four techniques are given in Table 1. All the parameters and constraint sets are the same in all four cases. There is a total of 4 constraints. The proposed model is run on a PC 586 compatible computer using the Matlab language. The results revelled that the proposed method significantly outperforms the GA and SA approach. The proposed approach found an optimum solution of 12.461 for as low as 1 to 18 runs the genetic-
based approach require as much as 1 to 500 runs
to find an solution of 14.661.
This means that the proposed approach has 16.02% improvement over the solution found by GA approach and 23.08% over SA approach.
Moreover, the simulated annealing approach (SA/PS) of [14] also generated an inferior solution of 17.24 for as much as 901 to 1000 runs which means that the optimum solution of ACO algorithm has an improvement of 23.6%. It is observed that PSO has outperformed all other algorithms [16]. Next ACO, SA and GA are ranked according to costs obtained from algorithms. The costs obtained and optimum machining conditions are shown in Table 1. From the results, it is clear that the proposed ACO approach significantly outperforms the other two methods, such as GA and SA. Clearly, the ACO approach provides a sufficiently approximation to the true optimum solution.
4 CONCLUSION
In this paper, non-conventional optimization techniques ACO has been studied for the optimization of machining parameters in turning operations. The hybrid ANFIS-ants integrates neural network, fuzzy logic and continuous ant colony optimization to model the machining system and to optimize machining process. ACO algorithm is completely generalized and problem independent so that can be easily modified to optimize this turning operation under various economic criteria. It can obtain a near-optimum solution in an extremely large solution space within a reasonable computation time. The algorithm can also be
Table 1. Comparison of results for ANFIS-ACO, GA, LP and PSO approach
					Optimum solution			Average
No.	Algorithm	Constraint set	Runs	vopt [m/min]	fopt [mm/rev]	aopt [mm]	cp [$]	optimiz. time [s]
1	PSO [11, 12]	tool-life; cutting force- power [13]; surface roughness;	1 to 25 1 to 150	101.211 103.377	0.231 0.217	0.44 0.51	12.461 12.235	3 7
2	Proposed ANFIS-ACO	tool-life; cutting force- power; surface roughness;	1 to 25 1 to 150	95.1926 97.433	0.3793 0.2934	0.84 0.89	12.423 12.314	2 6
3	SA [14]	tool-life; cutting force- power; surface roughness;	1 to 1000 1 to 1400	112.852 108.464	0.194 0.221	0.46 0.41	16.152 16.171	12 11
4	GA [15]	tool-life; cutting force- power; surface roughness;	1 to 150 1 to 500	102.165 98.122	0.039 0.313	1.268 0.612	18.394 14.661	7 9
extended to other machining problems such as [8] milling operations. The results of the proposed approach are compared with results of three non-traditional techniques (GA, SA and PSO). Among the four algorithms, PSO outperforms all other [9] algorithms.
5 REFERENCES
[10]
[1]	Čuš, F., Balič, J. (2000) Selection of cutting conditions and tool flow in flexible manufacturing system, The international journal for manufacturing science & [11] technology 2, p. 101-106.
[2]	Dorigo, E. (2006) The ant system: Optimization by a colony of cooperating agents, IEEE Transaction on Systems, Man
and Cybernetics 26, p. 1-13.	[12]
[3]	Liu, Y., Wang, C. (1999) Neural Network based Adaptive Control and Optimisation in the Milling Process, International Journal of Advanced Manufacturing Technology 15, p. [13] 791-795.
[4]	Milfelner, M., Župerl, U., Čuš, F. (2004) Optimisation of cutting parameters in high speed milling process by GA, Int. j. simul. [14] model. 3, p. 121-131.
[5]	Vijayakumar, K., Prabhaharan, P., Asokan, R., Saravanan, M. (2002) Optimization of multi-pass turning operations using ant [15] colony system, International Journal of Machine Tools and Manufacture 3, p. 633639.
[6]	Župerl, U., Čuš, F. (2004) A determination
of the characteristic technological and [16] economic parameters during metal cutting, Journal of Mechanical Engineering 5, p. 252-266.
[7]	Čus, F., Balič, J. (2003) Optimization of cutting process by GA approach, Robot. comput. integr. manuf. 19, p. 113-121.
Župerl, U., Čuš, F. (2003) Optimization of cutting conditions during cutting by using neural networks, Robot. comput. integr. manuf. 19, p. 189-199.
Ozcan, E., Mohan, C. (1998) Analysis of a simple Particle Swarm Optimization system, Intelligent Engineering Systems Through Artificial Neural Networks 1, p. 253-258. Shi, Y., Eberhart, R. (1998) Parameter selection in particle swarm optimization. Evolutionary Programming VII: Proc. EP98, New York: Springer-Verlag, p. 591-600. Angeline, P.J. (1998) Evolutionary Optimization Versus Particle Swarm Optimization: Philosophy and Performance Differences, Proceedings of the 7th ICEC p. 601-610.
Eberhart, R.C., Shi, Y. (1998) Comparison Between Genetic Algorithm and Particle Swarm Optimization, Proceedings of the 7th ICEC p. 611-616.
Kopač, J. (2002) Cutting forces and their influence on the economics of machining,
Journal of Mechanical Engineering, no. 3, p. 121-132.
Mulc, T., Udiljak, T, Čuš, F., Milfelner, M. (2004) Monitoring cutting- tool wear using signals from the control system, Journal of Mechanical Engineering no. 12, p. 568-579. Župerl, U., Čuš, F., Muršec, B., Ploj, A. (2004) A Hybrid analytical-neural network approach to the determination of optimal cutting conditions, J. mater. process. technol. 157/158, p. 82-90. Župerl, U., Čuš, F., Gečevska, V.(2007) Optimization of the characteristic parameters in milling using the PSO evolution technique, Journal of Mechanical Engineering, no. 6, p. 354-368.
Paper received: 17.10.2007 Paper accepted: 25.09.2008
Radio Frequency Identification Technology Application in
Disassembly Systems
Gordana Ostojic1, - Milovan Lazarevic1 - Stevan Stankovski1 - Ilija Cosic1 - Zoran Radosavljavic2
1	University of Novi Sad, Republic of Serbia
2	ABS Holding, Beograd, Republic of Serbia
This paper presents the results of developing a model of RFID technology application in disassembly systems as a solution for a problem of rapid arrival of numerous products at a waste dump. During the process of disassembly and dismantling the basic components, they should be redirected to the disassembly systems for renewal, reprocessing and recycling. An integral part of the WEEE (Waste Electrical and Electronic Equipment) directive is the product take back strategy, which supports the endeavor to recycling as efficient as possible. System processes, like disassembly, make it possible to selectively separate the renewable, non-recycling and dangerous components from those which are recyclable. Appropriately planned process of disassembly, together with recycling and waste disposal, can help to efficiently manage the products during their life cycle. In order for something to be achieved, proper strategies should be considered. The collection of data about all kinds of flows of products, materials, parts/subassemblies and dangerous components/materials are necessary at the end of the life cycle. By applying RFID (Radio Frequency Identification) technologies to the systems for refining the outdated product, the management of all the above mentioned flows can be improved. Information gathered in this way is reliable, precise and dynamic. They could provide optimum management with products that have come to the end of their work lifetime. © 2008 Journal of Mechanical Engineering. All rights reserved.
Keywords: radio frequency identification technology, end of life cycle, disassembly systems
0 INTRODUCTION
Contemporary production conditions demand the application of distributed production concept, because there is an enormous pressure on the manufacturers to comply with market changes and continuous shortening of the product life cycle [9]. Virtual Manufacturing Systems (VMS) are currently more and more indispensable for obtaining the information about future properties and the state of manufacturing in any production company [8], and a help for dealing with the problem of dynamic changes and shortening of the product life cycle. RFID technology could be appropriate solution for problems regarding automatic identification and data acquisition. Information gathered in this way could be crucial for designing and functioning of VMS and Virtual Disassembly System (VDS).
There is a need for finding a good solution for a problem of production of certain types of products and their disposal into the waste dumps, in order to reduce and control the quantity of such waste, because the waste is being made in ever-increasing quantities. According to some
researches, quantity of electrical appliances being used in every household is about 3.3 tones for one citizen per life time of which: large household appliances 69%, small household appliances 8%, information technology and telecommunications equipment 7%, consumer equipment 13%, lighting equipment < 1%, electrical and electronic tools 2%, toys, leisure and sports equipment < 1%, monitoring and control instruments < 1% [7]. Having this in mind, production systems for the processing of such waste are designed and put into use.
Disassembly is just one of the processes in the life cycle of a product [8] and lately it has attracted a lot of attention, considering its key role in reassembling and recycling of products. This is due to ecological and economical reasons. The echological side of the problem is seen in ending numerous products at waste dumps and in depletion of non-renewable natural riches. The economical side of the problem of disassembly is seen in the need for a design of the disassembly system in a way that the value of the disassembly process result is grater then the resources invested for its proper functioning [4].
* Corr. Author's Address: Faculty of Technical Sciences, Trg D. Obradovica 6, 21000 Novi Sad, Republic of Serbia, goca@uns.ns.ac.yu
The end result of the disassembly is frequently changing, depending on the state of the product, especially when we realize that we are talking about technologically outdated products.
Strategies for managing products at the end of their life cycles, the problem of shaping the production system to refine the products at the end of the life cycle and using of RFID technology are presented in this paper work. Other similar researches have been done in this field [10] and [11]. This approach of using RFID technology is rather new and it is a challenge for a research.
1 STRATEGIES FOR PRODUCTS AT THE END OF THE LIFE CYCLE
First step in designing disassembly system process is to consider possible end of life strategies for products. Strategies for products at the end of a life cycle represent methodes, which are used to conduct the general direction of products, and only suggestions are given for the management of a product at the end of a life cycle. Studies related with the strategies of the products end of a life cycle are numerous [4] and [5]. The most accepted, and in its character, the most comprehensive classification of the products end of a life cycle is [1]:
1.	re-use of used products,
2.	reconstruction of used products,
3.	usage of already used products for spare parts,
4.	recycling with disassembly,
5.	recycling without disassembly,
6.	dumping of the used products.
Re-use of already used products is a strategy that organizes the return of discarded products which are still in function. If such an interest exists, already used products are sold in the market.
Reconstruction of used products is applied due to modernize or to upgrade their performances. The purpose of this strategy is to attain a product, which is in quality less or very similar to the quality of the new products. The quality of the reconstructed products depends on the determined depth of disassembly. If a product is disassembled to the level of parts and a control and a replacement of all parts is conducted, the used products are brought to a high level of quality, required for the new products.
Also, it is possible to conduct the modernization of products, by replacing certain modules with contemporary ones, after applying the disassembly.
Appliance of already exploited products for spare parts is being frequently used. In certain companies, out of date products are being collected in an organized manner. The purpose of this strategy is to take a relatively small part of sub modules from a used product and use them for the above mentioned strategy, or for another purpose, and the rest will be used for material recycling.
Recycling with disassembly is a strategy used for separating parts made of different material, before its conversion in the process of disassembly. The purpose of this strategy is to use the materials from the used products and parts, by separating them in the procedure of disassembly into the component parts and with appropriate selection, depending on the determined type of material. These materials can then be used in the production of original or some other products.
Recycling without disassembly is a procedure, which is used to compact and compress the product and then crush it and sort it by type of material.
Disposal is, from the ecological point of view, the most inconvenient strategy for disposing products on the waste dumps. Having the above mentioned strategies in mind, it is necessary to design an appropriate production system.
2 STRATEGY SELECTION FOR PRODUCT AT THE END OF THE LIFE CYCLE
The production system for product processing at the end of life cycle has a quite complex structure, since there is a need for more then one technologicaly different subsystem like [4]:
1.	disassembly,
2.	reassembly,
3.	recycling,
4.	waste incineration,
5.	hazardous waste storage,
6.	waste storage.
The choice of strategies for reconstruction of used products (2), usage of already used products for spare parts (3) and recycling with disassembly (4) are made according with the both momentary product condition and suggestions taken from the database for particular product. A
production system for product processing, according with chosen strategies for product management at the end of the life cycle, is shown in the Figure 1. [4].
In the most general case, if for the given product (pi), all three potential strategies are chosen as possible, which comprise the need for disassembly (strategies 2, 3 and 4), then the production system for processing of such products contains in itself all the elements as in the previous figure. In case we choose only the strategy number 4, then a subsystem for repair does not exist.
When choosing strategies 3 and 4, a subsystem for repair possibly exists. Depending on the type of product and the type of repair, the repair subsystem does not have to be specially separated. It is important to notice that in the procedure of the product disassembly, during the parts selection, a flow of materials must be planed for the parts that are headed for reassembly. In other words, it is often very possible to conduct, in a same place, within one subsystem where the disassembly is conducted, a second assembly of the product. A subsystem is being shaped for disassembly/reassembly, with a developed procedure for disassembly, selection of parts/subsystems and then, the reassembly of the required elements. In this case, a line for disassembly and a line for reassembly (assembly) are completely overlapping.
3 PRODUCT DISASSEMBLY PROCESS
Disassembly can be defined as a process of separating a product into its basic parts or subsystems, including the analysis on the condition of products and the selection of dismantled parts [4]. That is always an assembly of operations, which are conducted on technological systems for disassembly with the help of certain tools and fixtures.
In the disassembly, the operation procedure is accomplished according to an adequate technological procedure, which is designated for every work place in particular. The procedure implies, in the most general case, the following [4]:
•	accomplishing operation with the help of appropriate tools and fixtures,
•	analysis of the state and the diagnosis of the disassembled components (part/subsystem),
•	selection of the disassembled components (part/subsystem) according to previously accomplished analysis of the condition and the diagnosis.
Basic problems in designing and working processes of disassembly systems are in a component selection phase. It is a result of a lack of information about products, and different product condition arrived in disassembly system. That is the reason for expansion of product design documentation with another document - scenario for component selection (Table 1).
Managing EOL products according to strategies (S) 2, 3 and 4 bacis material flow
system for DISASSEMBLY
PRODUCT DATABASE
RECYCLE OF
MATERIALS
S 2
И
S 3
и
system for REASSEMBLY
1 - Reuse of parts in basicproducts
\S 2. 3 i 4
Reuse of parts )[ ( HAZARDOUS - H )
( WASTE - W ) (INCINERATION - I)
product
Pj
2 - Reuse of parts in diffrent products
Fig. 1. Production system for processing the products at the end of the life cycle
In essence, we distinguish the next possibilities for the selection of components after the process of disassembly:
•	dangerous components - materials (H (hazard)),
•	material recycling (R),
•	reusable (P),
•	finishing (D),
•	incinerate (I (incineration)),
•	waste disposal (W (waste)).
Scenario for component selection is important document not only in designing disassembly system process, but later when system is functioning. It enables dynamic correction of variant component selection (parts/ subassemblies). There are many possible selection alternatives for some components (Table 1.). The reason is that products arrive in disassembly system in different conditions. It is important to emphasize that not all parts are necessary to pass through the phases of condition analysis and diagnosis. This can be applied in the case when in a selection scenario (procedure) for the disassembled part it is not foreseen to have more possible variants of selection, but only one (e.g. recycling). In this case, right after the process of disassembly, a selection of the components is accomplished according to the previously determined scenario.
4 IMPLEMENTATION OF RFID TECHNOLOGY IN A (SUB) SYSTEM FOR DISASSEMBLY
In the (sub) systems of disassembly, we often find obstacles for different reasons. One of them is a problem of a lack of any kind of
information regarding the newly arrived products for processing (disassembly) and their distribution, after the operation, from specific work places [3]. Before and after conducting certain disassembly operations, information are crucial for efficient and effective decision making and for general management of the work processes.
Improvement of the quality of transferring information for conducting certain operations of disassembly, and then for the analysis of the state, diagnosis and selection of the disassembled components into appropriate flows, is one of the steps for general improvement of the processes for managing products at the end of the life cycle.
With the aim of faster distribution of real time information to according information flow nodes, it is necessary to use RFID technologies.
4.1. RFID Technologies
Radio Frequency IDentification (RFID) is a technology that enables automatic reading of multiple objects at the same time, without the need for individual scanning. The tag keeps in itself an Electronic Product Code (EPC) of every object that is read with the help of a remote reader.
EPC is a 96-bit numerical code written on a "smart tags" memory chip, which is fixed to individual products and physical objects. In this way, AUTO ID makes the dynamical acquisition of data possible, and products identification is located in every product with a unique print [2].
Table 1. Component selection scenario
Possible strategies for product:										
Part ID	Modul ID	s c Оч	Disassem-bly level		Possible variants of selection after disassembly					
					H hazard	R recycle	P1/2 reuse	D remanuf.	I inciner.	te E> d w
										
										
In every mentioned phase of the work process it is possible to upgrade the process by applying the RFID technologies, because of the advantages compare to other identification technologies.
Tasks that needs to be performed in disassembly system are complex and they involve not only disassembly proces but later analysis and diagnosys of component condition and their selection in adequate material/component flows. Decision about material/component variant selection is made according to the established diagnosis and suggested component/material variant selection obtained form the disassembly documentation database accordig with the RFID product identification i.e. document named Component selection scenario (Fig 2.)
Problems are mostly noted in [4]:
•	providing instructions for performing technological processes of disassembly,
•	selection process of disassembled components (parts/ subsystems / materials),
•	divergence - dissipation of the material flows is obvious and especially characteristic for the disassembly processes; controling the flows and the quantity in the material warehouse for disassembled components (parts / subsystems / materials).
In these parts of information flows it is possible to apply RFID technologies with the goal of: gathering real time data, improving the quality and the availability of certain types of information needed for not only disassembly process but also for the selection of disassembled parts and reassembly process.
Fig. 2. Material flows during the processing of an electric motor
4.2. A Model of RFID Technology Application in the Disassembly Subsystem
When designing a disassembly system one of the problems arising is the way of gathering information from products meant to be disassembled. Various technologies for automatic identification can be applied like barcode and others but we have developed a model of RFID technology application in the disassembly subsystem.
The model presented in this paper is a starting point of a research project conceived at the Institute for Industrial Systems in Novi Sad (Republic of Serbia). The concept of implementation of RFID technology in a disassembly process, applied in Laboratory for Assembly and Disassembly Systems at the Institute for Industrial Systems, is shown in Fig. 3.
In the control station (1) one of the possible strategies (strategies for reconstruction of used products (2), usage of already used products for spare parts (3) and recycling with disassembly 4) is being selected for the product
Fig. 3. RFID technology implemented in the disassembly process and selection of disassembled parts of
the products
that has to be disassembled. After selection, RFID transponder (tag) is being put on the base part of the product (3) which corresponds to the class and type of the product, for which the strategy has been chosen, with its EPC. After that, the product is being put on the assembly line and then moves to the processing phase. In the work station, the RFID tag reader (2) reads an EPC and uploads set of instructions from the database for the technological procedure of disassembly, in the form of a visual presentation on the monitor in front of the worker. Instructions are in a step by step form. They are activated by taking appropriate types of tools, and after returning them to their station, the next step is activated.
Another possibility is putting tags on tools and checking usage of tools with the help of RFID reader (6). If the worker takes by mistake different tool the system alerts with the adequate massage. If a task is being executed without tools, initiation of the next instruction is done manually.
After the operation (set of operations) designated for that work station is completed, the set of instructions ends. The product is afterwards placed on the assembly line, and then on some of the other work stations. After reading its signal from the RFID tag, the identification of the object for that work place is being performed. If the object is supposed to be processed in that work station, the signal light flashes and the worker pick the object from the assembly line. After that the process is continued as in the previous operation with a set of instructions designed for that work place and for that product. If all the work stations are busy, the object is circling on the assembly line until the moment some of them are free. The tag has to be on the base part all the time. The base part is the last that leaves the disassembly process.
If some component (part or subassembly) can be used again according to strategy for usage of already used products for spare parts, after disassembly, then an appropriate tag is put on that component at momentary work station. The tag carries in itself an EPC that corresponds to the component on which it is being put. By placing the component with a tag on the assembly line, it is transported to the warehouse for later use.
Products, for which strategy for reconstruction of used products is selected, are moving all the time, from one phase to another, together with all the disassembled parts in the appropriate transport unit (e.g. a palette or a box -so-called kit). After completing all of the disassembly operations (required for executing reconstruction of the appropriate degree), the whole palette with all its disassembled
components is being redirected to the overall subsystem, that is, toward the preparation warehouse for the product reconstruction.
Secondary materials, meaning materials that are going to be recycled, are being directed to adequate containers for the secondary material with the help of sensors which can recognize different types of materials, and the help of actuators (4), which push them into adequate containers. On each of the containers (5 for recycling, 7 for further disassembly processing) there is a tag-transponder, which corresponds to the type of material for which the container is designated.
Analyzing previous system with manual data acquisition and installed RFID system we came to the conclusion that overall time that product spends on disassembly line (from it's arrival to control station till putting it into containers) has been decreased for more than 17% (Table 2., Fig. 4.). It is important to mention that quantity of disassembled products is not big enough to provide fully valid statistically model of the impact of RFID technology on disassembly processes, since research was conducted in laboratory conditions.
This kind of concept enables a complete control of all material flows in the disassembly process. Also, it could be possible to track the number of parts in a warehouse and types of material and material quantity for recycling and for waste dumps.
One of the basic problems in the disassembly system is designing and organizing a disassembly system for different types of products.
Table 2. Experimental results
Average time for disassem. (min/ piece)	t1	12	13	14	t5	t6	t7	t8	*9	t10	t11	t12	t13	t14	t15	t16	t17	t18	t19	t20	Z tii
Manual disassembly	5.5	5.2	6.5	6.9	7.5	6.2	8.2	9.7	8.0	7.8	5.1	5.3	9.5	9.0	8.4	8.2	5.0	5.3	7.0	9.0	143.3
Disassembl y with RFID use	6.3	6.2	5.0	4.9	5.0	9.0	5.2	5.9	7.2	6.2	5.3	5.4	7.6	6.8	7.7	4.9	5.1	5.0	8.6	4.8	122.1
Model-type of monitor disassembled		<N S	3 S	^t- S	s	ю S	t--S	oo s	0\ S	M10	M11	M12	M13	M14	M15	M16	M17	M18	M19	M20	
Z tji (manual disassembly) > S tü (disassembly using RFID) (laboratory conditions conclusion: 17% shorter time - by using RFID)																					
-manual disassembly -disassembly with RFID use
10
1 3 5 7 9 11 13 15 17 1£ Model-type of monitor disassembled
Fig. 4. Average time for manual disassembly comparing to disassembly with RFID technology
It is uncommon to organize a disassembly system for only one type of product, unless this way of the systems functioning is strategically planed.A suggested system design has a higher degree of flexibility in the sense of possibilities to process different types of products including different variants of the same product.
Savings in time and space required for the selection of components (parts / subsystems / materials) are also noticeable.
5 CONCLUSION
The RFID technology has not been in wider usage in production, assembly and disassembly processes for various reasons. Some of them are: the popularity of the barcode, higher expenses due to RFID tags, privacy and security measures, lack of consensus on standards. However, some things are changing (e.g. the limited possibilities of barcodes in different conditions are being noticed, the tag prices are falling...) and slowly, the advantages of the RFID technology are being noticeable.
By implementing of RFID technology in the disassembly process it would be possible to quickly gather necessary information for the disassembly process, basically about the structure and the composition of the materials in the product. This information is necessary to define the technological procedure of disassembly completely and without any difficulties. Also, there can be integrated information about date of the production, so the system can be able to decide about later usage
of the product in reassembling. All the products of the older generation, which currently arrive to the disassembly subsystems, carry with them exactly this problem - the lack of information.
The benefits arriving with the use of the RFID technologies are multiple. As stated above, the possibilities of supervision, control and data acquisition in real time for the whole process is upgraded by using the RFID technology.
The model of RFID technology in the disassembly process presented in this paper is a starting point of a research project conceived at the Institute for Industrial Systems in Novi Sad. It is important to mention that quantity of disassembled products used in this research is not big enough to provide fully valid statistically model of the impact of RFID technology on disassembly processes, since research was conducted in laboratory conditions. For a valid statistical model it would be necessary to implement it in manufacturing site. There is another challenge for overcoming problems with high level of electrical noise coming from many electrical devices in manufacturing site which interfere with the writing and reading of RFID tags that could be tested when the model is implemented in manufacturing site.
6 REFERENCES
[1] Rose, C.M. (1999) Product End-of-Life Strategy Categorization Design Tool, Accepted for publication in Journal of
12
8
6
S 4
2
0
Electronics Manufacturing (Special Issue on electronic product reuse, remanufacturing, disassembly and recycling strategies.)
[2]	Fleisch, E., Tellkamp, C.H. (2003) The Impact of Higher Inventory Accuracy on Supply Chain Performance: A Simulation of Auto-ID Technology in a Retail Supply Chain, Massachusetts Institute of Technology, M-Lab Working Paper No. 16 Institute of Technology, University of St. Gallen Publications, Switzerland.
[3]	McFarlane, D., Sarma, S., Chirna, J.L., Wonga J.Y., Ashtonb, K. (2003) Auto ID systems and intelligent manufacturing control, Engineering Applications of Artificial Intelligence, vol. 16, no. 4, June 2003, p.365-376, Intelligent Manufacturing Journal.
[4]	Lazarevic, M. (2006) Contribution to the Product Disassembly System Design According to Acknowledged product End of Life Strategies, Master Thesys, Republic of Serbia.
[5]	Mehl, C., Beiter, A., Ishii, K. (1994) Design for Injection Molding: Using Dimensional Analysis to Assess Fillability, Proceedings of the 1994 ASME Design Automation Conference, Minneapolis, MN, (September 1994).
[6]	Ishii, K. (1994) Life-cycle Engineering Design. In Waldron M. (ed.), Design Theory, Methodology and Tools. Springer, Berlin Heidelberg New York.
[7]	ICER (2004) Industry Council for Electronic Equipment Recycling, WEEE Green List Waste Study, Report Prepared
by ICER for the Environment Agency, (April 2004).
[8]	Debevec, M., Perme, T., Noe, D. (2004) Decision making process in virtual manufacturing regarding human resources. V: IFAC Multitrack Conference on Advanced Control Strategies for Social and Economic Systems, Vienna, Austria, September 2 to 4, 2004 : ACS'04 : preprints volume. [Vienna: University of Technology], p.6.
[9]	Ostojić, G., Jovanović, V., Stevanov, B., Stankovski, S., Cosić, I. Collaborative Design in the Assembly Systems, 3rd International CIRP Sponsored Conference on Digital Enterprise Technology, DET'06, Setubal, Portugal: Escola Superior de Technologia, 18-20 septemper, 2006, p. 185- 193.
[10]	Parlikad, A. K. (2003) The Impact of Product Identity Information on Effectiveness of Product Disassembly Processes, Hughes Hall, PhD First Year Report,Center For Distributed Automation And Control, Manufacturing And Management Division, Department Of Engineering, University Of Cambridge September 2003.
[11]	Park, H.-S. (2003) Method For Disassembly Sequence Planning Of An End-Of-Life Car, The 14th International DAAAM Symposium "Intelligent Manufacturing & Automation Focus on Reconstruction and Development", 22-25th October 2003, Sarajevo, Bosnia and Herzegovina.
Paper received: 15.07.2008 Paper accepted: 25.09.2008
Flexibility and Complexity of Effective Enterprises
Rado Maksimo vić - Bojan Lalić * University of Novi Sad, Faculty of Technical Sciences, Department of Industrial Engineering and Management, Novi Sad, Serbia
The aim of this research was to give contribution to the efforts that are being made to develop the procedures of structural designing of industrial systems - highly effective enterprises. For that purpose, this paper analyses the conditions and possibilities that would enable those structures to adapt to changes in the surroundings - flexibility and management adequacy of organizational structures - by lowering the degree of complexity. Special focus is given to Mass Customization - tailoring the production to the needs and preferences of the customer. This requires high flexibility of a system as this is what determines the costs in this type of production.
The original contributions of this paper are the definitions and determination of the measures of the two most important characteristics of an enterprise - complexity and flexibility, and establishing their interdependence. While in the great body of literature complexity is measured by size (number of structural elements), this paper observes the complexity degree as comprising a number of interrelationships between the elements of a structure, beside the number of elements. Flexibility of the structures of an enterprise consists of three interdependent components: technological component, capacity component andflexibility of flows. © 2008 Journal of Mechanical Engineering. All rights reserved.
Keywords: production systems, enterprise system, organizational structure, enterprise flexibility, system complexity
1 INTRODUCTION AND LITERATURE OVERVIEW
Flexibility, structure of a system, complexity and customer-oriented production are terms used when considering trends in the development of the realistic requirements of the market [1] and predicting their further development. Flexibility can be defined as the ability of a system to quickly adapt to new circumstances [2] and [3]. It is the ability of a system to respond to changes as quickly as possible and at minimum cost and effort [4]. It is a well-known fact that production costs are reduced with the increase of products produced all the way to the minimum defined by basic costs [5]. Therefore, the term optimum number of products is introduced as an important parameter in observing the relation between the costs and the capacity of the production structures - the relation that involves the estimate of a system's flexibility. The increase of flexibility degree of a system has a negative effect because of its increased complexity, the result of which are limitations in the effective realization of processes in the system.
During the past twenty years, complexity theory has been regarded as an epitome of a completely new way of understanding nature. It has introduced and delineated adaptive systems (species, animals, plants, viruses etc.) as interactive networks of agents and tried to determine the behaviour within the networks [6] to [8].
A special view on a quality of enterprise's production structures involves approaches for its design by using simulation methods. Corresponding methods and techniques as tools for analyzing key performance indicators of production systems are described in [9] to [13].
As a result of the most recent researches into flexibility, mass customization can be seen as a response of flexible structures of a system to unpredictable changes in the surroundings. A model used here was the one that examines the relationships between the unpredictability of the surroundings, production flexibility and work results. Still, the idea of mass customization cannot give a complete answer to the question of production of a large number of various products which would satisfy the criteria of effectiveness, efficiency, and concerning the customer, the criterion of acceptable price [14] and [15].
*Corr. Author's Address: University of Novi Sad, Faculty of Technical Sciences, Trg Dositeja Obradovića 6,
Novi Sad, Serbia, blalic@uns.ns.ac.yu
Literature on mass customization has mainly focused on two areas: 1) the factors influencing companies to shift from mass production to mass customization [16] and 2) the implementation of mass customization [17]. Few authors have written about the success of customer-oriented mass production and this within the research of the markets [18] and [19]. Considering the efforts of some authors to determine a favourable relation and methodology and thereby solve the problems of flexible structures with low enough degree of complexity which can offer tailor-made products, it can be concluded that each of the mentioned components
should be dealt separately with the introduction of common limit functions [20].
2 FLEXIBILITY AND COMPLEXITY OF ENTERPRISES
2.1. Production Structures' Flexibility
Earlier researches on the production structures of industrial systems conducted at the IISE (Institute of Industrial Systems Engineering, Novi Sad, Serbia) [21] formed the basis for the development of (Fig. 1) effective enterprises: 1) change of the flow designing approach -individual to group and 2) change of the structure designing approach - process to product.
b) Group Approach to Flows Designing Fig. 1. The basic changes in approaches for production structures designing
The result of the mentioned changes in the approach is the creation of the Working Unit, the basic module of an effective enterprise -designated as WU in Fig. 1. Working Unit is defined as part of the production structure of an enterprise capable to carry out a certain task which is part of the work programme, should conditions of adequate space, technological equipment and the required structure of employees be met. Working Unit has the following characteristics:
-	it is independent of the other parts of the system's structure concerning the human resources and technical capacity,
-	it is responsible for completion of part of a programme, concerning the amount, quality and deadlines and
-	it is suitable for process automation. According to above definition, Working
Unit (WU) is a concept, in literature well known as Production Cell, but with defined differences. It is a part of enterprise's production structure (for machining or assembling) that is maximum independent from all other production structure parts in sense of its ability and capability for making groups of similar working objects. Therefore, Production Cell holds high flexibility level and it is enabled to all production operations demanded by each group of similar working objects for which it has been previously installed.
Similarity of working objects is providing conditions for high degree or total automation of processes for the Production Cell. Working Unit has all characteristics of Production Cell but beside its executive (production) independence it
has to have an organizational and controlling independence too, which means its total responsibility for quantity, quality, and delivery terms of similar working objects, and also for organizing and managing of processes. So we can say that Production Cell can be Working Unit if its competence is not limited just on production functions but also on planning, controlling, and processes improvement.
Flexibility has been defined in specific researches [22] to [24] as one of the basic characteristics of production structures that is of vital importance.
2.2. Organization Structures' Complexity
Functional structure of an enterprise consists of a group of functions of the enterprise (Fig. 2) [21] which are determined by the needs of going on a mission and achieving the goals of the enterprise. The project of organizational structures, based on the project of production structures, determines the structure of the other functions of an enterprise: Top management, marketing, development, commerce, financing, administration and logistics.
3 THE PRODUCTION STRUCTURES FLEXIBILITY - RESPONSE ON CHANGES
The ability of enterprises to adapt to changes in the surroundings and to the disorders in the work process is their extremely important characteristic called flexibility [22] to [27].
Fig. 2. Enterprise's Functional structure
Considering the characteristics of enterprise structures and the character of changes, three components of flexibility can be defined:
-	characteristics of elements - technological flexibility,
-	capacity of system elements - capacity flexibility,
-	dependability of system flows - flexibility of flows.
The degree of flexibility is a measure of structure flexibility.
It is defined as the likelihood of a system to successfully adapt to changes in the surroundings and to the current needs of the work process. Accordingly, it is possible to determine the components of flexibility [2] and [3] and their measures (Fig. 3).
3.1. Technological Flexibility
Technological flexibility is determined by the parameters of technological system elements and by the characteristics of the work object. The measure of technological flexibility of a system 's structures [28] to [29] (Fig. 3a) is represented by
Fig. 3a. Technological Flexibility
the likelihood with which the given element of a structure, within the certain installed parameters, will accept a group of work objects on which part of the work should be done in accordance with the projected technological procedures.
3.2. Capacity Flexibility
Capacity flexibility is determined by the ability of elements, parts of the structure and the entire system to do that amount of work that is necessary for manufacturing the projected amount of the work object. The measure of capacity flexibility [28] to [30] is determined by (non)existence of capacity reserve as represented in Fig. 3b):
K i — K i	K i
ri _ eu	ep _ л	ep
k = K~i =1 - KT
eu eu (1)
where fk is the degree of capacity of flexibility of a workplace "i" in the system (i =1,2...m), Keui - installed and Kep' - required capacity of that workplace.
3.3. Flexibility of Flows
Flows flexibility is determined by flows capacity (Fig. 3c), the relation between structure complexity degree (xp) and maximum complexity degree of the structure with a determined number of elements (xu):
к
fP =-
Km	(2)
Considerations of production structures flexibility indicate the existence of a close relationship between some components of flexibility in a way that:
Fig. 3b. Capacity Flexibility
Number of structure elements ( m ) Fig. 3c. Capacity Flexibility
-	parameters of structure elements, i.e. the value of technological flexibility degree and
-	the value of the existing capacity and the reserve of the capacity, i.e. the value of capacity flexibility degree,
in the sense of compatibility between the technological and capacity flexibility in sections of flow, enable relationships between them, i.e. flows flexibility value.
Fig. 3 represents the basic dependability between components:
-	technological component - on the work object characteristics and on the parameters of technological structures,
-	capacity component - on the relation load-capacity, achieved in the process of design,
-	flexibility of flows - on the complexity degree of flows, achieved in the process of design.
3.4. Research on the Technological Component of Production Structures Flexibility
Research into the value of the technological component of a system's structure in the conditions of implementation of the IISE -
approach to design of production, organizational and control structures of industrial systems, points to significant possibilities for maintaining certain characteristics on the desired level.
The main result of the research was the following [28] and [29]:
-	Using the sample of 30 production programmes of real industrial systems, the technological component of flexibility was determined in the conditions: STATE -individual approach to flow designing and process approach to structure designing, and PROJECT - group approach to flow designing and product approach to structure designing. More than 10,000 work objects
and 100 technological systems were analysed;
-	In accordance with the definition presented in part 3.3 and presentation in Fig. 3, basic dimensions of parts were analysed and technological component of flexibility determined, taking into consideration the possibility of accepting the work object, as shown in Fig. 4.
Technological system: Characteristic:
0250 UNIVERSAL LATHE
DIAMETER OF PARTS
BEFORE DESIGNING
AFTER DESIGNING
Size of sample: Interval beginning: Interval end: Iinterval width:
120 0
300 15
Distribution: NORMAL ^x(d) = 150.000 Ox(d) = 70.863
Size of sample: Interval beginning: Interval end: Iinterval width:
75 30 210 15
Distribution: NORMAL
^x(d) = 120.000
CTx(d) = 28.336
DISTRIBUTION DIAGRAM
DISTRIBUTION DIAGRAM
ACCOUNTING OF FLEXIBILITY
ACCOUNTING OF FLEXIBILITY
xg(d) = 180
xd(d) = 45
Pg(d) = 0.6628 Pd(d) = 0.0694
fTd = 0.5934
xg(d) = 180
xd(d) = 45
Pg(d) = 0.9830 Pd(d) = 0.0040
fTd = 0.9790
Fig. 4. An example of results of Technological Flexibility research
3.5. The Possibilities of Designing Flexible Production Structures
Research on the flexibility of production structures [29] has shown that when group approach is used in designing flows and object approach in designing production structures - the division of the system's structure into working units [21], as a result of the narrowing of the area of work object characteristics divergence in the working unit, variants of structure can be formed in the case of technological flexibility (Fig. 5) in which the technological component does not decrease in relation to state.
On the contrary, elements of structure -technological systems with an increased reserve for accepting and manufacturing the work object -occur in the greatest number of the observed cases.
4. THE DECREASE OF ORGANIZATIONAL STRUCTURES COMPLEXITY
- A CONDITION FOR EFFECTIVE ENTERPRISE MANAGEMENT
4.1. Complexity - the Basic Characteristic of the Structure of an Enterprise
The basic goals of the process of enterprise structure development are: the ability
to achieve a satisfactory (or set) effects/investment ratio and high control adequacy, which are conditioned by the increase of structures complexity - the most important inherent limit to the realization of an enterprise's effects.
4.1.1 The Definition
Complexity degree or variety of an enterprise's organizational structure [28], [29] and [31] denotes a variety of flows network in an enterprise, determined by the basic approach to the definition of structure complexity.
This approach is based on the number of elements and the number of connections ratio, using the equation:
Z m
s. =
(4)
where:
m - the total number of organizational structure elements, mi - number of organizational structure
4.1.2 Connections in Organizational Structure
The structure of an enterprise, the structure of its functions and the basic structure of connections between parts of the organizational structure are determined [21] by the quality of approach and implemented design procedures.
Fig. 5. Increasing of Technological Flexibility by changing Approach to Structure Designing
m
The basic between parts of shown in Fig. 6.
structures of connections organizational structure are
4.1.3 The Number of Organizational Connections
Mutual connections are established between parts of organizational structure. These connections (Fig. 7) establish interdependency between the elements. The character of connections may be:
-	Connections type: major о minor and
-	Mutual connections type: minor о minor.
The position of elements in the structure, concerning the total numbers of hierarchy levels,
the position of the observed element in relation to its minor and major elements, is of great importance when discussing organizational structure complexity.
The major О minor ratio in organizational structure is determined by a number of hierarchy levels and management range where:
-	Hierarchy level is part of organizational structure in vertical direction of connections, with one or more elements for defined working area (levels: enterprise, function, department, worker).
-	Management range - r is the number of minor elements controlled by one major element.
Fig. 6. The Variety of Connections in Organizational Structure
Fig. 7. Determination of Number of Connections in Structure
Management range determines the relationship between elements of two contiguous levels. Management range enables [21] the determination of the number of connections between the structure's elements in the observed part of the structure - mq, using the equation:
mi = r ( 2r-1 + r -1)	(5)
4.2. Complexity of Organizational Forms
With different cases of management range, the number of connections increases: r = 4 (4 minors) ^ 44 conn.; r = 5 (5 minors) ^ 100 conn. r = 6 (6 minors) ^ 222 conn.; r = 7 (7 minors) ^ 490 conn. Using this definition, it is possible to determine the dependence complexity degree for organizational structure part between one major
element and its minor elements and management range for different cases of organizational structure types (Fig. 8).
The types of organizational structures in Fig. 8 are the following [21] and [31]:
-	PROCESS TYPE of Organizational Structure
-	centralistic, or functional organizational structure (Fig. 8a),
-	PRODUCT TYPE of Organizational Structure
-	(non)centralistic, or divisional organizational structure (Fig. 8b),
-	PROJECT TYPE of Organizational Structure
-	known as matrix organizational structure (Fig. 8c),
-	"ORCHESTRA" TYPE of Organizational Structure - a fictitious form of organizational structure taken into consideration for comparison due to the lowest degree of complexity (Fig. 8d).
TOP MANAGEMENT
0 123456789 10
—Management range (r)
Fig. 8a. PROCESS TYPE of Organizational Structure
Fig. 8b. PRODUCT TYPE of Organizational Structure
Fig. 8c. PROJECT TYPE of Organizational Structure
Fig. 8d. "ORCHESTRA" TYPE of Organizational Structure
4.3. Needs and Possibilities of Organizational Structures Simplification
on organizational structure in real industrial systems
Research characteristics (enterprises) points to the necessity of eliminating all the installed limits for effective management of the work process, especially decreasing the complexity degree [28] and [29].
The possibilities of designing organizational structures with low degree of flows complexity, according to the given definition, various analyses and the presentation in Fig. 9, are reflected in the right choice of structure type. A detailed analysis of variants within a certain structure type is needed, however, with a special emphasis on the number of elements and their interrelations - the number of hierarchy levels and management range.
Research on the complexity degree of an enterprise's organizational structures shows that the complexity degree, beside the basic dependence on the number of elements and connections in a structure, is a consequence of the quality of the organizational structure project.
The quality of organizational structure project depends on:
a) Type-Variant of the Organizational Structure
The choice of the approach to organizational structure development - process, product, matrix or "orchestra" type results in the total number and specific character of connections between structure elements:
-	Process type - a variant that demands direct, group and indirect connections between elements and results in high complexity degree,
-	Matrix type - a variant that demands direct and group connections between elements and also results in high complexity degree,
-	Product type - a variant that considers the installed principles of team work, demands group connections between elements and results in low complexity degree, and
-	Orchestra" type - a variant with the lowest complexity degree, a theoretical variant - the goal in the process of organizational structure designing.
b) Management Range
5 MASS CUSTOMIZATION
Combined with a number of hierarchy levels, management range is a direct result of the process of organizational structure design because:
-	Management range harmonizes the enterprise's functional activities and determines the number of structural parts on the first hierarchy level and their relationships, and
-	Management range affects the design of structural parts, the total number of hierarchy levels and relationships between structural elements; most notably, management range makes a compromise between formal and informal organizational structure.
Mass customization basically refers to applied flexibility of business and production structures towards meeting the customer's requirements. As the demands of the market and development of their trends are more or less predictable (Fig. 10), the need for implementation of intelligent concepts is growing.
The period of value added time and total reconfiguration life cycle are getting shorter in time (Fig. 11). This is the crucial fact that introduces mass customization as a concept and flexibility as an answer in industrial systems.
Fig. 9. Simplification of Organizational Structures - Possibilities
Fig.10. Trends in market demands
Fig. 11. Reduction of added time period
Mass customization is regarded as a strategy for firms to move closer to the customer. It combines elements of mass production and individualization. It can reduce the costs of a firm and increase its productivity. It is estimated that mass customization products have a potential to reach a market share of around 30%.
The implementation of a mass customization strategy requires a shift of the internal organization of a firm irrespective of whether the firm operated in the past as a mass producer or produced tailor-made individual solutions. Every staff member of the future mass customer - not only the staff responsible for production and assembly - must understand the principles of mass customization and their role in the customer-oriented production system. In comparison to the system of mass production, a much higher flow of information has to be processed and shared between the relevant function units. The implementation of a mass customization strategy thus requires, apart from new production equipment and the integration of information technologies, the definition of a new work organization with different roles and routines compared to the old system.
All this leads to a unified direction towards implementing flexibility as the only solution in structure planning and deployment.
6 CONCLUSION
Research on flexibility of production systems based on system approach indicates, as the example of technological component of flexibility shows, that the implementation of group approach in flow design and product approach in structure design create the necessary
conditions for the design of effective production structures.
Systematically based and guided researches on organizational structure characteristics, as shown in this paper, indicate certain possibilities of generalizing the approach to establish the definition and determine Enterprise's Complexity Degree.
With this approach, a number of structural elements and a variety of relations between them are the basic parameters which define the complexity degree of organizational structure and simultaneously determine the complexity of an enterprise's information flows. Therefore, the complexity degree of organizational structure determined upon those parameters enables comparison of the designed structure variants using the quality defined as Control Adequacy.
The implementation of mass customization requires from industrial firms a reorganization of their internal structures and processes and additionally a more intensive collaboration with suppliers and customers. As the implementation of mass customization depends on the efficient interior communication processes and the willingness of workforce to learn and gain knowledge, as well as on the close collaboration with suppliers, service providers and customers, a cultural proximity between the involved parties smoothens the process of change.
Flexibility and complexity research results helped in defining and measures of key performances which are illustrating quality of enterprise's structure. In this way through different analyses the basics for quality evaluation and real enterprise's structure comparing had been set. However, characteristics of flexibility and complexity of enterprise's structure, how they are
defined in this work, in furthers research could be used as criteria for analyzing and choosing the optimal variant in designing procedures of enterprises structure.
7 REFERENCES
[1]	Pine, II, J. Mass Customization: The New Frontier in Business Competition, Boston: Harvard Business School Press, 1992.
[2]	Fricke, E., et al. Design for changeability of integrated systems within a hyper-competitive environment, Conference "Systems Approach to Product Innovation and Development in Hyper-Competitive Environments", INCOSE, Colorado, 2000.
[3]	Schulz, A. P., Fricke, E. Incorporating flexibility, agility, robustness, and adaptability within the design of integrated systems - key to success? 18th D ASC, Gateway to the NewMillenium, IEEE, 1999.
[4]	Upton, D. M. The management of manufacturing flexibility. California Management Review, 1994, vol. 36, no. 2, p. 72-89.
[5]	Schips, B. Einführung in die Volkswirtschaftslehre, Vorlesungsunterlagen. ETH Zürich: Institut für Wirtschaftsforschung, 2000.
[6]	Langston, C. (n.d.) Studying artificial life with cellular automata. Physica.
[7]	Marion, R., Uhl-Bien, M. Complexity theory and al-Qaeda: Examining complex leadership, Emergence. A Journal of Complexity Issues in Organizations and Management, 2003, vol. 5, p. 56-78.
[8]	Miles, R., Snow, C. C., Matthews, J. A., Miles, G. Cellular network organizations in twenty-first century economics (ed. W. E. Halal and K. B. Taylor), New York: Macmillan, 1999, p. 155-173.
[9]	Pandza, K., Polajnar, A., Buchmeister, B. Strategic management of advanced manufacturing technology. Int. Journal of Advanced Manufacturing Technology, 2005, vol. 25, no. 3/4, p. 402-408.
[10]	Vujica-Herzog, N., Polajnar, A., Tonchia, S. Development and validation of business process reengineering (BPR) variables: a survey research in Slovenian companies. Int. Journal of Production Research, Dec. 2007, vol. 45, no. 24, p. 5811-5834.
[11]	Kremljak, Z., Polajnar, A., Buchmeister, B. A heuristic model for the development of production capabilities. mJournal of Mechanical Engineering, Nov. 2005, vol. 51, no. 11, p. 674-691.
[12]	Palčič, I., Polajnar, A., Pandža, K. A model for the effective management of order-based production. Journal of Mechanical Engineering, July/August 2003, vol. 49, no. 7/8, p. 398-412.
[13]	Buchmeister, B., Kremljak, Z., Pandza, K., Polajnar, A. Simulation study on the performance analysis of various sequencing rules. International Journal of Simulation Modelling (Int J Simul Model), 2004, vol. 3, no. 2-3, p. 80-89.
[14]	Zipkin, P. The Limits of Mass Customization. MIT Sloan Management Review, Spring 2001, vol. 42, no. 3, p. 81-87.
[15]	Buchmeister, B. Investigation of the bullwhip effect using spreadsheet simulation. International Journal of Simulation Modelling (Int J Simul Model), March 2008, vol. 7, no. 1, p. 29-41, doi:10.2507/IJSIMM07(1)3.093.
[16]	Kotha, S. Mass Customization: Implementing the Emerging Paradigm for Competitive Advantage. Strategic Management Journal, 1995, vol. 16 (special issue), p. 21-42.
[17]	Swamidass, P. M., Newell, W. T. Manufacturing strategy, environmental uncertainty and performance: a path analytic model. Management Science, 1987, vol. 33, p. 509-524.
[18]	Boynton, A. C., Victor, B. Beyond Flexibility: Building and Managing the Dynamically Stable Organization. California Management Review, Fall 1991, vol. 34, no.1, p. 53-66.
[19]	Broekhuizen, T. L. J., Alsem, K. J. Success Factors for Mass Customization: A Conceptual Model. Journal of Market-Focused Management, Dec. 2002, vol. 5, no. 4, p. 309-330.
[20]	Hauser, D. P., de Weck, O. L. Flexibility in component manufacturing systems: evaluation framework and case study. Journal of Intelligent Manufacturing, June 2007, vol. 18, no% 3, p. 421-432.
[21]	Zelenović, D., Cosić, I., Maksimović, R. Design and Reenginering of Production Systems: Yugoslavian (IISE) Approaches,
Vol. I6 in Monograph "Group Technology and Cellular Manufacturing" - State-of-the-Art Synthesis of Research and Practice, Massachusetts: Kluwer Academic Publishers, 1998, p. 517-537.
[22]	Zelenović, D. M. Flexibility - A Condition for Effective Production Systems. International Journal of Production Research, 1982, vol. 20, no. 3, p. 319-337.
[23]	Zelenović, D., Burbidge, L. J., Ćosić. I., Maksimović, R. The Division of large complex production systems into independent, autonomous units. Proc. of 13th International Conference of Production Research, "Global Frontiers in Production", Jerusalem, 1995, p. 213-215.
[24]	Zelenović, D., Tesić, Z. Period batch control and group technology. International Journal of Production Research, 1988, vol. 26, no. 4, p. 539-552.
[25]	Shewchuk, J. P., Moodie, C. L. Definition and Classification of Manufacturing Flexibility Types and Measures. International Journal of Flexible Manufacturing Systems, 1988, vol. 10, no. 4, p. 325-349.
[26]	Zelenović, D., Šešlija, D., Ćosić, I., Maksimović, R. On the Flexibility of Robotic
Assembly. Proceedings of Xth International Conference on Production Research, Nottingham, 1989, p. 552-553.
[27]	Tasic, T., Buchmeister, B., Acko, B. The development of advanced methods for scheduling production processes. Journal of Mechanical Engineering, Dec. 2007, vol. 53, no. 12, p. 844-857.
[28]	Zelenović, D., Maksimović, R. Flexibility of effective enterprises. International Journal of Industrial Systems, 1999, vol. 1, no. 2, p. 33-38.
[29]	Maksimović, R. Decreasing of organization structures complexity - a condition for effective enterprise management. International Journal of Industrial Systems, 1999, vol. 1, no. 2, p. 123-128.
[30]	Buitenhek, R., Baynat, B., Dallery, Y. Production capacity of flexible manufacturing systems with fixed production ratios.
International Journal of Flexible Manufacturing Systems, Jan. 2002, vol. 14, no. 3, p. 203-225.
[31]	Burbidge, J. L. Period Batch Control, Oxford: Oxford University Press, Clarendon Press, 1996.
Paper received: 17.03.2008 Paper accepted: 25.09.2008
Reliability and Efficacy of Identification Systems and Supply Chain Management1
Robert Brumnik* - Zvone Balantič University of Maribor, Faculty of Organizational Science, Kranj
The processes of production and logistics often involve the requirement to reliably identify the individuals responsible for certain operational procedures (complaints, process audits, preventive-corrective actions due to non-conformance). The individuals in charge of these procedures usually have their own way of identity confirmation (signature, PIN codes, chip cards2, biometric identifications, camera, etc.). It is thereby necessary to reduce the scope of information to the legally acceptable limit that insures personal integrity and confidentiality.
Because of the continuous optimization and automation of processes there is an increasing trend towards »simple identification systems« in the production and logistics processes. Biometry makes the identification process faster and simpler by using people's unique characteristics3 without the need for any additional identification elements. However, it is necessary to research the reliability and efficacy parameters of this identification method in order to avoid unnecessary complications that could arise from selecting unsuitable technology.
© 2008 Journal of Mechanical Engineering. All rights reserved.
Keywords: production processes, logistic processes, identification, automation, reliability, efficiency, biometry
0 INTRODUCTION
Production logistics must ensure an effective flow of material, tools and services during the whole production process and between companies. Solutions for traceability of products and people (identification and authentication) are very important parts of the production process. The entire production efficacy and final products quality depend on the organization and efficiency of the logistics process. The capability of a company to develop, exploit and retain its competitive position is the key for increasing company value [7].
Globalization dictates to the industrial management an effective, lean5 manufacturing,
downsizing and outsourcing. The requirements of modern times are development and the use of wireless technologies such as the mobile phone. The intent is to develop remote maintenance, remote servicing and remote diagnostics [8]. With the increasing use of new identification technologies, it is necessary to explore their reliability and efficacy in the logistics process.
The new identification systems are achieving extremely fast development in the last ten years with the evolution of microelectronics and it enables practical application in the branch of automation of logistics and production. It is necessary to research and justify every economic investment in these applications.
1	Supply Chain Management (SCM); the process of planning, implementing, and controlling the operations of the supply chain as efficiently as possible. Supply Chain Management spans all movement and storage of raw materials, work-in-process inventory, and finished goods from point-of-origin to point-of-consumption.
2	Chip card (Smart card, Integrated Circuit card - ICC or Contact less RFID card) is defined as any pocket-sized card with embedded integrated circuits which can process information. This implies that it can receive input which is processed - by way of the ICC applications - and delivered as an output. There are two broad categories of ICCs. Memory cards contain only nonvolatile memory storage components, and perhaps some specific security logic. Microprocessor cards contain volatile memory and microprocessor components.
3	Characteristics; elements of unique personal identification (fingerprints, cornea, iris, DNK).
4	Radio-frequency identification (RFID) is an automatic identification method, relying on storing and remotely retrieving data using devices called RFID tags or transponders. RFID tag is an object that can be applied to or incorporated into a product, animal, or person for the purpose of identification using radio waves. Some tags can be read from several meters away and beyond the line of sight of the reader. Most RFID tags contain at least two parts. One is an integrated circuit for storing and processing information, modulating and demodulating a (RF) signal, and other specialized functions.
5	Lean manufacturing; Lean is essentially a business discipline that is built around obeying only the customer's demand signals (or "pull") and getting rid of waste everywhere in the supply chain, waste in overproduction as well as in inventory [9].
*Corr. Author's Address: University of Maribor, Faculty of Organizational Science, Kidričeva 55a, Kranj, Slovenia, robert.brumnik@metra.si
The production process needs to be efficacious and carefully planned with the support of dynamic analysis and optimization tools (MS Visio, Process Simulator, etc.). In this paper the most important quantitative characteristics of reliability are explained. The authors also show the methodology for defining reliability and efficacy of identification systems in the process of production and logistics and provide experimental research of personal identification systems6 based on reliability and efficacy parameters. Furthermore, an identification system of a real production-logistics system was upgraded based on automation and informatization.
In a comparative study based on wireless RFID and Biometric Identification Systems (see Figure 1.), the authors:
•	show the availability and efficacy analyses in the processes of informatization and automation of production and logistics systems,
•	extend reliability estimation of identification systems (RFID and biometric) based on significant reliability characteristics,
•	research cost analysis of investment in an identification system,
•	provide contribution to science by researching the process of production and logistics to ensure optimal procedures of automated identification.
A review of scientific databases shows that the area of assessing the reliability of identification systems in the process of production and logistics is not well explored. In modern production and logistics processes (automobile industry, aircraft-space industry, pharmacy, forensics, etc.) it is necessary to have a fast and reliable control over the flow of material and people.
Fig. 1. Self-organizing wireless network Identification technologies in the production logistic industry
Companies such as army and automobile equipment suppliers can verify the serviceability of qualified parts. By using unique serial numbers of business events and transactions, connected to individual parts, it is possible to prevent any imitations or construction parts without warranty.
This paper deals with the systematical relations within identification systems. Statistical processing and conclusion forming were conducted using a tools for statistical treatment and reliability defining - Weibull++7. The aim of this research is improvement of the theoretical model, which will enable a better stability of identification in real dynamic systems. The theoretical research is followed by optimization including dynamic changes that can occur in the production-logistics process. Optimization as a function of automation will happen with linear programming7 and numerical methods in order to minimize the production costs. Simultaneously, empirical data processing and development of a mathematical model take place.
6	Personal Identification Systems; Recent events have heightened interest in implementing more secure personal identification (ID) systems to improve confidence in verifying the identity of individuals seeking access to physical or virtual locations in logistic process. A secure personal ID system must be designed to address government and business policy issues and individual privacy concerns. The ID system must be secure, provide fast and effective verification of an individual's identity, and protect the privacy of the individual's identity information.
7	Linear programming; in mathematics, linear programming (LP) problems involve the optimization of a linear objective function, subject to linear equality and inequality constraints. More formally, given a polytope (for example, a polygon or a polyhedron), and a real-valued affine function.
1 DEFINING THE PROBLEM AND RESEARCH PARAMETERS
The availability of a production-logistic process is the probability that the system is functioning well at a given moment or is capable of functioning when used under certain circumstances. Reliability by definition is probability (capability) of the system to perform under stated conditions defined by function and time [4]. It is one of the most important characteristics of efficacy of identification systems and has an impact on safety and efficiency of the system. Increasing the system's reliability means less improper uses, higher safety, less repair procedures and shorter identification time and consequently causes higher system availability. Implementing higher reliability in early development phases and its assurance during the use of the identification system requires the knowledge of methods and techniques of reliability theory and their interactions.
Many different characteristics are used to measure the reliability of identification systems and their components. Some of them are connected to time functions; others represent average time functions. Which of these characteristic are relevant in specified cases depends on the set goals, selected method of analysis, and the availability of data.
Characteristics of reliability are based on mean time intervals to the occurrence of failure. Time to failure is a random magnitude and we will mark it with symbol ti. In this paper we give definitions and statistical estimations of basic reliability characteristics.
Reliability characteristics used in this research are:
•	MTTF - mean time to failure
•	MTBF - mean time between failures
•	MTTR - mean time to repair
•	F(t) - unreliability function
•	X(t)- failure rate
•	ß - shape parameter
a.	ß<1 temporary failure frequency X(t) decreases (early period, system implementation)
b.	ß=1 temporary failure frequency X is constant (normal system operation)
c. ß >1 temporary failure frequency X increases (exploitation, ageing)
The shape parameter (ß) changes the configuration of the temporal distribution of operational failures.
1.1. Quantitative Reliability Characteristics
Unreliability function F(t) is defined by the equation:
F (t ) = P(ti < t )	(1)
F(t) is therefore the probability of a system to become non-functional in the interval between 0 and t.
If we observe a number of systems or system components we can calculate the statistical estimation for the unreliability function by the equation:
F (t ) =
N0 - N (t )
N
(2)
N(t) - number of working/functional samples in the interval (0,t)
N0 - number of samples at the start of observation at t = 0
Reliability function R(t) is complementary to unreliability function. We can define it using the equation:
R(t ) = 1 - F (t ) = P(tt > t )
(3)
R(t) is the probability for a system or a component to become non-functional after a time period t. A statistical estimation of the reliability function we can define using the equation:
R(t ) =
N (t )
Nn
(4)
The product of the time to failure function and dt is the probability of the system or its component to become non-functional in the interval (t, t+dt). We can calculate the function F(t) by differentiation of the unreliability function by time:
F (t ) =
dF (t ) dt
(5)
The statistical estimation for f(t) can be calculated with the equation:
f (t ) =
N (t ) - N (t + At )
N0 At
(6)
where At is interval {t, t + At).
Product of Failure rate Л and dt is the conditional probability of a system/part of system to become non-functional in the interval
(t, t+dt).
Momentary frequency of failure rate can be written as:
X(t ) =
f (t )
X(t ) =-
R(0	(7)
The statistical estimation for Л is defined with the equation:
N(t) - N(t + At)
N (t ) At	(8)
For many systems or system parts the function 2(t) has a characteristic "bathtub" configuration (Figure 2.). The life cycle of systems can be divided into three periods: early damaging period, normal working period and ageing or exploitation period. Л in first period decrease in second period Л is constant and Л growth in third period.
i <
ф		
early damaging	period of nomisi	period of ageing or
perici	functioning	sKplotation
		\
Fig. 2. "Bathtub" curve [4]
2 THE METHODOLOGY OF RESEARCHING THE RELIABILITY OF IDENTIFICATION SYSTEMS IN THE PRODUCTION-LOGISTIC PROCESS
2.1. Reliability of RFID Identification
Systems
The research was conducted on Memory and Microprocessing identificators that can be installed onto the construction elements in the production-logistic process. Identification of persons in production-logistic processes is provided by biometric identificators which are unique to every person. Memory Identificators do not have a processor and therefore can not dynamically process data. Cards are designed to save the value or tokens for one time or continuous use.
Microprocessing identificators usually contain a processor, input-output unit and various kinds of data storage. They are able to dynamically process data. At the moment 8-, 16-, and 32-, bit processors are in use and have in average 16 to 32 Kb EEPROM and 3 Kb RAM. Input-output unit transmits 9.6 to 115 Kbits per second (only half duplex mode is possible). In terms of processor power they can be compared to the IBM-XT computer and cards with Crypto coprocessor in some function significantly exceed the 50 MHz 486 computer.
With adequate construction [1], the majority of operations and logs can be transferred from smart cards to PCs that have better working and process capabilities. For the cryptosystem RSA8 with public keys, the recommended key length is 2000 bits. Adding components (e.g. coprocessor) increases the cost of cards and at the same time their reliability and safety are reduced. The conditions caused by the deficiency of data storage capacities or processing power can be improved with new technology (such as Cryptosystems with Elliptical Curves9).
8	RSA; The mathematical details of the algorithm used in obtaining the public and private keys are available at the RSA Web site.
Briefly, the algorithm involves multiplying two large prime numbers (a prime number is a number divisible only by that number
and 1) and through additional operations deriving a set of two numbers that constitutes the public key and another set that is the private key.
9	Elliptical curve cryptography (ECC) is a public key encryption technique based on elliptic curve theory that can be used to create faster, smaller, and more efficient cryptographic keys. ECC generates keys through the properties of the elliptic curve equation instead of the traditional method of generation as the product of very large prime numbers. The technology can be use in conjunction with most public key encryption methods, such as RSA.
They enable shorter safety keys and faster processing (with existing processor) and keep the same level of safety.
2.2.	Reliability of Biometric Identification
Systems
Definitions used in reliability calculation of biometric identification systems and terminology:
•	FAR10 is defined as the percentage of identification instances in which false acceptance occurs,
•	FRR11 is defined as the percentage of identification instances in which false rejection occurs,
•	Mean time to failure (MTTF), mean time between failures (MTBF) and mean time to repair (MTTR),
•	classification of failures,
•	failures data bases.
In contrast to the classic methods of identification, in biometric methods probability needs to be considered. All sensors are subject to noise and errors. The largest problem is the development and implementation of a safe crypto algorithm. All limitations are summarized in the two terms: FRR and FAR. It a system is highly sensitive, the FAR value is low, but FRR is higher. In a system of low sensitivity the situation is reversed. Such us system accept almost everyone (FAR > FRR). It is therefore necessary to make compromise in the sensitivity of a system. It can also be regulated so that the FAR and FRR values are equal, the so-called EER (Equal Error Rate). Lower EER means a more accurate system. In application where the speed of identification is more important than safety (e.g. hotel rooms), the high FAR value can be allowed [3].
2.3.	Identification and Verification (Authentication)
It often happens that we use the term identification when we talk about verification and vice versa. Identification is a term used for
identifying a person based on their biometrical data. This mostly involves a database of biometric data with which the momentary information is compared until the most similar or same image is found. We search among N persons in the database so this way is called »1:N« or »One to many comparison«. With personal identification we look for a person's identity (e.g. name). In verification however, we ascertain if this is indeed the person they claim to be [6], so there is only one comparison (1:1). Since we know the person's name, we compare the data read by the sensor with the data stored in the database.
2.4. Fingerprint
Fingerprint recognition is the oldest form of all the biometric methods and they are secure from mutations. Fingerprint images are skin folders and furrows and have different details which can easily be read by a biometric module (Fig. 3.). Details are located on the end of furrows or on the joints of folders. The global images made by skin folders, furrows and details on a finger are different for each person and are therefore very adequate for recognizing a person. To recognize a fingerprint, approximately 100 bits are enough for detail searching methods, while high security systems store information in few Mbytes per image. We never store real fingerprints in the database. There is no possible way to recognize a person from the stored images without the use of special equipment. In correlation methods, the amount of data is higher.
^^ Q
Fig.3. Fingerprint Reader Module
(Suprema Technical Manual, 2007)
10	AR (False Aceptance Rate); This can be expressed as a probability. For example, if FAR is 0.1 percent, it means that on average, one out of every 1000 impostors attempting to breach the system will be successful.
11	FRR (False Recetion Rate); For example, if FRR is 0.05 percent, it means that on average, one out of every 2000 authorized persons attempting to access the system will not be recognized by that system.
3 RESULTS AND DISCUSSION
For the duration of research it is necessary to define reliability characteristics of RFID and biometric identification systems. Reliability characteristics of system components can be determined by testing, changing the functioning in the exploitation phases, catalogues and test reports or reference books (most known is the MIL HDBK 21712).
3.1. Reliability Parameters MTTF, MTBF of a RFID System Reader
1 n
MTTF = fR(t )dt =-Z ti = 76.5 days
n i=1
1n
MTBF = JR(t)dt =-Z ti = 78.6 days
The failures that were considered for defining MTTF, MTTR and MTBF (See Table 1.) of a RFID system are the following:
•	Failures in Software operating (reader can not read RFID Tags).
•	Failures in Hardware operating (RFID reader/antenna, impossible programming of RFID Tags or Microchips).
3.2. Reliability parameters MTTF, MTBF of Biometric Identification Reader
1 n
MTTF = J R(? )dt =-Z ti= 88.8 days
1n
MTBF = jR(t)dt =-Z ti= 90.1 days
The failures that were considered for defining MTTF and MTBF of a Biometric system are following (See Table 2).
Failures in Software operating (impossible read or recognition of fingerprint images) Failures in Hardware operating (Biometric Reader, PCBs13). Failures as a consequence of sensor operating: FAR, FRR.
3.3. Failure Rate X(t) of RFID Biometric Identification Systems
and
Reliability of the RFID module can be defined with the Failure Rate parameter X(t) in different periods:
•	early damaging period,
•	period of normal functioning,
•	period of ageing or exploitation.
To define Failure Rate the Weibull model was used. It can also be used for models where Aft) can not be illustrated by constant or linear functions. The reliability parameters were defined using graphic method (Weibull++7 Software) and the results of the graphic methods are presented on the following figures:
•	Reliability Function Rft) of RFID system by ß=2.6535 (Fig. 4.).
•	Failure rate fft)/Rft) of RFID system by ß=2.6535 (Fig. 5.).
•	Reliability Function Rft) of BIOMETRIC system by ß=2. 6024 (Fig.6.).
•	Failure rate fft)/Rft) of BIOMETRIC system by ß=2. 6024 (Fig. 7.).
3.3.1 Times to failures fsee Table 1) of RFID identification system samples and corresponding appraisal
Pairs [t;,FXO ] (See Table 3.) were
drawn in the probability web of a chosen (Weibull) probability distribution.
Times to failures and belonging point estimations (Fig .4.) shown during the ageing period or exploitation phase of RFID system ß=2.6535 (ß >1).
MIL HDBK 217 [10]; this military standard is used to estimate the inherent reliability of electronic equipment and systems based on component failure data. It consists of two basic prediction methods: Parts-Count Analysis and Part-Stress Prediction. The general failure model in MIL-HDBK-217 and Bellcore TR-332 is the form: ^ _	[11].
3 PCB (Printed Circuit Board) is used to mechanically support and electrically connect electronic components using conductive pathways, or traces, etched from copper sheets laminated onto a non-conductive substrate. Alternative names are printed wiring board (PWB), and etched wiring board. A PCB populated with electronic components is a printed circuit assembly (PCA), also known as a printed circuit board assembly (PCBA).
Measured time parameters to terminal damage of the RFID system (ti, i=1,2,3):
Table 1. MTTF - MTTR - MTBF for RFID System
Ser. no.	Time to Failure1	Time to Failure2	Time to Failure3	MTTF	Average value
22345	13	139	48	66.7	
22359	27	106	42	58.3	
22346	54	106	58	72.7	
22347	54	110	83	82.3	
22348	72	96	73	80.3	76.5
22349	90	82	88	86.7	
22360	116	28	93	79.0	
22375	87	29	115	77.0	
22381	51	40	145	78.7	
22387	60	36	155	83.7	
Ser. no.	Service procedure trial1	Service procedure trial2	Service procedure trial3	MTTR	Average value
22345	1	1	1	1.0	
22359	1	1	1	1.0	
22346	2	3	2	2.3	
22347	2	0	3	1.7	
22348	5	3	7	5.0	2.1
22349	1	1	1	1.0	
22360	4	1	2	2.3	
22375	4	2	1	2.3	
22381	4	3	4	3.7	
22387	1	0	1	0.7	
Ser. no.	Time to repeated start1	Time to repeated start2	Time to repeated start3	MTBF	Average value
22345	14	140	49	67.7	
22359	28	107	43	59.3	
22346	56	109	60	75.0	
22347	56	110	86	84.0	
22348	77	99	80	85.3	78.6
22349	91	83	89	87.7	
22360	120	29	95	81.3	
22375	91	31	116	79.3	
22381	55	43	149	82.3	
22387	61	36	156	84.3	
Measured time parameters to terminal damage of the biometric system (ti? i=1,2,3):
Table 2. MTTF - MTTR - MTBF fo BIOMETRIC System
Ser. no.	Time to Failure1	Time to Failure2	Time to Failure3	MTTF	Average value
36365	53	89	88	76.7	
36359	60	106	73	79.0	
36366	87	106	88	93.0	
36364	86	161	88	106.3	
36368	102	130	13	81.7	88.8
36369	99	102	98	99.7	
36360	56	150	93	99.7	
36345	57	90	126	91.0	
36381	81	52	117	83.3	
36384	90	65	105	80.0	
Ser. no.	Service procedure trial1	Service procedure trial2	Service procedure trial3	MTTR	Average value
36365	1	1	1	1.0	
36359	0	1	0	0.3	
36366	1	3	2	2.0	
36364	1	0	1	0.7	
36368	1	3	1	1.7	1.2
36369	2	1	1	1.3	
36360	2	1	1	1.3	
36345	3	1	1	1.7	
36381	2	1	1	1.3	
36384	2	0	1	1.0	
Ser. no.	Time to repeated start1	Time to repeated start2	Time to repeated start3	MTBF	Average value
36365	56	90	89	77.7	
36359	60	105	73	79.3	
36366	88	107	90	95.0	
36364	85	161	89	105.0	
36368	103	133	16	83.3	90.1
36369	101	103	99	101.0	
36360	58	151	96	101.0	
36345	60	91	127	92.7	
36381	83	53	118	86.7	
36384	92	65	106	81.0	
3.3.1 Times to failures (see Table 1) of RFID identification system samples and corresponding appraisal
Pairs [ti,F"(ti) ] (See Table 3.) were
drawn in the probability web of a chosen (Weibull) probability distribution.
Table 3. Times to failures and belonging appraisal for RFID system
Mean time to first failure (RFID)										
i	1	2	3	4	5	6	7	8	9	10
ti	13	27	54	54	72	90	116	87	51	60
F(t )	0.05	0.12	0.19	0.26	0.33	0.4	0.48	0.55	0.62	0.66
										
Mean time to second failure (RFID)										
i	1	2	3	4	5	6	7	8	9	10
ti	139	106	106	110	96	82	28	29	40	36
F (t )	0.05	0.12	0.19	0.26	0.33	0.4	0.48	0.55	0.62	0.66
										
Mean time to third failure (RFID)										
i	1	2	3	4	5	6	7	8	9	10
ti	48	42	58	83	73	88	93	115	145	155
F(t )	0.05	0.12	0.19	0.26	0.33	0.4	0.48	0.55	0.62	0.66
..: - J 1.Л. j - :: J:J:I ..-I'ILI--
Fig. 4. Reliability function of RFID system by ß=2.6535
Times to failures and belonging point estimations (Fig .4.) shown during the ageing period or exploitation phase of RFID system ß=2.6535 (ß >1).
3.3.2 Times to failure (see Table 2.) of Biometrie identification system samples and corresponding appraisal
Fig.5. Failure rate f(t)/R(t) of RFID system byß=2.6535
Pairs [\,F(tt ) ] (Table 4.) were drawn i
m
the probability web of a chosen (Weibull) probability distribution.
Table 4. Times to failures and corresponding appraisal for BIOMETRIC system
Mean time to first failure(BIOMETRIC)										
i	1	2	3	4	5	6	7	8	9	10
ti	53	60	87	86	102	99	56	57	81	90
F(t )	0.05	0.12	0.19	0.26	0.33	0.4	0.48	0.55	0.62	0.66
Mean time to second failure (BIOMETRIC)										
i	1	2	3	4	5	6	7	8	9	10
ti	89	106	106	161	130	102	150	90	52	65
F(t )	0.05	0.12	0.19	0.26	0.33	0.4	0.48	0.55	0.62	0.66
										
Mean time to third failure (BIOMETRIC)										
i	1	2	3	4	5	6	7	8	9	10
ti	88	73	88	88	13	98	93	126	117	105
F(t )	0.05	0.12	0.19	0.26	0.33	0.4	0.48	0.55	0.62	0.66
Rdi«SoftWcibulH-+ ? - www.adiaSaft.oom
Reliability vs Time Plot
Time, (t)
Fig. 6. Reliability function R(t) of BIOMETRIC sytem by ß=2.6024
RHieSoft WsrtsiJI++- ? - www,fieliaSoft.com
Failure Rate vs Time Plot
Time, {ф
Fig. 7. Failure rate f(t)/R(t) of BIOMETRIC system byß=2.6024
4 CONCLUSIONS
Biometric methods are becoming a very popular alternative to traditional identification systems in production-logistic processes where identification of people is necessary. Our research has shown that the ageing of biometric system begins later compared to RFID identification systems. The results indicate high availability the biometric identification systems and lower maintenance costs. There are many benefits to
using biometric systems, such as no need for any additional identification elements. The use of biometric methods simplifies identification and increases reliability because biometric identification elements are not portable (fingerprints) and prevent non-authorized uses. Results of this research indicate the following:
1. better reliability of biometric systems regarding reliability parameters MTTF, MTBF and X(t);
•	MTTF of biometric systems are improved by 12.3 days.
•	MTBF of biometric systems are improved by 11.5 days.
•	The most critical parameter of the RFID systems - X(t), does not need to be considered in biometric systems. In a biometric system, there is no need for RFID cards or RFID tags for identification.
2.	For biometric identification there is no need for RFID cards or tags which are the most critical parts in RFID Identification System. Experiments show that most cards fail within one year.
3.	Time of servicing biometric readers is shorter than time of servicing RFID readers by an average of 1 day. This is a better result by 30% and consequently biometric systems have better availability.
4.1 Return of investment with optimizing production logistic
On the basis of the results of this research and customer feedback information, it can be concluded that the investment into automation of personal identification in the production-logistic processes is returned within 10 to15 months. The exact time depends on the degree of automation and the quantity of identification places). Of the many industrial branches these advantages and solutions will be a necessity for the pharmaceutical sector, where the processes must ensure safe distribution. Pharmaceutical companies have to deal with the problem of fake and altered medicaments (the estimated loss of is 75 billion dollars a year until 2010). According to predictions, biometric identification technology will reach vast rates of development. An indication of maturity of the biometric system is the amount of investments in the field. In the year 2002, the US government invested 16.63 million dollars into the biometric industry. The expected income of biometric industry in USA in 2007 was 153 million dollars. Expected growth of income between the years 2000 and 2007 is 67% [6].
5 SUMMARY AND FUTURE WORK
The usefulness of biometric systems is shown in production-logistic environment where personal
identification is needed. From this research it is evident that the ageing period of biometric systems begins later compared to RFID (card identification) systems. The results also show that the availability of biometric identification systems is higher and therefore maintenance costs are lower. Functional and ergonomic advantages of biometry are clear because there is no need for any cards or other elements of identification in the production-logistic process. The use of biometric systems will make identification simple and at the same increase reliability due to non-transferability of identification elements (fingerprints) and prevent improper use. It can be expected that biometric technology will attain Slovenia in spite of doubts expressed by some institutions (office for personal data protection). Many open ethical questions arise, mostly on human personality, privacy and control. However researches such as this on reliability and availability unequivocally show that biometric technology has an advantage both in practical use and data safety.
Personal responsibility and accuracy in fields such as legislation, regulation adjustment, and production and supply chain management in global technical operations are more easily controlled using automated identification. With the automation of identification there are also the possibilities of merging and comparing current process data with data from integral information systems (ERP, MRII, etc.) or other business applications.
6 REFERENCES
[1]	Balantič, Z. (2006) Multimedia spiral architecture development for effective medical education. WSEAS Transactions on Computers, Athens, Greece, vol. 5, no. 10, 2293-2300.
[2]	Bigun, E.S., Bigun, J., Duc, B., Fischer, S. (1997) Expert Conciliation for Multi Modal Person Authentication Systems by Bayesian Statistics. Personal Authentication, Crans-Montana, Switzerland, pp. 327-336.
[3]	Hicklin, A., Watson, C., Ulery, B. (2005) The Myth of Goats: How many people have fingerprints that are hard to match? NIST Interagency Report 7271.
[4]	Hudoklin, A., Rozman, V. (2004) Reliability and availability of systems human-machine. Publisher: Moderna organizacija, Kranj.
[5]	Hong, L., Jain, A. (1998) Integrating Faces and Fingerprints for Personal Identification. IEEE Transactions on Pattern Analysis and Machine Intelligence, vol. 20, no. 12, pp. 1295-1307.
[6]	Mraović, M. Biometric methodes in access control systems. University of Ljubljana, Faculty of Electrical Engineering, Ljubljana, Slovenia, 2003.
[7]	Polajnar, A. (2005) Excellence of toolmaking firms : supplier - buyer -toolmaker: Collection of Conference consultation, Portorose, 11.-13. october 2005.
[8]	Polajnar, A. (2003) Exceed limits on new way : supplier - buyer - toolmaker: Collection of Conference consultation, Portorose, 14.-16. october 2003.
[9]	Kerr, J. What does »lean« really mean?. Special report, Logistics Management, 2006 URL:
http://www.logisticsmgmt.com/article/CA63 34579.html (acquired:17.05.2008).
[10]	MIL-HDBK-217, Reliability Prediction of Electronic Equipment. U.S. Department of Defense
URL:http://www.itemuk.com/milhdbk217.ht ml (acquired: 12.05.2008)
[11]	Jones, J. and Hayes, J. (1999) A Comparison of Electronic-Reliability Prediction Models. IEEE Transactions on Reliability, vol. 48, no. 2, pp. 127-134.
Paper received: 24.03.2008 Paper accepted: 25.09.2008
Mechanical and Metallurgical Properties of Aluminium and Copper Sheets Joined by Cold Pressure Welding
Kaan Ozel1, - Mumin Sahin1 - Aysegul Akdogan2 1 Trakya University, Mechanical Engineering Department, Edirne, Turkey 2 Yildiz Technical University, Mechanical Engineering Department, Istanbul, Turkey
Cold pressure welding is a special welding method that has been used in applications such as assembly of various parts at an increasing rate in recent years. In the present paper, cold pressure welding was applied to commercial purity aluminium and copper sheets as lap welding and a 150 metric ton hydraulic press was used for the process. As the surface roughness and the weld deformation ratia of aluminium sheets increased, tensile strength of the joints also increased. Purchased specimens with original roughness had the lowest weld deformation as-is and it was not possible to join these sheets at 30% weld deformations. Fatigue tests showed that joined sheets resisted against low fluctuating tensile stresses. Hardness increases due to local hardening at the interface as a result of cold deformation. Also EDX (Energy Dispersive X-ray) measurements clearly show that Al-Cu joints contain an intermetallic compound layer at the interface which does not affect the joint strength to a great extent. Results showed that the cold pressure welding technique in lap form resulted in strong Al-Al joints and the intermetallic layer formed in Al-Cu joints did not affect the joint strength to a great extent. © 2008 Journal of Mechanical Engineering. All rights reserved.
Keywords: cold pressure welding, metallography, mechanical properties, surface roughness, deformation ratio
0 INTRODUCTION
Cold pressure welding can be applied by bringing surfaces of virgin metal specimens into close contact. Cold pressure welding takes place due to the breakdown of the surface layers caused by bulk plastic deformation. It is a solid phase welding process that can be performed on a large number of possible metal combinations.
Cold pressure welding has particularly been applied within the last fifty years, due to the fact that the process can be carried out easily at room temperature without using complex and expensive equipment. Cold pressure welding also has the advantage of being applicable to metal pairs that cannot be joined with either melt welding methods or to those metal pairs that pose utmost difficulty with respect to melt welding.
Cold pressure welding is used to join aluminium cables, various types of kitchen furniture, electrolysis cells, and communication lines. It is also used to join wires and rods and in production of heat exchangers as coolers.
The important variables of the method are; surface preparation before processing,
deformation, properties of the welding material or material pairs and pressure. Thus, one of the most important aspects of cold pressure welding is the properties of the surface before welding. The most commonly used method for surface preparation is cleaning the metal surfaces with a solving agent and brushing them with a wire brush. Wire brushing results in the formation of a hard brittle layer that prevents the metal from getting dirty (from grease, contaminant and oxide). It has been found that bonding occurs as a result of the cracking of this layer with the corresponding contact of metals [1]. Heating or chemical cleaning methods may also be applied. Deformation is the most important process variable. There is a minimum deformation -surface spread out or a reduction value for each material during cold pressure welding.
Mohamed et al. [2] investigated the mechanism of pressure welding in aluminium, copper, silver and gold. Bay [3] examined the bonding mechanism of cold pressure welding and mechanisms producing metallic bonds in cold welding [4]. Tabata et al. [5] investigated cold pressure welding of aluminium and copper by
*Corr. Author's Address: Trakya University, Mechanical Engineering Department, Edirne, Turkey,
kaanozel@trakya.edu.tr
butt upsetting. Bond criterion in cold pressure welding of aluminium was examined [6]. Unal et al. [7] investigated the effects of process parameters on the welding strength in the cold pressure welding of aluminium. Altan et al. [8] obtained the surface roughness depending on welding strength in the cold pressure welding of aluminium. Li et al. [9] examined interfacial energy and the match of cold pressure welded Ag/Ni and Al/Cu. Li et al. [10] investigated the interfacial bonding state on different metals Ag, Ni in cold pressure welding. Krishna et al. [11] directed process parameter optimization to obtain high weld strength in the cold solid state in joining sintered steel and copper powder. Sahin et al. joined plastically deformed steels by friction welding [12]. Tylecote informed about pressure welding practice [13]. Sahin et al. investigated the application of cold pressure welding to aluminium and copper sheets [14]. Iordachescu et al. obtained the FEM Model of Butt Cold Welding [15]. Kim et al. described fabrication of organic light-emitting devices by low-pressure cold welding [16]. Okumura et al. developed the composite materials fabricated from multi-layered 5052 aluminium alloy foils and titanium foils by cold pressure welding [17]. A titanium-flake reinforced aluminium-matrix composite was prepared from multilayered foils by cold pressure welding [18]. Kim et al. investigated micro patterning of organic electronic devices by cold-welding [19]. Dariel et al. Studied acid-assisted consolidation of powder compacts [20]. Zhang et al. made a fractographic investigation of weld formation for cold welding [21]. Kuzin studied optimization of technological parameters for cold pressure welding of thin sheets of AD1M aluminium [22].
In the present paper, aluminium and copper sheets were joined by cold pressure welding, namely, lap welding. A 150 metric ton hydraulic press was used for the welding process. Before welding, a wire-brushing process was applied in order to prepare the aluminium and copper sheets, their roughness was determined using a surface roughness equipment and they
were joined at different deformation ratia. The effects of deformation ratia and surface roughness on tensile strength of welded joints were investigated. Tensile tests and fatigue tests were carried out, hardness variations and micro-structures of the joints were examined. The joints were examined using EDX (Energy Dispersive X-ray) analysis in order to have an insight into the phases occurring during welding at the interface. Soundness of the joints was also investigated using non-destructive techniques radiographic inspection technique so as to evaluate the occurrence of defects.
1 COLD PRESSURE WELDING 1.1. Process Characteristics
Extent of deformation is one of the most important factors in cold pressure welding. Supposing that the basic parameter in cold pressure welding is the degree of deformation normally expressed as the reduction R or the surface expansion X of the bonding surface, plastic deformation of the metal pair is necessary in order to obtain a bonding.
In butt-welding, the experimentally measured extension (deformation) R is given by
R = A - A
A
(1)
where A0 is the original cross - sectional area and A is the extended area after processing. True fractional metallic area revealed at a certain extension R is then:
AA
R
A R +1
(2)
This Equation, which is valid for butt cold pressure welding, is given by
h - h
R =■
h
(3)
for lap welding where h0 is the original thickness of the sheet and h is the instantaneous thickness at deformation ratio R [2] and [3].
On the other hand, Equation 2 is also valid for lap welding. A specific threshold surface extension or reduction (minimum welding
deformation) is required for bond establishment at the atomic level. This deformation depends on metal-metal pairs, joining shape and thickness and surface preparation. It should also be noted that welding strength increases as deformation increases. However, too many plastic deformations also cause a decrease in weld strength. Surface preparation before welding influences weld strength to a great extent. The most widely used surface pre-preparation technique is removing the grease and brushing with a wire brush. Nickel coating of metal surfaces before processing is known to produce effective results. Also, application of normal pressure on the welding surface affects weld strength in a positive manner [2], [3], [7] and [8].
1.2. Bond Formation Mechanism
Microstructural examination of SEM microphotographs was used to develop an understanding of the mechanisms underlying bond formation on the wire brushed surfaces. Wire brushing during mechanical surface preparation forms a hard and brittle surface film at metal surface which is referred to as the cover layer. Observations have shown that bond formation is carried out by means of the stages given in Fig. 1.
Fig. 1. The bond formation mechanism in cold pressure welding [4]
First the cover layer is fractured of by the effect of pressure (Fig. 1.a). Further increase in
surface extension caused extrusion of metallic material through the crack in the cover layer (Fig.1.b). Finally, increase in deformation leads to real contact between metals resulting in the formation of a real bond (Fig. 1.c).
2 EXPERIMENTAL PROCEDURE
Aluminium and copper sheets (2.75 mm thickness) were joined using lap form of cold pressure welding. The properties of aluminium and copper materials used in the present study are given in Tables 1 and 2, respectively.
Table 1. The chemical composition and the tensile strength of Aluminium material used in the experiments
Chemical Composition	% 1.34 Fe, % 0.489 Si, % 0.439 Mg, % 0.913 Zn, % 0.107 Mn, % 0.0249 Cr, % 0.0135 Ti, % 0.005 Sn, % 0.0536 Pb, % 0.0179 Ni, % 0.003 Sb, % 1.12 Cu, % 95.47 Al
Tensile Strength	170 MPa
Surface Roughness	Arithmetical Average (Ra) = 0.30 |m
Table 2. The chemical composition and the tensile strength of Copper material used in the experiments
Chemical Composition	% 0.02920 Fe, % 0.00100 Si, % 0.00050 Mg, % 0.00100 Zn, % 0.00050 Mn, % 0.00100 S, % 0.00050 Bi, % 0.00108 Sn, % 0.00287 Pb, % 0.00596 Ni, % 0.00200 Sb, % 0.00230 P, % 0.00050 Al, % 99.95 Cu
Tensile Strength	360 MPa
Surface Roughness	Arithmetical Average (Ra) = 0.30 |im
The aluminium and copper sheets were 10x150 mm specimens and lap welding was applied in a single direction punch as shown in Fig. 2. Pressure needed for the process was applied using the 150 metric ton capacity press system (Figs. 2 and 3).
j 2.75
t
E>
П
Fig. 2. Schematic illustration of cold pressure welding
Fig. 3. The hydraulic press
All parts used in the experiments were cleaned using acetone oil and then they were brushed using a wire brush. A 60 mm diameter rotating steel wire-brush was used. Test surfaces were brushed at 510 r.p.m. wire brush rotational speed. The arithmetical average of surface roughness of the sheets prepared was used to determine the effect of surface roughness on weld strength. PRAZIS - RUG-03 surface roughness equipment was used to measure the surface roughness (Fig. 4). Arithmetic average surface roughness was found as Ra = 1, 3, 5 ^m.
Fig. 4. The equipment for surface roughness measurement
Surfaces prepared were subjected to cold pressure welding shortly after the preparation. The application of welding for 10 minutes affected the weld strength greatly. Increasing the welding time to over 10 minutes caused the weld strength to diminish to a great extent. Extent of deformation was measured by determining reduction (R) over the total thickness of welded parts.
3 EXPERIMENTAL RESULTS AND DISCUSSION
3.1.	Preparation of the Metal Sheets
Effect of deformation ratio and surface roughness on cold pressure welding of commercial purity aluminium and copper was investigated using deformation ratios of 30%, 45%, 50%, 60% (3.85 mm, 3 mm, 2.75 mm, 2.2 mm, respectively) and an arithmetic average surface roughness Ra = 1, 3, 5 ^m. Surface roughness was provided by a revolving brush, and the sheets were wiped with acetone after brushing.
3.2.	Tensile Test Results
Cold pressure welding in lap form was applied to wire brushed metal sheets at different deformation ratios. Tensile tests using an INSTRON 8501 dynamic testing machine were applied on the cold pressure welded sheets to determine their weld strengths. Acceptable weld strength was obtained at a surface roughness of Ra = 5 p.m and 60% deformation ratio. It was not possible to join the purchased specimens having original surface roughness as-it-is at 30% weld deformation, the lowest extent of deformation used in the present study. Figure 5 shows the variation of weld strength with deformation for different surface roughness values, while Figure 6 shows the variation of weld strength with surface roughness at different extents of deformations.
Acceptable weld strength in the aluminium joints was obtained at 60% deformation ratio and 5 ^m surface roughness (Figures 5 and 6). Therefore further experiments to join copper sheets together and to join aluminium sheets to the copper sheets were performed only at 60% deformation ratio and a surface roughness of 5 ^m (Figs. 5 and 6).
£
£ "S
с
fD
Й -Ш
'w с
0 1 2 3 4 5 6
Surface Roughness (Ra)
- -о- - Al - Al 30% Def.
» Al - Al 45% Def. —д. - Al - Al 50% Def.
—□-Al - Al 60% Def.
-Cu - Cu 60% Def.
—*-Al - Cu 60% Def.
Fig. 5. Relationship between tensile strength and surface roughness at different weld deformations
CD CL
ra с £ w
■(Л
с
®

0 0,1 0,2 0,3 0,4 0,5 0,6 0,7
Deformation Ratio (%)
—+ - Al-Al Joint for Surface Roughness (Ra)=1 ■O - Al-Al Joint for Surface Roughness (Ra)=3 —£—Al-Al Joint for Surface Roughness (Ra)=5
• Cu-Cu Joint for Surface Roughness (Ra)=5 A Al-Cu Joint for Surface Roughness (Ra)=5
Fig. 6. Relationship between tensile strength and weld deformation at different surface roughness
The length of bond zones were found to increase with increasing deformation which further leads weld strength to increase. Weld strength also increases with surface roughness (Figs. 5 and 6).
3.3. Fatigue Test
Fatigue tests of cold-welded aluminium joints were conducted using an INSTRON 8501 hydraulic fatigue machine (Fig. 7). Tests were done at a frequency of 10 Hz Fatigue tests were applied to specimens that had the highest strength, namely to samples having a surface roughness of Ra = 5 pm and joined at 60% weld deformation. Dimensions of the specimens were set according to ASTM E-466 (Fig. 8).
Fig. 7. INSTRON 8501 hydraulic fatigue machine
30
2.75
Fig. 8. Dimensions of the specimens used in fatigue tests
Welding interfaces were located in midsection of the fatigue specimen. Fatigue tests were conducted superimposing fluctuating tensile loads on a constant tensile load that can produce 40 MPa of tensile stress. When stress value in fatigue tests was increased, sheets joined were ruptured at the interface of the parts.
Fluctuating tensile stress amplitudes were varied between 10 MPa and 20 MPa and numbers of cycles to fracture were recorded. Sheets joined were capable of resisting fluctuating tensile stress (Fig. 9). Observations during fatigue tests showed that ruptures parts are usually detached from the welding interface. Joined sheets could not supply higher strength due to the defects (micro-cracks, inclusions or not fully bonded surfaces etc.) at the interface of the joints.
80
60
20
0
Fig. 9. The fatigue test results, <7mean = 20 MPa
3.4.	Results of Microstructural Examinations
Optical microscopy was used to study the microstructure of the welded interface both for aluminium joints and aluminium to copper joints that have an average surface roughness of Ra = 5 pm and welded at a 60% deformation ratio after etched in picral (Figures 10 to 13).
The vertical scratches owing to brushing are clearly visible on the fragments of the cover layer (Figs. 11 to 13). Scratch-brushing was carried out in longitudinal direction parallel to the direction of deformation. Extended areas of bonding regions and un-bonded regions of the cover layer are confined to isolated regions. Therefore, the bond fracture is ductile and occurs after numerous local necking [3].
3.5.	EDX Analysis of Joints
Scanning electron microscopy (SEM) and energy dispersive X-ray (EDX) analysis were performed to have an insight into the phases
Fig. 11. Microstructure at interface of joined aluminium parts having Ra = 5^.m and 60% deformation
Aluminium
Copper
100 pm
Fig. 12. Microstructure at interface of welded aluminium to copper parts having Ra = 5jum and 60% deformation
Copper
A3
WWt
10 pm
Fig. 10. Microstructure of aluminium parts
Fig. 13. Microstructure at interface of welded aluminium to copper parts having Ra = 5jum and 60% deformation
was utilized by means of software that allows piloting the beam and scanning along a surface or a line to obtain X-ray cartography or concentration profiles by elements, respectively.
Fig. 14 (a) shows EDX analysis points defined on the SEM micro structure at the interface region of the cold pressure welded Al-Al joints. Figure 14 (b) and (c) illustrate the EDX analysis results taken from point 3 of the SEM micrograph of the Al-Al joint and the respective EDS point analysis.
20.0 kV
Fig. 14. a) SEM microstructure of Al-Al joint
Energy keV
Points	Elements	Line	Intensity (c/s)	Conclusion
1	Al	Ka	1852.48	96.940 wt. %
	Ax	Ka	28.12	3.060 wt. % (100.000 wt. % Total)
2	Al	Ka	1537.79	97.614 wt. %
	Ar	Ka	17.99	2.386 wt. % (100.000 wt. % Total)
3	Al	Ka	1404.12	97.824 wt. %
	Ar	Ka	14.93	2.176 wt. % (100.000 wt. % Total)
4	Al	Ka	1378.65	97.151 wt. %
	Ar	Ka	19.41	2.848 wt. % (100.000 wt. % Total)
5	Al	Ka	1495.16	100.000 wt. % (100.000 wt. % Total)
Fig. 14. c) EDS point analysis results according to SEM microstructure
Figure 15 (a) shows EDX analysis of the points defined on the SEM microstructure at the interface region of the cold pressure welded Al-Cu joints. Figures 15 (b), (c) and (d) illustrate the EDX analysis results of point 1 on the Al side, the point 3 on the Cu side of the SEM micrographs. The EDS results confirm that an intermetallic compound layer does not exist in Al-Al, whereas Al-Cu joints have an intermetallic compound such as Cu3Al, Cu4Al3, CuAl and CuAl2 which does not affect joint strength to a great extent [23] to [25]. This is well enough evidence that strong joints can be produced by cold pressure welding method.
Fig. 14. b) EDX analysis result taken from point 3 represented to SEM image
Fig. 15.a)
b) EDX analysis result taken from point 1 represented to SEM image
c) EDX analysis result taken from point 3 represented to SEM image

Energy keV
Energy keV
Points	Elements	Line	Intensity (c/s)	Conclusion
1	Al Ar	Ka Ka	1357.82 12.08	98.170 wt.% 1.830 wt.% (100.000 wt. % Total)
2	Al Ar	Ka Ka	1659.40 20.20	97.522 wt.% 2.478 wt.% (100.000 wt. % Total)
3	Cu	Ka	1134.00	100.000 wt. % (100.000 wt. % Total)
4	Cu	Ka	1188.01	100.000 wt. % (100.000 wt. % Total)
5	Cu	Ka	1205.98	100.000 wt. % (100.000 wt. % Total)
Fig. 15. SEM microstructure of the cold pressure welded interface region between Al-Cu joints having Ra 5jum and 60% deformation ratio and EDS analysis results
3.6. Results of Hardness Examination
Hardness variations at the interface of joined parts were obtained by micro hardness tests under a load of 200 g. Measuring locations are given in Fig. 16. Hardness variations in vertical direction with respect to the weld-centre are shown in Fig. 17.
it
^ Q I Finishing point for hardness measurement
Ш
шшшш

Starting point fer hardness measurement
Fig. 16. Hardness test orientations at cross-section ofjoined parts
Hardness values are about the same at the interfaces of the parts having different surface oughness values and deformed at 60%. Hardness of aluminium material purchased is about 53 HV. Hardness of the joined parts is higher due to local hardening which is a result of cold deformation. The effect of the surface roughness on hardness variations is much less than that of the deformation ratio (Fig. 17). A similar result as to the increase in hardness due to local hardening is observed for the Al-Cu joint. Then, ductility is a mechanical property used to describe the extent to which materials can be deformed plastically without fracture. Aluminium is more ductile
material than copper. It means that Al can be easily deformed according to Cu. Al sheet is plastically deformed in a greater extend than Cu when overall deformation ratio 60%. As a result, the hardness of a ductile material as aluminium is lower than that of less ductile material as copper [51 and [61.
Aluminium Side Copper Side
с "D ra X
о >
140 130 120 110 100 90 80 70 60
0,5 1	1,5	2
Vertical Distance (mm)
—»—(Al-Al) Ra=1	- m- (Al-Al) Ra=3
—Д—(Al-Al) Ra=5	—□— (Al-Cu) Ra=5
Fig. 17. Hardness variations along the vertical direction
3.7. Non-Destructive Evaluation by Radiographic Inspection
Inspection (NDI) is the examination of an object or material with technology that does not affect its future use. NDI can be used without destroying or damaging a product or material. Because it allows inspection without interfering with a product's final use, NDI provides an excellent balance between quality control and cost-effectiveness. NDI can and should be used in
any phase of a product's design and manufacturing process, including materials selection, research and development, assembly, quality control and maintenance. Commonly used non-destructive inspection methods include liquid penetrant, magnetic particle, eddy current and radiographic inspection, ultrasonic inspection, tomography, and real-time radiography. Radiographic testing is one of the oldest methods of non-destructive testing and has been in use for approximately five decades. Radiography using X-rays is one of the NDT techniques used for imaging the joints to detect and locate defects. In the present study, Aluminium joints were evaluated by radiographic inspection using RIGAKU 200 kV test equipment. Figure 18 is an example of the radiographic patterns for an aluminium joint produced from sheets having a surface roughness of Ra = 5 pm and welded at 60% deformation. As seen from the inspection figure, almost there are no defects in the joints. But, there can be very small weld defects (micro-cracks, inclusions or not fully bonded surfaces etc.) because the joined sheets do not resist against high static and dynamic loads.
Fig. 18. An example from radiographic patterns used in this work
3.8. Statistical Analysis of Data
The basis of this approach is the assumption of a simplified linear model for the optimization parameter ^ given by
r\= ß0+ß1x1+ß2x1+......, where x1, x2... are the
factors which ^ depends on and ß0, ß1, ß2..., etc, represent the 'true' values of the corresponding unknowns. From the results of an experiment comprising a finite number of trials, one can arrive at sample estimates of the coefficients, ß, which are then usually fitted into a linear regression equation of the type y=b0+b1x1+b2x2+..., where y is the response function and the bs are the "estimated" values of the ßs. In simple terms, each coefficient represents
the influence of the corresponding factor on the quality of the tensile strength expressed by the optimization parameter [12] and [13]. Parameter optimization was carried out using factorial design of experiments. In the present study; aluminium specimens obtained by machining was chosen as an example model. Deformation ratio and pre-upsetting surface roughness were chosen as the two factors. Then, the tensile strength data were subjected to statistical analysis to understand the influence of individual effects of the factors. The other parameters were kept constant. Regression equation was obtained from this analysis. Correlation coefficient was also obtained from the statistical analysis. Experimental results are given in Table 3.
Table 3. Experimental results
Trial No	Surface Roughness of Parts (Ra-^m) xt	Deformation Ratio (%) x2	Tensile Strength of Joined Parts (MPa) y
1	1	0.30	0.192
2	1	0.45	2.021
3	1	0.50	4.362
4	1	0.60	4.590
5	3	0.30	0.974
6	3	0.45	2.267
7	3	0.50	4.650
8	3	0.60	58.700
9	5	0.30	1.527
10	5	0.45	3.410
11	5	0.50	5.810
12	5	0.60	132.100
Optimum estimates of regression coefficients were obtained using the Fisher method ratio. The resulting equation is also given here:
y = -94,739 + 8,230 • x1 +191,204 • x2
(4)
The correlation coefficient using Eq. (4) is about 0.70 in respect of tensile strength. Therefore, it is quantitatively shown that the effects of deformation ratia and surface roughness on the tensile strength are very significant, as expected.
4 CONCLUSIONS
-	Cold pressure welding of the commercial purity aluminium and copper in lap form was successfully applied to Al-Al and Al-Cu joints.
-	As the surface roughness and the weld
deformation ratia of aluminium sheets increased, tensile strength of the joints also increased.
-	Purchased specimens with original roughness
had the lowest weld deformation as-it-is and it [1] was not possible to join these sheets at 30% weld deformations. However, it was possible to join these specimens at deformation ratios greater than [2]
70 %.
-	Micrographs of specimens having a surface roughness of 5 ^m and deformed at 60% [3] deformation ratio clearly reveal bond formation at
the interface of joined parts.
-	Hardness values of joints are about the same at [4] interfaces of sheets having different surface roughness and produced at equal deformation. Hardness results in Al-Cu joints are similar to [5] those of aluminium joints. Hardness increases due
to local hardening at the interface as a result of cold deformation.
-	Fatigue tests showed that joined sheets resisted [6] against low fluctuating tensile stresses.
-	EDX measurements clearly show that Al-Cu joints contain an intermetallic compound layer at [7] the interface which does not affect the joint strength to a great extent.
-	Even if radiographic testing showed no defects
at the welded joint, there could be very small [8] weld defects since the joined sheets do not resist against high static and dynamic loads.
-	Tensile strength of joined parts can be expressed in terms of the process parameters by regression equation obtained by statistical analysis.	[9]
5 NOMENCLATURE
X Surface expansion of bonding surface (%)	[10]
R Reduction (%)- Deformation Ratio
A0 Original cross-sectional area (mm)
A Extended area after process (mm)
h0 Original thickness of sheet (mm)
h Instantaneous thickness at deformation (mm) [11]
Ra Surface roughness (^m)
6 ACKNOWLEDGEMENTS
The authors would like to thank Trakya [12] University / Edirne, Yildiz Technical University / Istanbul and Hema Industry / Qerkezköy -Turkey for the help provided in the experimental part of the study. And, authors also thank to [13] Serkan Sahin, SAMKO / Istanbul - Turkey, for helps in non-destructive inspection.
6 REFERENCES
Tylecote, R. F. (1957) Investigations on Pressure Welding, Welding Research-British Welding Journal 1(3), p. 117-135. Mohamed, H. A., Washburn, J. (1975) Mechanism of Solid State Pressure Welding, Welding Journal 54(9), p. 302-310. Bay N. (1979) Cold Pressure Welding - The Mechanisms Governing Bonding, Journal of Engineering for Industry 101, p. 121-127. Bay N. (1983) Mechanisms Producing Metallic Bonds in Cold Welding, Welding Research Supplement 62(5), p. 137-142. Tabata, T., Masaki, S., Azekura, K. (1985) Cold Pressure Welding of Aluminium and Copper by Butt Upsetting, Bull. of JSME 28(235), p. 162-167.
Tabata, T., Masaki, S., Azekura, K. (1989) Bond Criterion in Cold Pressure Welding of Aluminium, Mat. Sci. & Tec. 5, p. 377-381. Unal, A., Altan, E. (1989) Effects on Welding Strength of Process Parameters in Cold Pressure Welding of Aluminium, 2nd Nat. Weld. S., Istanbul-Turkey, p. 336-343. Altan, E., Unal, A. (1990) Obtaining Surface Roughness Depended on Welding Strength in Cold Pressure Welding of Aluminium, 4th Mach. Des. and Man. Congress, METU, Ankara-Turkey, p. 291-298. Li, Y. T., Du, Z. Y., Ma, C. Y. (2002) Interfacial Energy and Match of Cold Pressure Welded Ag / Ni and Al / Cu, Trans. Nonferr. Met. Soc. China, 12(5), p. 814-817. Li, Y. T., Du, Z. Y., Tao, Y. Y. (2003) Interfacial Bonding State on Different Metals Ag, Ni in Cold Pressure Welding, Trans. Nonferr. Met. Soc. China, 13(2), p. 276-279.
Krishna, B. V., Venugopal, P., Rao, K. P. (2003) Optimization of Process Parameters in Cold Solid State Joining of Sintered Steel and Copper P / M Preforms, Trans. Indian Inst. Met., 56(4), p. 363-373. Sahin, M., Akata, H. E. (2003) Joining with Friction Welding of Plastically Deformed Steel, Journal of Materials Processing Technology, 142(1), p. 239-246. Tylecote R. F. (1957) Pressure Welding in Practice, Welding Technology-British Welding Journal, 4(3), p. 113-119.
[14]	Sahin, M., Ozel. K. (2007) Investigation of the Usage of Cold Pressure Welding to Aluminium and Copper Sheets, 6th Nat. [20] Weld. Tech. C, Ankara-Turkey, p. 219-225.
[15]	Iordachescu, M., Iordachescu, D., Scutelnicu, E., Ocana, J. L. (2007) FEM Model of Butt Cold Welding, Sci. & Tec. [21] Weld. and Join., 12(5), p. 402-409.
[16]	Kim, C., Forrest, S. (2003) Fabrication of Organic Light-Emitting Devices by Low- [22] Pressure Cold Welding. Adv. Mat., 15(6), p. 541-545.
[17]	Okumura, Y., Saji, S., Anada, H. (2001) Composite Materials Fabricated From Multi- [23] Layered 5052 Aluminum Alloy Foils and Titanium Foils by Cold Pressure Welding. [24] Int. J. Mat. & Prod. Tec., p. 494-499.
[18]	Okumura, Y., Saji, S., Anada, H. (2000) Titanium-Flake Reinforced Aluminum- [25] Matrix Composite Prepared From Multilayered Foils By Cold Pressure Welding. Adv. Eng. Mat, 2(12), p. 818.
[19]	Kim, C., Burrows, P., Forrest, S. (2000) Micropatterning of Organic Electronic
Devices by Cold-Welding, Science, 288(5467), p. 831-833. Dariel, M., Ratzker, M., Eichmiller, F. (1999) Acid-Assisted Consolidation of Powder Compacts: Cold-Welding or Cold Sintering, JMS, 34(11), p. 2601. Zhang, W., Bay, N. (1997) Cold Welding -Fractographic Investigation of the Weld Formation, Weld. J., 76(9), p. 361-366. Kuzin V. (1985) Optimization of The Technological Parameters of Cold Pressure Welding Thin Sheets of AD1M Aluminum, Weld. Prod. 32(4), p. 18-20. Welding Handbook, (1991) 8th Ed., Weld. Proc., Cold welding, AWS, 2, p. 900-908. Thomas K. (1993) Welding, Brazing and Soldering, Cold Welding, ASM Handbook, 6, p. 307-310.
Abbasi, M., Taheri, A. K., Salehi M. T. (2001) Growth rate of intermetallic compounds in Al / Cu bimetal produced by cold roll welding process. Journal of Alloys and Compounds, 319, p. 233-241.
Paper received: 20.12.2008 Paper accepted: 25.09.2008
Safe Operation of Welded Structure with Cracks at Elevated Temperature
Meri Burzić1, - Radica Prokić-Cvetković2 - Biljana Grujić3 - Ivana Atanasovska4 - Živoslav Adamović5
1 Institute "GOŠA", Belgrade, Serbia 2 Faculty of Mechanical Engineering, Belgrade, Serbia 3 Innovation Centre, Belgrade, Serbia 4 Institute "Kirilo Savić", Belgrade, Serbia 5 Faculty of Technical Engineering, Zrenjanin, Serbia
The fatigue crack growth rate parameters and conditions for abrupt fracture of thick joint in steel at room and operating temperature were analysed. Fatigue cracks generated from sharp weld defects are initial cracks that grow through either the weld joint region or the base metal in accordance with Paris law. Service life of a welded structure depends on position and orientation of the existing sharp weld defect. Differentpre-cracked specimens were used in this experimental investigation.
They were cut from the base and weld metals and heat-affected zone. In comparison with the base metal, weld joint region showed higher crack growth rate at operating and room temperatures. Fatigue crack growth rate was higher at operating temperature irrespective of the position. Reliability of structure with initial longitudinal cracks positioned in the heat-affected zone was lower than with initial transversal cracks located in the weld metal. © 2008 Journal of Mechanical Engineering. All rights reserved. Keywords: welded structures, fatigue cracks, fracture toughness, proof test
0 INTRODUCTION
Weld defects arise in manufacture of welded structures. During normal operation of such structures, sharp defects in weld joint region act as sites from which fatigue cracks form and then grow. Cracks of critical size jeopardize structural integrity. Due to the complex nature of fusion welding and human factor, the size, location, type, and orientation of defects cannot be predicted. Only a thorough post- manufacture inspection of weld joints provides necessary information about the actual weld defect presence in welded structures.
The most jeopardizing type of sharp weld defects are two-dimensional defects oriented normal to the direction of fluctuating stress. Their direct effects on the strength of weld joints are treated as the effects of cracks (crack-like defects). Fracture mechanics is used to assess the severity of macroscopic two-dimensional defects in relation to design loading. There are some complex features that make thae application of fracture mechanics difficult such as residual stresses, interaction of cracks with weld geometry, material properties variations due to
dissimilar weld and base metals and especially micro structural heterogeneities of weld joint region resulting from the welding thermal cycles.
Tensile welding residual stresses appearance and local material embrittlement are fundamental for various cracking phenomena of welds \1]. Interaction of stresses during structure operation and existing cracks often leads to unexpected weld joint fracture. Actually, cracks originating from sharp weld defects grow during service life of welded structures. They have to remain smaller than the critical crack size, otherwise, they will cause weld joint fracture in brittle or quasi-brittle manner. Disintegration of a welded structure is very likely if highly loaded weld joint collapses. A superior resistance of weld joint against the fatigue crack growth is of great importance for longer service lives of welded structures.
The resistance of metallic materials to fatigue crack growth and brittle fracture depends on the micro structure. Properties of the base metal (BM) meet requirements in standards. The weakest links are always weld joints consisting of heat-affected zone (HAZ) and weld metal (WM). Microstructure of both in as-welded condition
*Corr. Author's Address: Institute "GOŠA", Belgrade, Serbia, merib@neobee.net
807
results from chemical composition and welding thermal cycles.
Microstructure and properties of weld joint region can be analysed in details by using samples of materials cut from actual weld joints [2]. Alternative is an analysis performed with samples of materials with simulated micro structure. In this case, thermal conditions during welding have to be simulated either on samples of BM in order to prepare particular HAZ areas [3] or on samples of single-run WM in order to prepare particular multi-run WM areas [4]. Using combination of both, i.e. samples from weld joint and samples with simulated microstructure is an effective approach, too [5].
The experimental results of fracture toughness measurement and fatigue-crack growth rate measurement are shown and discussed in this paper from the leak-before-break concept point of view. Fracture properties of weld joint region and non-affected base metal were determined using the specimens machined from the samples of material cut from a real welded plate.
1 EXPERIMENTALS 1.1. Materials and Specimens
The steel used in this study is A-387 Gr. 11 Class 1 steel designed for operation at elevated temperatures. Its chemical composition and basic mechanical properties at room temperature are shown in Table 1 [6]. A 96 mm thick double-U
shaped welded test coupon was available for the research. Root passes were deposited by metal manual arc welding (MMA) with coated electrode LINCOLN Sl 19G (AWS: E8018-B2), the rest of the weld-groove was filled at both sides by submerged arc welding (SAW) with wire LINCOLN LNS 150 and flux LINCOLN P230. Chemical compositions of both consumables are shown in Table 2. Basic mechanical properties for all-weld metals at room temperature are shown in Table 3 [6]. The WM is stronger than BM (overmatching).
Welding technology specification was prepared according to standard EN 288-3 [7]. Operating temperature is not specified in this standard. It is not required to test the behaviour of the weld joints at the operating temperature.
Weld joint with sharp initial weld defects in the WM and HAZ areas was evaluated in respect of the structure safe operation. The specimens for the fracture toughness assessment and fatigue crack growth rate measurement were machined from the welded test coupon as shown in Figure 1.
Three-point bend specimens (TPB) were used for fracture toughness testing at room temperature. Their shape and dimensions are shown in Figure 2. Due to specific design of the high-temperature chamber, the specimens looked like compact tensile specimens (CT) used for fracture toughness testing at operating temperature. Their shape and dimensions are also shown in Figure 2.
Table 1. Chemical composition and basic mechanical properties of the steel
C	Si	Mn	P	S	Cr	Mo	Yield stress	Tensile strength	Elongation	Impact energy
Mass. %							MPa		%	J
0.15	0.29	0.54	0.022	0.011	0.93	0.47	325	495	35	165
Table 2. Chemical composition of filler metals
Filler metal	C	Si	Mn	P	S	Cr	Mo
	Mass %						
LINCOLN Sl 19G	0.08	0.045	0.35	0.025	0.025	1.10	0.50
LINCOLN LNS 150	0.11	0.18	0.37	0.020	0.020	1.04	0.47
Table 3. Mechanical properties of all-weld metals
Filler metal	Yield stress	Tensile strength	Elongation	Impact energy
	MPa		%	J
LINCOLN Sl 19G	505	640	23	> 95
LINCOLN LNS 150	490	610	26	> 100
Bending specimens (B) were used for fatigue-crack growth-rate measurement. Their dimensions were 10*10*55 mm. The type of all specimens, their position, and orientation in the test coupon in relation to the weld axis is clearly indicated in Figure 1. The notches and cracks were located in the BM, WM and HAZ.
Fig. 1. View of the welded test coupon with specimens sampling
The values of J-integral were calculated from registered dependence of force versus load-point displacement just when unloading sequence started. The diagrams J - Aa were plotted using those values and corresponding crack increments. At first, a regression line was drawn in the linear section of each J - Aa diagram. JIc-value, critical J-integral, was obtained with intersecting J - Aa diagram and a parallel line to regression line. This line intersects x-axis at Aa = 0.15 mm. The diagrams J - Aa at room and operating temperature valid for the BM are shown in Figs. 3b and 4b, the diagrams valid for the WM in Figs. 5b and 6b, whereas the diagrams valid for the HAZ in Figs. 7b and 8b. Average values of
determined JIc-values extracted from those diagrams are listed in Table 4 [10].
2 RESULTS 2.1. Fracture toughness
Fracture toughness was experimentally determined according to the standards [8] and [9]. Single-specimen method was used. Three specimens were notched and precracked in the BM, three in the WM and three in the HAZ. The specimens were loaded and successively partly unloaded at room temperature and at 540°C. The registered slope between force, F, and crack mouth opening displacement, 5 (CMOD), in the course of specimen unloading enabled determination of the crack size, a, and every crack increment, Aa, respectively. The examples of diagrams F - 5 plotted at room and operating temperature valid for the BM are shown in Figs. 3a and 4a, diagrams valid for the WM in Figs. 5a and 6a, whereas diagrams valid for the HAZ in Figs. 7a and 8a.
The values of J-integral were calculated from registered dependence of force versus load-point displacement just when unloading sequence started. The diagrams J - Aa were plotted using those values and corresponding crack increments. At first, a regression line was drawn in the linear section of each J - Aa diagram. JIc-value, critical J-integral, was obtained with intersecting J - Aa diagram and a parallel line to regression line. This line intersects x-axis at Aa = 0.15 mm. The diagrams J - Aa at room and operating temperature valid for the BM are shown in Figs. 3b and 4b, the diagrams valid for the WM in Figs. 5b and 6b, whereas the diagrams valid for the HAZ in Figs. 7b and 8b.
	""■о	„3 0'			CD
			F		со со
à		_з		-jI 0.02 A	
		1 60			
Ш-5--
Fig. 2. Fracture toughness specimens (TPB specimens above and "CT" specimens below)
Average values of determined Jic-values extracted quality area of treated weld joint is WM whereas from those diagrams are listed in Table 4 [10].	the lowest HAZ. Testing temperature does not
In respect of fracture toughness the highest change this fact.
Table 4. Fracture toughness, JIc, plane-strain fracture toughness, KIc, threshold stress-intensity range and parameters of fatigue crack growth rate C and m
Area	T, °C	JIc, kJ/m2	KIc, MPa m1/2	AKth, MPa m1/2	C, nm/cycle	m
BM	20	63.5	120.9	6.8	4 ■ 10-3	2.1
WM		81.3	133.7	6.8	8 ■ 10-4	2.8
HAZ		51.7	106.6	6.7	2 ■ 10-4	3,5
BM	540	43.4	88.4	5.9	1 ■ 10-3	3.0
WM		57.2	101.6	6.2	5 ■ 10-4	3.5
HAZ		38,9	83.7	6.1	3 ■ 10-4	3.9
				BM - 1 - 1 t = 20oC	
					
,rT7	ттт				
P'	III	Пт			
			г		
					
					
1					
8 12 S, mm
16 20
J 150-
a ^ 100-
50
4	6	8
Aa, mm
a)	b)
Fig. 3. Diagrams F — S and J—Aa for the BM at room temperature
						BM - 1 - 1 J. = 63.5 kJ/m2	
							
			—s*"	-п—а-			
							
JLf							
							
12-
10-
BM - 2 - 1 t=540oC
4	6	8
S, mm	Aa, mm
a)	b)
Fig. 4. Diagrams F — S and J—Aafor the BM at operating temperature
30
25
20
J
0
0
4
8
6
4
2
0
WM - 1 - 1 t = 20oC
2Э 150
а
5, mm	Aa, mm
a)	b)
Fig. 5. Diagrams F — S and J—Aa for the WM at room temperature
4	6	8
5, mm	Aa, mm
a	b
Fig. 6. Diagrams F — S (a) and J — Aa (b) for the WM at operating temperature
20-
M 20
8 12 5, mm
a
							HAZ - 1 - 1 = 20oC
							
							
	T	к					
1			\				
							
			1				
							
300-
250-
200-
J3 150100
50
Aa, mm b
					1 HAZ- - 1 J_ = 51.4 kT/m2	
						
/	!					
/' С	' 1					
li У /'пг /v '	1					
H ' к 1						
10 12
Fig. 7. Diagrams F — S (a) and J—Aa (b) for the HAZ at room temperature
300
250
200
100
J
50
0
4
12
10
8
6
4
2
0

0
0
2
0
4
					HAZ- 2 - 1 T = 39.8 kJ/m2		
							
	! /						
	/						
							
							
8	12	16	20	0	2	4	6
s, mm	Aa, mm
a b Fig. 8. Diagrams F — S (a) and J—Aa (b) for the HAZ at operating temperature
2.2. Fatigue-crack growth-rate parameters
Fatigue-crack growth-rate parameters were experimentally determined according to the standard ASTM E 647 [11]. Charpy-size specimens were notched to a depth of 2 mm in the WM and HAZ areas and in the BM. They were bend-loaded in moment control at room temperature and at 540°C on a high-frequency resonant pulsator. Resistant foil-gauges were attached on the specimens in order to register crack size changes during oscillating loading (see Figure 9). In the course of successive small crack increments, the stress-intensity factor range, AK, was kept constant. Simultaneous corrections of loading moment were performed during fatigue crack growth. Fatigue crack growth rate, da/dN, was calculated as a quotient of crack increment, Aa, and number of cycles, N.
Fig. 9. Specimen with firmly cemented crack size gauge with indicated bend-loading
The fatigue crack growth rate rapidly decreased when AK when approaching the threshold stress-intensity factor range, AKth. On the other side, when AK came up to Kc-value fatigue crack grew faster.
Experimental diagrams da/dN - AK represented in double-logarithmic scale at room temperature valid for the BM, WM, and HAZ are shown in Figure 10a and those at operating temperature in Figure 10b.
The linear portion of relationship between the fatigue crack growth rate and stress-intensity factor range is known as Paris law [12]:
= C -(AK f	(1)
dN	w
where constants C and m are material-dependent.
Fatigue-crack growth-rate parameters extracted from diagrams are listed in Table 4 [13].
3 EVALUATION OF TEST RESULTS
If mechanical properties are available, plane-strain fracture toughness, KIc, is indirectly determined from the JIc-values. The following expression is used:
K,
1 - v2
(2)
where E is Young's modulus and v Poisson's number.
Estimated value of E at temperature of 540°C is 82% of the same value at room temperature [14]. We took the same value of v at
10
8
6
4
2
0
J Ic - E
room temperature and 540°C for the calculation of KIc-values given in Table 4.
Variations of KIc in the weld joint region in comparison with BM are extremely significant. Critical crack size, ac, when weld joint fractures at a fixed stress level is strongly KIc dependent. By applying formula
K,
= g • Y(a)^rc • ac
Critical crack size is calculated as
K
\2 Ic I
1
я I g • Y(a) I
(3)
(4)
where Y(a) is shape factor and a stress normal to the crack plane.
When fatigue crack grows in accordance with Paris law, stress-intensity factor range is greater than the threshold stress-intensity factor range, AKth.
If the fatigue crack growth rate parameters C and m are available, the number of cycles to fracture, N, will be determined using Equation 1. The following expression has to be solved:
da
ai Y(a) • a2
= C • я2
• (a)m • JdN
(5)
where ai and af are initial and final crack size, respectively.
Shape factor of an infinite 96-mm thick wall with different types and sizes of cracks are [15]:
>	Small half-elliptic surface crack with length-to-depth ratio 2.42 (Figure 11a): Y = 0.734
>	Half-elliptic surface crack with length-to-depth ratio 2.83 penetrating half of the wall-thickness (Figure 11b): Y = 0.86
>	Half-elliptic surface crack with length-to-depth ratio 4.2 approaching opposite wall surface (Figure 11c): Y = 1.234
>	Through-thickness crack (Figure 11d): Y=1.
4 DISCUSSION WITH CONCLUSION
If during cyclic loading an existing crack, previously generated from a sharp weld defect, had grown to the size when anywhere along the crack contour stress-intensity factor attains plane strain fracture toughness, KIc-value, an abrupt fracture of weld joint would occur. This size is defined as the critical crack size. If size of fatigue crack attains the critical crack size, weld joint will fracture. The result can be a catastrophic disintegration of the whole structure.
104
10 -
102
!
10
10
10
10
T = 20oC BM WM HAZ
10

Л
A
/N
•y
104
103
102
101
Z 10"
10"
10
10
T = 540 C ■ BM • WM » HAZ
/Л 1 • ■
V
102
10 10 100 101 AK, MPa m1/2	a)	AK, MPa m1/2	b)
Fig. 10. Diagrams da/dN - AK for the BM, WM, and HAZ at room temperature (a) and at 540 C (b)
ac =
a
m
0
2c,
2cfs
2c,
— = 2.42
2cf
- = 2.83
t/2
t/2
2cl
2ac

	<-* «-* i 2c, i i i	
M	1 1	i
2c,
- = 4.20
Fig. 11. Four types of fatigue cracks: small initial half-elliptic surface crack a, (a), final half-elliptic surface crack af (b), wall-penetrating crack when leakage starts al (c), critical and non-critical
through-thickness cracks ac, cl (d)
Assume that initial inner surface crack in the weld joint area is already a long crack. For the linear-elastic treatment, the depth of this crack, a,, has to be much greater than the plastic zone size, ry (Figure 11a).
a, ^ 50 • ry	(6)
Plastic zone ahead of the crack tip develops as the result of interaction between a crack and stress. Its size depends on the stress-intensity factor, K, material yield stress, Rp, and stress-field configuration. ' 1
л2
_K
VRp У
—	plane stress condition 2я
—	plane strain condition 6я
(7)
Operating stress of the structure does not exceed 100 MPa. Inner surface crack 5 mm-deep fulfils the condition in Equation 6. Cracks of this size were found in the structure during regular inservice inspections. Therefore, those cracks grow in accordance with Paris law. Proof pressure test performed after in-service inspections led to the stress 100% higher than maximum operating stress.
It is great advantage to operate a pressure-plant designed based on leak-before-break. Fatigue-crack penetration through the wall can be manifested either by loss of pressure or by leakage. Thanks to those obvious indications, an operator is capable to prevent final fracture of the plant by shutting it down. Abrupt fracture of
pressurized component could be jeopardizing for human lives and environment. Besides, a plant designed in accordance with leak-before-break concept allows periodical repairs or replacement of the damaged component.
The procedure is as follows:
1)	Calculation of the through-thickness crack size
which results in fracture, acthrough (subscript c
denotes critical size for fracture).
2)	Calculation of the depth of surface crack in an infinite thick wall which results in fracture,
acsurface infinite 96-mm thick wall 3) Comparison of the acsurface
surface
with the wall
thickness t. If acsurface < t, crack will not penetrate the wall in a stable manner before fracture.
4)	If acsurface > t, the crack will penetrate the wall. Depth of crack approaching the opposite surface of the wall, al, is t, whereas its length 2ci = 4.2*a, (subscript l denotes the size for leakage to start).
5)	The crack penetrating the wall grows further and becomes a through-thickness crack of length 2a = 2clsurface.
6)	If the critical crack size acthrough >> ccsurface, there is enough time to notice pressure loss or leakage.
Calculated size of part-through and through-thickness critical cracks in BM, WM, and HAZ are listed in Table 5. Sizes acsurface are greater than wall thickness (t = 96 mm). Crack
a
b
a
a
d
c
a
ry =
would certainly penetrate the wall before final fracture.
When crack would approach the opposite wall surface, its half-length on the inner surface would be c = 202 mm. This is not much less than critical through-thickness crack size under normal operating condition in the BM (249 mm) and especially in the HAZ (223 mm). Without any doubt, weld joint properties of this plant satisfy the leak-before-break concept, but its operating safety factor is a bit questionable.
Calculated critical sizes of the through-thickness crack in proof-test condition are listed in Table 5. They are much smaller than the half-length of the crack penetrating the wall. The possibility that the existing deep crack cannot be detected during in-service inspection after which proof-test should be performed may not be
neglected. Crack size acthrough in proof-test
condition could be crucial for further safe operation of the plant.
For higher reliability, it is beneficial to limit maximum allowable crack size rigorously, for instance, let the crack size be only one-half of the wall-thickness. Stress-intensity factor which is the result of this crack at proof stress is K = 67
MPa. This level of stress-intensity is lower than the plane-strain fracture toughness of BM, WM, and even HAZ. If during in-service inspections a careful effort were made to find all cracks on inner surface, safe operation of plant would be guaranteed.
Which cracks are more dangerous in the weld joint region - longitudinal cracks in the HAZ or transversal cracks in the WM? These cracks are often the result of hydrogen attack on hard areas of weld joints.
In terms of experimental data listed in Table 4, the cracks in the HAZ will grow faster than the cracks in the WM. Initial cracks in the HAZ could grow all the time through the material with the worst properties. Initial cracks in the WM grow at first in the WM, then go across HAZ, and continue outside the weld joint in the BM which properties are superior. Comparison of the number of cycles for an initial 5 mm-deep crack to grow to 50% of the final crack size (a = 24 mm) at room and operating temperatures is shown in Table 6. The basis is necessary number of cycles for crack growth in the HAZ at operating temperature.
Table 5. Critical sizes of part-thickness and through-thickness cracks in normal operating and proof test conditions
Area	T, °C	surface ac	ci	through ac	through ac
		operating condition			proof-test condition
		mm			mm
BM	20	864	202	465	116
WM		1056	202	569	142
HAZ		671	202	362	90
BM	540	462	202	249	62
WM		610	202	329	82
HAZ		414	202	223	56
Table 6. Time needed for the crack growth to half of the final crack size at operating temperature in relation to the time for growth in the weakest area of the weld joint region, i.e. HAZ
Area	T, °C	N/N0 operating condition
BM		51.8
WM	20	8.8
HAZ		4.5
BM		3.8
WM	540	1.8
HAZ		1
Quotients N/N0 listed in Table 6 are additional safety factors for the safe structure operation. The most dangerous situation is the presence of longitudinal cracks in the HAZ, [8] which grow through the HAZ under cyclic loading at temperature of 540°C.
5 REFERENCES	[9]
[1]	Z. Burzić, S. Sedmak, M. Manjgo (2001) The application of fracture mechanics in welded joint properties assessment, RIM [10] 2001, Bihać, pp. 451-460.
[2]	N. Gubeljak (1999) Fracture behavior of specimens with surface notch tip in the heat [11] affected zone (HAZ) of strength mismatched welded joints, International journal
of fracture, 100 (2) pp. 155-167
[3]	V. Gliha (2005) The microstructure and properties of materials at the fusion line, [12] Metallurgy, 44 (1), pp. 13-18.
[4]	D. Rojko, V. Gliha (2005) Simulations of transformation kinetics in a multi-pass weld, Materials and manufacturing processes, 20 [13] (5), pp. 833-849.
[5]	I. Rak, V. Gliha, M. Ko?ak (1997) Weldability and toughness assessment of Ti-microalloyed offshore steel. Metallurgical and materials transactions A, 28, pp. 199206.	[14]
[6]	M. Burzić, Z. Burzić, J. Kurai (2006) The prediction of residual life of reactors in RNP, [15] CertLab Pancevo.
[7]	EN 288-3, (1995) Approval of welding procedures for metallic materials-Part 3:
Welding procedure tests for arc welding of steels, Quality assurance in welding, Belgrade.
ASTM E1152-91 (1995) Standard Test Method for Determining J-R Curve, Annual Book of ASTM Standards, Vol. 04.01. pp. 724.
BS 7448 (1991) Fracture mechanics toughness tests. Part 1. Method for determination of KIc critical CTOD and critical J values of metallic materials, BSI. M. Burzić (2007) PhD Thesis, University of Novi Sad, Department of Technical Faculty, Serbia.
ASTM E647 (1995) Standard Test Method for Constant-Load-Amplitude Fatigue Crack Growth Rates Above 10-8 m/cycle, Annual Book of ASTM Standards Vol. 03. 01, pp. 714.
P.C. Paris, and F. Erdogan (1982) A Critical Analysis of Crack Propagation Laws, Trans. ASME, Journal Basic Eng., Vol. 85, No. 4, pp. 528.
M. Burzić, Z. Burzić, J. Kurai, Dž. Gaco (2007) Fatigue Behaviour of Alloyed Steel for High Temperature, First Serbian (26th YU) Congress on Theoretical and Applied Mechanics, Kopaonik, Serbia, pp. 10851090.
DIN 4133 (1991) Schornsteine aus Stahl, Berlin.
Y. Murakami, (1986), Stress Intensity factors Handbook, Pergamon Press.
Instructions for Authors
From 2008 Journal of Mechanical is published only in English language with Slovenian abstracts. Authors are entirely responsible for language correctness. If reviewer estimates that language is poor, Editorial can require native English proof-reading with certificate from the author once again.
Papers can be submitted electronically on Editorial's e-mail or by post.
Papers submitted for publication should comprise:
-	Title, Abstract, Keywords,
-	Main body of text
-	Tables and Figures (graphs, drawings or photographs) with captions,
-	List of References and
-	Information about the authors, corresponding author and his full address.
For papers from abroad (in case that none of authors is Slovenian) Editorial will provide Slovenian translation of the Abstract.
Papers should be short and should comprehend 8 to 12 pages.
THE FORMAT OF THE PAPER
The paper should be written in the following format:
-	A Title, which adequately describes the content of the paper.
-	An Abstract, which should be viewed as a mini version of the paper and should not exceed 250 words. The Abstract should state the principal objectives and the scope of the investigation, the methodology employed, summarize the results and state the principal conclusions.
-	An Introduction, which should provide a review of recent literature and sufficient background information to allow the results of the paper to be understood and evaluated.
-	A Theory or experimental methods used.
-	An Experimental section, which should provide details of the experimental set-up and the methods used for obtaining the results.
-	A Results section, which should clearly and concisely present the data using figures and tables where appropriate.
-	A Discussion section, which should describe the relationships and generalizations shown by the results and discuss the significance of the results making comparisons with previously published work. (Because of the nature of some studies it may be appropriate to combine the Results and Discussion sections into a single section to improve the clarity and make it easier for the reader.)
-	Conclusions, which should present one or more conclusions that have been drawn from the results and subsequent discussion and do not duplicate the Abstract.
-	References, which must be numbered consecutively in the text using square brackets [1] and collected together in a reference list at the end of the paper.
THE LAYOUT OF THE TEXT
Texts should be written in Microsoft Word format. Paper must be submitted in electronic version by e-mail or by post on CD.
Do not use the LaTeX text editor, since this is not compatible with the publishing procedure of the Journal of Mechanical Engineering.
Equations should be on a separate line in the main body of the text and marked on the right-hand side of the page with numbers in round brackets.
Units and abbreviations
Only standard SI symbols and abbreviations should be used in the text, tables and figures. Symbols for physical quantities in the text should be written in italics (e.g. v, T, n, etc.). Symbols for units that consist of letters should be in plain text (e.g. ms-1, K, min, mm, etc.).
All abbreviations should be spelt out in full on first appearance, e.g., variable time geometry (VTG).
Meaning of symbols and units belonging to symbols should be explained in each case or quoted in special table at the end of the paper before References.
Figures
Figures must be cited in consecutive numerical order in the text and referred to in both the text and the caption as Fig. 1, Fig. 2, etc. Pictures may be saved in resolution good enough for printing in any common format, e.g. BMP, GIF or JPG. However, graphs and line drawings should be prepared as vector images, e.g. CDR, AI.
All Figures should be prepared in black-and-white technique, without borders and on white grounding. All Figures should be sent separately in their original formats.
When labeling axes, physical quantities, e.g. t, v, m, etc. should be used whenever possible to minimize the need to label the axes in two languages. Multi-curve graphs should have individual curves marked with a symbol. The meaning of the symbol should be explained in the figure caption.
Tables
Tables must be cited in consecutive numerical order in the text and referred to in both the text and the caption as Table 1, Table 2, etc. In addition to the physical quantity, e.g. t (in italics), units (normal text), should be added in square brackets. Each column should have the title line. Tables should not duplicate information that is already noted anywhere in the paper.
Acknowledgement
Acknowledgement for co-operation or help can be included before References. Author should state the research (co)financer.
The list of references
All references should be collected at the end of the paper in the following styles for journals, proceedings and books, respectively: [1] Wagner, A., Bajsić, I., Fajdiga, M. Measurement of the surface-temperature field in a fog lamp using resistance-based temperature detectors. Strojniški vestnik -Journal of Mechanical Engineering, February 2004, vol. 50, no. 2, p. 72-79.
[2]	Boguslawski L. Influence of pressure fluctuations distribution on local heat transfer on flat surface impinged by turbulent free jet. Proceedings of International Thermal Science Seminar II, Bled, June 13.-16., 2004.
[3]	Muhs, D. et al. Roloff/Matek mechanical parts, 16th ed. Wiesbaden: Vieweg Verlag, 2003. 791 p. (In German). ISBN 3-52807028-5
ACCEPTANCE OF PAPERS AND COPYRIGHT
The Editorial Committee reserves the right to decide whether a paper is acceptable for publication, obtain professional reviews for submitted papers, and if necessary, require changes to the content, length or language.
The corresponding author must, in the name of all authors, also enclose a written statement that the paper is original unpublished work, and not under consideration for publication elsewhere.
On publication, copyright for the paper shall pass to the Journal of Mechanical Engineering. The JME must be stated as a source in all later publications.
Editorial does not return submitted materials. Unpublished material is not preserved and is not send anywhere else without author's consent.
Paper prepared for publishing will be send to authors in PDF format. Authors should make minor corrections if needed. With this author confirms paper for publishing.
PUBLICATION FEE
For all papers authors will be asked to pay a publication fee prior to the paper appearing in the journal. However, this fee only needs to be paid after the paper is accepted for publishing by the Editorial Board. The fee is €180.00 (for all papers with maximum of 6 pages), €220.00 (for all paper with maximum of 10 pages) and €20.00 for each addition page. Publication fee includes 25 separates of each paper send to corresponding author.
Vsebina
Strojniški vestnik - Journal of Mechanical Engineering letnik 54, (2008), številka 11 Ljubljana, november 2008 ISSN 0039-2480
Izhaja mesečno
Povzetki razprav
Kostanjevec T. Polajnar, A., Sarjaš A.: Razvoj izdelka s pomočjo večkriterijske analize	SI 129
Župerl U., Cuš F.: Optimiranje postopka obdelave z na koloniji temelječo kooperativno
iskalno tehniko	SI 130
Ostojić G., Lazarević M., Stankovski S., Cosić I., Radosavljavić Z: Uporaba tehnologije
radiofrekvenčne identifikacije v sistemih za demontažo	SI 131
Maksimović R., Lalić B.: Prilagodljivost in zapletenost učinkovitih podjetij	SI 132
Brumnik R., Balantič Z.: Zanesljivost ter učinkovitost razpoznavnih sistemov in Supply Chain
Management	SI 133
Ozel K., Sahin M., Akdogan A.: Mehanske in metalurške lastnosti aluminijeve in bakrene
pločevine, spojene po postopku hladnega varjenja s pritiskom	SI 134
Burzić M., Prokić-Cvetković R., Grujić B., Atanasovska I., Adamović Ž.: Varnost delovanja
varjene konstrukcije z razpokami pri povišani temperaturi	SI 135
Osebne vesti
Razpis za mesto glavnega in odgovornega urednika Strojniškega vestnika	SI 136
Magisterija in diplome	SI 137
Navodila avtorjem
SI 138
Razvoj izdelka s pomočjo večkriterijske analize
Tomaž Kostanjevec1, Andrej Polajnar1, Andrej Sarjaš2 1 Univerza v Mariboru, Fakulteta za strojništvo, Slovenija 2 Univerza v Mariboru, Fakulteta elektrotehniko, računalništvo in informatiko, Slovenija
Pri razvoju sanitarnih armatur poskušamo z uporabo razvitega modela v večkriterijski analizi napovedati trend razvoja. V večkriterijski analizi pa uporabimo tudi večrazsežni prostor, ki nam omogoča določanje časovnega argumenta v primerjavi s parametri izdelka. V določanju parametrov izdelka sodelujeta podjetje z notranjimi informacijami in tržišče s svojimi zahtevami. V tem pogledu je mogoče vzpostaviti inovativno okolje v razvoju novih izdelkov.
Ta prispevek navaja različne pristope k razvoju izdelkov, na osnovi katerih je razvita metoda večkriterijske analize za ugotavljanje bodočega trenda razvoja izdelka. © 2008 Strojniški vestnik. Vse pravice pridržane.
Ključne besede: sanitarni izdelki, razvoj izdelkov, večkriterialne analize, večrazsežni prostor
Slika 7. Polarni graf gibanja težišča v opazovanih letih
*Naslov odgovornega avtorja: Univerza v Mariboru, Fakulteta elektrotehniko, računalništvo in informatiko Smetanova 17, Maribor, Slovenija, tomaz.kostanjevec@uni-mb.si
Optimiranje postopka obdelave z na koloniji temelječo kooperativno iskalno tehniko
Uroš Župerl - Franci Cuš Univerza v Mariboru, Fakulteta za strojništvo, Slovenija
Preučevanje ekonomike pri opravilih obdelave z večimi prehodi ima pomembno praktično pomembnost. Ne-tradicionalne optimizacijske tehnike kot so genetski algoritmi, nevronske mreže in PSO optimizacija so vsepogosteje uporabljene pri reševanju optimizacijskih problemov. V prispevku je predstavljena več-ciljna optimizacij ska tehnika, ki temelji na algoritmu kolonije mravelj (ACO) in je uporabljena pri optimiranju rezalnih parametrov pri postopkih struženja. S tehniko se simultano optimirajo naslednji trije nasprotujoči si ciljni dejavniki: stroški opravila, čas obdelave in kakovost površine. Za ciljno funkcijo je uporabljena funkcija, ki maksimira dobiček opravila. Predlagan pristop uporabi prilagodni nevro-mehki inferenčni sistem (ANFIS) za predstavitev ciljne funkcije proizvajalca in algoritem kolonije mravelj (ACO) za določitev optimalnih ciljnih vrednosti. Nova razvojna tehnika ACO je podrobno predstavljena. Razvit je obsežen uporabniku prijazen programski paket za določevanje optimalnih rezalnih parametrov z uporabo predlaganega algoritma. Na primeru je prikazana uporabnost sistema in njegova učinkovitost. Rezultate smo primerjali in analizirali z metodami drugih raziskovalcev in priporočili v katalogih. Rezultati nakazujejo, da je predlagana paradigma kolonije mravelj učinkovita v primerjavi s tehnikami drugih raziskovalcev. © 2008 Strojniški vestnik. Vse pravice pridržane.
Ključne besede: odrezavanje, struženje, optimiranje, rezalni parametri
Slika 2. Arhitektura mehkih pravil trikotne pripadnostne funkcije
*Naslov odgovornega avtorja: Univerza v Mariboru, Fakulteta za strojništvo, Smetanova 17, Maribor,
Slovenija, uros.zuperl@uni-mb.si
Uporaba tehnologije radiofrekvencne identifikacije v sistemih
za demontažo
Gordana Ostojić1, - Milovan Lazarević1 - Stevan Stankovski1 - Ilija Ćosić1 - Zoran Radosavljavić2
1	Univerza v Novem Sadu, Republika Srbija
2	ABS Holding, Beograd, Republika Srbija
V prispevku so predstavljeni rezultati razvoja modela uporabe tehnologije adiofrekvenčne identifikacije v sistemih za demontažo kot rešitev za problem sprejema velike količine različnih izdelkov na odlagališče odpadkov. Osnovne komponente morajo biti v postopku razstavljanja in odstranjevanja usmerjene v sisteme za demontažo, kjer se opravita predelava za ponovno obdelavo in recikliranje. Sestavni del navodila OEEO (odpadna električna in elektronska oprema) je tudi strategija sprejemanja odpadnih izdelkov, ki podpira kar najbolj učinkovito recikliranje. Sistemski postopki kot je demontaža omogočajo selektivno ločevanje komponent, ki so obnovljive, jih ni mogoče reciklirati in so nevarne, od tistih, ki jih je mogoče reciklirati. Pravilno načrtovan postopek demontaže lahko skupaj z recikliranjem in odstranjevanjem odpadkov pomaga pri učinkovitem upravljanju z dobo trajanja izdelkov. Za doseganje ciljev so potrebne ustrezne strategije. Ob koncu dobe trajanja je nujno zbiranje podatkov o tokovih izdelkov, materialov, delov/sestavov in nevarnih komponent/materialov. Uporaba tehnologij RFID (radiofrekvenčna identifikacija) omogoča izboljšanje upravljanje z vsemi prej omenjenimi tokovi. Tako zbrane informacije so zanesljive, natančne in dinamične, zato lahko zagotavljajo optimalno upravljanje z izdelki, ki so na koncu dobe trajanja. © 2008 Strojniški vestnik. Vse pravice pridržane.
Ključne besede: tehnologija radiofrekvencne identifikacije, konec dobe trajanja, demontažni sistemi
Slika 3. Tehnologija radio frekvencne identifikacije, uporabljena v postopku demontaže in izbor
demontiranih delov izdelkov
*Naslov odgovornega avtorja: Univerza v Novem Sadu, Fakulteta tehniških znanosti, Trg Dositeja Obradovića 6, Novi Sad, Srbija, goca@uns.ns.ac.yu
Prilagodljivost in zapletenost učinkovitih podjetij
Rado Maksimović - Bojan Lalić* Univerza v Novem Sadu, Fakulteta tehniških znanosti, Oddelek za industrijski inženiring in menedžment, Novi Sad, Srbija
Cilj raziskave je bil dati prispevek prizadevanjem za razvoj postopkov snovanja strukture industrijskih sistemov — visokoučinkovitih podjetij. V spisu so analizirani pogoji in možnosti, ki tem strukturam omogočajo prilagajanje spremembam v okolju — prilagodljivost in ustreznost upravljanja organizacijskih struktur - z zmanjševanjem stopnje zapletenosti. Poseben poudarek je posvečen masovnemu prilagajanju po meri, torej prilagajanju proizvodnje potrebam in zahtevam kupcev. Za to je nujna visoka prilagodljivost sistema, saj prav ta določa stroške pri tovrstni proizvodnji.
Izvirni prispevek tega članka so definicije in določitve meril za dve najpomembnejši lastnosti podjetja, zapletenost in prilagodljivost, ter ugotavljanje njunih medsebojnih odvisnosti. Medtem ko se v literaturi zapletenost meri z velikostjo (številom strukturnih elementov), je stopnja zapletenosti v tem spisu obravnavana tudi kot število medsebojnih razmerij med elementi strukture. Prilagodljivost struktur podjetja vključuje tri medsebojno odvisne komponente: tehnološko komponento, sposobnost in prilagodljivost tokov.
© 2008 Strojniški vestnik. Vse pravice pridržane.
Ključne besede: proizvodni sistemi, strukture podjetij, prilagodljivost, zapletenost
Slika 7. Določitev števila povezav v strukturi
*Naslov odgovornega avtorja: Univerza v Novem Sadu, Fakulteta tehniških znanosti, Trg Dositeja Obradovića 6, Novi Sad, Srbija, blalic@uns.ns.ac.yu
Zanesljivost ter učinkovitost razpoznavnih sistemov in Supply Chain Management1
Robert Brumnik - Zvone Balantič Univerza v Mariboru, Fakulteta za organizacijske vede
V proizvodno-logističnih procesih se mnogokrat pojavijo zahteve po identifikaciji nosilnikov postopkov opravilnih dejavnosti (reklamacije, presoje postopkov, izvedeni preventivno-popravni ukrepi zaradi neskladnosti). Odgovorni nosilci teh dejavnosti so običajno ljudje, ki lahko svojo identiteto dokazujejo na različne načine (lastnoročni podpis, PIN kode, čipne kartice2, biometrična razpoznava, kamere..).Ob tem pa se moramo v postopku omejiti na postopke zbiranja informacij, ki niso sporni s stališča človeške celovitosti in zaupnosti.
Zaradi neprestane optimizacije ter avtomatizacije postopkov, je trend uvedbe "enostavnih identifikacijskih sistemo" v proizvodno-logistične postopke vedno večji. Biometrija omogoča hitro ter enostavno izvedbo postopka osebne razpoznave v logističnem postopku na osnovi značilk3, brez potrebnih dodatnih razpoznavnih elementov. Seveda pa je potrebno raziskati parametre zanesljivosti in učinkovitosti, v izogib nepredvidenim učinkom pri uvedbi obravnavanih tehnologij. © 2008 Strojniški vestnik. Vse pravice pridržane.
Ključne besede: proizvodni postopki, logistični postopki (RDIF4), sistemi ugotavljanja, avtomatizacija, zanesljivost, učinkovitost, biometrija
Slika 2. Krivulja "kopalne kadi"
1	Supply Chain Management; Logistična veriga, ki zajema planiranje, uporabo ter nadzor vseh logističnih postopkov v podjetju ter pri dobaviteljih in kupcih. V osnovi se ti procesi nanašajo na oskrbo, proizvodnjo, razdelitev in vračanje ostankov in odpadkov.
2	Cipne kartice (Pametne kartice, brezstične kartice - ICC ali RFID kartice); so plastične kartice žepne velikosti, z vgrajeno anteno in čipom za obdelavo podatkov. ICC kartice v splošnem delimo na dve kategoriji. Spominske kartice so lahko z vgrajenim breznapetostnim pomnilnikom in varnostno logiko. Mikroprocesorske kartice vsebujejo spominsko in mikroprocesorsko enoto.
3	Značilke; elementi, na osnovi katerih lahko enolično prepoznamo človeka (prstni odtis, roženica, šarenica, DNK.).
4	RFID identifikacija je avtomatska prepoznavna metoda , ki temelji na in brezkontaktni daljinski obdelavi podatkov, ki so shranjeni na RFID prepoznavku (tag). RFID prepoznavnik lahko vsadimo/namestimo v/na ljudi, živali ali ga namestimo na izdelek kjer nam služi za prepoznavo na osnovi radijskih valov. Nekatere RFID prepoznavke lahko preberemo z razdalje nekaj metrov, možnost branja pa je tudi iz za čelne črte RFID čitalca. Večina RFID prepoznavkov so sestavljeni iz dveh delov; integrirane enote za shranjevanje ter obdelavo podatkov in enote za modulacijo in demodulacijo RF signala .
*Naslov odgovornega avtorja: Univerza v Mariboru, Fakulteta za organizacijske vede, Kidričeva cesta 55a, Kranj, Slovenija, robert.brumnik@metra.si
Mehanske in metalurške lastnosti aluminijeve in bakrene pločevine, spojene po postopku hladnega varjenja s pritiskom
Kaan Ozel1, - Mumin Sahin1 - Aysegul Akdogan2 1 Trakijska univerza, Oddelek za strojništvo, Edirne, Turčija 2 Tehnična univerza Yildiz, Oddelek za strojništvo, Istanbul, Turčija
Hladno varjenje s pritiskom je poseben postopek varjenja, ki se zadnja leta vse bolj uporablja pri izvedbah kot je montaža raznih delov. V predstavljeni raziskavi je bil uporabljen postopek hladnega varjenja s pritiskom za izdelavo prekrovnega spoja aluminijeve in bakrene pločevine tržne čistoče v 150-tonski hidravlični stiskalnici. S povečevanjem površinske hrapavosti in deformacije zvarnih spojev aluminijeve pločevine se je povečala tudi natezna trdnost spojev. Kupljeni vzorci z izvirno hrapavostjo so imeli najmanjšo deformacijo zvarnega spoja in teh pločevin ni bilo mogoče spajati pri 30-odstotni deformaciji zvara. Utrujenostni preizkusi so pokazali, da so spojene pločevine odporne proti nateznim napetostim z majhno spremembo. Trdota se poveča zaradi lokalnega utrjevanja na stiku, ki je posledica hladnega deformiranja. Meritve EDX (energijsko disperzna rentgenska spektroskopija) jasno kažejo, da vsebujejo spoji Al-Cu na stiku plast spojine, ki pa ne vpliva v večji meri na trdnost spoja. Rezultati kažejo, da daje tehnika hladnega prekrovnega varjenja s pritiskom močan zvarni spoj Al-Al in da intermetalna plast v spojih Al-Cu ne vpliva v večji meri na trdnost spoja. © 2008 Strojniški vestnik. Vse pravice pridržane.
Ključne besede: hladno varjenje s pritiskom, metalografija, mehanske lastnosti, površinska hrapavost, deformacije
Slika 3. Hidravlična stiskalnica
*Naslov odgovornega avtorja: Trakijska univerza, Oddelek za strojništvo, Edirne, Turčija,
kaanozel@trakya.edu.tr
Prejeto: 20.12.2007 Sprejeto: 25.09.2008
Varnost delovanja varjene konstrukcije z razpokami pri
povišani temperaturi
Meri Burzić1* - Radica Prokić-Cvetković2 - Biljana Grujić3 - Ivana Atanasovska4 - Živoslav Adamović5
1 Inštitut "GOŠA", Beograd, Srbija Fakulteta za strojništvo, Beograd, Srbija
3 Inovacijski center, Beograd, Srbija 4 Inštitut "Kirilo Savić", Beograd, Srbija, 5 Tehniška fakulteta, Zrenjanin, Srbija
V prispevku so analizirani parametri hitrosti rasti razpok in pogoji za nenaden lom debelih zvarnih spojev jekla pri sobni in delovni temperaturi. Utrujenostne razpoke, ki nastanejo zaradi ostrih napak v zvaru, so začetne razpoke, ki v območju zvarnega spoja ali osnovnem materialu rastejo skladno s Parisovim zakonom. Doba trajanja varjene konstrukcije je odvisna od položaja in usmeritve obstoječih ostrih napak v zvaru. Pri eksperimentalni analizi so bili uporabljeni različni preizkušanci z vnaprej izdelanimi razpokami.
Preizkušanci so bili prerezani v območju osnovnega materiala, dodajnega materiala in toplotno vplivne cone. Hitrost rasti razpok v območju zvarnega spoja pri delovni in sobni temperaturi je večja kot pri osnovnem materialu. Hitrost rasti utrujenostnih razpok je bila pri delovni temperaturi večja ne glede na položaj. Zanesljivost konstrukcije z vzdolžnimi začetnimi razpokami v območju toplotno vplivne cone je bila manjša kot pri prečnih začetnih razpokah v osnovnem materialu. © 2008 Strojniški vestnik. Vse pravice pridržane.
Ključne besede: varjene konstrukcije, utrujenostne razpoke, lomna žilavost, preiskušanje

13
a-1

32
42
Slika 2: Preizkusni vzorci lomne žilavosti
*Naslov odgovornega avtorja: Inštitut "GOŠA", Beograd, Srbija, merib@neobee.net
SI 135
Univerza v Ljubljani Fakulteta za strojništvo
Izdajateljski svet revije Strojniški vestnik, Fakulteta za strojništvo, Univerza v Ljubljani
objavlja razpis za mesto
GLAVNEGA IN ODGOVORNEGA UREDNIKA Strojniškega vestnika
Pogoji:
-	doktorat znanosti s področja strojništva
-	izkušnje s področja publiciranja v znanstvenih in strokovnih medijih
-	uveljavljenost na znanstvenem in strokovnem področju strojništva
Funkcija glavnega iu odgovornega urednika Strojniškega vestnika se razpisuje za dobo 5 let.
Kandidati naj v pisni vlogi priloži svoj uredniški program in načrt dela.
Vloge pošljite na naslov: Strojniški vestnik Fakulteta za strojništvo Aškerčeva 6 1000 Ljubljana
{v zaprli kuverti z dobro vidno oznako RAZPIS ZA STROJNIŠKI VESTNIK) najkasneje do 8.12.2008.
V Ljubljani, 04. novembra 200я
Fakulteta za strojništvo, Aškerčeva 6, SI-10W Ljubljana, Tel.: (01) 4771 137, Faks: (01) 2518 567, E-pošla: mfo@sv-jme,eu
Magisterija in diplome
MAGISTERIJA
Na Fakulteti za strojništvo Univerze v Ljubljani je z uspehom zagovarjal svoje magistrsko delo:
dne 24. oktobra 2008 Jure Bezgovšek z naslovom: "Sistem za krmiljenje procesa laserskega tvorjenja zaporedja kapljic iz kovinske žice" (mentor: izr. prof. dr. Edvard Govekar).
Na Fakulteti za strojništvo Univerze v Mariboru je z uspehom zagovarjal svoje magistrsko delo:
dne 13. oktobra 2008 Tomaž Brajlih z naslovom: "Raziskava vplivnih faktorjev pri hitri izdelavi po postopkih slojevitih tehnologij" (mentor: doc. dr. Igor Drstvenšek).
DIPLOMIRALI SO
Na Fakulteti za strojništvo Univerze v Ljubljani so pridobili naziv univerzitetni diplomirani inženir strojništva:
dne 24. oktobra 2008: Jure GREGORC, Alan PODGORNIK, Andrej ŠARC.
Na Fakulteti za strojništvo Univerze v Mariboru so pridobili naziv univerzitetni diplomirani inženir strojništva:
dne 07. oktobra 2008: Vito TIČ.
Na Fakulteti za strojništvo Univerze v Ljubljani so pridobili naziv diplomirani inženir strojništva:
dne 09. oktobra 2008: Miloš LEBAN, Aleš ŠTEBE, Patrik ŠULIGOJ;
dne 10. oktobra 2008: Dejan BEDENE, Dejan BEDENE, Bojan JAGER, Bojan OBRENOVIC, Uroš RUDOLF, Andrej ZUPAN, David ŽVAB;
dne 13. oktobra 2008: Rok BOBNAR, Matevž BROJAN, Tomaž DIMEC, Uroš URANKAR.
Na Fakulteti za strojništvo Univerze v Mariboru so pridobili naziv diplomirani inženir strojništva:
dne 15. oktobra 2008: Toni NOVAK;
dne 30. oktobra 2008: Bojan CRNČEC, Miro HAJDINJAK, Aleksander KOROŠEC, Aleš KRIŠTOF, Martin NERAD, Jurij OSENJAK, Andrej POTOČNIK, Lovro ŠOLAR, Darko FRIŠČIC, Janko VERBEK.
Navodila avtorjem
Članki so v Strojniškem vestniku od leta 2008 objavljeni samo v angleškem jeziku s slovenskim naslovom, povzetkom ter sliko s podnaslovom v dodatku. Avtorji so v celoti odgovorni za jezikovno lektoriranje članka. V kolikor recenzent oceni, da jezik ni dovolj kakovosten, lahko uredništvo zahteva ponovno lektoriranje usposobljenega lektorja ter potrdilo o opravljenem lektoriranju.
Članki morajo vsebovati:
-	naslov, povzetek, ključne besede,
-	besedilo članka,
-	preglednice in slike (diagrami, risbe ali fotografije) s podnaslovi,
-	seznam literature in
-	podatke o avtorjih, odgovornega avtorja in njegov polni naslov.
Članki naj bodo kratki in naj obsegajo približno 8-12 strani.
Člankom so lahko priložene tudi dodatne računalniške simulacije ali predstavitve, pripravljene v primerni obliki, ki bodo bralcem dostopne na spletni strani revije.
VSEBINA ČLANKA
Članek naj bo napisan v naslednji obliki:
Naslov, ki primerno opisuje vsebino
članka.
-	Povzetek, ki naj bo skrajšana oblika članka in naj ne presega 250 besed. Povzetek mora vsebovati osnove, jedro in cilje raziskave, uporabljeno metodologijo dela, povzetek rezultatov in osnovne sklepe.
-	Uvod, v katerem naj bo pregled novejšega stanja in zadostne informacije za razumevanje ter pregled rezultatov dela, predstavljenih v članku.
-	Teorija.
-	Eksperimentalni del, ki naj vsebuje podatke o postavitvi preskusa in metode, uporabljene pri pridobitvi rezultatov.
-	Rezultati, ki naj bodo jasno prikazani, po potrebi v obliki slik in preglednic.
-	Razprava, v kateri naj bodo prikazane povezave in posplošitve, uporabljene za pridobitev rezultatov. Prikazana naj bo tudi pomembnost rezultatov in primerjava s poprej objavljenimi deli. (Zaradi narave posameznih
raziskav so lahko rezultati in razprava, za jasnost in preprostejše bralčevo razumevanje, združeni v eno poglavje.)
-	Sklepi, v katerih naj bo prikazan en ali več sklepov, ki izhajajo iz rezultatov in razprave.
-	Literatura, ki mora biti v besedilu oštevilčena zaporedno in označena z oglatimi oklepaji [1] ter na koncu članka zbrana v seznamu literature.
OBLIKA ČLANKA
Besedilo članka naj bo pripravljeno v urejevalniku Microsoft Word. Članek nam dostavite v elektronski obliki (lahko po elektronski pošti). Ne uporabljajte urejevalnika LaTeX, saj program, s katerim pripravljamo Strojniški vestnik, ne uporablja njegovega formata. Enačbe naj bodo v besedilu postavljene v ločene vrstice in na desnem robu označene s tekočo številko v okroglih oklepajih.
Enote in okrajšave
V besedilu, preglednicah in slikah uporabljajte le standardne označbe in okrajšave SI. Simbole fizikalnih veličin v besedilu pišite poševno (kurzivno), (npr. v, T, n itn.). Simbole enot, ki sestojijo iz črk, pa pokončno (npr. ms-1, K, min, mm itn.).Vse okrajšave naj bodo, ko se prvič pojavijo, napisane v celoti, npr. časovno spremenljiva geometrija (ČSG). Vse veličine morajo biti navedene, ko se prvič pojavijo, v besedilu ali za enačbo.
Slike
Slike morajo biti zaporedno oštevilčene in označene, v besedilu in podnaslovu, kot sl. 1, sl. 2 itn. Posnete naj bodo v ločljivosti, primerni za tisk, v kateremkoli od razširjenih formatov, npr. BMP, JPG, GIF. Diagrami in risbe morajo biti pripravljeni v vektorskem formatu, npr. CDR, AI.
Vse slike morajo biti pripravljene v črno-beli tehniki, brez obrob okoli slik in na beli podlagi. Ločeno pošljite vse slike v izvirni obliki.
Pri označevanju osi v diagramih, kadar je le mogoče, uporabite označbe veličin (npr. t, v, m itn.). V diagramih z več krivuljami, mora biti vsaka krivulja označena. Pomen oznake mora biti pojasnjen v podnapisu slike.
Preglednice
Preglednice morajo biti zaporedno oštevilčene in označene, v besedilu in podnaslovu, kot preglednica 1, preglednica 2 itn. K fizikalnim veličinam, npr. t (pisano poševno), pripišite enote (pisano pokončno) v oglatih oklepajih.
Seznam literature
Vsa literatura mora biti navedena v seznamu na koncu članka v prikazani obliki po vrsti za revije, zbornike in knjige:
[1]	Wagner, A., Bajsić, I., Fajdiga, M. Measurement of the surface-temperature field in a fog lamp using resistance-based temperature detectors. Strojniški vestnik -Journal of Mechanical Engineering, February 2004, vol. 50, no. 2, p. 72-79.
[2]	Boguslawski L. Influence of pressure fluctuations distribution on local heat transfer on flat surface impinged by turbulent free jet. Proceedings of
International Thermal Science Seminar II, Bled, June 13.-16., 2004.
[3] Muhs, D. et al. Roloff/Matek mechanical elements, 16th ed. Wiesbaden: Vieweg Verlag, 2003. 791 p. Translation of: Roloff/Matek Maschinenelemente. (v nemščini) ISBN 3-528-07028-5
SPREJEM ČLANKOV IN AVTORSKE PRAVICE
Uredništvo Strojniškega vestnika si pridržuje pravico do odločanja o sprejemu članka za objavo, strokovno oceno recenzentov in morebitnem predlogu za krajšanje ali izpopolnitev ter terminološke korekture.
Avtor mora predložiti pisno izjavo, da je besedilo njegovo izvirno delo in ni bilo v dani obliki še nikjer objavljeno. Z objavo preidejo avtorske pravice na Strojniški vestnik. Pri morebitnih kasnejših objavah mora biti SV naveden kot vir.
Plačilo objave
Avtorji vseh prispevkov morajo za objavo plačati prispevek v višini 180,00 EUR (za članek dolžine do 6 strani), 220,00 EUR (za članek dolžine do 10 strani) ter 20,00 EUR za vsako dodatno stran. Prispevek se zaračuna po sprejemu članka za objavo na seji Uredniškega odbora. Po objavi prejme avtor članka 25 separatov članka.
www.irt3000.com
Guide through abundant information from
-	metalworking industry
-	automation and informatisation
-	processing of non-metals
-	advanced technologies
EVERYTWO MONTHS ON MORE THAN 140 PAGES
The IRT3000 magazine brings articles about technological and developmental achievements, presents interesting individuals and successful companies, innovative products, advanced projects... Bringing interviews with experts and fair reports, the magazine is an informative and educative media, offering the readers useful information for their profession. The magazine also presents important professional and general economy topics, needed by the companies from listed braches for efficient operations. It is also a forum for idea exchange between academia and industry, at the same time co-creating professional terminology and supporting the networking of science and entrepreneurship as a leading professional magazine.
Contact us for the advertising price list! e-mail: info@irt3000.si
LUXURY
FOR THE PASSENGERS
MINIBUSES MIDIBUSES INTERCITY BUSES LINE BUSES AIRPORT BUSES
VIVEO VIVETH MARBUS TL MARBUS TLL NEOPLAN
TOVfìRNfì VOZIL
Vü/ MARBUS MlißlßOR d.o.o.
VIATOR&VEKTOR GROUP
9 770039 248001 ISSN □D3T-24ÜG
http://www.sv-jme.eu
9770039248001