DE1947903A1 - Method and device for cold forming of plates or the like. made of thermoplastic material - Google Patents

Description

PATENT LAWYERS

DIPL-JNQ. F. THIELEKE ■ _FR1CKE DR-INQ. R. DDRINQ DIPL.-PHYS. DR. J. FRICKE

BRAUNSCHWEtG MUNICH

1285

Uniroyal Inc., 1230 Avenue of the Americas New York, 20, New York, USA

Method and device; For cold forming of plates or (IrI. made of thermoplastic material

The invention relates to a method and a device for cold forming of plates, panels, strips, sheets or the like. made of thermoplastic material.

In general, thermoplastic materials are viewed as those materials which can only be found with great difficulty let cold form. Many metals, e.g. copper, brass, aluminum, steel and lead can be cold-formed deform, e.g. by rolling, embossing, drawing, pressing, Turning or the like. In all of these cases, the ductile metal is brought into a desired shape by on A force is exerted on the metal, which causes the deformation to separate of metal overcomes. However, if the same process is applied to plastic materials found that fractures or cracks occur * or that the material reverses the cold forming and then again takes the shape it possessed before cold forging Has. This latter phenomenon, which appears as an elastic memory

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nis is called, occurs even more strongly when higher Temperatures can be reached.

Many attempts have been made to make thermoplastic material cold forming, especially at room temperature. Man has used the tools commonly used in metalworking. However, the result has shown that such thermoplastic materials respond very poorly to cold deformation react and show either constrictions, cracks or breaks or only poor drawability.

After the cold forming of thermoplastic materials brings such difficulties with it, one has to deform these materials already the still viscous molten material Polymer molded under pressure by extrusion, injection molding, or other recognized techniques.

It is the object of the present invention to provide a method which in a simple way creates the prerequisite that even thermoplastic materials without the described Disadvantages can be cold formed.

According to the invention, this object is achieved in that initially the starting material is reduced in its thickness to a desired value by compression, the material on

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a temperature below its softening temperature is maintained, whereupon the compressed material on the way of cold forming into the desired workpiece shape will. The compression of the material is essential here at temperatures below the softening temperature below simultaneous reduction in thickness. Surprisingly, it has been shown that this pretreatment allows the material without Difficulty being cold formed into the desired shape can without the difficulties that have arisen so far appear.

It has been found that when the compressive forces are applied at higher temperatures, the thermoplastic material relaxes, making it extremely difficult to deform. This is especially true if the temperature of the thermoplastic material reaches the softening temperature recognized for the material. In this Trap relaxes the thermoplastic sheet or panel in to the extent that compression cannot affect the cold formability of the panel in the slightest.

The starting material can advantageously be produced by cold rolling compressed to the desired thickness.

Although the temperature of the thermoplastic material can be raised a little for the implementation of the new process,

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as long as it remains below the softening temperature. However, temperatures are preferred which are approximately at room temperature, so be around 25 ° C and below.

The new process makes the cold forming of thermoplastic Material is extremely simplified and can be carried out at high production speed, while at the same time exceptionally high quality molded workpieces are obtained. At the same time, there are considerable costs in terms of equipment compared to injection molding and similar processes.

In one case, the process according to the invention can thermoplastic material can be rolled in a biaxial manner by first cold rolling it in one direction, whereupon the sheet or sheet rotated 90 ° and rolled again is, the two rolling directions are perpendicular to each other. It was found that in this manner of implementation of the new process all previously used in cold forming occurring problems could be avoided. However, it was also found that when the panel was pressed together by rolling in only one direction before cold forming, the cold formability and the resulting workpiece are essential could be improved. However, the improvement and advantages are not as conspicuous in simple rolling as

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for workpieces that have previously been biaxially rolled.

It was also found that the required Compression can also be done with the help of a press. When a sheet of thermoplastic material is in is compressed in such a press, the pressure is equal to the ratio of the force applied by the press and the area of the thermoplastic sheet. The maximum size of the thermoplastic sheet used to reduce its thickness Can be compressed in a press is determined by the maximum force applied with the help of the press can be. For this reason, the use of a press is currently at least somewhat restricted. However, it was found that the cold deformability of such sheets made of thermoplastic material, which is prepared by cold compression have been similar to the properties of thermoplastic Is panels which have been prepared by biaxial rolling. The squeezed panels clearly show essential better cold forming results compared to those thermoplastic materials that are not at all rolled or rolled only in one direction. The effect of the press on the thermoplastic sheet material is equivalent to the effect obtained by multi-axis rolling the sheet. We found that there were no differences between the cold-formed products there are which

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from cold-pressed sheets and cold-rolled biaxially rolled sheets.

The beneficial effect of compression can also be achieved by putting the thermoplastic material on cold extrusion. The panel is pushed through a molding tool, which has a beveled or has a decreasing cross-section channel to reduce the thickness of the panel. If in addition to the reduction in thickness the extrusion die is designed so that the extruded sheet extends in a direction perpendicular to the direction of flow, So can expand in width, the effect in the end is practically the same as with a biaxial rolled sheet. If the extrusion tool is so designed that an expansion of the panel in width with the reduction the thickness is not possible, the end effect is about the same as a sheet rolled in one direction.

An advantage of biaxial cold extrusion over biaxial cold rolling is that in the first Case the length of the thermoplastic sheets or tapes that treated is not limited. In biaxial cold rolling, the width of the rolls is decisive for the maximum Size of the treated panels.

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The invention is described below with reference to schematic drawings explained in more detail using several exemplary embodiments.

1 is a perspective view of a first embodiment of an apparatus for carrying out the new method.

FIG. 2 is a cross section taken along section line 2-2 of FIG. 1.

Fig. 5 is a schematic perspective view of another Embodiment of an apparatus which is suitable for carrying out the method.

FIG. 4 shows a cross section along the section line 4-4 of the device according to FIG. 3.

Figure 5 illustrates one by means of two side views Forming device for cold forming according to the method according to the invention, wherein the rterkstück to be deformed in two different Forming phases is shown.

Finally, FIG. 6 is a view of a test device in a representation similar to FIG. 5.

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Fig. 1 shows an extrusion device 100 with an entry zone in the form of a slot 106 and an exit zone in the form of a slot 108. The cross section of the entry and feed zone 106 of the extrusion die is approximately the same the cross-section and size of the thermoplastic sheet 102 which is tooled below the softening temperature should be squeezed cold. However, the lead-in section of the entry zone is not shown in FIG Way beveled to the entry of the leading edge of the panel

102 to the zone 106 to facilitate. The transition zone 107 continuously decreases in thickness until the desired compression or reduction in thickness of the panel between the Entrance zone 106 and the exit zone 108 is reached.

The width 110 of the passage opening of the extrusion tool is constant in all three zones including the transition zone 107, so that the material extruded by cold means

103 has the same width as the untreated panel 102 according to FIG Fig. 2 has. Only the thickness of the panel 102 is due to compression when passing through the transition zone 10 7 correspondingly reduced. The molding tool 100 shown is therefore suitable for compression in one direction thermoplastic material.

A set of driven rollers 101 and 101 'are driven so that that the thermoplastic sheet material 102 in the in

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1 and 3 is advanced in the direction shown and is finally introduced into the corresponding strand tool. if the panel 102 passes through the extrusion tools 100 or 100 ', it is compressed and emerges as a cold Ways extruded material 103, 103 '(Figs. 2 and 4) of reduced thickness out of the tool.

In the case of the mold 100 ', one takes place in two directions acting cold extrusion takes place, since not only the thickness but also the width 110 '(Fig. 4) of the narrowing Transition section 107 'of the mold cavity is changed. The width increases in the direction towards the exit end 108 '. This change in breadth along with the change the thickness of the mold cavity allows the panel 102 to be in the zone during the compression of the thickness 107 expands in the direction of width.

As indicated above, certain thermoplastic Materials have the properties to relax again to their natural initial state when they are increased Temperatures are rolled. Here all the improvements that are otherwise achieved for cold forming work again. lost. To avoid this difficulty, the materials must be used during thinning or compression be kept at temperatures well below

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the softening temperature. You should be at this temperature or rolled at a lower temperature or in some other way be squeezed. During the rolling or compression process, resistance to deformation arises in the sheet material due to the deformation Warmth. This heat development can lead to a temperature increase, which is the case with certain thermoplastic Substances even the softening temperature of the under

A rolling process or the compression process of standing material can reach. In order to avoid that these undesirable temperatures are reached, the generation of heat must thereby be avoided or reduced that the press rolls or press plates are carefully cooled. The increased Temperatures can also be avoided by carefully extending the rolling process, i.e. by performing multiple rolling passes with only slight reductions in thickness during each rolling step or by changing the speed the rollers decrease accordingly. The increase in the

The number of rolling passes significantly reduces the force that has to be applied by the rolls and also reduces the generation of heat.

The speed at which the thickness of the. Thermoplastic Material can be decreased is due to the thermal conductivity of the material and the thickness of the board. If the thermoplastic material shows good thermal conductivity,

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or if the initial or starting thickness requires only a slight reduction in thickness, the sheet material can move more quickly and treated with a higher percentage of reduction in thickness without the risk of the occurrence of a excessive heating is to be feared.

It should be noted that the thermoplastic sheet that compressed and cold formed by the process, a single sheet or a composite or laminated one Blackboard can be. The composite panel can consist of sheets of the same material or can be of different Materials be combined.

When a composite panel is dealt with, either can suitable means can be used to the individual sheets or the like. to connect with each other. For this purpose, for example an adhesive can be used. Likewise, to connect the sheets, pressing the sheets together under elevated Temperatures are applied.

We have further noted that the technique of biaxially rolling the thermoplastic material is preferably carried out so that about 50 % of the required reduction in thickness is achieved when rolling in a first direction, followed by rolling in a direction perpendicular thereto. This technique leads

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to a rolled sheet material of extraordinarily good quality Properties in contrast to a process in which the directions are changed after each rolling pass. The advantages are, among other things, that the compressed thermoplastic material shows less waviness than if after each salt pass the direction is changed. However the sequence of the rolling process does not significantly affect the cold formability of the cold-rolled sheet material.

It was also found that products which are treated according to the method described before they are treated, before they are cold worked, show a significantly improved resistance to external fractures, i.e. to fractures which are based on the action of a solvent on a material under tension. It was also found that a marked improvement in the impact resistance of the t cold formed product is achieved when the thermoplastic Material has been pretreated according to the new process is.

Excellent workpieces have been cold formed from thermoplastic Materials such as polypropylene, polyvinyl chloride (PVC) of high or low molecular weight, and acrylonitrile butadiene styrene (ABS) of high or low molecular weight, if these materials in sheet form have been reduced in their thickness by more than 50% before the cold forming took place

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has found. If these sheet materials are only compressed by 25% or less in their thickness, one obtains articles with less good properties after cold forming, which exhibit various of the undesirable characteristics of the type described above. In some cases it has been noted that best results have been obtained by first reducing the thickness of the thermoplastic materials up to about 75% , while in certain cases reducing the thickness up to 90% for the best results in terms of thickness Perform cold forming. Certain ABS compositions, such as polypropylene and polyethylene, are examples of the latter group. Other thermoplastic materials, such as PVC and Teflon in particular, are unsuitable for withstanding thickness reductions of more than 70% , so that particular care must be taken if these materials have to be prepared for cold forming.

In order to test the cold formability of numerous thermoplastic materials that are available, a new cup pull test was developed to obtain uniform measurements. This test for thermoplastic materials is similar to the well known cup pulling test that has long been used to measure the ductility of metals. In the known method, the cup is produced in the following way: a disc with the radius B is placed between a deep-drawing tool and a blank hold-down

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inserted. This disk is then drawn into the molding tool by a molding die with radius A. A measure of the deformability of the material is the limiting draw ratio, which is defined as the maximum value of B / A at which a cup can still be formed. In the newly developed test, which is illustrated in FIG. 6, a disc of thermoplastic material 4 with a radius B is inserted between a die 1 and a guide member 2. In order to avoid excessive pressure on the disc, a spacer ring 5 µm The disk 1 is placed. The disk is then drawn into the die by a punch 3 of radius A behind ¹ . For given values of B and A, the depth of the shaped cup when the first defect occurs is a measure of the deformability. In addition to the depth of the cup when a defect occurs, the uniformity of the thickness of the walls and the depth of the cup can also be used if a widening or constriction occurs. This modified test differs from the conventional cup pulling test in that a spacer ring is provided to prevent any pressure other than that from the forming die from being applied to the disc to be tested. While a metallic sample must be tested several times in order to obtain the maximum value of the limiting draw ratio, the thermoplastic materials tested according to the new method only need to be measured once.

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The spacer ring, as it has been described above in the test experiments, is also used with advantage in production of cold formed parts. As shown schematically in Fig. 5, a thermoplastic sheet 4 is on the upper support surface la of a die 1 placed so that the Material covers the drawing opening 7. During the drawing process, the punch 3 is lowered and presses the thermoplastic material 4 into the opening 7. While the plastic material is drawn into the mold opening 7 by the punch 3, occur in the circumferential direction acting stresses in the remaining flange of the starting material. These stresses can be undesirable Effect folds of the flange. The usual solution to this problem is to have the thermoplastic starting material clamped between the hold-down device 2 and the support surface la of the die with sufficient pressure to cause folding to avoid. However, it is extremely difficult to select and maintain necessary and appropriate pressures. If the pressure on the plastic material is too great, the plastic material will be held too tight and can not enough flow into the opening, so that errors occur due to the resulting pulling effect. These difficulties as well as the risk of folding the flange are avoided by placing a spacer 5a around the blank thermoplastic material is inserted around between the die 1 and a guide 2. The spacer 5a can be in the form

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a spacer ring, the thickness of which is not less than the thickness of the starting material 4. Advantageously the spacer ring is even slightly larger than the thickness of the thermoplastic sheet material. By maintaining the distance between the support surface la of the die 1 and the guide 2, substantially equal to the thickness of the thermoplastic material or to a value that is not

^ is smaller than the thickness and not more than 10 % greater than the thickness, it is achieved that the portion of the sheet material 4, which surrounds the central, the mold opening 7 covering part, move relatively freely in the direction of the opening during the drawing process can, while at the same time it is prevented that significant movements of the flange occur in the direction perpendicular to the support surface la. The guide part 2 and the die are firmly clamped together. By using the spacer ring 5a, the need to set a pressure on the starting material is avoided and at the same time

W tig ensures that folding of the flange area of the starting material cannot occur. It is understood that the concept can also be obtained in other ways, provided that it is ensured that a required sufficient distance between the guide 2 and the support surface la is maintained. Of course, the same principle can also be applied to such blanks or starting materials which do not have a circular outline or which are not reshaped into a uniform shell shape. So both

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for example, the same measure with advantage also with rectangular Cut-outs and bowls with a rectangular outline use.

In the preferred embodiment when using the spacer ring 5a ", the drawing process is ended before the edge or edge of the starting material reaches the constriction of the die. If this point is exceeded, the effect of maintaining a constant distance is diminished and it folds can occur.

The following examples show the cold formability of various thermoplastic materials, determined according to the new cup pulling test. It should be noted, however, that these examples serve only for illustration and are not to be construed as a limitation of the following claims.

Example series I

In the following examples, cups with a diameter of 4.5 cm were used formed from discs 10 cm in diameter. The slices were cut from natural and cold-rolled sheets, the maximum depth of the cells before fractures occur as a measure of the cold deformability of the material can be. The table below shows the thickness of the panels before and after cold rolling, the percentage

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the reduction in thickness, the depth of the cup at the point of constriction, as far as a constriction has occurred, as well as the depth of the cup at the moment at which a fracture point was created was established. In some cases, cup breakage did not occur, even at a depth of 3.5 cm, which the greatest attempted depth is. In these cases, the well-known sign indicated that the value was greater than 3.5 cm is.

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Material origin final thickness depth in Lent Thick Thickness Reduction Inches

ke in inches in inches in %

SECTION .038
.048
.076
.126
.090
.126 PVC .040
«050
.070
.090
.120 Polypropy
len .038
.050
.058
.080
.090
.120 Teflon .120
.250 Polysulfones .060
.120 nylon .070
.140 Styrene
Acrylonitrile
Copolymer .030
.060 Noryl .032
.082

Polypheny- .055
len-oxides .085

χ = no constriction

.038 .040 .040 .063 .040 .040

.040 .040 .040 .040, 040

.038 .040 .040 .040 .040 .040

.120 .120

.060 .060

.070 .070

.030 .030

.032 .036

.055 .050 0 17 47 50 55 68

0 20 43 55 67

0 20 31 50 55 67

0 52

0 50

0 50

0 50

0 56

0 41

Occurrence of constriction or expansion

Depth in inches when fracture occurs

.2

.42

.80

.75

X X X X X

.22 .35 .50 .65 .65 χ

.5 χ

.3 χ

X X

X X

.2 .42 .85 .75 .92 1.22

1.25-1.30 1.3

.22 1.4

.7 1.1

.2 OK

0 0.5

0.14

+ = Reduction in thickness through biaxial Rollers

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- 20 sample series II

In the following series of examples, various thermoplastic Materials tested using the new cup pull test. These examples are either in a Directional or biaxially rolled. Or untreated, as detailed in the table. All pans, molded from the material were 3.8 cm in diameter. ,

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Material washer- origin- final- type of depth in depth

diam
ser, inch 3
3
3 borrowed
Thickness,
customs ge thickness,
customs Rolling inches at in inches
Occurrence when
of entering
lace up from
gene break χ 7/8
.2 9/16
.15 7/16 SECTION 3.
3.
3. 75
75
75 .100
.100
.050 .050
.050
.050 Biaxial
Uniaxial
unrolled χ no break
χ 11/16
χ 0 PVC 3.
3.
3. 3
3
3
75
75 .100
.100
.050 .050
.050
.050 Biaxial
Uniaxial
unrolled χ no break
χ no break
.3 1 3/16
χ 1 9/16
χ no fraction + Teflon 3.
3.
3.
3.
3. 5
5
5
75
75 .100
.100
.050
.100
.100 .050
.050
.050
.050
.050 Biaxial
Uniaxial
unrolled
Biaxial
Uniaxial χ no break
χ no break
. 1 5/8
χ no break
χ 1 inch Poly-
sulfone 3.
3.
3.
3.
3. O
O
O .100
.100
.050
.100
.100 OOOOO
IO IO IO IO IO
OOOOO
• · · · · Biaxial
Uniaxial
unrolled
Biaxial
Uniaxial χ no break
χ no break
χ 11/16 Nylon 66 3.
3.
3. 75
75
75 .130
.130
.070 .070
.070
.070 Biaxial
Uniaxial
unrolled χ no break
χ no break
.4 1 3/16 Polycar
bonat 3.
3.
3. .100
.100
.050 .050
.050
.050 Biaxial
Uniaxial
unrolled

+ = The Teflon panels rolled in one direction showed a strong tapering and the depth of the cup on the flat ones Points was less than 1.4 cm. The non-occurrence of a break in this case must not lead to the conclusion that that there is better cold formability than the biaxially rolled samples.

χ = no constriction.

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Example series III

In the following series of examples, lamellae were used for panels made of different thermoplastic materials firmly bonded together, cold rolled in two directions and then formed into cells.

P IHa: A board the size of 15 χ 15 cn and a thickness of 1.5 mm of polyvinyl chloride was combined with a panel of the same size and thickness made of an acrylonitrile-butadiene-styrene copolymer resin by pressing the leaves together for 20 minutes at 177 ° C.

UIb: A five-layer panel was made by five tablets measuring 15 χ 15 cm for a period of 20 minutes were compressed at 177 C. The individual sheets were made of 0.375mm polyvinylchloride, 1mm ABS, 0.25mm Polyvinyl chloride, 1mm ABS and 0.375mm polyvinylchloride. the composite sheet with a thickness of 3 mn became biaxial cold rolled to a thickness of 1.5 mm and then successfully formed.

HIc: A board measuring 15 χ 15 cm and 2.5 mm thick made of polysulfone (polyarylene-polyether-polysulphone resin) with a board measuring 15 χ 15 cm and 0.625 mm thick

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made of ABS by moistening the surfaces of each board with a solvent (dimethylformamide) and pressing the sheets together tied together. The laminated material of 3.1 mm thick was then cold rolled to a thickness of 1.5 mm and successfully cold formed.

Example series IV

Cold biaxial extrusion of thermoplastic materials with subsequent cold forming gives the same results as the previous rolling of the material in two directions.

IVa: A strip of high-density polyethylene, 8.9 cm wide and 2.5 mm thick was extruded in two directions to reduce the thickness from 2.5 to 1.27 mm (50 % reduction in thickness), while the Width increased from 8.9 to 15.2 cm. A 8.2 cm diameter disc of the extruded material was tested by the new cup drawing method. The results of this test as well as the results for the test of a disc 8.2 cm in diameter from a sample which has been pretreated by rolling in two directions are given below:

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original- final- depth in depth in fracture

Thickness Ge Thickness cm at cm at kraft

in cm in cm occurrence occurrence

one one

Sniffing fracture
tion

extruded polyethylene 0.25 0.132 2.234 2.79 1020

rolled

Polyethylene 0.25 x 0.125 2.15 2.84 1020

IVb: A strip of ABS rubber-plastic material was made
biaxially extruded to reduce the thickness from 2.5
1.78 mm. Tests for tensile strength and impact strength were carried out, which showed identical results,
like tests in which ABS was initially cold-rolled in two directions and thereby reduced in thickness from 2.5 mm to 1.78 mm.

Expectations

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Claims (13)

- 25 claims 1.) Process for cold forming of plates, sheets, strips or sheets of thermoplastic. Material, characterized in that first the material through Compression is reduced in thickness to a desired value, with the material at a temperature below its softening temperature is maintained, whereupon the compressed material is cold-formed into the desired workpiece shape is transferred. 2. The method according to claim 1, characterized in that the starting material by cold rolling is compressed to the desired thickness. 3. The method according to claim 2, characterized in that the starting material in at least is rolled in two different directions. 4. The method according to claim 1, characterized in that the thickness of the starting material means Cold pressing is reduced. 5. The method according to claim 1 to 4, characterized in that the reduction in thickness of the starting material takes place at about room temperature (25 ⁰ C). 0098U / 1799 6. The method according to claim 3, characterized in that the starting material is initially through Rolling in one sighting is reduced by half the required value in its thickness and the further reduction the thickness is done by rolling in a direction offset by 90 " 7. The method according to claim 1 to 6, characterized in that one of several as the starting material Boards or the like * composite layer material used will. 8. A method according to claim 1, characterized geke η η - ι is characterized in that the compression of the starting material takes place to the desired thickness on the way of cold extrusion. 9. The method according to claim 8, characterized in that the starting material during the Thickness reduction can be widened. 10. Apparatus for carrying out the method according to claim 1, characterized by a cold pressing or rolling device for the starting material and a cold forming device for the starting material compressed with a reduction in thickness. 009814/1799 11. The apparatus of claim 10 having a matrix consisting of form punch and die assembly _t characterized by a guide (2, 5, 5a) which, instead of a blank holder of the support surface (la) of the die (1) is associated, and the durch.welche Regions of the workpiece surrounding the die opening (7) can be guided without any noticeable constraint in such a way that they can move essentially freely towards the die opening, but not in directions transverse to the support surface. 12. The device according to claim 11, characterized in that the guide consists of a spacer (5 or 5a) on the support surface (la) and an element (2) surrounding the die opening (7) and resting on the spacer . 13. The device according to claim 12, characterized in that the height of the spacer (5 or 5a) corresponds at least to the thickness of the workpiece (4). 0098ΊA / 1799 ι ** · ♦ Blank page