EP2712688B1 - Die cushion drive and method for operating a die cushion drive - Google Patents

Description

The invention relates to a die cushion drive. according to the features of the preamble of claim 1. Such a die cushion drive is for example in the EP-A-1882534 disclosed.

The invention also relates to a method for operating such a draw cushion drive. A movable die cushion can be provided in a hydraulic press. The movement of the drawing cushion is achieved by means of a drawing cushion drive. In hydraulic presses, the pressure in the hydraulic medium is generated in particular by means of a pump that can be driven by an electric motor.

EP 1 882 534 A1 describes a hydraulic die cushion device for a press.

EP 0 417 752 A2 describes a hydraulic or mechanical press, with four piston-cylinder units performing hydraulic clamping of the blank holder during the drawing process.

EP 1 138 406 A2 further describes a die cushion press wherein the force and position of the die cushion is controlled.

EP 1 844 871 A2 discloses a die cushion press wherein the pressure is controllable by a lower die.

It is an object of the invention to specify an effective die-cushion drive or to specify an effective method for operating a die-cushion drive.

The object is achieved in a draw cushion drive with the features according to claim 1 or in a method for operating a draw cushion drive according to claim 3. Further embodiments of the claimed device and the claimed method result from claims 2 and 4 to 9, respectively.

In the case of a hydraulic drawing cushion, a defined, controlled counterforce is applied in the forming area. This is done, for example, by means of one or a plurality of hydraulic cylinders, a plurality means at least two. The hydraulic fluid (in particular oil) displaced by a movement of a hydraulic cylinder in a chamber of the cylinder is e.g. drained into a tank.

When controlling the force exerted by the drawing cushion or when controlling the movement exerted by the drawing cushion, a high level of accuracy is advantageously required from a process engineering point of view. This means that sensors and / or controllers as well as actuators in particular have a sampling time of «1 ms in order to achieve a fast reaction of an actuator. Examples of sensors are: pressure sensor, Speed sensor, position sensor, etc. Examples of actuators are: hydraulic valve (in particular a proportional valve or a servo valve), a hydraulic pump (in particular a servo pump), an electrical machine (in particular a synchronous machine or an asynchronous machine).

In the case of pressure regulation only by means of hydraulic pumps, it is difficult to achieve rapid rise times, with hydraulic pressure accumulators being able to be used for supplying system pressure in one embodiment of the draw cushion drive, these being charged using pump technology.

In one embodiment of the draw cushion drive, hydraulic draw cushions use accumulator hydraulics and fast continuous valves. In doing so, however, it is difficult to regain energy from a movement of the drawing cushion. In one embodiment, however, a pneumatic pressure accumulator is filled, for example via a retreating hydraulic cylinder, with which an upward movement of the drawing cushion is then implemented. When an electrically driven die cushion is used, energy can be recovered by operating an electrical machine in generator mode.

In a further embodiment of the die cushion drive, a pump is used on each piston side of the hydraulic cylinder, which can be driven by means of electrical machines, the electrical machines being able to be operated as a generator to recover energy. A generator operation is then advantageously possible for each direction of movement of the hydraulic cylinder.

In one embodiment of a die cushion drive, it has a first pump, a first electrical machine for driving the first pump and a hydraulic cylinder or a plurality of hydraulic cylinders. The hydraulic cylinder or cylinders each have a first chamber and a second chamber for hydraulic fluid, the first pump being provided for feeding the first chamber or the first chambers of the hydraulic cylinders, the hydraulic cylinder or the hydraulic cylinders being mechanically connected to a drawing cushion. In order to enable energy recovery, the electric machine can be operated as a generator. If hydraulic fluid is pressed through the pump, the pump serves as a drive for the electrical machine, which generates electrical energy in generator mode and feeds it back into a power network and / or into a capacitor and / or into an intermediate circuit of a drive system.

In one embodiment of the die cushion drive, a pump (in particular a servo pump) supplies a plurality of first chambers (in particular upper chambers of the respective hydraulic cylinder) together. This reduces the number of electrical as well as mechanical components if a pump driven by an electrical machine is not to be provided for each first chamber of a multiplicity of hydraulic cylinders.

In one embodiment of the die cushion drive, there is a pressure sensor for measuring the hydraulic pressure in a first pressure line between the first pump and the hydraulic cylinder or the plurality of hydraulic cylinders. The pressure sensor serves as an aid to set a pressure in the first chamber of one of the hydraulic cylinders by means of the first pump. The sensor measures an actual value that can be used for pressure regulation or pressure control.

In addition to the first chamber, the hydraulic cylinder or hydraulic cylinders also each have a second chamber, the second chamber being in particular a lower chamber. One or a plurality of hydraulic cylinders is provided for each drawing cushion, with separate pressure sensors being provided for the second chambers in one embodiment. In particular, there is at least one pressure sensor each for a plurality of hydraulic cylinders with respect to the second chambers and / or a continuous hydraulic valve and / or a servo pump available. The servo pumps are each mechanically coupled to an electrical machine that can be operated as a motor or as a generator. The pressure sensors can also be attached to pressure lines which are directly connected to the respective second chamber of the cylinder in order to measure the pressure in the second chamber.

In one embodiment of the die cushion drive, a first hydraulic cylinder from the plurality of hydraulic cylinders is connected to its second chamber via a second pressure line with a second pump, a second hydraulic cylinder from the plurality of hydraulic cylinders having its second chamber connected to a third pump via a third pressure line is. In this way, each of the first chambers of the hydraulic cylinders can be fed via only one pump and the respective second chambers of these cylinders can be fed or emptied separately from one another via different pumps that are separate from one another. This enables flexible control of different hydraulic cylinders.

In one embodiment of the die cushion drive, the second pressure line is connected to a first valve and the third pressure line is connected to the second valve, in particular a first pressure sensor for measuring the pressure in the second pressure line and a second pressure sensor for measuring the pressure in the third pressure line is available. In addition to the pumps connected to the second chambers of the hydraulic cylinders, it is possible via the valves to discharge hydraulic fluid from the respective second chamber. The valves can be a proportional valve or a servo valve. The valves, like the electrical machines for driving the pumps (especially the servo pumps), are actuators for regulating the die cushion drive.

In one embodiment of the draw cushion drive, the valve is used as an actuator for a pilot control when hydraulic fluid is from the second chamber of the respective cylinder is discharged. The pumps assigned to the second chambers can be used as actuators for pressure regulation.

In order to be able to control the drawing cushion even better or to be able to operate the drawing cushion drive more energy-efficiently, the valve is used as an actuator for pressure control and the respective electrically driven pump, which is assigned to the second chamber of the respective cylinder, as an actuator for the pilot control . The valves have a fast response behavior and are therefore very well suited as actuators for fast control. Due to the coupling of the electric machine and pump, this actuator has a lower stiffness with regard to the regulation, so that it is advantageous not to use it for the pressure regulation but as an actuator for the pressure pilot control. This can also have the advantage that through the generator operation of the electrical machine, energy can be fed back into a power grid. Since a lower volume flow of hydraulic fluid is required as a manipulated variable for regulation by the valve, if this is compared with a valve that serves as an actuator for a pressure regulator, the result is that comparatively more hydraulic fluid is passed through the pump in a displacement phase can, which is directly coupled to the second chamber.

In one embodiment of the die cushion drive, the first electrical machine can be controlled by means of a first drive control, the second electrical machine being controllable by means of a second drive control, the third electrical machine being controllable by means of a third drive control, with a data bus connecting the drive controls to one another in terms of data. The pressure control of the drawing cushion with the valve is also advantageously integrated as a manipulated variable in a control device which also has the drive control or also a large number of the drive controls. By integrating the regulations the signal propagation times improve and a faster, improved regulation of the drawing cushion is established.

In a method for operating a die cushion drive, pressure regulation and precontrol are active during a controlled movement of the die cushion. A pump is used for pilot control, which is also referred to below as a second pump with reference to the following figure designation. The second pump is coupled to a second electrical machine. The electrical machine therefore drives the pump or is driven by it, in particular in generator operation. The electrical machine is advantageously operated as a generator during a period in which the pilot control is active. This period is, in particular, a period in which a ram of the press exerts a force on the drawing cushion and the ram and the drawing cushion move in the same direction. The first valve is used as an actuator of the pressure control. The valve is, for example, a proportional valve or a servo valve. The energy efficiency of the press can be increased by the generator operation of the electric machine of the pump, which is connected to the pressure line of the valve.

In one embodiment of the method for operating a draw cushion drive, a draw cushion drive is used which has one of the configurations already described. Further configurations of the die cushion drive are also described in the following description of the figures.

In one embodiment of the method, when the ram of the press hits the draw cushion, the pressure control is switched over. Switching takes place, for example, from position control or speed control to position control. Regulator types known from control engineering can be used to regulate position, speed or pressure.

In one embodiment of the method, the draw cushion is pre-accelerated before the ram strikes the draw cushion. This enables a reduction in disturbance variables for the regulation of the die cushion when the ram and die cushion meet.

In one embodiment of the method, a pilot control of the drawing cushion is carried out, so that the pilot control takes place by means of the second pump or in particular also by means of a third pump or further pump as the actuator for this pilot control. The second, third or further pumps are connected to chambers of hydraulic cylinders in such a way that hydraulic fluid is displaced from these chambers when pressed (displacement phase).

In one embodiment of the method, these chambers are also each connected to a valve. In a variation of the method, the valves are closed when the second and the third pump serve as a drive for the respective electrical machine operated as a generator. In a further variation, these valves are active as actuators (open or closed) and are used to regulate the pressure of the die cushion. In one embodiment of the method, relief is carried out at the end of the pulling area. This additionally improves the system behavior.

In one embodiment of the method for operating a die cushion drive, both pressure control and precontrol are active in a displacement phase, and in particular an evaluation factor for the precontrol can be changed. This evaluation factor can be changed (reduced or increased) before the regulation and / or during the regulation. This can be used to set what influence the pilot control has on the behavior of the drawing cushion.

In one embodiment of the method for operating a die cushion drive, the first pump is inactive in the displacement phase. The first pump is the pump, which is a multitude supplied with hydraulic fluid from similar chambers of different hydraulic cylinders. The first pump is advantageously connected to the second or third or further pump in such a way that hydraulic fluid can be exchanged. For example, hydraulic fluid from the valves or the second or third or further pump can press hydraulic fluid through the passive first pump. In this passive operating state, the first pump can serve as a drive for the first electrical machine connected to it, which can also be operated as a generator and can thus feed back electrical energy.

In one embodiment of the method for operating a draw cushion drive, the first pump is activated in a phase of an upward movement of the draw cushion. Both the first pump and all other pumps can advantageously be operated in four quadrants. This also applies accordingly to the electrical machines that are coupled to the pumps.

FIG 1

eine erste Phase eines Pressvorgangs einer Presse mit einem Ziehkissen;

FIG 2

eine zweite Phase eines Pressvorgangs einer Presse mit einem Ziehkissen;

FIG 3

eine dritte Phase eines Pressvorgangs einer Presse mit einem Ziehkissen.

FIG 4

einen Ziehkissenantrieb ohne Steuerventile;

FIG 5

einen Ziehkissenantrieb mit einem Drucktank;

FIG 6

einen Ziehkissenantrieb mit je zwei Pumpen pro Zylinder; und

FIG 7

einen Ziehkissenantrieb mit nur einer Gemeinschaftspumpe.

The invention is described below by way of example with reference to figures. It shows:

FIG 1

a first phase of a pressing process of a press with a die cushion;

FIG 2

a second phase of a pressing process of a press with a die cushion;

FIG 3

a third phase of a pressing process of a press with a drawing cushion.

FIG 4

a die cushion drive without control valves;

FIG 5

a die cushion drive with a pressure tank;

FIG 6

a die cushion drive with two pumps per cylinder; and

FIG 7

a die cushion drive with only one shared pump.

1. 1. Eine Abwärtsbewegung des Stößels und ggf. eine Vorbeschleunigung des Ziehkissens vor dem Auftreffpunkt;
2. 2. Eine Verdrängungsphase: Beim Auftreffen des Stößels auf das Ziehkissen wird in Druckregelung umgeschaltet und am Ende des Ziehbereichs wird gegebenenfalls entlastet;
3. 3. Eine Aufwärtsbewegung des Stößels und anheben des Ziehkissens in eine Ausgangsstellung.

A sequence of a pressing process of a press with a drawing cushion can be broken down into the following steps (phases):

1. 1. A downward movement of the ram and possibly a pre-acceleration of the die cushion before the point of impact;
2. 2. A displacement phase: When the ram hits the die cushion, pressure control is switched and, if necessary, the pressure is relieved at the end of the drawing area;
3. 3. An upward movement of the ram and lifting of the die cushion to a starting position.

In order to better describe these steps, the following is an example of the Figures 1 to 3 referenced. It will Figure 1 used to describe the first step, Figure 2 to describe the second step and Figure 3 to describe the third step. In the description of the figures, the same reference symbols are used for elements of the same type.

The representation according to Figure 1 shows a schematic section of a press 40 with a ram 32 and a drawing cushion 2. The potential directions of movement 33 of the ram 32 and the potential directions of movement 34 of the drawing cushion 2 are shown by arrows. A drawing cushion drive 1 is provided for moving the drawing cushion 2. This drawing cushion drive 1 has the drawing cushion 2 and a first 3 and second 4 hydraulic cylinder 3, 4 connected to it. A drawing cushion can also be moved with a number of hydraulic cylinders of one or more than two, but this is not possible Figures 1 to 3 is not shown. The first hydraulic cylinder 3 has a first chamber 21 (upper chamber) and a second chamber 23 (lower chamber). The second hydraulic cylinder 4 also has a first chamber 22 (upper chamber) and a second chamber 24 (lower chamber). The first chambers 21 and 22 of the hydraulic cylinders 3 and 4 are fed or emptied via a first pressure line by means of a first pump 8. The second chamber 23 of the hydraulic cylinder 3 is fed or emptied via a second pressure line 26 by means of a second pump 9. The second chamber 24 of the hydraulic cylinder 4 is fed or emptied via a third pressure line 27 by means of a third pump 10. The first pump 8 is coupled to a first electrical machine 5. The second pump 9 is coupled to a second electrical machine 9. The third pump 10 is coupled to a third electrical machine 7. The electrical machines 5, 6 and 7 can be operated as a motor or generator, with drive controllers 28, 29 and 30 being provided for regulating the electrical machines 5, 6, 7. Although not every part of a drive is shown, for example the converter itself is not shown, it can be seen that a first drive control 28 controls the first electrical machine 5, that a second drive control 29 controls the second electrical machine and that a third drive control 30 controls the third electrical machine regulates. The drive controls 28, 29 and 30 are connected to one another in terms of data technology via a data bus 31. A higher-level drawing cushion control 35 is also connected to the data bus. Valves 15 and 16, for example, can also be controlled by means of the higher-level drawing cushion control 35. In one embodiment of the die cushion drive 1, various regulators can also be integrated into one regulating device, although this is not shown. The valves 15 and 16 can be divided into a first valve 15 and a second valve 16. The first valve 15 is connected to the second pressure line. The second valve 16 is connected to the third pressure line 27. The first, second and third pumps 8, 9 and 10 as well as the first and second valves 15 and 16 are connected to one another via a collecting line 36. The collecting line 36 can be emptied into a tank 20 or can receive hydraulic fluid from the tank. To measure hydraulic pressures, a first pressure sensor 11 is provided for the second pressure line 26, a second pressure sensor 12 is provided for the third pressure line 27 and a third pressure sensor 13 is provided for the first pressure line. The pressure sensors 11, 12 and 13 detect in particular for a Pressure control actual pressure values. The data connection of the pressure sensors 11, 12 and 13 to the pressure control is not shown in the figures in order to maintain clarity.

In the Figures 1 to 3 The directions of movement 14 of the die cushion 2 and the direction of flow 17, 18 and 19 of the hydraulic fluid are shown by arrows.

The Figure 1 is intended to represent a first phase of a pressing process, it being possible for the first phase to be preceded by further phases, not shown. In one embodiment of the die cushion drive 1, a common servo pump 8 (first pump) can provide the oil supply (oil is a hydraulic fluid) to all the die cushion cylinders (first hydraulic cylinder 3 and second hydraulic cylinder 4) in the first phase (downward movement), with a pilot control for the die cushion cylinder 3 and 4 via individual pumps (second pump 9 and third pump 10) per cylinder 3 and 4 is controlled. The first and second valves 15 and 16, which are particularly required as hydraulic valves in the second phase, are advantageous here; closed in this first phase. In the second phase (displacement phase), which is closer to the Figure 2 is described, the pressure control via the hydraulic valves 15 and 16 is started with the impact of the plunger 32 on the die cushion 2 (between the ram and the die cushion is the part not shown to be pressed) and on the other hand, the movement is started via the respective servo pump 9 and 10 of the die cushion.

The representation according to Figure 2 shows how Figure 1 a die cushion drive 1, the plunger 32 resting on the die cushion 2. A material to be pressed in between is not shown. With the Figure 2 phase two is shown in which the pressure control of the drawing cushion 2 has been switched over. If the second pump 9 and the third pump 10 are now used as actuators for a pilot control and the first valve 15 and the second valve 16 are used as When actuators are used for pressure control, this combination has the advantage of rapid control via valves and, in addition, the ability to feed back pumps with servomotors in particular (second electrical machine 6 and third electrical machine 7). In one embodiment, the pressure control can also advantageously be used for pilot control via the servo pumps 9 and 10. A common servo pump 8 (first pump) can also be switched off or a common system pressure can be built up with it.

In the representation after Figure 3 a third phase, an upward movement of the drawing cushion 2, is shown, with the plunger no longer being shown in FIG. The upward movement is illustrated by arrow 14. The upward movement is controlled or regulated via the respective servo pump (second and third pump 9 and 10) of the die cushion cylinder (s) 3 and 4. For better movement control, a counter pressure can be built up via the common system pressure pump (first pump 8). The directions of flow 17, 18 and 19 for the hydraulic fluid are reversed compared to steps 1 and 2, as is also the case in FIG Figure 3 is shown.

By combining the servo pump and hydraulic valve in the displacement phase, rapid pressure control can be achieved via the valve and the main oil flow (this is the hydraulic fluid) can be fed back as a generator via the servo pump. If the valve and pump would both regulate the pressure regulation in the displacement phase, they may work against each other. To avoid this, the main oil flow is e.g. Dissipated via pumps two and three and regenerative energy is fed back through the pressure. Fast response times in the control can be achieved via the valves 15 and 16.

The figures described below focus on the hydraulic concept of the die cushion drive.

In the embodiments according to Figures 4 to 6 it is not part of the invention. The examples serve to explain alternative embodiments.

The representation according to Figure 4 shows a variation of the die cushion drive 1, wherein in the illustrated variation the die cushion drive 1 only provides the pumps 9 and 10 for the second chambers 23 and 24 of the hydraulic cylinders 3 and 4 and no valves, as in FIG Figures 1 to 3 shown. This configuration without control valves has the advantage that fewer mechanics are used, which can fail. By using the pumps 9 and 10, which can be driven by the electrical machines 6 and 7, pressure regulation and precontrol can also be carried out. The pumps 9 and 10 serve as actuators for the pilot control and for the pressure regulation. The electrical machines 6 and 7 can continue to be operated as a generator if the second chambers 23 and 24 are made smaller, the pump 8 advantageously being used as an actuator for pressure control.

The representation according to Figure 5 shows a die cushion drive 1, the first chambers 21 and 22 being supplied with hydraulic fluid via a pressure tank 47. The pressure tank 47 forms a type of battery pump. This differs from the one in Figure 4 shown. This also allows complex mechanics to be reduced, which increases the reliability.

The representation according to Figure 6 shows a die cushion drive 1 in which the first chambers 21 and 22 of the hydraulic cylinders 3 and 4 are operated by separate pumps 8 and 42. The first chamber 21 of the hydraulic cylinder 3 is connected to the first pump 8 via a fourth pressure line 43, the pressure in the pressure line 43 via a fourth Pressure sensor 45 is measurable. The first chamber 22 of the hydraulic cylinder 4 is connected to the fourth pump 42 via a fifth pressure line 44, the pressure in the pressure line 44 being measurable via a fifth pressure sensor 45. The
Using 4 pumps, two for each cylinder, has the advantage that hydraulic cylinders 3 and 4 are more independent from each other are adjustable. Each hydraulic cylinder 3, 4 has an additional actuator for pressure regulation and / or pilot control, which does not directly influence the behavior of other cylinders, as is the case with a jointly used pump for the first chambers Figure 4 the case is. The pump 42 is connected to the electrical machine 41. Since two pumps are assigned to each cylinder and thus also two electrical machines, at least one of the electrical machines per cylinder can be operated as a generator if the other is operated as a motor. Both electrical machines can also be operated with motors, which may help improve the control quality in pressure regulation.

The representation according to Figure 7 shows a further variation of a die cushion drive 1. In the system shown, the first pump 8 is used to build up hydraulic pressure for the entire hydraulic system. The first hydraulic cylinder 3 is connected with the first and second chambers 21, 23 to a first 3/4-way valve 48. The connection is made via the second pressure line 26 and the fourth pressure line 43. The first pressure sensor 11 is used to measure the pressure in the second chamber 23. The fourth pressure sensor 45 is used to measure the pressure in the first chamber 21. The second hydraulic cylinder 4 is connected to the first and second Chamber 22, 24 connected to a second 3/4-way valve 49. The connection is made via the third pressure line 27 and the fifth pressure line 44. The second pressure sensor 12 is used to measure the pressure in the second chamber 24. The fifth pressure sensor 46 is used to measure the pressure in the first chamber 22. There is only one pump 8 that is connected to the electric machine 5 is coupled, wherein the electric machine 5 can be operated as a motor as well as a generator.

Claims (9)

1. Die cushion drive (1) having a first pump (8), a first electrical machine (5) for driving the first pump (8) and a plurality of hydraulic cylinders (3, 4), wherein the hydraulic cylinders (3, 4) have a first chamber (21, 22) and a second chamber (23, 24), wherein the first pump (8) is provided for supplying the first chambers (21, 22) of the hydraulic cylinders (3, 4), wherein the hydraulic cylinders (3, 4) are mechanically connected to a die cushion (2),
   wherein a first hydraulic cylinder (3) of the plurality of hydraulic cylinders (3, 4) is connected with its second chamber (23) via a second pressure line (26) to a second pump (9), wherein a second hydraulic cylinder (4) of the plurality of hydraulic cylinders (3, 4) is connected with its second chamber (24) via a third pressure line (27) to a third pump (10),
   wherein the second pump (9) and the third pump (10) are each embodied as servo pumps, wherein the servo pumps are each mechanically coupled to an electrical machine which can be operated both as a motor and also as a generator,
   wherein the second pressure line (26) is connected to a first valve (15) and wherein the third pressure line (27) is connected to the second valve (16), wherein a first pressure sensor (11) for measuring the pressure in the second pressure line (26) and a second pressure sensor (12) for measuring the pressure in the third pressure line (27) is present,
   wherein the die cushion drive (1) comprises a die cushion regulator (35), which during operation is embodied to regulate the pressure of the die cushion (2) and to preliminarily control the movement of the die cushion (2),
   characterised in that a third pressure sensor (13) for measuring the hydraulic pressure is present in a first pressure line (25) between the first pump (8) and the hydraulic cylinders (3, 4), that during operation the measurement of the first (11), second (12) and third pressure sensor (13) is used by the die cushion regulator (35) for pressure regulation of the die cushion (2), that the respective valve (15, 16) and the respective servo pump (9, 10) are linked to the die cushion regulator (35) in such a way that the respective valve (15, 16) is an adjustment element for the pressure regulation and the respective servo pump (9, 10), which is assigned to the second chamber of the respective cylinder, is an adjustment element for the preliminary control.
2. Die cushion drive (1) according to claim 1, wherein the first electrical machine (5) is able to be regulated by means of the first drive regulator (28), wherein the second electrical machine (6) is able to be regulated by means of a second drive regulator (29), wherein the third electrical machine (7) is able to be regulated by means of the third drive regulator (30), wherein a data bus (31) connects the drive regulators (28, 29, 30) for data transmission.
3. Method for operating a die cushion drive (1) according to claim 1 or 2, wherein during a controlled movement of the die cushion (2) a pressure regulation and a preliminary control are active, wherein the second pump (9) and the third pump (10) are used for preliminary control, wherein the second pump (9) is coupled to a second electrical machine (6) and the third pump is coupled to a third electrical machine (7), wherein during the preliminary control the electrical machines (6, 7) are operated as generators, wherein the respective valve (15, 16) is used as an adjustment element of the pressure regulation.
4. Method according to claim 3, wherein a die cushion drive (1) according to one of claims 1 or 2 is used, wherein a switchover to pressure regulation is undertaken when a plunger (32) strikes the die cushion (2).
5. Method according to claim 3 or 4, wherein the die cushion (2) is pre-accelerated before the plunger (32) strikes the die cushion (2).
6. Method according to claim 3, wherein a strain relief is carried out at the end of the press area.
7. Method according to one of claims 3 to 6, wherein pressure regulation and preliminary control are both active in an expulsion phase, wherein especially an evaluation factor for the preliminary control is able to be changed.
8. Method according to one of claims 3 to 7, wherein the first pump is inactive in the expulsion phase.
9. Method according to one of claims 3 to 8, wherein in a phase of an upwards movement of the die cushion (2) the first pump (8) is active.

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