A. GÖK: 2D NUMERIC SIMULATION OF SERRATED-CHIP FORMATION IN ORTHOGONAL CUTTING OF AISI316H ... 953–956 2D NUMERIC SIMULATION OF SERRATED-CHIP FORMATION IN ORTHOGONAL CUTTING OF AISI316H STAINLESS STEEL NUMERI^NA 2D SIMULACIJA NASTANKA NAZOB^ANEGA ODREZKA PRI PRAVOKOTNEM REZANJU AISI316H JEKLA Arif Gök Amasya University, Faculty of Technology, Department of Mechanical Engineering, 05100 Amasya, Turkey arif.gok@amasya.edu.tr Prejem rokopisa – received: 2017-04-06; sprejem za objavo – accepted for publication: 2017-05-30 doi:10.17222/mit.2017.038 Low thermal conductivity, high strength, high ductility and high work-hardening tendency of austenitic stainless steels are the main factors that make their machinability difficult. This study investigates the influence of material modelling on the serrated-chip formation during the orthogonal cutting of the AISI316H stainless steel using finite-element simulations. Turning tests were carried out at three different cutting speeds and constant depth of cut and feed rate. Predictions were compared with the orthogonal-cutting tests and found to be in agreement. Keywords: AISI 304 stainless steel, finite-element method, serrated-chip formation, machinability Nizka toplotna prevodnost, visoka trdnost, velika duktilnost in sposobnost mo~nega utrjevanja so glavni vzroki za to, da se austenitno nerjavno jeklo te`ko mehansko obdeluje. V {tudiji so avtorji modelirali tvorbo nazob~anega ostru`ka med pravo- kotnim rezanjem AISI316H nerjavnega jekla. Za modeliranje so uporabili metodo kon~nih elementov (MKE). Preizkusi stru`enja so bili izvedeni pri treh razli~nih rezalnih hitrostih ter pri konstantni globini reza in pomikanja. Rezultate modeliranja so primerjali s prakti~nimi preizkusi pravokotnega rezanja (stru`enja). Ugotovili so, da se prakti~ni rezultati preizkusov dobro ujemajo z rezultati MKE-modeliranja. Klju~ne besede: AISI 304 nerjavno jeklo, metoda kon~nih elementov, tvorba nazob~anih ostru`kov, sposobnost strojnega obdelovanja 1 INTRODUCTION Austenitic stainless steels, characterised by a high work-hardening rate and low thermal conductivity 1, are used to fabricate chemical and food-processing equip- ment, as well as machinery parts requiring high corro- sion resistance.2 They are generally regarded as more difficult to machine than carbon and low-alloy steels on account of their high strength, high work-hardening tendency and poor thermal conductivity.3,4 Problems such as poor surface finish and high tool wear are common.5 Work hardening is recognised to be responsible for the poor machinability of austenitic stainless steels.6 In addition, they bond very strongly to the cutting tool during cutting and when a chip is broken away, it may bring with it a fragment of the tool, particularly when cutting with cemented carbide tools. When machining this material, cutting-force variation is also much more obvious than in the case of machining unalloyed steel.1 Especially, in order to increase the productivity and tool life in the machining of the AISI304 and AISI316 series stainless steel, it is necessary to develop a reliable FE model for different cutting processes. To accurately analyse this process using numerical methods such as the finite-element analysis (FEA), the knowledge of the material constitutive behaviour under these severe load- ing conditions is a pre-requisite and hence correct work- material flow-stress data need to be used. In fact, the success and reliability of numerical models are heavily dependent upon the work-material-flow stress, friction parameters for the tool and work-material interfaces, the fracture criterion and thermal parameters.3,7–10 Many studies on the chip formation have been published by now. Titanium alloys are used in most of these studies. M. Bäker11 studied the influence of the material law determining the plastic flow on the chip formation of titanium alloys at high cutting speeds, while T. Özel et al.12 studied constitutive-material models to simulate the serrated-chip formation, including also other materials. In parallel with these investigations, M. Sima and T. Özel13 investigated the influence of con- stitutive-material models and elastic/viscoplastic finite- element formulation on a serrated-chip formation for modelling the machining of the Ti–6Al–4V titanium alloy. R. Alvarez et al.14 analysed the effect of eight constitutive models on the saw-toothed chip formation in Ti6Al4V orthogonal cutting. In another study carried out by G. Chen et al.15, a Johnson-Cook material model with an energy-based ductile-failure criterion was developed using a titanium-alloy (Ti–6Al–4V) high-speed machin- ing FEA. D. Umbrello16 presented a finite-element anal- ysis (FEA) of machining TiAl6V4 for both conventional and high-speed cutting regimes. Work to date has shown that little work has been carried on the determination of Materiali in tehnologije / Materials and technology 51 (2017) 6, 953–956 953 MATERIALI IN TEHNOLOGIJE/MATERIALS AND TECHNOLOGY (1967–2017) – 50 LET/50 YEARS UDK 52-17:62-493-026.775:621.9 ISSN 1580-2949 Original scientific article/Izvirni znanstveni ~lanek MTAEC9, 51(6)953(2017) the chip formation when machining AISI304 stainless steels. In a study carried out by J. Q. Xie et al.17, the theory of shear banding was included in the analysis of chip formation and chip instability. They used analytic and experimental methods to study these characteristics. This work aims to investigate the serrated-chip formation in the machining of the AISI304 stainless steel using finite-element simulations. 2 EXPERIMENTAL PART 2.1 Turning process Turning processes were performed on a CNC turning lathe that has a capacity of 10kW using AISI 1045 samples with dimensions of Ø50 mm × 100 mm. The rake angle was 0° and the clearance angle was 5°. The turning processes were carried out using the turning parameters from Table 1. The cutting length for the turning processes was chosen to be 10 mm. Table 1: Turning parameters Parameters Value Cutting speed – Vc (m/min) 100 Feed rate – f (min–1) 0.1 Depth of cut – ap (mm) 0.5 2.2 Numeric analysis In 2D numeric simulations, the cutting tool and the workpiece consist of a tetrahedral mesh. While the mesh structure of the workpiece consists of 1453 elements and 1547 nodes, the mesh structure of the cutting tool consists of 770 elements and 823 nodes. The mesh structure of the model of the workpiece and cutting tool is given in Figure 1. However, the workpiece model was constrained by the lateral surfaces and lower surface. The contact algorithm for the interface of the cutting tool and workpiece was defined as the master and slave in the software. As the friction model for these two elements, the Coulomb model of friction was selected because it uses low cutting speeds. The Cockcroft-Latham fracture criterion was selected as the damage criterion. The Cockcroft-Latham criterion is given in Equation (1). According to the Cockcroft-Latham damage criterion, damage occurs when the accumulated stress state D, over the plastic strain, reaches the critical damage value (Dcr). The Dcr was selected to be 90 for all the cutting simulations because it had the most suitable chip form. The friction coefficient for the simulation study was calculated to be 0.41 for the normal machining and 0.60 for the damage criterion. This coefficient of the friction between the tool and the chip in orthogonal cutting was calculated using Equations (2) and (3).18 Fc and Ft forces were obtained experimentally; Fs, Ns, F and N forces depend on them and can be calculated from Figure 2. D d f = ∫    1 0 (1) A. GÖK: 2D NUMERIC SIMULATION OF SERRATED-CHIP FORMATION IN ORTHOGONAL CUTTING OF AISI316H ... 954 Materiali in tehnologije / Materials and technology 51 (2017) 6, 953–956 MATERIALI IN TEHNOLOGIJE/MATERIALS AND TECHNOLOGY (1967–2017) – 50 LET/50 YEARS Figure 2: Two-dimensional (2D) force system in turning operations (Merchant’s force circle) Figure 1: Mesh process μ = tan = F N (2) μ = F F F F t c c t + − tan tan   (3) 2.3 Material model While the workpiece was selected as AISI 316h, the cutting tool was selected to be tungsten carbide (WC). The mechanical and thermal properties of the WC and AISI 316h are given in Table 2.19 The flow-stress curve of the workpiece-material model was taken from refe- rence19. The flow stress was defined as a function of the strain, strain rate and temperature as seen in Figure 3. The flow stress () in Equation (4) was selected to ex- hibit the true material behavior as a function of the effec- tive plastic strain (), effective strain rate () and tempe- rature (T). The flow-stress curves are very important for high-temperature applications such as metal cutting.   = ( ,  , )T (4) Table 2: Mechanical and thermal properties of the drill bit and bone materials19 Workpiece-material properties (AISI 316h316H) Modulus of elasticity (GPa) 20 °C (210) Poisson’s ratio 0.3 Thermal-expansion coefficient (10–6 °C–1) 93.33 °C (1.20×10 –5) Thermal conductivity(W/mK) 100 °C (17) Heat capacity (N/mm2 °C) 93.33 °C (2.78) Emissivity 0.7 Cutting-tool-material properties (WC) Modulus of elasticity (GPa) 650 Poisson’s ratio 0.25 Thermal-expansion coefficient (10–6 °C–1) 5 Thermal conductivity(W/mK) 59 Heat capacity (N/s /mm/°C) 15 Emissivity 0 3 RESULTS At the end of the study, force variations occurred in the normal machining (NM) and the machining with damage criterion (MWDC) was very different, as seen in Figure 4. As seen in Table 3, while the MWDC de- formed-chip thickness was lower than during the NM, the chip ratio and shear-angle values were higher during the MWDC than during the NM. Good agreement bet- ween experimental tests and FEM simulations was found for cutting forces and shear-angle values, as shown in Figures 5 and 6. A. GÖK: 2D NUMERIC SIMULATION OF SERRATED-CHIP FORMATION IN ORTHOGONAL CUTTING OF AISI316H ... Materiali in tehnologije / Materials and technology 51 (2017) 6, 953–956 955 MATERIALI IN TEHNOLOGIJE/MATERIALS AND TECHNOLOGY (1967–2017) – 50 LET/50 YEARS Figure 5: Deformed-chip thickness and shear angles for the NM and MWDCFigure 3: Flow-stress curves for the workpiece material19 Figure 4: Force variations occurred during NM and MWDC the chip formation when machining AISI304 stainless steels. In a study carried out by J. Q. Xie et al.17, the theory of shear banding was included in the analysis of chip formation and chip instability. They used analytic and experimental methods to study these characteristics. This work aims to investigate the serrated-chip formation in the machining of the AISI304 stainless steel using finite-element simulations. 2 EXPERIMENTAL PART 2.1 Turning process Turning processes were performed on a CNC turning lathe that has a capacity of 10kW using AISI 1045 samples with dimensions of Ø50 mm × 100 mm. The rake angle was 0° and the clearance angle was 5°. The turning processes were carried out using the turning parameters from Table 1. The cutting length for the turning processes was chosen to be 10 mm. Table 1: Turning parameters Parameters Value Cutting speed – Vc (m/min) 100 Feed rate – f (min–1) 0.1 Depth of cut – ap (mm) 0.5 2.2 Numeric analysis In 2D numeric simulations, the cutting tool and the workpiece consist of a tetrahedral mesh. While the mesh structure of the workpiece consists of 1453 elements and 1547 nodes, the mesh structure of the cutting tool consists of 770 elements and 823 nodes. The mesh structure of the model of the workpiece and cutting tool is given in Figure 1. However, the workpiece model was constrained by the lateral surfaces and lower surface. The contact algorithm for the interface of the cutting tool and workpiece was defined as the master and slave in the software. As the friction model for these two elements, the Coulomb model of friction was selected because it uses low cutting speeds. The Cockcroft-Latham fracture criterion was selected as the damage criterion. The Cockcroft-Latham criterion is given in Equation (1). According to the Cockcroft-Latham damage criterion, damage occurs when the accumulated stress state D, over the plastic strain, reaches the critical damage value (Dcr). The Dcr was selected to be 90 for all the cutting simulations because it had the most suitable chip form. The friction coefficient for the simulation study was calculated to be 0.41 for the normal machining and 0.60 for the damage criterion. This coefficient of the friction between the tool and the chip in orthogonal cutting was calculated using Equations (2) and (3).18 Fc and Ft forces were obtained experimentally; Fs, Ns, F and N forces depend on them and can be calculated from Figure 2. D d f = ∫    1 0 (1) A. GÖK: 2D NUMERIC SIMULATION OF SERRATED-CHIP FORMATION IN ORTHOGONAL CUTTING OF AISI316H ... 954 Materiali in tehnologije / Materials and technology 51 (2017) 6, 953–956 MATERIALI IN TEHNOLOGIJE/MATERIALS AND TECHNOLOGY (1967–2017) – 50 LET/50 YEARS Figure 2: Two-dimensional (2D) force system in turning operations (Merchant’s force circle) Figure 1: Mesh process μ = tan = F N (2) μ = F F F F t c c t + − tan tan   (3) 2.3 Material model While the workpiece was selected as AISI 316h, the cutting tool was selected to be tungsten carbide (WC). The mechanical and thermal properties of the WC and AISI 316h are given in Table 2.19 The flow-stress curve of the workpiece-material model was taken from refe- rence19. The flow stress was defined as a function of the strain, strain rate and temperature as seen in Figure 3. The flow stress () in Equation (4) was selected to ex- hibit the true material behavior as a function of the effec- tive plastic strain (), effective strain rate () and tempe- rature (T). The flow-stress curves are very important for high-temperature applications such as metal cutting.   = ( ,  , )T (4) Table 2: Mechanical and thermal properties of the drill bit and bone materials19 Workpiece-material properties (AISI 316h316H) Modulus of elasticity (GPa) 20 °C (210) Poisson’s ratio 0.3 Thermal-expansion coefficient (10–6 °C–1) 93.33 °C (1.20×10 –5) Thermal conductivity(W/mK) 100 °C (17) Heat capacity (N/mm2 °C) 93.33 °C (2.78) Emissivity 0.7 Cutting-tool-material properties (WC) Modulus of elasticity (GPa) 650 Poisson’s ratio 0.25 Thermal-expansion coefficient (10–6 °C–1) 5 Thermal conductivity(W/mK) 59 Heat capacity (N/s /mm/°C) 15 Emissivity 0 3 RESULTS At the end of the study, force variations occurred in the normal machining (NM) and the machining with damage criterion (MWDC) was very different, as seen in Figure 4. As seen in Table 3, while the MWDC de- formed-chip thickness was lower than during the NM, the chip ratio and shear-angle values were higher during the MWDC than during the NM. Good agreement bet- ween experimental tests and FEM simulations was found for cutting forces and shear-angle values, as shown in Figures 5 and 6. A. GÖK: 2D NUMERIC SIMULATION OF SERRATED-CHIP FORMATION IN ORTHOGONAL CUTTING OF AISI316H ... Materiali in tehnologije / Materials and technology 51 (2017) 6, 953–956 955 MATERIALI IN TEHNOLOGIJE/MATERIALS AND TECHNOLOGY (1967–2017) – 50 LET/50 YEARS Figure 5: Deformed-chip thickness and shear angles for the NM and MWDCFigure 3: Flow-stress curves for the workpiece material19 Figure 4: Force variations occurred during NM and MWDC 4 CONCLUSIONS In this study, a finite-element model was developed to see the effect of a serrated-chip formation in the ma- chining of the AISI304 stainless steel using finite-ele- ment simulations. A computer-aided numerical simula- tion of the turning process was also performed using DEFORM – 2D software. It can be said that the 2D FEM model gives reasonable results compared to the experi- mental results in view of cutting forces, thrust force and shear angles. This proves the accuracy of the developed 2D FEM model, which can be used for this type of turning simulations. 5 REFERENCES 1 S. Coromant, Modern metal cutting: a practical handbook, Sandvik Coromant Press, 1st ed., 1994 2 M. P. Groover, Fundamentals of Modern Manufacturing: Materials, Processes, and Systems, Prentice Hall, Wiley, 1996 3 E. M. Trent, Metal Cutting, Elsevier Science, Butterworth-Heine- mann, 2016 4 J. Paro, H. Hänninen, V. Kauppinen, Tool wear and machinability of X5 CrMnN 18 18 stainless steels, Journal of Materials Processing Technology, 119 (2001), 14–20, doi:10.1016/S0924-0136(01) 00877-9 5 D. O’Sullivan, M. Cotterell, Machinability of austenitic stainless steel SS303, Journal of Materials Processing Technology, 124 (2002), 153–159, doi: 10.1016/S0924-0136(02)00197-8 6 L. Jiang, Å. Roos, P. Liu, The influence of austenite grain size and its distribution on chip deformation and tool life during machining of AISI 304L, Metallurgical and Materials Transactions A, 28 (1997), 2415–2422, doi: 10.1007/s11661-997-0198-z 7 T. H. C. Childs, Material Property Needs in Modeling Metal Machining, Machining Science and Technology, 2 (1998), 303–316, doi:10.1080/10940349808945673 8 M. C. Shaw, Metal Cutting Principles, Oxford University Press, 2005 9 K. Maekawa, T. Obikawa, Y. Yamane, T. H. C. Childs, Metal Ma- chining: Theory and Applications, Elsevier Science, 2013 10 V. P. Astakhov, Metal Cutting Mechanics, Taylor & Francis, 1998 11 M. Bäker, The influence of plastic properties on chip formation, Computational Materials Science, 28 (2003), 556–562, doi:10.1016/ j.commatsci.2003.08.013 12 T. Ozel, M. Sima, A. Srivastava, Finite element simulation of high speed machining Ti-6Al-4V alloy using modified material models, Transactions of the NAMRI/SME, 38 (2010), 49–56, 13 M. Sima, T. Özel, Modified material constitutive models for serrated chip formation simulations and experimental validation in machining of titanium alloy Ti–6Al–4V, International Journal of Machine Tools and Manufacture, 50 (2010), 943–960, doi:10.1016/j.ijmachtools. 2010.08.004 14 R. Alvarez, R. Domingo, M. A. Sebastian, The formation of saw toothed chip in a titanium alloy: influence of constitutive models, Journal of Mechanical Engineering, 57 (2011), 739–749, doi:10.5545/sv-jme.2011.106 15 G. Chen, C. Ren, X. Yang, X. Jin, T. Guo, Finite element simulation of high-speed machining of titanium alloy (Ti–6Al–4V) based on ductile failure model, The International Journal of Advanced Manu- facturing Technology, 56 (2011), 1027–1038, doi:10.1007/s00170- 011-3233-6 16 D. Umbrello, Finite element simulation of conventional and high speed machining of Ti6Al4V alloy, Journal of Materials Processing Technology, 196 (2008), 79–87, doi:10.1016/j.jmatprotec.2007. 05.007 17 J. Q. Xie, A. E. Bayoumi, H. M. Zbib, Analytical and experimental study of shear localization in chip formation in orthogonal machin- ing, Journal of Materials Engineering and Performance, 4 (1995), 32–39, doi: 10.1007/bf02682702 18 P. J. Arrazola, T. Özel, Investigations on the effects of friction mo- deling in finite element simulation of machining, International Journal of Mechanical Sciences, 52 (2010), 31–42, doi:10.1016/ j.ijmecsci.2009.10.001 19 DEFORM-3D Material Library, http://home.zcu.cz/~sbenesov/ Deform2Dlabs.pdf, 12.04.2017 A. GÖK: 2D NUMERIC SIMULATION OF SERRATED-CHIP FORMATION IN ORTHOGONAL CUTTING OF AISI316H ... 956 Materiali in tehnologije / Materials and technology 51 (2017) 6, 953–956 MATERIALI IN TEHNOLOGIJE/MATERIALS AND TECHNOLOGY (1967–2017) – 50 LET/50 YEARS Figure 6: a) Cutting and b) thrust force for MWDC Table 3: Comparison of NM and MWDC Cutting speed (m/min) Undeformed chip thickness, t (mm) Deformed chip thickness, tc (mm) Chip ratio, rc Shear angle, (with Eg. 17) Shear angle,  (FEM) NM 100 0.5 1.85 0.268 15 17 MWDC 100 0.5 0.76 0.657 33.304 37 A. GÖK et al.: EFFECTS OF CUTTING PARAMETERS AND TOOL-PATH STRATEGIES ON TOOL ACCELERATION ... 957–965 EFFECTS OF CUTTING PARAMETERS AND TOOL-PATH STRATEGIES ON TOOL ACCELERATION IN BALL-END MILLING U^INKI REZALNIH PARAMETROV IN STRATEGIJA ZA POSPE[EK ORODJA PRI MEHANSKI OBDELAVI S KROGLI^NIM FREZALOM Arif Gök1, Kadir Gök2, Mehmet Burak Bilgin1, Mehmet Ali Alkan3 1Amasya University, Faculty of Technology, Department of Mechnical Engineering, 05100 Amasya, Turkey 2Celal Bayar University, Favulty of Technology, Department of Mechanical and Manufacturing Engineering, 45100 Manisa, Turkey 3Mu  gla Sitki Kocman University, Ula Vocational High School, Department of Energy, 48000 Mu  gla, Turkey arif.gok@amasya.edu.tr Prejem rokopisa – received: 2017-04-08; sprejem za objavo – accepted for publication: 2017-06-22 doi:10.17222/mit.2017.039 The determination of the cutting-parameter values that cause increases in vibration values is important to minimize the errors that can occur. Thus, the first aim of this study was to investigate the optimum cutting-parameter values and tool-path strategies in ball-end milling of the EN X40CrMoV5-1 tool steel with three coated cutters using the Taguchi method. The parameters taken into consideration are the cutting speed, feed rate, step over and tool-path strategies. The second aim of the study, a model for the tool acceleration as a function of the cutting parameters, was obtained using the response-surface methodology (RSM). As a result, the most effective parameter within the selected cutting parameters and cutting strategies for both inclined surfaces and different coatings was the step over. In terms of tool coatings, the most deteriorating coating for the tool acceleration on both inclined surfaces was the TiC coating. In addition, the response-surface methodology is employed to predict the tool-vibration values depending on the cutting parameters and tool-path strategy. The model generated gives highly accurate results. Keywords: inclined surfaces, ball-end milling, tool acceleration, Taguchi method, response-surface methodology, response optimization Neoptimalni rezalni parametri med mehansko obdelavo lahko povzro~ijo ne`elene vibracije in posledi~no napake. Prvi cilj avtorjev te {tudije je bil dolo~iti optimalne vrednosti rezalnih parametrov in strategije potovanja orodja med mehansko obdelavo orodnega jekla EN X40CrMoV5-1 s krogli~nim frezalom s tremi rezili z razli~no prevleko (TiC, TiN in TiAlN). Za to so upora- bili Taguchi-jevo metodo. Parametri, ki so jih avtorji zajeli v {tudiji so bili: hitrost rezanja, velikost odvzema, korak odvzema (preskok) in strategija poti orodja. Drugi cilj avtorjev te {tudije je bil izdelati model pospe{evanja orodja v odvisnosti od rezalnih parametrov, z uporabo metodologije odziva povr{ine (angl. RSM). Ugotovili so, da je korak odvzema (angl.: step over) naju~inkovitej{i parameter med izbranimi rezalnimi parametri in rezalnimi strategijami, tako za oba izbrana nagiba (ukrivljenosti) povr{ine, kot tudi izbrane trde prevleke. Med izbranimi trdimi prevlekami se je v vseh pogojih frezanja kot najslab{a izkazala TiC prevleka. RSM metodologija dodatno omogo~a napoved vibracij orodja v odvisnosti od rezalnih parametrov in izbrane strategije poti orodja. Izdelani model daje zelo to~ne rezultate. Klju~ne besede: nagib (ukrivljenost) povr{ine, mehanska obdelava s krogli~nim frezalom, pospe{ek orodja, Taguchi metoda, metodologija odgovora povr{ine, optimizacija odgovora 1 INTRODUCTION Nowadays, machining is one of the most important methods for manufacturing technologies and it remains up-to-date.1 In the machining of inclined surfaces, tight machining tolerances are generally requested for the processes of finishing and semi-finishing, which are accomplished using indexable insert ball-end mills.2,3 The forces that occur at high cutting speeds, especially during hard machining, and at high rates of metal removing, cause excessive, irregular vibrations of cutting tools during the machining. These vibrations cause the cutting tools to break, disrupting the process stability and the quality. Therefore, generating the optimum cutting parameters is crucial to obtain high productivity in the manufacturing process of complex geometries and to reach the desired tolerance values.4,5 The studies carried out in the field commonly focus on: 1) the effect of cutting parameters and cutting strategies of plain-surface milling, 2) analytical tool-acceleration calculations and measure- ments for end-milling and turning operations. W. H. Yang and Y. S. Tarng6 worked on the optimi- zation of the cutting parameters for turning operations so that both optimum cutting parameters were demonstrated and the basic cutting parameters affecting the cutting performance in turning were defined. M. Kurt et al.7 worked on the optimization of the cutting parameters for the finish surface and the accuracy of the hole diameter during dry drilling. In this way, optimum cutting conditions were obtained with the process optimization. C. Gologlu and N. Sakarya8 investigated the effects of tool-path strategies on the surface roughness for pocket-milling operations using cutting parameters with Materiali in tehnologije / Materials and technology 51 (2017) 6, 957–965 957 MATERIALI IN TEHNOLOGIJE/MATERIALS AND TECHNOLOGY (1967–2017) – 50 LET/50 YEARS UDK 621.927:621.9.07:621.926.5 ISSN 1580-2949 Original scientific article/Izvirni znanstveni ~lanek MTAEC9, 51(6)957(2017)