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Investigation on punched edge formability
Matthias Schneider, Uwe Eggers
Salzgitter Mannesmann Forschung GmbH
Eisenhüttenstrasse 99, 38239 Germany
[email protected], [email protected]
Abstract: There are several test procedures to rate the sensitivity of the formability of
steels with punched edges but only one is fixed as a standard. The influence on the
results of an ISO 16630 hole expansion are listed and some of the main influences
evaluated with the help of an optical measurement system. Due to the high influence of
a technician’s perception on the ISO 16630 test result some optimised procedures are
presented and compared. The potential of the offline analysis of such an expansion test
is demonstrated.
Keywords: formability, high strength steel, material testing, hole expansion
1. PROBLEM DISCRIPTION
The increasing demands for lightweight design in the automobile and truck sector have
significantly pushed the innovations of new steel grades. In addition to the body in
white, the chassis is today and will be in the future a wide application area for modern
steel grades. Thus the steel producers have accepted the challenge to combine
formability and strength. The thermomechanically rolled steels, dual phase or bainitic
steels are promising regarding this demand. To use their good forming and performance
characteristics the steel has to be described in detail with the relevant mechanical
properties. For the estimation of the material failure under forming conditions the
forming limit curve (FLC) [ISO 12004-2] is very common. In some cases the FLC has
its deficits but there is an optimisation approach [Merklein et al., 2010].
In the production of chassis parts there are often operations which can not be estimated
by the FLC. Zones of a part that get punched and afterwards formed into a collar or a
Blankholder
Specimen
Punch
Die
a b
Blankholder
Specimen
Punch
Die
Blankholder
Specimen
Punch
Die
Blankholder
Specimen
Punch
Die
a b
Figure 1; a) Schematic description of the ISO 16630 tool
b) example for a specimen during forming
flange. These punched edges in high strength steels are less formable than the untreated
material. Therefore there is a need for an additional test to determine a characteristic
value parallel to the FLC to estimate the edge behaviour. At the moment the ISO 16630
[ISO 16630] is the only test procedure that is fixed by a norm. Here the punched hole of
the specimen gets expanded by a conical punch as schematically shown in Figure 1.
After a crack has appeared, the hole expansion ratio λ [%] is calculated.
1000
0⋅
−=
D
DDhλ
λ Hole expansion ratio [%]
D0 Start diameter [mm]
Dh End diameter [mm]
(1.1)
Besides the ISO 16630 test, various other tests or test ideas exist. The KWI test was
invented at the “Kaiser Wilhelm Institute” which were reorganised and named “Max-
Planck-Institute” later on. Here a drilled hole is expanded by a flat bottom punch. In
2010, the Salzgitter Mannesmann Forschung (SZMF) introduced its own hole expansion
test version in the frame of the joint project “Sheared Edge Formability” funded by
Stiftung Stahlanwendungsforschung and coordinated by Forschungsvereinigung
Stahlanwendung e.V. In this project, together with the Institute of Institute of Metal
Forming and Metal-Forming Machines (IFUM), Leibniz Universität Hannover, the
SZMF investigates damage and formability of the sheared edge of cold rolled dual-
phase steels. The proposed test combines the hemispheric Nakajima punch from the
FLC test together with a specimen with a punched hole. BMW uses the same tool
geometry with a punched Nakajima specimen in their “BMW Kantenrisstest” [Illig,
2006][ISO 12004-2].
6. Specimen
6.1 Quality of punched edge surface
6.2 Hole position to stamp position
Hole expansion
ISO 16 630Process step 1: PunchingProcess step 2: Expanding
1. Operator 2. Machine
7. Evaluation
3. Tool
2.1 Deviation of the deformation rate
3.4 Wearing of the punching tool
3.2 Geometry of forming die
3.1 Surface conditions (friction) of the forming tool
7.1 Influence of measuring point due
to non-round hole
7.2 Tilt of the
measuring equipment
1.2 Response time
1.1 Different perception of crack-start (switch-off-
criterion)
4. Material
4.1 Homogeneity of
properties
4.2 Sheet thickness
4.3 Mechanical properties(Rp0,2, Rm, A80)
2.2 Direct/ indirect view on the specimen (delay
of image transfer)
2.3 Overrun after stopping the machine
7.3 Technician operation with tactile measuring equipment
5. Procedure
5.1 Punching speed
5.2 Punching conditions (fixing, guidance)
...
... ... ...
... ...
...6. Specimen
6.1 Quality of punched edge surface
6.2 Hole position to stamp position
Hole expansion
ISO 16 630Process step 1: PunchingProcess step 2: Expanding
1. Operator 2. Machine
7. Evaluation
3. Tool
2.1 Deviation of the deformation rate
3.4 Wearing of the punching tool
3.2 Geometry of forming die
3.1 Surface conditions (friction) of the forming tool
7.1 Influence of measuring point due
to non-round hole
7.2 Tilt of the
measuring equipment
1.2 Response time
1.1 Different perception of crack-start (switch-off-
criterion)
4. Material
4.1 Homogeneity of
properties
4.2 Sheet thickness
4.3 Mechanical properties(Rp0,2, Rm, A80)
2.2 Direct/ indirect view on the specimen (delay
of image transfer)
2.3 Overrun after stopping the machine
7.3 Technician operation with tactile measuring equipment
5. Procedure
5.1 Punching speed
5.2 Punching conditions (fixing, guidance)
...
... ... ...
... ...
...
Figure 2; Influences on the results of ISO 16630
A higher deformation of the edge in comparison to the middle zone can be easily
archived by an optimised punch geometry. [Held et al., 2009] showed the results of a
punch formed like a diabolo toy.
There are many other ideas of loading a blanked edge till the first crack appears [Nitta et
al., 2008][Bouaziz et al., 2010]. Additionally first ideas of using the gathered
information for an estimation of produceability can be found [McEwan et al., 2009].
Thus the ISO 16630 is the only standardised test which valuates the formability of
punched edges and therefore it is surveyed in detail. The influences on the result of an
ISO 16630 test are listed in Figure 2.
2. INFLUENCES ON ISO 16630
Probably the biggest influences as shown in Figure 2 are the punching tool and the
punching process. These influences were analysed but will be not published in this
paper. Here the focus lies on the influences which could be evaluated with the help of
the optical measuring system Aramis [Friebe et al., 2006].
For all following research activities the same batch of hot rolled material with a
thickness of 3.5mm was used. All the specimens were painted before the test for post
analysing with the Aramis system. The punch movement during the test was stopped as
per a normal ISO 16630 test and the λ was recorded.
2.1 Visual perception of the crack There were investigations to use the punch force of an ISO 16630 test as an indicator
for a crack [Dünckelmeyer et al., 2009]. But this method seems to work only on some
steel grades. It is more common, that a technician stops the movement of the punch at
the moment the first crack runs through the complete thickness of the specimen. During
the test the illumination of the specimen and the distance of the technician’s visual line
of sight might not be perfect. Eliminating these secondary effects pictures of the
specimen were taken during the forming by the Aramis system. One of these pictures is
shown in Figure 1b. The pictures were taken with a frequency of 10Hz. ISO 16630
limits the punch velocity to a maximum of 1mm/s which means that the punch moves
maximally 0.1mm from one picture to another. Based on the results of 10 parallel tests
the visual perceptions of 5 different technicians were recorded. This investigation was
split into three cycles as shown in Figure 3.
Cycle Data Emulation
a Real time film sequence Direct view or online video screen
b Chronologic picture to picture Quasistatic testing
c Picture to picture with optional
stepping backwards
Picture grabbing and post analysis
Figure 3; Test order
The picture numbers taken by the technicians were computed into hole diameters by an
appropriate approximation and afterwards into a hole expansion ratio. The data for the
functions are based on photogrammetric pixel measurements, which allow to detect 3D
points in the Aramis software without any facet-information on the specimens surface
and additionally very close to the edge. The results of the three cycles are shown in
Figure 4. Some scratches in the paint caused some error values but a good portion of the
results show similar detections of cracks. An effect of training or somehow
familiarisation can be seen. With a lower punch velocity (emulated in cycle 2) the crack
had been detected earlier. The last cycle increased this effect. It can be summarised that
the punch velocity or the analysing velocity has an influence on the λ-value but it has no
influence on the deviation of the visual perception of different technicians. Figure 5
shows the scattering inside one cycle and inside one specimen as bar chart of the
standard deviation. It can be pointed out that none of the cycles show significantly
better results.
A scattering value of 10 specimens was generated to visualise the effect of the
technicians influence. The lowest and the highest λ-value of each specimen was
excluded and the mean value was calculated. The scattering of these values can be
understood to be the scattering of the material. The standard deviation of this material
scattering is represented in Figure 5 (horizontal lines). The scattering is large compared
with the characteristic value which ought to be detected.
Result of one technicianSpread of result for one specimen
Mean of the three middle results
0%
10%
20%
30%
40%
50%
60%
70%
80%
90%
a b c a b c a b c a b c a b c a b c a b c a b c a b c a b c
1 2 3 4 5 6 7 8 9 10
Number of specimen (1-10) and cycle (a-c)
Ho
le e
xp
an
sio
n r
atio
[%
]H
ole
expansio
nra
tio
[%] 90
80
70
60
50
40
30
20
10
0
Result of one technicianSpread of result for one specimen
Mean of the three middle results
Result of one technicianSpread of result for one specimen
Mean of the three middle results
0%
10%
20%
30%
40%
50%
60%
70%
80%
90%
a b c a b c a b c a b c a b c a b c a b c a b c a b c a b c
1 2 3 4 5 6 7 8 9 10
Number of specimen (1-10) and cycle (a-c)
Ho
le e
xp
an
sio
n r
atio
[%
]H
ole
expansio
nra
tio
[%] 90
80
70
60
50
40
30
20
10
0
Figure 4; Results of three cycles of picture analysis
0
5
10
15
20
25
30
a b c a b c a b c a b c a b c a b c a b c a b c a b c a b c
1 2 3 4 5 6 7 8 9 10
Number of specimen (1-10) and cycle (a-c)
Sta
ndard
devia
tion
of hole
expansio
nra
tio
[%]
Standard deviation of results of 5 technicians
Standard deviation of mean results of the 10 specimen
0
5
10
15
20
25
30
a b c a b c a b c a b c a b c a b c a b c a b c a b c a b c
1 2 3 4 5 6 7 8 9 10
Number of specimen (1-10) and cycle (a-c)
Sta
ndard
devia
tion
of hole
expansio
nra
tio
[%]
Standard deviation of results of 5 technicians
Standard deviation of mean results of the 10 specimen
Figure 5; Scattering among the cycles of the 10 specimens
2.2 Reaction time
Subsection 2.1 identifies the influence of the reaction time at the perception of the crack
as the difference of cycle a (real time) and cycle b (quasistatic). The influence of the
reaction time depends on the hole expansion velocity λ°. Formula 2.1 gives a first
estimation of λ°. The real specimen deforms first to the typical caldera form which
causes a lower λ° at the beginning of the expansion. After that the velocity increases
which was exemplarily measured for one specimen and plotted in Figure 6 as black
dots. The orange dots represent the results of the 10 specimen from subsection 2.1.
0
2
4
6
8
10
12
14
0 20 40 60 80 100
Hole expansion ratio [%]Hole
expansio
nvelo
city
[%/s
]
1 Specimen during forming
10 Specimen at crack timesmm
s
mm
D
D
s
mms
mmv
Dp
%5.11
10
15.1
15.160tan
1
tan
0
==°
=°
=°==°
λ
α
vp Punch
velocity
[mm/s]
α Punch
angle
[°]
D° Hole
diameter
change
[mm/s]
(2.1)a b
0
2
4
6
8
10
12
14
0 20 40 60 80 100
Hole expansion ratio [%]Hole
expansio
nvelo
city
[%/s
]
1 Specimen during forming
10 Specimen at crack timesmm
s
mm
D
D
s
mms
mmv
Dp
%5.11
10
15.1
15.160tan
1
tan
0
==°
=°
=°==°
λ
α
smm
s
mm
D
D
s
mms
mmv
Dp
%5.11
10
15.1
15.160tan
1
tan
0
==°
=°
=°==°
λ
α
vp Punch
velocity
[mm/s]
α Punch
angle
[°]
D° Hole
diameter
change
[mm/s]
(2.1)a b
Figure 6; Hole expansion velocity:
a) approximation b) test results
These velocities were determined close to the time the crack appears which caused
some lager scattering.
It was described in subsection 2.1 that a lower expansion velocity reduces the influence
of the reaction time and causes a lower mean value of λ. A time or punch travel
dependent expansion velocity might overlie the values of the ISO 16630 results.
A material which is very sensible on punched edge cracking shows cracks at early
stages of the test. Therefore these cracks appear at a lower expansion velocity, which
causes a lower influence of the reaction time and thereby an even lower expansion ratio.
2.3 Effect of online or offline measurement Subsections 2.1 and 2.2 gave an impression of the negative influence of the perception
of the crack on the ISO 16630 results. One improvement might be the decoupling of
forming (or destroying) the specimen and the perception of the crack. This would allow
a quasistatic picture analysis or an automated analysis with an optical measurement
system. If this offline analysis would be realised, the specimen would be measured in a
loaded condition. The λ-value of a loaded specimen should be higher than of the
unloaded specimen due to spring back effects.
Offline Aramis crack detection (loaded)
Gap between offline and online detection of crack (loaded)
Influence of load state (loaded-unloaded)
Tactile measurement of unloaded specimen (unloaded)
18
18
15
11
16
2613
1712
1,7
2,4
1,1
1,4
1,9
2,1 1,5
1,7 2,3
0
10
20
30
40
50
60
70
80
1 2 3 4 5 6 7 8 9
Numer of specimen
Ho
le e
xpansio
nra
tio
[%]
Offline Aramis crack detection (loaded)
Gap between offline and online detection of crack (loaded)
Influence of load state (loaded-unloaded)
Tactile measurement of unloaded specimen (unloaded)
18
18
15
11
16
2613
1712
1,7
2,4
1,1
1,4
1,9
2,1 1,5
1,7 2,3
0
10
20
30
40
50
60
70
80
1 2 3 4 5 6 7 8 9
Numer of specimen
Ho
le e
xpansio
nra
tio
[%]
Figure 7; Influence of load state compared with crack perception
To rate the influence of elastic elongation 9 specimens were treated as fixed in the ISO
standard. The tests were captured by Aramis and analysed afterwards. Based on the
pictures, the technician recognised the crack systematically earlier than his colleague at
the forming press. The gaps between both expansion ratios were up to 26% as shown in
Figure 7. With the help of the optical measuring system the state of maximal punch
travel and the state of unloading were detected. The change in the expansion ratio was
always lower than 2.4%.
Therefore the influence of the load state can be treated as insignificant which
legitimates an offline analysis of the test.
3. ALTERNATIVES TO THE ISO 16630 PROCEDURE
3.1 Motivation and target As discussed in subsection 2 the ISO 16630 procedure carries some fields for
improvement. Besides the targets listed in Figure 8, an optimisation should aim on the
reduction of the scattering among different technicians. This might be reached with an
abrupt crack initiation and a quick crack growth.
3.2 Adapted KWI test
One alternative procedure to ISO 16630 is the KWI, where the hole should not be
drilled as provided but be punched with a defined blanking clearance. For this operation
the blanking tool for the ISO 16630 specimen can be used. The forming with the flat
bottom KWI punch allows a full analysis with an optical measuring system. A
disadvantage of the flat punch is the insensibility of the burr side. If the testing
procedure should bring up sensitivity on the position of the burr there has to be some
strain gradient through the sheet thickness accordingly at the blanked edge.
Domain Target
Testing facility 1.1 Common testing equipment
Tool for punching 2.1 Standard parts/ tools
Procedure
3.1 Easy to understand
3.2 Robust
3.3 Low time consuming
3.4 Low dependency on technician perception
3.5 Useable for a large variety of steels
3.6 Sheet thickness independent
Analysis 4.1 Low dependency on technician perception
4.2 Possibility for automation (quality check)
Result
5.1 Hole expansion ratio (quality check)
5.2 Comparability between testing institutes
5.2 Main crack direction (anisotropy) (research aspects)
5.3 Strain deviation (anisotropy) (research aspects)
5.4. Time dependent information (research aspects)
Figure 8; Targets for test optimisation
3.3 Nakajima test with punched hole
Another common tool set is the hemispheric Nakajima punch and adequate die, which is
used for the evaluation of the FLC. A quadratic sheet with a blanked hole in the middle
as the specimen can be formed until the crack appears. The punch geometry causes a
burr side sensitivity but it is also able to cause an inappropriate angle between the
specimen and the camera. If the angle is close to 45° Aramis looses the facets. The
maximal angle a specimen can obtain is constrained by the tested material and the start
diameter. Within the framework of the FOSTA project 830 the dual phase steel grade
HCT780XD was tested at SZMF like proposed above and a start diameter of 20mm was
rated a useful. If the diameter was too large it caused the loss of facets and the opposite
caused holes with a small circumference and therefore less facets. At present there is a
lack of experience to judge the ideal diameter for the test. Nevertheless for the blanking
operation a standard blanking tool set can be used.
3.4 Comparison of three hole expansion tests The results of an ISO 16630 test are already shown in section 2. This is now compared
with the results of a KWI test (with punched hole) and a hole expansion with a
Nakajima punch (all blanked with 12% clearance). The ISO 16630 and the KWI hole
diameter is fixed to 10mm. For the Nakajima test a hole with a diameter of 20mm was
blanked out (in accordance to the FOSTA project 830).
Figure 9 shows the comparison of the determined hole expansion ratios. The mean
value is similar although the gauge length differs (2 different hole diameters). It is
peculiar that the standard deviation of the ISO 16630 results is much higher than the
deviation other two tests. This fact can be consolidated for the tested hot rolled material
concerning the KWI and the ISO 16630 with the internal data base of SZMF. The lower
deviation might be a result of the loading conditions or of a clearer crack start or quicker
growth. Both was seen during the forming of the specimen of Figure 9.
0
10
20
30
40
50
60
70
80
1 2 3 4 5 1 2 3 4 5 1 2 3 4 5
KWI Nakajima ISO 16630
Hole
expansio
nra
tio
[%]
Result of 1 specimen
[%]
Standard devation of
expansion ratio [%]
Maximimal expansion
ratio [%]
Minimimal expansion
ratio [%]
Mean expansion ratio
[%]
0
10
20
30
40
50
60
70
80
1 2 3 4 5 1 2 3 4 5 1 2 3 4 5
KWI Nakajima ISO 16630
Hole
expansio
nra
tio
[%]
Result of 1 specimen
[%]
Standard devation of
expansion ratio [%]
Maximimal expansion
ratio [%]
Minimimal expansion
ratio [%]
Mean expansion ratio
[%]
Figure 9; Comparison of different hole expansion tests
After the test the pictures were analysed with Aramis and the punch velocities were
measured. With this information all following expansion velocities were normalised to a
punch velocity of 1mm/s (scattering in the range of 0.9 and 1.2mm/s). To achieve
comparable results all specimens were measured based on the pixel point method even
if the KWI and Nakajima specimens were sprayed with the typical white surface with
black dots. The mean velocity of 3 time sections (5 parallel specimens for each of the 3
test versions) are shown in Figure 10. The ISO 16630 test shows a similar curve
progression and mean value at crack time already determined and presented in Figure 6.
The KWI has the same expansion speed until the crack appears. After that moment the
crack growth is the fastest of the three tests. This crack behaviour enables a punch force
controlled stop criteria for the test, which was positively tested at SZMF. The test
variant with the Nakajima punch shows the same acceleration in the moment of the
crack. Additional to this advantage it also shows a lower expansion speed in the time
section the crack starts. This behaviour allows a detailed analysis of the crack. Although
this low expansion velocity causes a high number of pictures at the state of crack start
the visual perception is very abrupt compared with the ISO 16630. The KWI shows an
even faster crack initiation. A high crack growth is a chance for an explicit perception
and an easier criterion for automated crack detection.
The sensitivity of the burr side, the good expansion velocity behaviour and the use of
standard parts makes the Nakajima test with a blanked hole to be a promising hole
expansion test. Additionally it can be analysed as simply as the ISO 16630 test with a
sliding calliper or for research projects with an optical measurement system.
0
2
4
6
8
10
12
14
16
18
20
From start up to
2s before crack
From 1s before
crack up to the
crack
From crack until
1s afterwards
Hole
exp
ansio
nvelo
city
[%]
KWI
ISO 16630
Nakajima with hole
Lines define the mean values
0
2
4
6
8
10
12
14
16
18
20
0
2
4
6
8
10
12
14
16
18
20
From start up to
2s before crack
From 1s before
crack up to the
crack
From crack until
1s afterwards
Hole
exp
ansio
nvelo
city
[%]
KWI
ISO 16630
Nakajima with hole
Lines define the mean values
KWI
ISO 16630
Nakajima with hole
Lines define the mean values
Figure 10; Expansion velocity of different hole expansion tests
3.5 Potential of strain measurement at hole expansion
If an hole expansion test is captured by a optical measurement system there are many
possibilities for an offline analysis of the test [Mackensen et al., 2009]. Figure 11a
shows an example. The contour plot gives an impression on the strain on the surface of
the specimen. But it is not usable for a detailed characterisation of one or a comparison
of different materials. For detailed investigations diagrams with some time and place
dependent information about the major strain would be very useful. Figure 11b shows a
diagram which fulfils these requirements. Every curve is the result of a circular section
around the blanked hole. At the beginning of the test all major strains on the circular
section are zero. This state is visualised as a dot (or a circle with radius of 0) in the
middle of the diagram. During the forming the strains increase and form circles or
crosses (regulated by the anisotropy). The time between each circle is one second. If the
radius changes abruptly this is an indication of a crack. For a nearly planar isotropic
material the crack can be indentified very easily. An anisotropic material as shown in
Figure 11b requires a more complex criteria.
Due to the method of operation of Aramis the strain can not be measured direct on the
edge. If the distance to the edge is too small, there is no place for a facet and therefore
no strain information. Here a distance of about 1mm was used to achieve a closed circle
of results.
80
60
40
20
0
20
40
60
80
80 60 40 20 0 20 40 60 80
a b
80
60
40
20
0
20
40
60
80
80 60 40 20 0 20 40 60 80
80
60
40
20
0
20
40
60
80
80 60 40 20 0 20 40 60 80
a b
Figure 11; a) Contour plot of major strain
b) Polar diagram of major strain of Nakajima expansion
4. SUMMARY AND CONCLUSION
The ISO 16630 hole expansion test is the only test focused on the formability of a
punched edge that is fixed by a standard. Unfortunately this test is not completely
satisfactory. The influence of the perception of the crack is a main handicap. To avoid
this influence an offline analysis of the test might be helpful. To gather more
information out of one test a geometry or strain measurement can be useful. An analysis
method is proposed.
In the future, the influences on the new test will be determined following the same
strategy as already done for the ISO 16630 test.
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Bending Test: A Promising New Way for an Optimal Characterization of Cut-
Edges Ductility”; IDDRG2010; Graz; Austria 2010
[Col et al. 2008] Col, A.; Jousserand, P.; „Mechanisms Involved in the Hole Expansion
Test“; IDDRG2008; Olofström; Sweden 2008
[Dünckelmeyer et al., 2009] Dünckelmeyer, M.; Karelova, A.; Krempasky, C.;
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[Friebe et al., 2006] Friebe, H.; Galanulis, K.; Erne, O.; Müller, E.; „FLC
Determination and Forming Analysis by Optical Measurement Systems“;
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[ISO 12004-2] International Standard ISO 12004-2 „Metallic materials – guidelines for
the determination of forming-limit diagrams“
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Technical Specification ISO 16630; Switzerland 2003
[McEwan et al., 2009] McEwan, C.; Underhill, R.; Langerak, N.; Botman G.; de
Bruine, M.; „A New approach to predicting edge splits- the combined FLC/HEC
Diagram“; IDDRG2009; Holden; USA 2009
[Merklein et al., 2010] Merklein, M.; Kuppert, A.; Mütze, S.; Geffert, A.; „New Time
Dependent Method for Determination of Forming Limit Curves Applied to
SZBS800“; IDDRG2010; Graz; Austria 2010
[Nitta et al., 2008] Nitta, J.; Yoshida, T.; Hashimoto, K.; Kuriyama,Y.: „Development
of the Practical Evaluation Test and a Study of Numerical Evaluations of Edge
Fracture for Stretch Flangeability of Sheet Metal Forming“; IDDRG2008;
Olofström; Sweden 2008
[Mackensen et al., 2009] Mackensen, A.; Golle, M.; Golle, R.; Hoffmann, H.;
„Determination of the Hole Expansion Properties of AHSS Using an Optical 3D
Deformation System“; IDDRG2009; Holden; USA 2009
ACKNOWLEDGEMENT
The financial support of the Stiftung Stahlanwendungsforschung in the frame of the
joint project “Sheared Edge Formability” coordinated by Forschungsvereinigung
Stahlanwendung e.V. and the collaboration with the Institute of Metal Forming and
Metal-Forming Machines (IFUM), Leibniz Universität Hannover, is gratefully
acknowledged.
