FORMING STATION AND METHOD FOR HOT FORMING A BLANK MADE OF METAL, IN PARTICULAR ALUMINUM

Abstract

A forming station for forming a blank made of metal. A heating device has a first hot plate that is hydraulically adjustable, and a second hotplate connected to a counter bearing. The first hotplate and the second hotplate are adjustable relative to one another between an open position, in which they are mutually spaced apart, such that the blank can be inserted into or removed from an intermediate space formed between the hotplates, and a closed position in which the blank is clamped between the hotplates. A forming device has a first die part and a second die part which, for forming the blank, are adjustable relative to one another between an open position and a closed position. The heating device and the forming device have a common adjusting device which synchronously adjusts the first hot plate of the heating device and the first die part of the forming device.

Description

This nonprovisional application is a continuation of international application no. PCT/EP2024/074934, which was filed on September 6, 2024, and which claims priority to German patent application no. 10 2023 124 450.7, which was filed in Germany on September 11, 2023, and which are both herein incorporated by reference.

BACKGROUND OF THE INVENTION

Field of the Invention

The invention relates to a forming station for hot forming a blank made of metal, in particular aluminum, comprising a heating device which has a first hotplate which is hydraulically adjustable, and a second hotplate which is connected to a counter bearing, wherein the first hotplate and the second hotplate are adjustable relative to one another between an open position in which they are mutually spaced apart such that the blank can be inserted into or removed from an intermediate space formed between the hotplates, and a closed position in which the blank is clamped between the hotplates, and comprising a forming device which has a first die part and a second die part which, for the purpose of forming the blank, are adjustable relative to one another, in particular hydraulically, between an open position and a closed position. Furthermore, the invention relates to a method for hot forming a blank made of metal, in particular aluminum, in a corresponding forming station.

Description of the Background Art

It has long been known to reshape a metal blank, e.g., made of steel or aluminum, or a blank formed of a thermoplastic, in a hydraulic press. For this purpose, the blank, which is a flat plate, is heated to a desired temperature in a heating device and then transferred to a forming device in which the blank is formed into the desired configuration between two die parts, which are brought together by means of an in particular hydraulic press. The shaped component is then usually cooled and, if necessary, also cut to size or punched.

To manufacture the components economically, it is necessary to keep the cycle time, i.e., the duration of the individual method steps, as short as possible and, in particular, to heat the blank as quickly as possible. However, in many cases this is associated with a structurally complex design.

SUMMARY OF THE INVENTION

It is therefore an object of the present invention of creating a forming station for a blank made of metal, in particular aluminum or plastic of the type mentioned, with which the blank can be heated quickly to a desired temperature and which has a structurally simple design.

With regard to the forming station, this object is achieved by a forming station in that a common, in particular hydraulic, adjusting device be provided for the heating device and the forming device, which synchronously adjusts the first hotplate of the heating device and the first die part of the forming device, that the heating device and the forming device have a common ram which bears the first hotplate and the first die part and is adjustable by means of the in particular hydraulic adjusting device, and that the second hotplate be mounted on a hydraulic clamping device which has a plurality of hydraulic piston-cylinder units with which the second hotplate can be clamped indirectly or directly or clamped against the first hotplate.

Preferably, the forming station according to the invention is used for a blank made of a 2000, 6000, or 7000 aluminum alloy; however, the invention is not limited thereto.

According to an example of the invention, the basic idea is to attach the upper first heating plate of the heating device and the upper first die part of the forming device to the common ram, and to move them synchronously by means of a single, in particular hydraulic, adjusting device. Rapid heating of the blank, e.g., to at least 100 K°/s, can be achieved if there is a high and uniform, full-surface contact pressure between the hotplates and the blank. This can be achieved by the hydraulic clamping device acting upon the lower second hotplate with the plurality of hydraulic piston-cylinder units. In particular, according to the invention, the deflections of the first hotplate and the second hotplate are compensated for by the clamping device.

The first hotplate can be connected to the adjustable ram of the forming station and be adjusted thereby. The plurality of hydraulic clamping devices which are preferably arranged in a field-like pattern are integrated into the counter-bearing which bears the lower second hotplate. This can consist, for example, of the clamping devices or the corresponding piston-cylinder units being positioned in a 4x5 matrix to form a preferably flat cushion, i.e., four rows of five spaced-apart piston-cylinder units are provided, which accordingly form a 4x5 field. Other numbers of piston-cylinder units are also possible, wherein a rectangular field is preferred. In particular, the piston-cylinder units can lie directly next to one another.

The piston-cylinder units can each be pressurized with hydraulic pressure and are in particular dimensioned in such a way and preferably operated such that the deflections of the upper first hotplate and also the lower second hotplate and therefore also the blank clamped therebetween are compensated for under force.

The hotplates can be designed such that they can follow the deflections of the press ram arising during operation, i.e., they are relatively flexible such that there is full-surface contact between the blank and the hotplates.

The piston-cylinder units of the clamping device can be supplied with pressure in the form of a communicating tube such that the piston-cylinder units are uniformly adjustable.

In a further example, it can be provided to divide the total number of piston-cylinder units into several groups and to supply these groups with pressure independently of one another in order to generate regionally different contact pressure. The piston-cylinder units within a group are then uniformly adjustable.

It can also be provided that the piston-cylinder units can each be subjected to pressure individually and independently of each other in order to achieve a desired, freely selectable clamping force distribution via the field or the cushion.

On at least some piston-cylinder units and preferably on all piston-cylinder units, a pressure piece serving as a chuck be always arranged on their second side facing the hotplate. The pressure pieces can be interchangeable and designed the same for all piston-cylinder units; however, it is also possible to use different pressure pieces in order to thereby adjust the level of clamping force for a plurality of piston-cylinder units or all piston-cylinder units.

It has proven advantageous if the piston-cylinder units do not act directly upon the second hotplate, but, rather, when a distribution plate is arranged between the piston-cylinder units and the second hotplate. The distribution plate preferably consists of steel and can have a thickness within a range from 30 mm to 100 mm.

The distribution plate can rest on the piston-cylinder units and be floatingly mounted thereon. In this way, the distribution plate can undergo displacements and deformations in its plate plane without excessive constraining stresses occurring.

Preferably, the distribution plate can bear the second hotplate which is either placed directly on the distribution plate or supported thereon with interposed insulation. Preferably, the second hotplate is fastened to the distribution plate.

The second hotplate can have thermal insulation on its side facing the piston-cylinder units or the distribution plate, by which it rests on the distribution plate. According to the invention, it can also be provided that the second hotplate be surrounded by additional insulation on its side edges.

Preferably, a guide device can be provided for the distribution plate, which can undergo a displacement perpendicular to its plate plane by the piston-cylinder units, in order to prevent lateral deflection of the distribution plate. Preferably, the distribution plate is guided on guide pins, wherein, in a possible embodiment of the invention, the guide pins penetrate the distribution plate with clearance such that the floating bearing of the distribution plate on the piston-cylinder units is not hindered.

Preferably, the blank should touch the hotplates just before the forming station reaches the closed position, i.e., when the hotplates move together and clamp the blank between them. It should also preferably be provided that the blank quickly come out of contact with the hotplates after being heated to the desired temperature. In a further development of the invention, a hydraulic lifting device can therefore be provided, by means of which the blank can be lifted from the second hotplate into a lifted position.

The lifting device can have a plurality of lifting pins that sit on and are connected to a common lifting plate. The lifting plate, together with the lifting pins, can be moved and adjusted, for example, with the aid of in particular hydraulic piston-cylinder units or by means of gas springs, wherein, in a further development of the invention, it can be provided that the lifting pins and preferably also the lifting plate be pretensioned into the lifted position by the gas springs or the piston-cylinder lifting units.

If the blank to be heated is inserted in the intermediate space between the first hotplate and the second hotplate, the lifting pins protrude from the top side, facing the first heating plate, of the second hotplate. The blank is placed on the lifting pins such that it is at a distance from the second hotplate. When the two hotplates are brought together and moved toward one another, the blank is pressed against the pretension caused by the gas springs or caused by the piston-cylinder lifting units against the second hotplate.

When the two hotplates are moved apart again after heating the blank, the gas springs or the piston-cylinder lifting units push the blank away from the second hotplate due to their pretension and lift the blank off it.

The forming station according to the invention provides that a common ram with a common, in particular hydraulic, adjusting device be provided for the heating device and the forming device such that the upper first hotplate of the heating device and the upper first die part of the forming device are adjusted synchronously. The common adjusting device can alternatively also be adjustable mechanically, e.g., by means of one or more eccentrics, by means of at least one servo drive or by means of a spindle drive.

The forming station possesses a lower counter bearing on which the lower second hotplate and the lower second die part are preferably fixedly arranged. Since the upper first hotplate and the upper first die part are attached to a common ram which can be moved up and down by means of the usual, in particular hydraulic, adjusting device, not only is the heating device adjustable between the open position and the closed position, but the forming device can also be adjusted synchronously therewith between a corresponding open position and a corresponding closed position by means of the ram.

In a further development of the invention, a spray device is provided in the forming station with which a lubricant can be sprayed onto the blank from above and/or from below.

The spray device can be arranged such that the blank is sprayed with the lubricant only after being removed from the heating device. In this case, the spray device can be arranged such that the blank can be sprayed with the spray medium during the transfer of the blank between the heating device and the forming device and/or in the forming device.

A component made from the formed blank can be cooled directly in the forming device. This can be achieved if a cooling device is integrated into the forming device, and in particular into the upper first die part and/or into the lower second die part.

The invention also relates to a method for hot forming a blank made of metal, in particular aluminum, in a forming station having the aforementioned design. The ram is moved together with the upper first hotplate and the upper first die part by means of the in particular hydraulic adjusting device from an open starting position (top dead center) in the direction of the blank to be formed and the blank to be heated, until the upper die part at time t₁ comes into contact with the blank to be formed, and the blank to be formed is then formed by adjusting the ram and the upper first die part until an end position (bottom dead center) is reached.

Synchronous with the upper first die part, the upper first hotplate is moved toward the blank to be heated by adjusting the shared ram. In so doing, the upper first hotplate comes into contact with the blank to be heated and presses it against the pretension of the lifting pins in the direction of the lower second hotplate until it makes contact. The lower second hotplate is clamped against the upper first hotplate at time t₂ by means of the hydraulic clamping device or by means of the plurality of piston-cylinder units, with the interposition of the blank to be heated. Preferably, the time t₂ of the clamping process is later by a time interval Δt than the time t₁ of the beginning of the forming process. Preferably, the time interval Δt is between 0.01 s and 5.0 s and in particular between 0.01 s and 1.0 s. In a further development of the invention, it can be provided that the clamping device clamp the second hotplate against the upper hotplate only when or after the forming station has reached the bottom dead center.

In the following, the process of heating and forming a blank will be explained by way of example.

To heat the blank to be heated, it is introduced into the heating device by means of the feed conveyor, wherein the forming station is in its open position, i.e., its upper starting position. In this case, the blank rests on the lifting pins and is at a distance from the lower second hotplate. Subsequently, the in particular hydraulic adjusting device of the ram is activated such that the ram, together with the upper first hotplate, is moved vertically downwards until it comes into contact with the top side of the blank. A further downward movement of the ram and the upper first hotplate causes the blank, together with the lifting pins, to be pressed downwards against their pretension and against the surface of the lower second hotplate such that the blank is clamped between the upper first hotplate and the lower second hotplate.

Then, the piston-cylinder units are activated and exert an additional clamping force on the lower second hotplate via the floatingly mounted distribution plate, which is dimensioned such that the deflections of the upper first hotplate and the lower second hotplate arising as a result of the clamping are compensated for, and such that the blank must be subjected to a clamping force approximately constant across its surface.

After the heating of the blank, the ram is moved back up by means of the in particular hydraulic adjusting device such that the forming station is open. The blank heated in the previous step is removed from the heating device and placed on the blank holders of the lower second die part of the forming device. This blank is now the blank to be formed.

By means of the feed conveyor, another blank to be heated is simultaneously fed to the heating device.

By activating the in particular hydraulic adjusting device, the ram is lowered together with the upper first die part and the upper first hotplate until the upper first die part is resting on the top side of the blank to be formed, wherein the forming has, however, not yet begun. At the same time, the upper first hotplate can come into contact with the top side of the blank to be heated, which rests on the lifting pins, in the heating device.

As the ram moves further downwards, the upper first die part presses the blank to be formed in the forming device into the mold contour of the lower second die part, thereby forming the blank into a desired configuration.

By means of the downward movement of the ram, the first hotplate presses the blank to be heated downwards in the heating device against the pretension of the lifting pins until the blank to be heated comes into contact with the lower second hotplate.

When the ram is in its lower end position (bottom dead center), the blank to be formed is formed by the upper first die part and the lower second die part into the desired component in the forming device.

In the heating device, the hydraulic clamping device with the piston-cylinder units is preferably activated after the start of the formation of the blank to be formed in the forming device, and in particular after reaching the bottom dead center, and presses the distribution plate and therefore also the lower second hotplate upwards against the upper first hotplate. In this way, it is possible to hold the blank to be heated in the heating device with a relatively high surface pressure of ≥ 5 N/mm² and in particular ≥ 10 N/mm² between the two hotplates.

While the blank to be heated is clamped in the heating device and is being heated, the cooling device is activated in the forming device, thereby cooling the formed component.

The forming station then reopens as the ram moves upwards. The formed component can then be removed by means of the discharge conveyor, while at the same time, the heated blank is transferred from the heating device to the forming device. Additionally, a new blank to be heated is introduced into the heating device via the feed conveyor, and the previously described cycle is repeated.

Further scope of applicability of the present invention will become apparent from the detailed description given hereinafter. However, it should be understood that the detailed description and specific examples, while indicating preferred embodiments of the invention, are given by way of illustration only, since various changes, combinations, and modifications within the spirit and scope of the invention will become apparent to those skilled in the art from this detailed description.

BRIEF DESCRIPTION OF THE DRAWINGS

The present invention will become more fully understood from the detailed description given hereinbelow and the accompanying drawings which are given by way of illustration only, and thus, are not limitive of the present invention, and wherein:

FIG. 1 shows a schematic representation of a forming station,

FIG. 2 shows schematic side view of a heating device of the forming station,

FIG. 3 shows a field of a clamping device with a plurality of hydraulic piston-cylinder units,

FIG. 4 shows the forming stations according to FIG. 1 immediately before the forming of the blank,

FIG. 5 shows the forming station according to FIG. 4 during the forming of the blank, and

FIG. 6 shows the forming station according to FIG. 5 at the end of the forming of the blank.

DETAILED DESCRIPTION

FIG. 1 shows a schematic representation of a forming station 1 for heating and subsequently forming a metal blank P. The forming station 1 comprises a heating device 10 shown on the right and a forming device 20 shown on the left side.

The heating device 10 has an upper first hotplate 11 which is attached to the underside of a support plate 15 via an interposed insulation 16. The support plate 15 sits together with the insulation 16 and the upper first hotplate 11 on the underside of a ram 32 which can be moved vertically up and down by means of an in particular hydraulic adjusting device 30, shown only schematically, as indicated by the double arrow V.

A first die part 21 of the forming device 20 is held on the underside of a bearing plate 23 which is also fastened to the underside of the ram 32. A cooling device 33 is integrated into the first die part 21.

The heating device 10 and the forming device 20 possess a common lower counter bearing 31 on which a lower second hotplate 12 of the heating device 10 and a lower second die part 22 of the forming device 20 are supported.

The lower second hotplate 12, with interposed insulation 17, is mounted on a distribution plate 13 which rests on a hydraulic clamping device 25 which has a plurality of hydraulic piston-cylinder units 26 that are supported on the counter bearing 3 indirectly or directly on their underside facing away from the distribution plate 13. The design of the heating device 10 is described in detail below.

Between the lower second hotplate 12 and the lower second die part 22, a spray device 34 is arranged, by means of which a lubricant can be sprayed onto the top side and/or the bottom side of the blank P.

The lower second die part 22 possesses a mold contour 35 and blank holders 24 on which the blank P can be placed before its forming.

A cooling device 33 is also integrated into the lower second die part 22.

On the right side of FIG. 1, a feed conveyor is schematically indicated by an arrow Z, with which the blank to be formed can be fed to the forming station. The blank P to be formed is gripped by a (not shown) transfer device and transported thereby through the individual devices of the forming station 1 and, after passing through the forming station 1 and after being formed into a component, is transferred to a discharge conveyor, which is indicated by an arrow A.

In FIG. 2, the heating device 10 for heating the blank P made of metal, in particular aluminum, is shown in more detail. The heating device 10 possesses the upper first hotplate 11, which is held on the ram 32 with interposed insulation 16 and the support plate 15. By means of the only hinted at, in particular hydraulic, adjusting device 33, the ram 32 together with the support plate 15 and the upper first hotplate 11 can be adjusted vertically up and down in a known manner (arrow V).

The counter bearing 31 comprises a fixed base plate 36, on which an intermediate plate 19 rests, which is enclosed by wall elements 37 forming a trough 38. In an interior space 39 of the trough 38, the hydraulic clamping device 25, which has a plurality of piston-cylinder units 26, is arranged in the form of a grid, as shown in FIG. 3. In the illustrated exemplary embodiment, four rows of five spaced-apart piston-cylinder units 26 each are provided to form the grid field, i.e., a total of twenty piston-cylinder units 26.

A pressure piece 40 serving as a chuck is arranged on the piston-cylinder units 26, on their side facing the lower second hotplate 12. The size of the pressure pieces 40 makes it possible to vary the size of the clamping force.

The distribution plate 13 is placed on the top side of the piston-cylinder units 26 and floats on the piston-cylinder units 26. Vertical guide pins 14, which pass through the distribution plate 13 with clearance, prevent the distribution plate 13 from deflecting excessively laterally.

On its upper side facing the upper first hotplate 11, the distribution plate 13 bears the lower second hotplate 12. The lower second hotplate 12 can have a conventional design and bears the thermal insulation 17 on its underside facing the piston-cylinder units 26, by which it rests on the distribution plate 13. Additionally, the lower second hotplate 12 is surrounded on its side walls by further insulation 17a. The upper first hotplate 11 and the lower second hotplate 12 can be heated in the usual way, for which, for example, an embedded resistance heater can be used.

A lifting device 27 is provided for the lower second hotplate 15. The distribution plate 13 and the lower second hotplate 12 are penetrated by a plurality of lifting pins 28 arranged at a distance from one another with clearance. The lifting pins 28 are seated at their lower end, facing away from the lower second hotplate 12, on a common lifting plate 29, which in turn rests on hydraulic lifting cylinders 41 that are supported at the other end on the intermediate plate 19. By activating the lifting cylinders 41, the lifting plate 29 together with the lifting pins 28 can be raised and lowered.

By means of the lifting cylinders 41, the lifting pins 28 are pretensioned into their lifted position in which they protrude from the upper side of the lower second hotplate 12.

In FIG. 2, the upper first hotplate 11 and the lower second hotplate 12 are shown in their open position in which they are arranged at a mutual distance, forming an intermediate space 18. If the upper first hotplate 11 and the lower second hotplate 12 are in the shown open position, the blank P to be heated can be inserted into the intermediate space 18 and placed on the top side of the lifting pins 28, as shown in FIG. 2.

In the following, the process of heating and forming a blank is explained with reference to the figures.

To heat the blank P, it is introduced into the heating device 10 by means of the feed conveyor Z, wherein the forming station 1 is in its open position, i.e., its upper starting position (top dead center), as shown in FIG. 1. In this case, the blank P rests on the lifting pins 28 and is at a distance from the lower second hotplate 12. Subsequently, the in particular hydraulic adjusting device 30 of the ram 32 is activated such that the ram 32, together with the upper first hotplate 11, is moved vertically downwards until it comes into contact with the top side of the blank P. A further downward movement of the ram 32 and the upper first hotplate 11 causes the blank, together with the lifting pins 28, to be pressed downwards against their pretension and against the surface of the lower second hotplate 12 such that the blank P is between is clamped between the upper first hotplate 11 and the lower second hotplate 12.

Then, the piston-cylinder units 26 are activated and exert on the lower second hotplate 12 via the floatingly mounted distribution plate 13 an additional clamping force which is dimensioned such that the deflections arising as a result of the clamping of the upper first hotplate 11 and the lower second hotplate 12 are compensated for, and such that the blank P is subjected to a clamping force approximately constant across its surface.

After the heating of the blank P, the ram 32 is moved back up by means of the in particular hydraulic adjusting device 30 such that the forming station 1 is open. The blank P heated in the previous step is removed from the heating device 10 and placed on the blank holders 24 of the lower second die part 22 of the forming device 20. This blank is now the blank to be formed.

By means of the feed conveyor Z, another blank P to be heated is simultaneously fed to the heating device 10. This state is shown in FIG. 1.

By activating the in particular hydraulic adjusting device 30, the ram 32 is lowered together with the upper first die part 21 and the upper first hotplate 11. FIG. 4 shows a state during the lowering movement of the ram 32, in which the upper first die part 21 is currently resting on the top side of the blank P to be formed, wherein the deformation has, however, not yet started. At the same time, the upper first hotplate 11 comes into contact with the top side of the blank to be heated, which rests on the lifting pins 18, in the heating device 10. This state is shown in FIG. 4.

As the ram 32 moves further downwards, the upper first die part 21 presses the blank to be formed in the forming device 20 into the mold contour of the lower second die part 22, thereby forming the blank P into a desired configuration. By means of the downward movement of the ram 32, the first hotplate 11 presses the blank to be heated downwards in the heating device 10 against the pretension of the lifting pins 28 until the blank to be heated comes into contact with the lower second hotplate 12. This state is shown in FIG. 5.

FIG. 6 shows the phase of the forming process in which the ram 32 is in its lower end position (bottom dead center). In the forming device 20, the blank to be formed is formed by the upper first die part 21 and the lower second die part 22 into the desired component.

In the heating device 10, the hydraulic clamping device 25 with the piston-cylinder units 26 is preferably activated after reaching the bottom dead center, and presses the distribution plate 23 and therefore also the lower second hotplate 22 upwards against the upper first hotplate 11. In this way it is possible to hold the blank to be heated in the heating device 10 with a relatively high surface pressure of ≥ 5 N/mm² and in particular ≥ 10 N/mm² between the two hotplates 11 and 12.

While the blank P to be heated is clamped in the heating device 10 and is being heated, the cooling device 33 is activated in the forming device 20, thereby cooling the formed component.

The forming station 1 then reopens as the ram 32 moves upwards. The formed component can then be removed by means of the discharge conveyor A, while at the same time, the heated blank is transferred from the heating device 10 to the forming device 20. Additionally, a new blank to be heated is introduced into the heating device 10 via the feed conveyor Z, and the previously described cycle is repeated.

The invention being thus described, it will be obvious that the same may be varied in many ways. Such variations are not to be regarded as a departure from the spirit and scope of the invention, and all such modifications as would be obvious to one skilled in the art are to be included within the scope of the following claims.

Claims

1. A forming station for hot forming a blank made of metal, in particular aluminum, the forming station comprising: a heating device that has a first hot plate that is hydraulically adjustable; a second hotplate connected to a counter bearing, the first hotplate and the second hotplate being adjustable relative to one another between an open position, in which they are mutually spaced apart, such that the blank is adapted to be inserted into or removed from an intermediate space formed between the hotplates, and a closed position in which the blank is clamped between the hotplates; a forming device that a first die part and a second die part which, for the purpose of forming the blank, are hydraulically adjustable relative to one another between an open position and a closed position; a distribution plate that indirectly bears the second hotplate; and a guide to prevent the distribution plate from deflecting laterally, wherein the heating device and the forming device are provided with a common hydraulic adjusting device that synchronously adjusts the first hot plate of the heating device and the first die part of the forming device, wherein the heating device and the forming device have a common ram that bears the first hot plate and the first die part and is adjustable via the hydraulic adjusting device, wherein the second hotplate is mounted on a hydraulic clamping device that has at least two hydraulic piston-cylinder units with which the second hotplate is adapted to be clamped indirectly or directly against the first hotplate, wherein a distribution plate is arranged between the piston-cylinder units and the second hotplate and rests on the piston-cylinder units and is floatingly mounted thereon, and wherein the second hotplate has thermal insulation on its side facing the distribution plate, via which it rests on the distribution plate.

2. The forming station according to claim 1, wherein the piston-cylinder units are arranged in a field-like grid.

3. The forming station according to claim 1, wherein the piston-cylinder units are adjustable individually or in groups or uniformly.

4. The forming station according to claim 1, wherein the distribution plate is guided on guide pins.

5. A method for hot forming a blank made of metal, in particular aluminum, in the forming station according to claim 1, the method comprising: moving the ram together with the first hotplate and the first die part via the hydraulic adjusting device from an open starting position (top dead center) in a direction of the blank to be formed and the blank to be heated, wherein the first die part comes into contact with the blank to be formed at a time t1; and forming the blank to be formed by adjusting the ram and the first die part until an end position (bottom dead center) is reached, wherein the second hotplate via the hydraulic clamping device is clamped against the first hotplate at a time t2 with the blank to be heated interposed, wherein the time t2 is later by a time interval Δt than time t1, wherein 0.01 s ≤ Δt ≤ 1.0 s.

6. The method according to claim 5, wherein the second hotplate is clamped via the hydraulic clamping device against the first hotplate only when or after reaching the end position (bottom dead center) with the blank to be heated interposed.