H. BAYRAM, N. S. KÖKSAL: INVESTIGATION OF THE GEOMETRICAL ACCURACY AND THICKNESS ...
111–116
INVESTIGATION OF THE GEOMETRICAL ACCURACY AND
THICKNESS DISTRIBUTION USING 3D LASER SCANNING OF
AA2024-T3 SHEETS FORMED BY SPIF
PREISKAVA GEOMETRIJSKE NATAN^NOSTI IN RAZPOREDITEV
DEBELINE S TRIDIMENZIONALNIM LASERSKIM SKENIRANJEM
PLO^EVINE IZ AA2024-T3, PREOBLIKOVANE S STOPNJUJO^IM
PREOBLIKOVANJEM KOVINE
Halil Bayram1,2, Nurullah Sinan Köksal3
1Uludað University, Department of Automotive Engineering, Bursa, Turkey
2Amasya University, Department of Automotive Engineering, Amasya, Turkey
3Celal Bayar University, Department of Mechanical Engineering, Manisa, Turkey
halilbayram@uludag.edu.tr
Prejem rokopisa – received: 2015-09-16; sprejem za objavo – accepted for publication: 2015-12-16
doi:10.17222/mit.2015.296
Incremental sheet forming (ISF) is developed in order to meet the increasing demand for sheet metal forming and because it is a
more economical method. First of all, this method gains attention become it is a die-less method. Furthermore, process
flexibility and higher formability are other advantages of this method. In this study, AA2024-T3 sheets with a determined
geometry and parameters were formed using the ISF method. Among the forming process parameters, tool path, step size and
lubrication parameters were changed. The tool diameter, feed rate, spindle speed, angle of the wall and the tool coating
parameters were kept constant. The thickness distributions and geometrical accuracy of the processed samples with the
three-dimensional laser scanning method were examined accurately. It is clear from the results that the tool path that spirals and
always keeps in touch is more successful than the tool path that makes it an incremental process. ISF is preferable to die
production for limited production runs because it is more economic and the processing time is short.
Keywords: incremental sheet forming, single point incremental sheet forming, aluminum alloy AA2024, laser scanning
Stopnjujo~e preoblikovanje plo~evine (angl. ISF) je bilo razvito z namenom zadovoljiti povpra{evanje po razli~nem
preoblikovanju plo~evine na bolj ekonomi~en na~in. Ta metoda vzbuja pozornost, ker gre za metodo brez orodja. Drugi dve
prednosti te metode sta: fleksibilnost procesa in ve~ja preoblikovalnost. V pri~ujo~i {tudiji je bila plo~evina iz AA2024-T3
preoblikovana z dolo~eno geometrijo in parametri z uporabo metode ISF. Med postopkom preoblikovanja so bili spreminjani
procesni parametri, kot je pot orodja, velikost koraka in parametri mazanja. Premer orodja, hitrost podajanja, hitrost vrtenja,
naklon stene in parametri prekritja orodja, so bili konstantni. Razporeditev debelin in geometrijska natan~nost izdelanih vzorcev
so bili natan~no preiskani s tridimenzionalnim laserskim skeniranjem. Rezultati so pokazali, da sta spiralna pot orodja in stalen
stik bolj uspe{na od poti orodja, ki dela postopoma. Pokazalo se je tudi, da je pri omejeni koli~ini postopek ISF relativno bolj
ekonomi~en kot postopek z orodjem in tudi ~as izdelave je kraj{i.
Klju~ne besede: stopnjujo~e preoblikovanje plo~evine, enoto~kovno stopnjujo~e preoblikovanje plo~evine, aluminijeva zlitina
AA2024, lasersko skeniranje
1 INTRODUCTION
Incremental sheet forming (ISF), one of the new
production procedures, is developed to form sheet metal
without using die. This method has advantages of pro-
cess flexibility, product independent tooling and higher
formability. So, it aims to decrease both the prototyping
time and the set-up costs of forming, especially for a
small number of pieces. However, traditional sheet metal
forming methods are too much dependent on the number
of parts because of the time and cost. Especially in
productions having a large number of products, these
methods are preferred since the cost will be reduced for
each part.1–4 The production with ISF, which is also
defined as die-less forming for limited parts suitable for
the usage area is preferred.5 In sheet metal production,
factors such as the time, die and prototype costs become
disadvantages for limited production.
It is essential in forming to keep the necessary
strength minimum depending on the size, geometry and
time of production and to form without any damage.
Particularly in the part production special for the person
and the place, quick and suitable solutions are found by
using three-dimensional laser scanning.6
ISF can be applied to the specially designed ma-
chines and many computer numerical control (CNC)
milling stands providing the opportunity of manufactur-
ing. In addition, this method is categorized as single-
point incremental sheet forming (SPIF) and two-point
incremental sheet forming (TPIF). SPIF is the simplest
way as a system.4,7 They are named positive forming and
negative forming, respectively. Whereas in the two-point
incremental sheet forming, the tool starts to form from
Materiali in tehnologije / Materials and technology 51 (2017) 1, 111–116 111
MATERIALI IN TEHNOLOGIJE/MATERIALS AND TECHNOLOGY (1967-2017) – 50 LET/50 YEARS
UDK 620.1:67.017:621.375.826 ISSN 1580-2949
Original scientific article/Izvirni znanstveni ~lanek MTAEC9, 51(1)111(2017)
the center, it forms through the center in the single-point
incremental sheet forming.8
The performance of the forming process is related to
the geometry of tools. Hemisphere and ball forms are
preferred in tools and their sizes are determined
according to the given geometry. The head diameters of
tools starts from 6 mm and can be up to 100 mm for
large parts. The selection of the tool diameter is deter-
mined by looking at the lowest concave of the desired
geometry. Besides, coating can be applied to tools in
order to reduce the friction and prolong the life of the
tool.8,9
There is no standard part geometry to identify the
maximum angle of the wall during forming. The forming
limit and maximum inclination angle of the wall have
been searched with frustum of cone studies without
cracks.5,9 Feed rate, spindle speed, step size, tool diame-
ter, lubrication, tool path and angle of wall are important
parameters affecting ISF.10,11 The maximum angle of the
wall has been investigated with two diameter, step-size
and sheet-thickness parameters. This value is determined
with the experimental solutions applied for different
geometries.12,13
Many studies have been conducted related to the
forming and mechanisc of various materials with the ISF
method.14–17 The relation of the roughness on the surface
of the material in ISF with the tool radius, step size and
inclination angle of its parts has been searched numeri-
cally and experimentally.18,19
The most common four parameters affecting the
strength necessary for forming as desired without any
damage during forming are the tool diameter, step size,
right of the angle of part wall or wall and sheet metal
thickness. Tool diameter has been examined in detail,
because it is the contact area that stress is intensified
generally.15,20–23
Suitable selection of the tool and the lubrication in
ISF is essential for the successful forming and a homo-
geneous surface quality. The effect of the tool and lubri-
cation in steel, aluminum and titanium sheets on the
quality of the surface treating was investigated with SEM
and the measuring device for surface roughness.24,25
The comparison of theoretical calculations and the
suitability after forming depends on doing the measure-
ments after the processing accurately. For this purpose,
the three-dimensional laser scanning technique has been
utilized in measurements. This method is one of the
contactless test methods and it has a wide area of usage
because it provides economic and reliable measurements.
The stages of the measuring process are computerized as
three-dimensional point clouds (in STL format) by
scanning the samples with laser scanning. The point
clouds are saved and combined, pierced, the spaces are
filled, filtrated and three dimensional solid models of the
samples are obtained. At the end, all the necessary
measurements can be made over the solid model in a
computer environment and become comparable to the
geometries.3,25,26
In this study, the applicability of ISF to AA2024-T3
sheets, process performance and economic advantages
have been investigated. The other aim of this study is
prioritizing the process parameters in ISF. The samples
were formed by changing the tool path, step size and
lubrication parameters and the geometrical accuracy and
thickness alterations and have been measured by the
three-dimensional laser scanning method. The compa-
rison of ISF with the die production method was made
for this model and the optimum test parameters were
determined.
2 MATERIALS AND METHODS
2.1 Materials
In the study, AA2024-T3 commercial products in 200
mm × 200 mm × 1 mm sizes were used. The chemical
composition and mechanical properties of the material
are given in Tables 1 and 2.27
Table 1: Chemical composition of AA2024 sample (w/%)
Tabela 1: Kemijska sestava vzorca AA2024 (w/%)
Element Cu Mg Mn Fe Ti Zn Si Al
Standard 3.80-4.90
1.20-
1.80
0.30-
0.90
Max
0.50
Max
0.15
Max
0.25
Max
0.50
90.70-
94.70
Measured 4.59 1.49 0.54 0.10 0.02 0.02 0.07 93.14
Table 2: Mechanical properties of AA2024-T3 sample27
Tabela 2: Mehanske lastnosti vzorca AA2024-T327
Tensile strength (MPa) Strain failure (%)
Standard Experimental Standard Experimental
455 480 22.80 18.75
The experimental data in Tables 1 and 2 are values in
accordance with the standards.
2.2 Method
Incremental sheet processes applied to the samples
were made with the single-point incremental sheet
forming method in a First MCW300 CNC milling stand.
The processes were made after the measurement
precision of the retainer die specially manufactured for
this method was provided and the retainer die was tied to
the stand. AA2024-T3 samples which were laser cut in a
way to be tied to the die (200×200×1) mm were
anchored with the help of 8 M10 bolts during forming to
prevent the sliding.
An uncoated carbide tool with a 10 mm diameter was
chosen for the tool, which is one of the important
parameters in forming. The feed rate was kept constant
at 1000 mm/min and the spindle speed at 500 min–1 in all
the tests. The tool path, step size and lubrication para-
meters were changed in the processes. All the performed
parameters in this study are given in Table 3.
H. BAYRAM, N. S. KÖKSAL: INVESTIGATION OF THE GEOMETRICAL ACCURACY AND THICKNESS ...
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Table 3: All performed parameters
Tabela 3: Vsi uporabljeni parametri
Number of
experiment
Number of
tool path Step size Lubrication
1
1
0,2
A Lubricate
2 B Lubricate
3
0,5
A Lubricate
4 B Lubricate
5
2
0,2
A Lubricate
6 B Lubricate
7
0,5
A Lubricate
8 B Lubricate
Two different tool paths were designed using the NX
Unigraphics CAM program. The first tool path does the
step size as spirals and in this process the tool always
keeps in contact with the sheet metal. The second one is
the tool path always gives the step size from the same
point after completing the whole circuit in a horizontal
line. The perspective, side and top views of the 1st and
2nd tool paths are given in Figures 1 and 2 and again
doing the same process incrementally. If during this
process the tool does not contact with the sheet metal
continuously. The 0.2 mm, 0.3 mm, 0.5 and 0.7 mm
values were tested for step sizes and the 0.2 mm and 0.5
mm step sizes were chosen.
Two different lube lubricates of which technical pro-
perties are given Table 4 were chosen for the lubrication
in the application. The first one has been chosen as B
lubricate emulsion, which is the machining coolant and
the other one as the A lubricant.
Table 4: Technical properties of the used lubricants
Tabela 4: Lastnosti uporabljenih maziv
A Lubricate B Lubricate
Kinematic viscosity
(40 °C, mm2/s) 115-135 25-35
3 RESULTS
Solid models of the samples formed by the para-
meters determined with the incremental sheet forming
were obtained by the method of three-dimensional laser
scanning. Geometrical accuracies and thickness distri-
butions of the solid models and the geometries that are
H. BAYRAM, N. S. KÖKSAL: INVESTIGATION OF THE GEOMETRICAL ACCURACY AND THICKNESS ...
Materiali in tehnologije / Materials and technology 51 (2017) 1, 111–116 113
MATERIALI IN TEHNOLOGIJE/MATERIALS AND TECHNOLOGY (1967-2017) – 50 LET/50 YEARS
Figure 2: a) Perspective, b) side, c) top view of the tool path numbered 2
Slika 2: a) Perspektiva, b) stranski pogled, c) pogled z vrha na pot orodja {tevilka 2
Figure 1: a) Perspective, b) side, c) top view of the tool path numbered 1
Slika 1: a) Perspektiva, b) stranski pogled, c) pogled iz vrha na pot orodja {tevilka 1
Figure 4: B lubricant, the views of the sample having 0.2 mm step
size and 2nd tool path parameters
Slika 4: Mazivo B, izgled vzorca s korakom 0,2 mm in poti orodja
{tevilka 2
Figure 3: A lubricant, the views of the sample having 0.5 mm step
size and 1st tool path parameters
Slika 3: Mazivo A, izgled vzorca s korakom 0,5 mm in poti orodja
{tevilka 1
aimed to give to the samples were compared. Half of the
part geometries were taken for the examination because
they are symmetrical in this process. The views of the
samples obtained after the forming process are given in
Figures 3 and 4.
The thickness distribution of the samples after form-
ing have been measured by sectioning the solid models
obtained using thr CAD programs.
The values and measurement points of the samples
having 0.5 mm step size and the 1st tool path parameter
H. BAYRAM, N. S. KÖKSAL: INVESTIGATION OF THE GEOMETRICAL ACCURACY AND THICKNESS ...
114 Materiali in tehnologije / Materials and technology 51 (2017) 1, 111–116
MATERIALI IN TEHNOLOGIJE/MATERIALS AND TECHNOLOGY (1967-2017) – 50 LET/50 YEARS
Figure 6: B lubricant the results of geometric accuracy of the sample (a, b) having 0.2 mm step size and 2nd tool path parameters
Slika 6: Mazivo B, rezultati geometrijske natan~nosti vzorca (a, b), pri koraku 0,2 mm in poti orodja {tevilka 2
Figure 5: A lubricant, the results of geometric accuracy of the sample (a, b) having 0.5 mm step size and 1st tool path parameters
Slika 5: Mazivo A, rezultati geometrijske natan~nosti vzorca (a, b), pri koraku 0,5 mm in poti orodja {tevilka 1
Table 5: Measured thickness values of the inclined area (mm)
Tabela 5: Izmerjene vrednosti debeline na nagnjenem podro~ju (mm)
Number
of
measure-
ment
0.5 mm
step size/
1. tool
path
0.2 mm
step size/
2. tool
path
Number
of
measure-
ment
0.5 mm
step size/
1. tool
path
0.2 mm
step size/
2. tool
path
1 0.8912 1.0358 21 0.8004 0.9425
2 0.9458 1.1493 22 0.7955 0.9370
3 1.0151 1.2310 23 0.8082 0.9484
4 1.0309 1.2242 24 0.8091 0.9585
5 0.9328 1.1046 25 0.8072 0.9198
6 0.8853 1.0143 26 0.8081 0.9474
7 0.8373 0.9885 27 0.8129 0.9402
8 0.8102 0.9704 28 0.8141 0.9351
9 0.8012 0.9787 29 0.8233 0.9368
10 0.7961 0.9806 30 0.8238 0.9352
11 0.7837 0.9598 31 0.8209 0.9742
12 0.7850 0.9579 32 0.8033 0.9304
13 0.7860 0.9624 33 0.8192 0.9290
14 0.7910 0.9540 34 0.8215 0.9181
15 0.7902 0.9489 35 0.8189 0.9032
16 0.7894 0.9577 36 0.8160 0.8998
17 0.7956 0.9558 37 0.8076 0.9064
18 0.7914 0.9362 38 0.7916 0.8967
19 0.8070 0.9413 39 0.7371 0.8656
20 0.7998 0.9417 40 0.8280 0.9723
Figure 7: Graph shows measured thickness values of the inclined area
(mm)
Slika 7: Grafi~en prikaz izmerjene debeline na nagnjenem podro~ju
(mm)
and 0.2 mm step size and the 2nd tool path parameter
among the samples formed are given in Figures 5 and 6.
Comparative results of the measurements can be seen in
Figure 7.
4 CONCLUSION
AA2024 materials formed in an acceptable way
without being damaged by using incremental sheet
forming. The effective parameters in this process are the
lubricating fluid, the step size and the tool path. The type
of tool, the feed rate and the number of revolution para-
meters were kept stable.
The A and B lubricants were used for the lubricating
fluid, which is an effective parameter in forming. It was
observed in the examination after processing that these
two lubricating fluids were successful at the same rate.
Two different tool paths were used in the processes.
It is clear that the tool path that is always in contact with
the spirals is more successful than the tool path doing the
progressive process. When the tool path which follows a
spiral path and of which vertical steps enter from diffe-
rent points has been tried, different results could not be
obtained. The first tool path has given better results in
terms of geometrical accuracy and a homogeneous
thickness distribution in the forming products. It was ob-
served that the parameter having 0.5 mm step size
displayed more geometrical accuracy and a more homo-
geneous distribution than the one with the 0.2 mm step
size.
It was identified that the thickness alteration in the
product showed a change suitable to the theoretical cal-
culations by measuring accurately after ISF forming. In
the results of the accurate measurement method 3D laser
scanning, the alteration in the measured values in the
middle of the product has been obtained at an acceptable
level. The desired form with this method is the middle
part of the sample and its sides need to be removed after
the process. Therefore, it is not important that the alter-
ation in the side values after forming is too much.
The economy of the method has been investigated in
terms of die cost and labor cost, etc. Accordingly, the
incremental sheet forming method is cheaper than the die
production for the series of less than 500. However, if the
number exceeds this value, the method loses its eco-
nomic advantage. This method stands out in the private
and less numbered productions.
The process has been carried out by applying very
small strength compared to deep drawing and free from
the size of the product in sheet forming. Correspond-
ingly, it has been seen to stay in the safe area in the
forming limit diagram (FLD) during forming.
Acknowledgement
This work has been carried out with the financial
support from Celal Bayar University Scientific Research
Projects Commission (2014-078).
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