EP2595770B1 - Forming tool and method for hot forming and partially press hardening a workpiece made of sheet steel - Google Patents

Description

The invention relates to a forming tool for hot forming and partial press hardening of a workpiece made of sheet steel, with a die, an insertable for forming the workpiece in a recess of the die and a punch cooling device. In particular, the invention relates to a method for hot forming and partial press hardening of a workpiece made of sheet steel, in which the workpiece is heated prior to forming and then hot formed in a die and a die insertable into a recess of the die forming tool, wherein the forming tool Cooling device has.

The hot forming of blanks made of high-strength and ultra-high-strength steels for the production of press-hardened components has been established in vehicle construction in recent years. Among other things, numerous concepts for the production of partially hardened components with different structures have been developed. One from the DE 10 2006 019 395 A1 The known concept is the heating of a suitable steel existing board to a temperature above the austenitizing temperature and the immediately subsequent forming in a hot forming tool, which is equipped in at least one area with a heater for local adjustment of a softer microstructure. However, this known concept has the disadvantage that at least one heating device must be provided, which causes considerable operating costs. In addition, the permanent affects Heat exposure of the corresponding effective surface of the forming tool negatively on its life (lifetime).

The present invention has for its object to provide a method or forming tool for hot forming and partial press hardening of sheet steel, which allows in a simple manufacturing technology to produce on the metal component to be produced adjacent zones with different structures and thus different material properties.

According to the invention this object is achieved by the forming tool with the features of claim 1 and by the method with the features of claim 9.

The inventive method in which the workpiece is heated before forming and then hot formed in a forming tool, the forming tool having a cooling device, is characterized essentially in that in the closed state of the forming tool, the contact between the workpiece and the contact surfaces of the die and the punch is partially interrupted by moving apart a movable die part and a movable die part from a closed position to an open position.

Accordingly, the forming tool according to the invention comprises a die, a punch insertable into a depression of the die and a cooling device. According to the invention, the die is made of a first die part and at least one relative to the first die part movable second mold part formed while the punch of a first stamp member and at least one movable relative to the first stamp member second stamp member is formed, wherein the at least one movable second female part and the at least one movable second stamp member cooperate with an opening device, which causes the at least one second die part and the at least one second stamp part contact the workpiece with a shorter closing time than the first die part and the first stamp part.

The method according to the invention and the forming tool according to the invention thus make it possible, in a simple manufacturing technique, to produce adjacent zones with different structures and correspondingly different material characteristics, such as strength and elongation, on the metal component to be produced.

An advantageous embodiment of the forming tool according to the invention is that the mold parts are movably connected to a Matrizenträger and the punch parts movable with a punch carrier, wherein the Matrizenträger and the punch carrier are each provided with a plunger, and wherein the plunger in the closed state of the first female part and cause the first die part by a further approximation of Matrizenträger and punch carrier moving apart of the at least one second die part and the at least one second die part. This embodiment can be compared to conventional forming tools for hot forming and partial press hardening of steel blanks operate without significant additional energy consumption. Especially this embodiment does not require costly additional drive means for the moving apart of the tool parts, which serve to generate at least one zone with a relatively soft structure in the component. Rather, the already existing press ram can be used for this purpose, which serves for closing the forming tool, ie for moving the punch. When the rams of the die carrier and the punch carrier are moved back, the at least one second die part and the at least one second die part close again before opening the die and punch, whereby the area of the workpiece (component) in which the contact between the workpiece and the tool effective area has been interrupted, is looked up.

Another advantageous embodiment of the forming tool according to the invention is characterized in that the first mold part is rigidly connected and the at least one second mold part is movably connected to a die carrier, while the first stamp part is rigid and the at least one second stamp part is movably connected to a punch carrier, wherein the die carrier and the punch carrier are respectively provided with a forward and backward movement causing drive means, and wherein in the closed state of the first die part and the first die part, the drive means cause a movement apart of the at least one second die part and the at least one second die part. This variant of the forming tool according to the invention can be operated so that, as desired, with and without looking up the workpiece, ie with and without re-closing of the Matrizenträger movably connected to the female part and the movable with the punch carrier connected stamp part, can be manufactured. The timing at which the die member movably connected to the die carrier and the punch member movably connected to the punch carrier are moved apart can be variably controlled depending on the elongation to be set in the workpiece in the contact area of these tool parts. The drive means for moving apart the at least one second die part and the at least one second die part are preferably formed from hydraulic, pneumatic or hydropneumatic working cylinders.

Another preferred embodiment of the forming tool according to the invention provides that the at least one second die part and / or the at least one second die part, which are moved apart in the closed state of the forming tool, have a controllable tempering device, preferably a heater. As a result, it is possible not only to ensure with high reliability that one or more non-hardened regions are selectively produced on the workpiece; This embodiment also creates the possibility of variably setting its material properties, such as strength and elongation, in a specific region of the workpiece, depending on the requirements imposed on the component to be produced.

In an advantageous manner, the at least one second die part and / or the at least one second die part can be made of a material or have a surface coating that conducts heat poorly in order to specifically prevent the removal of heat in the areas of the workpiece which are not hardened. counteract. For example Ceramics could be used as a material with low thermal conductivity.

An advantageous embodiment of the method according to the invention is characterized in that the contact between the workpiece and the contact surfaces of the die and the punch of Umformwerkzeuges partially by repeated or multiple moving apart of the movable die part and the movable die part from the closed position to the open position and subsequent backward movement of the movable die part and the movable die part is interrupted clocked from the open position to the closed position. The cooling rate of the hot-formed workpiece can be arbitrarily reduced or varied in this way in a wide range. For example, if a continuous, i. interrupted contact between cooled forming tool and workpiece or component, the cooling rate of the component is 100 ° C / s, so can at a clocked contact time of 0.2 seconds per second (ie, 0.8 seconds per second there is no contact), the average cooling rate of Component be reduced to about 20 ° C / s.

Preferably, the clocked contact interruption is adjusted so that the sum of the contact times is less than the sum of the contact interruption times. Alternatively, the clocked contact interruption can also be set so that the sum of the contact times is equal to or greater than the sum of the contact interruption times.

Further preferred and advantageous embodiments of the device according to the invention and of the method according to the invention are specified in the subclaims.

Fig. 1

eine Schnittansicht eines Umformwerkzeuges im vollständig geschlossenen Zustand;

Fig. 2

eine Schnittansicht des Umformwerkzeuges der Fig. 1 im partiell geschlossenen Zustand;

Fig. 3

ein weiteres Umformwerkzeug im vollständig geschlossenen Zustand, in einer Schnittansicht;

Fig. 4

das Umformwerkzeug der Fig. 3 im partiell geschlossenen Zustand, in einer Schnittansicht;

Fig. 5

eine hydropneumatische Vorrichtung zum Antrieb und zur Steuerung der partiellen Öffnung des Umformwerkzeuges der Figuren 3 und 4; und

Fig. 6

ein Weg-Zeit-Diagramm, das eine getaktete Unterbrechung des Kontaktes von Umformwerkzeug und Werkstück bzw. geformten Bauteil veranschaulicht.

The invention will be explained in more detail with reference to a drawing illustrating several embodiments. Each show schematically:

Fig. 1

a sectional view of a forming tool in the fully closed state;

Fig. 2

a sectional view of the forming tool of Fig. 1 in the partially closed state;

Fig. 3

another forming tool in the fully closed state, in a sectional view;

Fig. 4

the forming tool the Fig. 3 in the partially closed state, in a sectional view;

Fig. 5

a hydropneumatic device for driving and controlling the partial opening of the forming tool the Figures 3 and 4 ; and

Fig. 6

a path-time diagram illustrating a clocked interruption of the contact of forming tool and workpiece or molded component.

In the drawing, various embodiments of a forming tool 1, 1 'according to the invention for hot forming and partial press hardening of a board made of high-strength or high-strength steel are shown. In the case of the board Component 2 to be produced is, for example, a bumper, a B pillar or another crash-relevant body component of a motor vehicle. The board (workpiece) consists for example of a manganese-boron steel, in particular a manganese-boron steel alloy 22MnB5.

Portions of the component (workpiece) 2 to be hardened must be rapidly cooled from the austenitizing temperature, while portions of the component 2 that are not to be hardened may not undergo rapid cooling.

The forming tools 1, 1 'shown in the drawing offer the possibility of partially interrupting the contact between the component and the tool acting surfaces.

The forming tool 1, 1 'is designed in the manner of a deep-drawing device and has a die 3. In the die 3, a recess (recess) 4 is formed, which images the outer shape of the produced, three-dimensionally shaped component 2.

In addition, the forming tool 1, 1 'comprises a punch 5, which determines the inner shape of the component 2 to be produced. The punch 5 can be moved by means of an adjusting device (press ram), not shown, from a remote from the die 3 starting position into a closed position in which it is fully retracted into the recess 4 of the die 3. The adjusting device comprises a control device which controls the speed with which the Stamp 5 enters the recess 4 of the die 3, controls.

The die 3 is subdivided into at least two die parts 3.1, 3.2 which are movable relative to each other on a stationary support, e.g. a plate 6 of a press table are held. Correspondingly, the punch 5 is subdivided into a corresponding number of punch parts 5.1, 5.2, wherein a respective stamp part 5.1, 5.2 is associated with a respective die part 3.1, 3.2. The stamp parts 5.1, 5.2 are also held relative to each other movable on a punch carrier 7, which is formed for example from a plate. The punch carrier or the plate 7 is mounted on the above-mentioned adjusting device, not shown here, by means of which the punch 5 can be retracted from a remote from the die 3 starting position in the recess 4 of the die 3.

In the FIGS. 1 to 4 each with the tool parts 3.1 shown on the left side, 5.1, the component 2 are partially cured, whereas the tool parts 3.2, 5.2 shown on the right side to prevent hardening of the component 2 by interrupting the contact of the component 2 and the tool effective surfaces 3.21, 5.21.

The active surface of the stamp part 5.1 shown on the left side and / or the active surface of the associated mold part 3.1 are cooled, while the active surfaces 3.21, 5.21 of the right side tool parts 3.2, 5.2, where another or relatively soft structure is to be set, cooled and / or preferably heated and / or made of a poorly thermally conductive material or a bad thermally conductive surface coating are performed. For this purpose, cooling channels 8 are introduced into the stamp part 5.1 and the die part 3.1 near the active surfaces. The cooling channels 8 are part of a cooling device, not shown further. Depending on the degree of cooling required in each case, the cooling channels are traversed by water, ice water, a frozen salt solution, liquid nitrogen or another cooling medium which is suitable for the rapid removal of large amounts of heat.

Likewise, in the second stamp part 5.2 and the female part 3.2 near their active surfaces 3.21, 5.21 fluid channels 9 a tempering introduced, which is also not shown here in detail. Through the channels 9 of the tempering a cooling medium, for example, a cooling oil is passed, which causes a moderate cooling of the tool parts 3.2, 5.2 in this area. Alternatively, at least through a part of the channels 9, in particular through the channels 9.1 arranged adjacent to the first or left-hand tool parts 3.2, 5.2, a heating fluid, e.g. Hot steam to be passed. Instead of fluid channels 9 and 9.1, heating cartridges, heating spirals or heating wires can also be integrated in the tool parts 3.2, 5.2, at which a different or relatively soft structure is to be set.

To produce the component 2, a board made of high-strength or very high-strength steel (for example made of 22MnB5) is first heated to austenitizing temperature in an oven, not shown here. Subsequently, the workpiece (board) is placed in the opened forming tool 1, 1 ', so that it lies with its edge on the upper side of the die 3. Then be Hold-down 10 attached, which hold down the workpiece in its edge region during the subsequent forming. The hold-down force exerted by the holding-down device 10 can be adjusted as a function of the respective forming speed, in order to enable an optimized subsequent flow of the workpiece 2 into the depression 4 of the die 3.

Then, the punch 5 is placed at high speed on the steel sheet, so that the highly cooled end face of the stamping part 5.1, at which a press hardening of the steel sheet 2 is to take place quickly comes into intensive contact with its associated surface portion of the steel sheet 2.

The in the FIGS. 1 to 4 Tool parts 3.2, 5.2 shown on the right are associated with an opening device which causes the second stamp part 5.2 and second die part 3.2 to contact the workpiece 2 with a shorter closing time than the first stamp part 5.1 and the first die part 3.1. The steel sheet 2 is quenched in this way in its section 2.1 so fast that there forms a microstructure or area with a hardness that is higher than the hardness of the adjacent to the section 2.1 section 2.2 of the steel sheet.

In the in the Figures 1 and 2 illustrated embodiment, the die parts 3.1, 3.2 and the stamp parts 5.1, 5.2 sprung against the associated plate 6 of the press table or the stamp plate 7 is supported. For this purpose, between the respective plate 6 or 7 and the die parts held thereon 3.1, 3.2 or stamp parts 5.1, 5.2 spring elements 11, for example, coil springs or the like arranged. Further, the plates 6 and 7 are provided with brackets 12 which form the matrices 3.1, 3.2 and stamp parts 5.1, 5.2 associated stops 13. By the spring elements 11, the movable die and stamp parts 3.1, 3.2, 5.1, 5.2 are stretched against the stops 13. The stamp parts 5.1, 5.2 and the plate-shaped punch carrier 7 in this case have recesses (apertures) 14, 15 for the hold-10 supporting push rods 16. The push rods 16 penetrate the recesses 14, 15 with play.

Furthermore, the sprung supported die and punch parts 3.1, 3.2, 5.1, 5.2 are each provided with (not shown) guides that specify the direction of movement of the die and stamp parts 3.1, 3.2, 5.1, 5.2 during closing and opening of the forming tool 1.

Furthermore, serving as Matrizenträger plate 6 and the plate-shaped punch carrier 7 with tappets 17, 18 are provided. The respective plunger 17, 18 penetrates an opening (through bore) 19, 20 formed in the stamping part 5.2 or die part 3.2. The plungers 17, 18 and, accordingly, the openings 19, 20 are arranged axially offset from one another.

In addition, the plate-shaped die carrier 6 and the punch carrier 7 are provided with further stops 21, 22 which face the rear sides of the linearly displaceable punch parts 5.1, 5.2 and die parts 3.1, 3.2. The tool parts 3.1, 5.1 facing end faces of the stops 21 have in the in Fig. 1 shown closed position of the forming tool 1 a distance A1 from the back of the Tool parts 3.1, 5.1, which is less than the distance A2, the rear sides of the tool parts 3.2, 5.2 facing end faces of the stops 22 of the tool parts 3.2, 5.2 have.

When the forming tool 1 is completely closed, cause the plunger 17, 18 in a further approximation of Matrizenträger 6 and punch carrier 7 a moving apart of stamp part 5.2 and die part 3.2, ie a partial opening of the forming tool 1, so that the contact between the component 2 and tool effective area is partially interrupted (see. Figures 1 and 2 ). The interruption of the contact of tool effective surface 3.21, 5.21 and component 2, ie the partial opening of the forming tool 1, takes place here before and after the press ram with the punch 5 has reached its bottom dead center with respect to the stationary press table 6.

About the ram speed, i. the speed with which the punch 5 is moved in the direction of the plate 6, as well as the distance of the stops 21, 22, the closing time of the punch member 5.2 and the female part 3.2 can be adjusted. When moving back the plunger 18 close before opening of female part 3.1 and stamp part 5.1, the female part 3.2 and the stamp part 5.2 again, whereby the area 2.2 of the component 2, in which a relatively soft structure was generated, is looked up again.

In the in the Figures 3 and 4 illustrated embodiment of the forming tool according to the invention 1 'are female part 3.1 and stamp part 5.1, where the component is to be partially cured, with the die carrier (Press table) 6 or punch carrier 7 rigidly connected. Die part 3.2 and stamp part 5.2, where a relatively soft microstructure in the component 2 is to be adjusted, however, via cylinder (working cylinder) 23 are movably supported relative to the die carrier 6 and die carrier 7.

The stamp parts 5.1, 5.2 and the plate-shaped punch carrier 7 in turn have recesses (through holes) 14, 15, which are penetrated by the depressors 10 supporting push rods 16 with game.

Also, the die carrier 6 and the punch carrier 7 with stops 13, 22 are provided which limit the range of movement of female part 3.2 and stamping part 5.2. The stops are formed on brackets 12, on which the female part 3.2 or stamp part 5.2 is also supported by spring elements 11. The spring elements 11, which are preferably designed as coil springs, engage on the side opposite to the working cylinder 23 of the stamping part 5.2 or die part 3.2.

By means of the working cylinder 23, which can be operated pneumatically, hydraulically or hydropneumatically, the interruption of the contact of tool effective surface 3.21, 5.21 and component 2 is realized in the bottom dead center of the press.

The forming tool 1 'according to the Figures 3 and 4 can be operated so that the forming and partial press hardening as desired with or without looking up the workpiece 2, ie with or without re-closing of movable die part 3.2 and movable stamping part 5.2 before opening the fixed to the press table (die carrier 6) or Stamp carrier 7 mounted die part 3.1 and die part 5.1, can be done.

In Fig. 5 is a device for driving and controlling the movable tool elements 3.2, 5.2 in the Figures 3 and 4 Outlined forming tool 1 'outlined. The device comprises a hydraulic cylinder 24 operating in the manner of a pump, which is driven by the press ram of the forming press during each press stroke. The hydraulic cylinder 24 is preferably filled with oil and connected via a hydraulic line 25 to the working cylinder 23 coupled to the movable die part 5.2 or movable die part. The respective working cylinder 23 here consists of a hydropneumatic cylinder, on whose one piston side the oil flowing through the hydraulic line 25 acts, while on the other side of the piston a compressed gas acts. The gas pressure in the cylinder 23 can be, for example, in the closed state of the movable die part 5.2 and the associated movable die part 3.2 at about 50 bar. With the reference numerals 13, 22 are in Fig. 5 denotes the stops of the movable stamping part 5.2.

In the hydraulic line 25, a valve 26, preferably a check valve is arranged. Further, a hydropneumatic pressure accumulator 27 is connected to the hydraulic line 25 between the check valve 26 and the working cylinder 23. The gas pressure in the accumulator 27 is in the closed state of stamp part 5.2 and female part 3.2, for example, about 250 bar. The hydraulic line 25 is further provided with a 3/2-way valve 28, from the third port, a valve 26 bridging the return line 29 is connected. In the return line 29, a valve 30 is also arranged, preferably a check valve, which acts opposite to the valve 26. Further, in turn, a hydropneumatic pressure accumulator 31 is connected between the valve 30 and the 3/2-way valve 28. The gas pressure in this pressure accumulator 31 is in the closed state of stamp part 5.2 and female part 3.2, for example, about 5 bar.

Fig. 6 shows a path-time diagram, which is a mode of operation of a forming tool according to the invention or of the forming tool 1 'according to the Figures 3 and 4 illustrated in which the contact between the workpiece 2 and the contact surfaces of the die and the punch of the forming tool 1 'is interrupted clocked by the movable die part 3.2 and the movable die part 5.2 several times from the closed position ( Fig. 3 ) in the open position ( Fig. 4 ) and vice versa from the open position to the closed position to be moved. In the in Fig. 6 As shown, the clocked contact time is set to about 0.2 seconds per second. The contact between the workpiece 2 and the contact surfaces of the movable die part 3.2 and the movable die part 5.2 is thus interrupted in this case by about 0.8 seconds per second. If the cooling rate of the hot-formed workpiece 2 in the region of the cooled die part 3.1 and the stamp part 5.1 of the forming tool 1 ', for example, 100 ° C / s, so may clocked interruption of the contact of the workpiece 2 relative to the cooled movable mold part 3.2 and the cooled movable die part 5.2 to a contact time of about 0.2 seconds per second, the average cooling rate in Area of the female part 3.2 and the stamp part 5.2 can be reduced to about 20 ° C / s.

The measure of the average cooling rate reduction depends essentially on the ratio of the time at which (partial) no contact between forming tool 1 'and component 2 exists, to the total cycle time. For the example given above, this means 0.8 s / 1 s = 0.8. The cooling rate thus drops by about 80% from 100 ° C / s to 20 ° C / s. However, since the cooling of the component does not depend exactly on the times at the same contact pressure, in which partial contact or partial contact between the component and cooled forming tool, the above formula describes only the basic tendency. The times of contact or contact interruption can be in the clocked operation according to the invention according to Fig. 6 vary in a wide range. Accordingly, with the described mode of operation, the average cooling rate over time can be reduced from 0 to approximately 100%.

The embodiment of the invention is not limited to the embodiments described above. On the contrary, further variants are conceivable which make use of the invention specified in the appended claims, even in the case of designs differing from those illustrated.

Claims (16)

1. Forming tool (1, 1') for hot forming and partially press hardening a workpiece made of sheet steel, comprising a die (3), a punch (5) which can be inserted into a cavity (4) of the die (3) to form the workpiece, and a cooling device (8), characterised in that the die (3) is formed of a first die part (3.1) and at least one second die part (3.2) which is movable relative to the first die part, while the punch (5) is formed of a first punch part (5.1) and at least one second punch part (5.2) which is movable relative to the first punch part, the at least one movable second die part (3.2) and the at least one movable second punch part (5.2) interacting with an opening device (17, 18; 23) which causes the at least one second die part (3.2) and the at least one second punch part (5.2) to contact the workpiece with a shorter closing time than the first die part (3.1) and the first punch part (5.1).
2. Forming tool according to claim 1, characterised in that the die parts (3.1, 3.2) are movably connected to a die carrier (6) and the punch parts (5.1, 5.2) are movably connected to a punch carrier (7), the die carrier (6) and the punch carrier (7) each being provided with a ram (17, 18), and the rams (17, 18) causing the at least one second die part (3.2) and the at least one second punch part (5.2) to move apart in the closed state of the first die part (3.1) and the first punch part (5.1) owing to the die carrier (6) and punch carrier (7) being moved closer together.
3. Forming tool according to claim 1, characterised in that the first die part (3.1) is rigidly connected and the at least one second die part (3.2) is movably connected to a die carrier (6), while the first punch part (5.1) is rigidly connected and the at least one second punch part (5.2) is movably connect to a punch carrier (7), the die carrier (6) and the punch carrier (7) each being provided with a drive means (23) causing a forward and a backward movement, and, in the closed state of the first die part (3.1) and first punch part (5.1), the drive means (23) causing the at least one second die part (3.2) and the at least one second punch part (5.2) to move apart.
4. Forming tool according to claim 3, characterised in that the drive means (23) are formed of hydraulic, pneumatic or hydropneumatic working cylinders.
5. Forming tool according to any of claims 1 to 4, characterised in that the first die part (3.1) and/or the first punch part (5.1) comprise a cooling device (8).
6. Forming tool according to any of claims 1 to 5, characterised in that the at least one second die part (3.2) and/or the at least one second punch part (5.2) comprise a controllable temperature conditioning device (9, 9.1).
7. Forming tool according to claim 6, characterised in that the temperature conditioning device (9, 9.1) is a heater.
8. Forming tool according to any of claims 1 to 7, characterised in that the at least one second die part (3.2) and/or the at least one second punch part (5.2) is made of a material which is a poor conductor of heat or has a surface coating which is a poor conductor of heat.
9. Method for hot forming and partially press hardening a workpiece made of sheet steel, in which the workpiece is heated prior to forming and is subsequently hot formed in a forming tool comprising a die (3) and a punch (5), the forming tool comprising a cooling device (8), in particular using a forming tool (1, 1') according to any of claims 1 to 7, characterised in that, in the closed state of the forming tool (1, 1'), the contact between the workpiece (2) and the contact surfaces of the die (3) and the punch (5) of the forming tool is interrupted in regions by moving apart a movable die part (3.2) and a movable punch part (5.2) from a closed position to an opened position.
10. Method according to claim 9, characterised in that, prior to the opening of the forming tool (1, 1'), the region (2.2) of the workpiece (2) in which the contact between the workpiece and the contact surfaces of the forming tool was interrupted in regions is restruck by moving the movable die part (3.2) and the punch part (5.2) back from the opened position to the closed position.
11. Method according to claim 9, characterised in that, after the partial press hardening of the formed workpiece (2), the forming tool (1') is opened without restriking the region (2.2) of the workpiece (2) in which the contact between the workpiece (2) and the contact surfaces (3.21, 5.21) of the forming tool (1) was interrupted in regions.
12. Method according to either claim 9 or claim 10, characterised in that the contact between the workpiece (2) and the contact surfaces of the die (3) and the punch (5) of the forming tool is interrupted in a clocked manner in regions by moving apart the movable die part (3.2) and the movable punch part (5.2) from the closed position to the opened position a number of times and subsequently moving the movable die part (3.2) and the movable punch part (5.2) back from the opened position to the closed position.
13. Method according to claim 12, characterised in that the clocked contact interruption is set such that the sum of the contact times is less than the sum of the contact interruption times.
14. Method according to claim 12, characterised in that the clocked contact interruption is set such that the sum of the contact times is equal to or greater than the sum of the contact interruption times.
15. Method according to any of claims 9 to 14, characterised in that the region (2.2) of the workpiece (2) in which the contact between the workpiece (2) and the contact surfaces (3.21, 5.21) of the forming tool (1, 1') is interrupted in regions is heated beforehand during the forming.
16. Method according to any of claims 9 to 15, characterised in that, during the forming, a holding force which is controlled according to the forming speed is exerted on an edge region of the workpiece (2).

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