U.S. patent application number 10/532360 was filed with the patent office on 2005-12-08 for method and apparatus for reducing wrinkle formation in deep drawing.
Invention is credited to Bolt, Pieter Jan, de Nooij, Margriet, Gunnink, Jan Willem, van Leeuwen, Jacobus Franciscus Cosmas, Werkhoven, Robert Jan.
Application Number | 20050268685 10/532360 |
Document ID | / |
Family ID | 32171726 |
Filed Date | 2005-12-08 |
United States Patent
Application |
20050268685 |
Kind Code |
A1 |
Bolt, Pieter Jan ; et
al. |
December 8, 2005 |
Method and apparatus for reducing wrinkle formation in deep
drawing
Abstract
A method and apparatus for deep drawing a product from a blank
(5), in which, during deep drawing, the blank (5) is held near its
edge by a downholder (8) against a die ring cooperating with the
downholder (8), thereby preventing, at least reducing wrinkle
formation in the blank, by adjusting, at the beginning of deep
drawing, the downholder (8) such that a downholder (8) force
exerted by the downholder (8) on the edge of the blank is
relatively small, and by controlling, during the further course of
the process, the downholder (8) on the basis of a predetermined
thickness trend of the mentioned edge during deep drawing and/or a
trend or critical value derived from this thickness trend.
Inventors: |
Bolt, Pieter Jan;
(Duivendrecht, NL) ; Gunnink, Jan Willem;
(Rijswijk, NL) ; van Leeuwen, Jacobus Franciscus
Cosmas; (Eindhoven, NL) ; de Nooij, Margriet;
(Eindhoven, NL) ; Werkhoven, Robert Jan; (Nuenen,
NL) |
Correspondence
Address: |
LUCAS & MERCANTI, LLP
475 PARK AVENUE SOUTH
15TH FLOOR
NEW YORK
NY
10016
US
|
Family ID: |
32171726 |
Appl. No.: |
10/532360 |
Filed: |
April 20, 2005 |
PCT Filed: |
October 23, 2003 |
PCT NO: |
PCT/NL03/00720 |
Current U.S.
Class: |
72/351 |
Current CPC
Class: |
B21D 22/21 20130101;
B21D 24/14 20130101 |
Class at
Publication: |
072/351 |
International
Class: |
B21D 022/00 |
Foreign Application Data
Date |
Code |
Application Number |
Oct 24, 2002 |
NL |
1021738 |
Claims
1. A method for deep drawing a product from a blank, in which,
during deep drawing, the blank is held near its edge by a
downholder against a die ring cooperating with the downholder,
thereby preventing, at least reducing wrinkle formation in the
blank, by controlling the downholder, characterized in that at the
beginning of deep drawing the downholder (8) is adjusted such that
a downholder force (F.sub.N) exerted by the downholder (8) on the
edge (6) of the blank (5) is relatively small and the further
control of the downholder (3) occurs on the basis of a
predetermined thickness trend of said edge (6) during deep drawing
and/or a trend or critical value derived from this thickness
trend.
2. A method according to claim 1, characterized in that during deep
drawing a parameter relevant to the wrinkle formation is measured
and compared with a critical value at which wrinkle formation
occurs, which critical value is predetermined, based on the
thickness trend of the blank edge (6) and/or a signal derived from
this thickness trend, and in which, when the measured parameter
exceeds or threatens to exceed this critical value, the downholder
(8) is controlled such that a downholder force (F.sub.N) exerted on
the edge (6) by the downholder (8) increases and the measured
parameter falls below the critical value.
3. A method according to claim 2, characterized in that the
parameter relevant to wrinkle formation is the downholder opening
(s.sub.o), defined as the perpendicular distance between the
downholder (8) and the die ring (10), and the critical value is the
predetermined thickness trend or the predetermined maximum
thickness increase of the edge (6).
4. A method according to claim 2, characterized in that the
parameter relevant to wrinkle formation is the speed (v.sub.o) at
which the downholder opening changes, and the critical value is the
predetermined speed trend or the predetermined maximum speed at
which the blank edge increases in thickness during deep
drawing.
5. A method according to any one of claims 2-4, characterized in
that the critical value is measured during a testing session,
previous to deep drawing.
6. A method according to any one of claims 2-4, characterized in
that the critical value is simulated by means of a dynamic model of
the blank (5) and the deep drawing process.
7. A method according to claim 1, in which the position of the
downholder (8) is controlled according to a predetermined range,
such that during deep drawing the downholder opening (s.sub.o),
defined as the perpendicular distance between the downholder (8)
and the die ring (10) substantially corresponds with a
predetermined thickness trend of the edge (6) to be expected during
deep drawing.
8. An apparatus for deep drawing a product from a blank (5),
comprising a downholder (8), a die ring (10) cooperating therewith,
for holding an edge (6) of the blank (5) during deep drawing, a
control (12) provided with means for storing therein a desired
downholder opening trend (s.sub.o), downholder opening speed trend
(v.sub.o) and/or a critical value derived therefrom, and
positioning means (9) for moving the downholder (8), the control
(12) being arranged to control the positioning means (9) such that
the movement of the downholder (8) is in agreement with the stored
downholder opening trend (s.sub.o), downholder opening speed trend
(v.sub.o) and/or a critical value derived therefrom.
9. An apparatus according to claim 8, in which the control (12) is
arranged to control the positioning means (9) such that a distance
between the downholder (8) and the die ring (10) is in agreement
with the stored downholder opening trend (s.sub.o) or a critical
value derived therefrom.
10. An apparatus according to claim 8 or 9, in which measuring
means (11) are provided to measure the downholder opening trend
(s.sub.o), the downholder opening speed trend (v.sub.o) and/or a
critical value derived therefrom, and in which the control (12)
comprises means for comparing signals measured with the measuring
means (11) with a downholder opening trend (s.sub.o), downholder
opening speed trend (v.sub.o), stored in the control (12) and/or a
critical value derived therefrom, and in which the control (12) is
arranged to control, on the basis thereof, the downholder (8) such
that the movement, speed or critical value of the downholder (8)
derived therefrom is in agreement with the stored downholder
opening trend, downholder opening speed trend and/or the critical
value derived therefrom.
11. A apparatus according to any one of claims 8-10, characterized
in that the measuring means (11) comprise a contactless sensor, for
instance an optical, capacitive or magnetic sensor.
Description
[0001] The invention relates to a method for deep drawing products
from a blank. More in particular, the invention relates to an
improved method for preventing, at least reducing wrinkle formation
in the blank during deep drawing.
[0002] During deep drawing a blank between a die and a punch
cooperating therewith, the edges of the blank are held by means of
a downholder against a die ring cooperating with this downholder.
It is important here to adjust the downholder such that a
downholder force exerted on the edges of the blank is, on the one
hand, sufficiently great to prevent wrinkle formation in the edges,
but is, on the other hand, not greater than is necessary, because
this promotes crack formation and, moreover, leads to high
frictional forces between the blank and the downholder and die
ring. Such frictional forces require a heavy design of the
apparatus, cost unnecessarily much energy during deep drawing, lead
to wear, and shorten the life of the apparatus.
[0003] In the known methods, the required downholder force is often
determined by `trial and error` during a series of experiments
preceding the actual deep drawing process. The found downholder
force is then multiplied by a security factor, in connection with
possible variations in the starting material, such as spreading in
thickness and composition. As a result thereof, the used downholder
force is eventually higher than is absolutely necessary, with all
the above-mentioned attendant drawbacks. Moreover, the experiments
cost time, material, and money, and the outcome is dependent on the
expertise of those who carry out the experiments.
[0004] DE 4 038 864 discloses a method in which at the beginning of
deep drawing the downholder force (F.sub.N) is preventively chosen
so high that this force is greater than a counterforce (F.sub.s) to
be expected in the blank. During deep drawing, the downholder force
is gradually reduced until a beginning of wrinkle formation is
observed. Then the downholder force is increased to above the
counterforce expected in the blank at that moment. This is repeated
until, at the end of the deep drawing process, the downholder force
is equal to zero. The wrinkle formation is detected by means of
measuring means which measure the distance between the downholder
and the die. The reproducibility of this publication lacks because
it is not explained in a manner clear to those skilled in the art
how to determine the counterforce to be expected. Moreover, it is
remarkable that in the known proposal the exerted downholder force
decreases while, as will turn out below, in the proposal according
to the invention the downholder force exactly increases in the
course of the process.
[0005] In this known method, too, the downholder force is therefore
higher than is necessary because, at the beginning of the method
and each time when wrinkle formation occurs, this force is
increased to above the counterforce to be expected in the blank.
Moreover, the height of the downholder force and the good action
thereof is strongly dependent on the accuracy with which the
counterforce can be predicted.
[0006] The invention contemplates providing a method in which at
least a number of the drawbacks inherent to the known methods are
removed. To this end, a method according to the invention is
characterized by the measures according to claim 1.
[0007] In a method according to the invention, the downholder force
is initially kept relatively low and increased only when this is
necessary, that is to say at a beginning wrinkle formation. It is
important here that this wrinkle formation can be recognized at an
early stage. In a method according to the invention, this is
achieved by taking into account the thickness trend of the edge of
the blank during deep drawing or a magnitude derived from this
thickness trend, such as, for instance, the speed of the thickness
trend. The thickness of the blank edge gradually increases during
deep drawing, because the diameter of the blank gradually decreases
and, therefore, material in the blank edge must be accommodated on
an increasingly smaller surface. If this thickness increase were
not taken into account, then every thickness increase would be
considered a beginning wrinkle formation, and the downholder would
wrongly be controlled, during which not only wrinkles, but also the
mentioned thickness increase would be suppressed, which leads to an
unnecessarily high downholder force.
[0008] In a method according to the invention, during deep drawing
the downholder force is gradually increased from a relatively low
value, instead of decreased from a preventively high value. As a
result thereof, the downholder force will always have a lowest
possible value, resulting in low frictional forces between the
apparatus and the blank. Consequently, the apparatus can be
operated at relatively low forces and relatively little energy and
thus be of relatively light design. Moreover, at such low forces
the risk of cracks of the blank will be minimal. As a result
thereof, less stringent requirements can be imposed on the starting
material with respect to, for instance, the homogeneity of the
material, the number of imperfections in the material grid per
volume unit and thickness variations in the blank. In this manner,
with qualitatively inferior starting material and at
correspondingly lower material cost a qualitatively good final
product can yet be realized. Moreover, the freedom in materials to
be used thus increases, so that new materials can more easily be
used.
[0009] Another advantage over the known methods is that a
counterforce to be expected in the blank need not be determined
previous to deep drawing. Nor need time-consuming and expensive
tests be carried out to determine a suitable beginning downholder
force, which is of great advantage, particularly for relatively
small product series.
[0010] Tests of applicant have shown that if during deep drawing
wrinkle formation in the edge of the blank is prevented in the
above-described manner, both wrinkles in the flange of the
deep-drawn final product (so-called primary wrinkles) and wrinkles
in the wall of the deep-drawn final product (so-called secondary
wrinkles) can be effectively prevented. In this specification, the
`edge of the blank` is understood to mean the part of the blank
located between the downholder and the die ring.
[0011] In a first preferred embodiment, a method according to the
invention is characterized by the measures according to claim
2.
[0012] In this embodiment, a parameter relevant to wrinkle
formation is measured and the downholder force is increased if this
measured parameter exceeds a predetermined critical range or
critical value, which range or which value is based on, at least
takes into account, the above-discussed thickness increase of the
blank or a magnitude derived from this thickness increase.
[0013] The downholder force can be increased stepwise, by a
predetermined step size, but can, for instance, also be regulated
to a desired value by means of known per se regulating algorithms,
such as, for instance, a proportionally, integratingly and/or
differentiatingly operating regulation, the measured parameter
again being located below the mentioned critical magnitudes (range
or value).
[0014] In a further elaboration of the first preferred embodiment,
a method according to the invention is characterized by the
measures according to claim 3.
[0015] The parameter relevant to wrinkle formation may, for
instance, be the downholder opening, defined as the perpendicular
distance between the downholder and the die ring. In that case, the
thickness trend or the maximum thickness increase of the blank edge
can be entered as critical range or critical value, respectively.
For if during deep drawing the downholder opening becomes larger
than the momentary thickness or the eventual maximum thickness of
the blank edge, this indicates wrinkle formation. The thickness
trend can be theoretically determined, by means of suitable
simulation programs, but can also be measured once, previous to
deep drawing of a new series of products. To this end, a constant
downholder force is adjusted, at which neither wrinkle formation,
nor crack formation occurs, and the downholder opening is measured
during deep drawing. Since no wrinkle formation occurs, it may be
assumed that the measured downholder opening is substantially equal
to the thickness increase of the blank. It is assumed here that the
measured thickness increase is independent of the adjusted
downholder force, or at least that the influence of the height of
the downholder force on the measured thickness increase is
negligibly small, within the operative area of the downholder force
important to the present use.
[0016] In a further elaboration of the first preferred embodiment,
a method according to the invention is characterized by the
measures according to claim 4.
[0017] Instead of or besides the downholder opening, the speed at
which this opening changes may also function as critical magnitude.
This speed may also be determined by simulation or a testing
measurement, in the above-described manner. Then the speed trend
may function as critical range or a speed value measured to be
highest during this trend as critical value. The downholder opening
speed trend is more sensitive than the downholder opening trend, so
that wrinkle formation can be recognized at an even earlier
stage.
[0018] Of course, both signals, the downholder opening trend and
the downholder opening speed trend, may also be used side by side,
the critical value or the critical range that is exceeded first
being decisive of the control of the downholder.
[0019] In a second preferred embodiment, a method according to the
invention is characterized by the measures according to claim
7.
[0020] In this method, not the downholder force, but the downholder
position is regulated, based on a predetermined thickness trend of
the blank. This thickness trend may, in the same manner as
discussed before, be simulated or measured. On the basis of this
thickness trend, the downholder may always be adjusted during deep
drawing such that the downholder opening is substantially equal to
the predetermined momentary thickness of the blank. Such a method
according to the invention offers the advantage that during deep
drawing the downholder opening and downholder speed need not be
measured and compared with a predetermined critical value.
Moreover, in this embodiment, too, the downholder force will be
minimal, at least not greater than necessary, with all the
attendant above-mentioned advantages.
[0021] Of course, a combination form of both preferred embodiments
according to the invention is possible as well, with primarily the
position of the downholder being regulated on the basis of a
predetermined thickness trend of the blank and secondarily the
downholder opening trend and/or downholder opening speed trend
being measured so that when the predetermined thickness trend does
not fully correspond with the real thickness trend (for instance,
because of variations in the starting material or hysteresis in the
downholder movement) correcting action can be taken by increasing
the downholder force.
[0022] The invention further relates to an apparatus for deep
drawing a product from a blank, suitable for use of a method
according to the invention.
[0023] In the further subclaims, further advantageous embodiments
of a method and apparatus according to the invention are
described.
[0024] In explanation of the invention, an exemplary embodiment of
a deep drawing apparatus and a method according to the invention
will be elucidated in more detail with reference to the drawing. In
this drawing:
[0025] FIG. 1 schematically shows a deep drawing apparatus
according to the invention;
[0026] FIG. 2 shows a diagram in which the trends of the upper and
lower limits of the admissible downholder force are plotted as a
function of the deep drawing ratio;
[0027] FIG. 3 shows a testing measurement with a downholder force
for determining a critical value and/or range in which wrinkle
formation occurs;
[0028] FIG. 4 a measurement in which the downholder opening and the
downholder force are plotted against time, with and without
regulation according to the invention;
[0029] FIG. 5A shows a simulation of the speed trend of the
downholder opening (v.sub.o) during deep drawing;
[0030] FIG. 5B shows a simulation of the downholder force
(F.sub.N), regulated on the basis of the speed from FIG. 5A;
[0031] FIG. 6 shows a photograph of a deep drawn product, with and
without regulation according to the invention;
[0032] FIG. 7 shows a deep drawn product with primary and secondary
wrinkles.
[0033] FIG. 1 shows an apparatus 1 for deep drawing products, with
which wrinkle formation in those products can be reduced and
preferably be completely suppressed. In this specification, wrinkle
formation is understood to mean the formation of both primary
wrinkles 21 in a flange 6 of the deep drawn product 15 and
secondary wrinkles 22 in wall parts 25 of the product 15, as
illustrated in FIG. 7. The apparatus and method according to the
invention are directed to suppressing both types of wrinkles.
[0034] The apparatus 1 comprises a die 2 provided with a die
opening 3 and a punch 4 arranged above this die opening 3. This
punch 4 can be moved by means of suitable positioning means 7 into
the opening 3, as shown in FIG. 1 on the right side. A blank 5 of
starting material placed over the opening 3 is thereby forced into
the opening 3 and deformed between the walls of this opening 3 and
the punch 4 to a desired final product 15. As appears from a
comparison of the left and the right half of FIG. 1, the starting
diameter D.sub.o of the blank 5 gradually decreases during this
deep drawing, which is accompanied by an increase in the thickness
d of the edge 6 and can further lead to wrinkle formation.
[0035] In order to prevent the edge 6 from wrinkling and rising
during deep drawing, a ring-shaped downholder 8 is arranged around
the punch 4, which downholder can be moved with suitable
positioning means 9 towards a die ring 10 extending around the die
opening 3 while clamping the edge 6 of the blank 5. A downholder
force F.sub.N exerted on the edge 6 by the downholder 8 will
thereby increase according as the downholder opening s.sub.o,
defined as the perpendicular distance between the downholder 8 and
the die ring 10, increases.
[0036] During deep drawing, the downholder force F.sub.N must
remain between two extreme limits, a lower limit F.sub.N,min and an
upper limit F.sub.N,max. These limits are graphically shown in FIG.
2, as a function of the deep drawing ratio. When the downholder
force F.sub.N falls below the minimum limit F.sub.N,min, wrinkles
will be formed in the product, while at exceeding the maximum limit
F.sub.N,max cracks will be formed in the product 15. In practice,
the downholder force F.sub.N is therefore adjusted to a `safe`
distance between both limits, so that a certain safety margin is
present, in connection with possible spreading in the starting
material (composition, thickness, etc.).
[0037] In a method according to the invention, the downholder force
F.sub.N is contrarily exactly kept as close to the lower limit
F.sub.N,min as possible. The risk of crack formation will thus be
reduced to a minimum. Moreover, this will also limit frictional
forces F.sub.w occurring during deep drawing between the blank 5
and the downholder 8 and the die ring 10, since these frictional
forces are proportional to the downholder force F.sub.N. Lower
frictional forces ensure that less lubricant suffices, that the
deep drawing process can take place under lower forces, with less
work, and that the whole arrangement can be of lighter design.
[0038] In order to keep the downholder force F.sub.N as low as
possible, at the beginning of deep drawing it is adjusted according
to the invention to a low value and increased only if wrinkle
formation occurs. Then the downholder force is increased to a value
necessary to suppress the detected wrinkles. The downholder force
F.sub.N will thus always be not greater than necessary to suppress
the momentary wrinkle formation.
[0039] For this method to function well, it is important to be able
to detect wrinkle formation at an early stage. It has been found
that both the downholder opening trend s.sub.o and the derivative
thereof over time, the downholder opening speed trend v.sub.o, are
measuring signals usable therefor. For these signals s.sub.o and
v.sub.o, a critical value can be determined in a manner to be
described below in more detail, exceeding of which involves wrinkle
formation.
[0040] The deep drawing apparatus 1 of FIG. 1 is therefore provided
with measuring means 11, with which the mentioned downholder
opening trend s.sub.o and/or downholder opening speed trend v.sub.o
can be measured. These measuring means 11 may, for instance,
comprise an optical, capacitive or magnetic sensor. The measuring
means 11 are connected to a control 12, which is provided with
means for comparing the measuring signals with a critical value or
critical range adjusted for those signals, and which control 12 is
further arranged to move, in case of exceeding the mentioned
critical magnitudes, the downholder 8 towards the die 2 by means of
the positioning means 9. These positioning means 9 may, for
instance, comprise a piston-cylinder assembly, an electrically
driven screw spindle, a piezo-electric element, or the like.
[0041] Previous to deep drawing a new product series, the critical
values can be determined during a testing measurement, by
measuring, during this test, the downholder opening trend s.sub.o
as shown in FIG. 3. It is clearly visible that the downholder
opening so initially has a substantially constant value (range
I-II) and then gradually increases at a constant inclination (range
II-III) corresponding with a constant downholder opening speed
v.sub.o. From point III, the measured downholder opening trend
s.sub.o shows a bend, and this trend increases more rapidly, which
indicates wrinkle formation P. On the basis of this measurement,
therefore, the range I-III can be implemented in the control 12 as
the sought critical downholder opening range. Instead thereof, bend
point III may also be introduced as critical downholder opening
value. When a downholder opening trend s.sub.o measured during deep
drawing exceeds the critical range or the critical value, the
thickness increase is greater than may be expected on the basis of
the testing measurement, which indicates wrinkle formation.
[0042] In a slightly modified variant of the above-described method
for determining the critical values, the deep drawing testing
measurement may also be carried out at such a high downholder force
F.sub.N that neither wrinkle formation, nor crack formation will
occur. This allows for the assumption that a downholder opening
trend s.sub.o measured during this test fully corresponds with the
thickness increase of the edge 6 of the blank 5. This measured
downholder opening trend may therefore be implemented in the
control 12 as critical range. Instead thereof, the maximally
measured thickness increase may also be introduced as critical
value.
[0043] In a comparable manner, besides or instead of the downholder
opening, the speed v.sub.o at which this downholder opening changes
may also be measured during the mentioned testing measurement. This
measured speed trend or a speed value measured to be highest during
this measurement can be introduced into the control 12 as critical
range or critical value for the downholder opening speed trend.
[0044] When a downholder opening speed v.sub.o measured during deep
drawing exceeds this critical range or this critical value, this
indicates wrinkle formation, since the downholder opening increases
more rapidly than may be expected on the basis of the normal
thickness increase.
[0045] Besides, it is pointed out that the critical speed value can
also be determined by the inclination of range II-III in FIG.
3.
[0046] FIG. 4 shows a measurement of the downholder opening s.sub.o
and the downholder force F.sub.N over time, with the thinly drawn
lines representing the trend without regulation according to the
invention, while the thickly drawn lines represent the trend when
the downholder force F.sub.N is controlled on the basis of the
critical downholder opening determined in FIG. 3. It is clearly
visible that the downholder force F.sub.N is stepwise increased
from the critical value determined in FIG. 3 (bend point III) and
thus effectively suppresses (see thickly drawn s.sub.o line)
wrinkle formation (see thinly drawn s.sub.o line).
[0047] FIG. 4 further clearly shows that the downholder force
initially begins relatively low and is increased only if this is
actually necessary. The force may be increased stepwise, at a
predetermined step size, or may be increased proportionally to the
measured deviation. Also possible are other known per se regulation
techniques, in which, for instance, use is made of integrating
and/or differentiating actions. The apparatus may also be provided
with a self-learning regulation, in which the step size of the
force F.sub.N is initially adjusted by an operator, and the
regulation itself adapts this value in the course of the process,
on the basis of fed back measuring data.
[0048] In FIG. 5A,B is shown a simulation in which the downholder
force is regulated on the basis of the measured opening speed
v.sub.o and a critical speed value predetermined in the
above-described manner, which, in the shown case, was approximately
1.times.10.sup.-4. It is clearly visible how the downholder force
F.sub.N is increased stepwise, each time when the downholder
opening speed exceeds the critical value. It is also visible that
the increase of the downholder force F.sub.N is greater according
as the exceeding of the critical value is greater.
[0049] FIG. 6 shows, on the left side, a flange 6' of a product
15', manufactured with a conventional deep drawing method (see the
thinly drawn lines in FIG. 4), while next to this, on the right
side, a product 15 is shown, which has been manufactured with a
method according to the invention (see the thickly drawn lines in
FIG. 4). It clearly appears that the product according to the
present method substantially has no wrinkles.
[0050] It will be clear that the critical values for the downholder
opening and the opening speed depend on the starting material and
the desired final product. These values are therefore determined
again, preferably preceding each new product series. This may be
done by means of a testing measurement, as described above. In case
of sufficient material data and process data, these values may also
be simulated by means of known per se software packages, so that no
testing measurements at all need be carried out anymore.
[0051] In an alternative embodiment of a method according to the
invention, not the downholder force is regulated on the basis of a
measured beginning of wrinkle formation (feed-back regulation), but
the position of the downholder and hence the downholder opening are
regulated according to a predetermined range, such that the
mentioned downholder opening corresponds with the thickness trend
of the blank 5 to be expected (forward regulation). The thickness
trend to be expected may be determined in the same manner as
described before with reference to FIG. 3. Such a forward
regulation has the advantage that during the actual deep drawing no
downholder opening or speed need be measured, so that a very simple
apparatus, without measuring means and without advanced control,
suffices.
[0052] The invention is by no means limited to the exemplary
embodiments shown in the specification and the drawing. Many
variations thereof are possible within the scope of the invention
defined by the claims.
[0053] Thus, depending on, inter alia, the distance over which deep
drawing is effected and the thickness of the starting blank, deep
drawing may take place in one or more steps. Furthermore, the
forward position regulation and fed-back force regulation may be
combined, the force regulation being able to correctingly act on
the position regulation.
[0054] These and many variations are considered to fall within the
scope of the invention defined by the claims.
* * * * *