HYDRAULIC FORMING MACHINE FOR PRESSING WORKPIECES, IN PARTICULAR FORGING HAMMER, AND METHOD FOR OPERATING A HYDRAULIC FORMING MACHINE, IN PARTICULAR A FORGING HAMMER

Abstract

The underlying invention relates particularly to a hydraulic forming machine, more particularly a forging hammer, for workpiece forming, comprising a hydraulic cylinder for driving a ram configured for workpiece forming, and a hydraulic circuit configured for operation of the hydraulic cylinder, wherein the hydraulic circuit has an actuator with an adjustably variable volume flow via which a first hydraulic working chamber of the hydraulic cylinder, used to accelerate the ram during the execution of a working stroke (A) for workpiece forming, can be provided with hydraulic fluid. The hydraulic circuit is configured to adjust and vary the volume flow of the valve or actuator, depending on a setpoint speed (Vsoll) of the ram to be achieved in an acceleration phase of a working stroke (A), and to optimize the subsequent movement phase.

Claims

1-15. (canceled)

16. A hydraulic forming machine, in particular a forging hammer, for workpiece forming, comprising: a hydraulic cylinder for driving a ram configured for workpiece forming, and a hydraulic circuit configured for operation of the hydraulic cylinder, wherein the hydraulic circuit has a valve with an adjustably variable volume flow, via which valve a first hydraulic working chamber of the hydraulic cylinder, used to accelerate the ram during the execution of a working stroke (A) for workpiece forming, can be provided with hydraulic fluid, wherein: the hydraulic circuit is configured to adjust and vary the volume flow of the valve depending on a setpoint speed (Vsoll) of the ram to be achieved in an acceleration phase of a working stroke (A), and the hydraulic circuit comprises a suction valve connecting the first hydraulic working chamber to a reservoir for hydraulic fluid, which suction valve is configured to fill the first hydraulic working chamber with hydraulic fluid from the reservoir in a movement phase which follows the acceleration phase and in which the setpoint speed (Vsoll) is substantially maintained.

17. The hydraulic forming machine according to claim 16, wherein: the valve is designed as a controllable valve, and the valve preferably comprises a directional continuous valve, a directional proportional valve, a directional servo valve and/or a directional control valve.

18. A hydraulic forming machine, in particular forging hammer, for workpiece forming, comprising: a hydraulic cylinder for driving a ram configured for workpiece forming, which ram is mechanically coupled to the hydraulic cylinder, and a hydraulic circuit configured to operate the hydraulic cylinder and having an actuator for setting a volume flow of hydraulic fluid for filling a first hydraulic working chamber of the hydraulic cylinder during the execution of a working stroke (A) immediately preceding the workpiece forming, with an acceleration phase for accelerating the ram to a setpoint speed (Vsoll), and a movement phase which follows the acceleration phase and in which the setpoint speed (Vsoll) is substantially maintained, wherein the hydraulic circuit and the actuator are configured to: adjust and vary the volume flow in the acceleration phase as a function of the setpoint speed (Vsoll) such that the setpoint speed (Vsoll) is reached, and reduce the volume flow in the subsequent movement phase to a post-flow volume flow, in such a way that the hydraulic pressure prevailing in the movement phase in the first hydraulic working chamber is substantially above the cavitation pressure of the hydraulic fluid.

19. The hydraulic forming machine according to claim 18, wherein: the actuator comprises an open-loop or closed-loop control valve and/or an open-loop or closed-loop control pump, the valve is preferably a directional continuous valve, a directional proportional valve, a directional servo valve and/or a directional control valve, and the pump preferably comprises a servo pump.

20. Hydraulic forming machine according to claim 18, further comprising: at least one pressure sensor is configured to measure the hydraulic pressure prevailing in the first and/or second hydraulic working chamber during the working stroke and/or return stroke, and the hydraulic circuit or the actuating unit, in particular a control unit, is configured to adjust and vary, in particular to regulate, the volume flow during a working cycle of the ram, but at least in the movement phase, as a function of the measured hydraulic pressure.

21. The hydraulic forming machine according to claim 18, wherein, at least one of: the hydraulic circuit, in particular an actuating unit or control unit, is configured to adjust and vary the volume flow in such a way that the hydraulic pressure in the first hydraulic working chamber in the movement phase corresponds to a predefined or predefinable pressure or is within a predefined or predefinable pressure range, wherein the predefined or predefinable pressure or pressure range is preferably between 2 and 6 bar, more preferably between 3 and 4 bar; the volume flow in the acceleration phase is adjusted in such a way that the movement phase corresponds to a range of 10% to 30%, in particular 10% to 20%, of the stroke of the hydraulic cylinder; and/or the volume flow in the acceleration phase is adjusted or varied in such a way that the length of the acceleration phase and accordingly the length of the movement phase and/or their ratio is set as a function of the setpoint speed (Vsoll) to be achieved in each case.

22. The hydraulic forming machine according to claim 18, wherein: the hydraulic circuit, in particular a control unit, is configured to adjust and vary the volume flow as a function of the setpoint speed (Vsoll) to be respectively achieved, preferably, the hydraulic circuit, in particular the control unit, is configured to dynamically adjust the volume flow based on a table of values for setpoint speeds and/or based on measured location and/or speed data (X or V) of the ram, and the forming machine further preferably comprises at least one sensor unit for measuring and/or storing location and/or speed data of the ram.

23. The hydraulic forming machine according to claim 18, wherein the hydraulic circuit is configured to: close the valve or the actuator at least temporarily substantially completely in the movement phase following the acceleration phase, and/or adjust and vary the volume flow, in particular to regulate it, in such a way that the acceleration phase is maximized while at the same time the movement phase is minimized, and/or, for a working stroke for accelerating the ram, starting from a reversal point located in the movement profile of the ram with zero ram speed and towards the setpoint speed (Vsoll), use only part of the total stroke of the hydraulic cylinder.

24. A method for operating a hydraulic forming machine for workpiece forming, wherein: in a working stroke (A) executed for the workpiece forming, a ram provided for the workpiece forming is accelerated in an acceleration phase by a hydraulic cylinder coupled to it, in the working stroke (A), a first hydraulic working chamber of the hydraulic cylinder is fed with hydraulic fluid via a valve with an adjustably variable volume flow through a hydraulic circuit, the hydraulic circuit, in the acceleration phase, adjusts and varies the volume flow of a valve as a function of a setpoint speed (Vsoll) of the ram to be achieved in the acceleration phase, and the first hydraulic working chamber, in a movement or braking phase which follows the acceleration phase and in which the setpoint speed (Vsoll) is substantially maintained, is filled by a suction valve which is present in the hydraulic circuit and which connects the first hydraulic working chamber to a reservoir for hydraulic fluid.

25. The method according to claim 24, wherein: the valve is designed as an open-loop or closed-loop control valve and preferably comprises a directional continuous valve, a directional proportional valve, a directional servo valve and/or a directional control valve, and the volume flow is adjusted and varied by means of the hydraulic circuit regulating the valve.

26. A method for operating a hydraulic forming machine for workpiece forming, wherein: in a working stroke (A) executed for the workpiece forming, a ram provided for the workpiece forming is accelerated in an acceleration phase by a hydraulic cylinder mechanically coupled to it, in the working stroke, a first hydraulic working chamber of the hydraulic cylinder is fed with hydraulic fluid via an actuator with an adjustably variable volume flow through a hydraulic circuit, and the hydraulic circuit: (i) in the acceleration phase, adjusts and varies the volume flow through the actuator as a function of the setpoint speed (Vsoll) in such a way that the setpoint speed (Vsoll) is reached, and (ii) in a movement phase which directly follows the acceleration phase and in which the setpoint speed (Vsoll) is substantially maintained, reduces the volume flow to a post-flow volume flow, in particular regulates it, such that the hydraulic pressure prevailing in the movement phase in the first hydraulic working chamber is substantially above the cavitation pressure of the hydraulic fluid.

27. The method according to claim 26, wherein the actuator is designed as a controllable valve and/or a controllable pump, wherein the valve preferably comprises a directional continuous valve, a directional proportional valve, a directional servo valve and/or a directional control valve, and wherein the pump preferably comprises a servo pump, and wherein in the method the volume flow of the actuator is regulated as a function of the setpoint speed (Vsoll), and/or the volume flow is dynamically adjusted and changed, in particular regulated, based on a hydraulic pressure measured in the first and/or second hydraulic working chamber (9, 10) by means of a pressure sensor (15, 18, 22), wherein, optionally, the volume flow is adjusted and varied in such a way that the hydraulic pressure in the first hydraulic working chamber in the movement phase, which is a braking phase, corresponds to a predefined or predefinable pressure or is within a predefined pressure range, wherein the predefined pressure or pressure range is between 2 and 6 bar, preferably between 3 and 4 bar.

28. The method according to claim 26, wherein: the volume flow is adjusted and varied, in particular regulated, as a function of the setpoint speed (Vsoll) to be achieved in each case, the volume flow is adjusted, in particular dynamically adjusted, preferably based on a table of values for setpoint speeds and/or based on measured location and/or speed data of the ram, and further preferably, location and/or speed data (X or V) of the ram are measured by at least one sensor unit and/or stored and used when setting the volume flow.

29. The method according to claim 28, wherein: the valve is substantially completely closed at least temporarily in the movement phase, which follows the acceleration, phase, and in the movement phase, hydraulic fluid is supplied to the first hydraulic working chamber substantially completely via the suction valve.

30. The method according to claim 26, wherein: the volume flow is adjusted and varied, in particular regulated, in such a way that the duration of the acceleration phase is maximized while at the same time the duration of the movement phase is minimized, optionally, the duration of the movement phase is 10% of the duration of the acceleration phase, and/or for a working stroke for accelerating the ram, starting from a reversal point located in the movement profile of the ram with zero ram speed and as far as the setpoint speed (Vsoll), only a part of the total stroke of the hydraulic cylinder is used, and wherein a subsequent return stroke is preferably correspondingly shortened.

31. The hydraulic forming machine according to claim 26, wherein: the hydraulic circuit, in particular a control unit, is configured to adjust and vary the volume flow as a function of the setpoint speed (Vsoll) to be respectively achieved, preferably, the hydraulic circuit, in particular the control unit, is configured to dynamically adjust the volume flow based on a table of values for setpoint speeds and/or based on measured location and/or speed data (X or V) of the ram, and the forming machine further preferably comprises at least one sensor unit for measuring and/or storing location and/or speed data of the ram.

32. The hydraulic forming machine according to claim 26, wherein the hydraulic circuit is configured to: close the valve or the actuator at least temporarily substantially completely in the movement phase following the acceleration phase, and/or adjust and vary the volume flow, in particular to regulate it, in such a way that the acceleration phase is maximized while at the same time the movement phase is minimized, and/or, for a working stroke for accelerating the ram, starting from a reversal point located in the movement profile of the ram with zero ram speed and towards the setpoint speed (Vsoll), use only part of the total stroke of the hydraulic cylinder.

33. The method according to claim 26, wherein: the volume flow is adjusted and varied, in particular regulated, as a function of the setpoint speed (Vsoll) to be achieved in each case, the volume flow is adjusted, in particular dynamically adjusted, preferably based on a table of values for setpoint speeds and/or based on measured location and/or speed data of the ram, and further preferably, location and/or speed data (X or V) of the ram are measured by at least one sensor unit and/or stored and used when setting the volume flow.

34. The method according to claim 26, wherein: the volume flow is adjusted and varied, in particular regulated, in such a way that the duration of the acceleration phase is maximized while at the same time the duration of the movement phase is minimized, optionally, the duration of the movement phase is 10% of the duration of the acceleration phase, and/or for a working stroke for accelerating the ram, starting from a reversal point located in the movement profile of the ram with zero ram speed and as far as the setpoint speed (Vsoll), only a part of the total stroke of the hydraulic cylinder is used, and wherein a subsequent return stroke is preferably correspondingly shortened.

Description

[0070] Exemplary embodiments of the invention are described in more detail below with reference to the drawing. In the drawing:

[0071] FIG. 1 shows schematically an example of the structure of a first embodiment of a forging hammer;

[0072] FIG. 2 shows schematically an example of a voltage applied to a directional control valve of the forging hammer used as an impact valve of the first embodiment, as a function of time for a work cycle;

[0073] FIG. 3 shows an opening diagram of a return valve in the operation of the forging hammer of the first embodiment;

[0074] FIG. 4 shows schematically an example of the structure of a second embodiment of a forging hammer;

[0075] FIG. 5 shows schematically an example of a voltage applied to a directional control valve of the forging hammer used as an impact valve of the second embodiment, as a function of time for a work cycle;

[0076] FIG. 6 shows schematically an example of a position and speed diagram of a ram during a working cycle.

[0077] FIG. 1 shows schematically an example of the structure of a hydraulically operated forging hammer 1 of a first exemplary embodiment. The forging hammer 1 is an example of a forming machine.

[0078] The forging hammer 1 comprises a ram 2 with a tool 3 attached thereto for forming a workpiece (not shown).

[0079] The ram 2 is coupled to a hydraulic cylinder 4. More precisely, the ram is mechanically coupled via a piston rod 5 to a piston 7 that is movable in a cylinder tube 6.

[0080] The hydraulic cylinder 4 is controlled via a hydraulic circuit 8. A first working chamber 9 of the hydraulic cylinder 4 and a second working chamber 10 are connected to the hydraulic circuit 8 via hydraulic lines. A pressing surface of the piston 7, also called the piston surface, faces the first working chamber 9, and a retraction surface of the piston 7, also called the annular surface, which faces away from the pressing surface, faces the second working chamber 10.

[0081] The hydraulic circuit 8 comprises a pump unit 11 with a motor-driven pump and control valves, the pump unit 11 being configured to generate a predefined system pressure.

[0082] Downstream of the pump unit 11 is a control valve or directional control valve 12 with a safety stage, which separates the pump unit 11, the second working chamber 10 and the storage unit 19 from the first working chamber 9 in a first directional switching position, and connects the first working chamber 9 to the pump unit 11, the second working chamber 10 and the storage unit 19 in a second directional switching position. The directional control valve 12 forms an impact valve for regulating a working stroke or a forging impact.

[0083] A brake valve 14 and a first pressure sensor 15 are provided between the directional control valve 12 and the first working chamber 9. The directional control valve 12, the brake valve 14, and the first pressure sensor 15 are connected to the first working chamber 9 via a first connection 16 present at an upper end of the cylinder tube 6.

[0084] The pump unit 11 is connected to a second connection 17 provided at a lower end of the cylinder tube 6. A second pressure sensor 18, a pressure repository 19 and a safety valve 20 are attached to the hydraulic line running between the pump unit 11 and the second connection 17.

[0085] A third connection 21 on the cylinder 6, located between the first connection 16 and the second connection 17, leads to a valve 27 which may selectively block the line leading to the third connection or switch it to a hydraulic tank 13. The line further comprises a third pressure sensor 22 and a throttle 28, by means of which a connection from the first connection 16 to the valve 27 is realized. The third connection 21 is closer to the first connection 16, for example in an upper third of the cylinder tube 6 that comprises the first connection 16.

[0086] The hydraulic circuit 8 further comprises a regulating unit 23, which is connected via data, control and regulation lines (not shown) to the components of the forging hammer 1 that are to be regulated or controlled, for example the pump unit 11, the directional control valve 12, the pressure sensors 15, 18, 22 and a path measuring unit 24. The path measuring unit 24 is configured to detect the position or the path travelled by the ram 2 and/or to determine the speed of the ram 2, e.g. from a path measurement.

[0087] The first working chamber 9 is connected to a reservoir 26 via a suction valve 25 at a connection present at an upper end of the cylinder tube 6.

[0088] In the case of the forging hammer 1 according to FIG. 1, the regulating unit 23, in particular the hydraulic circuit 8, is configured to adjust the impact energy generated by the kinetic energy of the ram 2 for forming a workpiece, in particular to adjust a setpoint speed corresponding to the impact energy, as will be described in more detail below.

[0089] Starting from the situation shown in FIG. 1, in which the ram 2 and correspondingly the piston 7 are in an upper reversal point, the ram 2 and tool 3 are accelerated by means of the first working chamber 9 being pressurized with hydraulic fluid, in particular hydraulic oil, via the directional control valve 12. Accordingly, the first working chamber 9 fills, as a result of which the piston 7 and correspondingly the ram 2 in a working stroke A move downwards, i.e. onto the workpiece that is to be formed. When the first working chamber 9 is pressurized, the ram 2 coupled to the piston 7 is accelerated.

[0090] The hydraulic circuit 8 is configured in such a way that the ram 2 is accelerated to a predefined or predefinable setpoint speed, corresponding to a predefined or predefinable impact energy.

[0091] When the piston 7 reaches the lower reversal point located in the region of the second connection 17, forming of a workpiece takes place at the forming point, with the ram 2 transferring the impact energy resulting from the setpoint speed to the workpiece.

[0092] The forming of the workpiece is followed by a return stroke R. The hydraulic pressure that is constantly present in the second work chamber 10 has an accelerating effect on the piston 7 and, accordingly, on the ram 2 in the return stroke direction. During the return stroke, the fluid present in the first hydraulic chamber 9 may flow via the third connection 21 to the valve 27. At least during the return stroke, this opens the way to the hydraulic tank 13, so that the hydraulic fluid may flow off there.

[0093] If the piston 7 passes over or closes the third connection 21 at the end of the return stroke phase or in the upper third of the cylinder 6, the hydraulic fluid flows from the first connection 16 via the throttle 28 to the valve 27 until the piston 7 and accordingly the ram 2 with tool 3 finally stop, which valve 27 is still switched to the hydraulic tank 13. The directional control valve 12 is completely or at least substantially closed during the entire return stroke phase.

[0094] Working stroke A and return stroke R form a working cycle of the forging hammer 1 that may be run through repeatedly.

[0095] The regulation or control of the working stroke A and return stroke R is described in more detail below.

[0096] The directional control valve 12 represents an example of a valve with an adjustably variable volume flow. Depending on which voltage or current, in particular which control or regulation signals, are applied to the directional control valve 12, the latter may be opened and closed steplessly. In particular, the directional control valve 12 may be opened and closed in a specific manner, for example in the form of a ramp, by corresponding regulation or control signals which are determined or generated by the regulation unit 23. Furthermore, the regulation unit 23 and the directional control valve 12 are configured, by way of a non-limiting example, with a cam controller, such that the opening time may be controlled for a predefined time, for example with an accuracy of 0.5 ms. Therefore, the volume flow of the directional control valve 12 may be adjusted and varied, with overall several manipulated variables being available for control of the directional control valve 12, i.e. the valve opening as such, and the opening time and the time profile of the valve opening.

[0097] The hydraulic circuit 8 and the regulation unit 23 are configured in such a way that the volume flow of the directional control valve 12 is controlled as a function of a setpoint speed of the ram 2 that is to be achieved in an acceleration phase of a working stroke A.

[0098] It should also be mentioned at this point that, in the illustrated embodiment of the forging hammer, the ram is moved up and down parallel to the direction of gravity S.

[0099] FIG. 2 shows in this connection an example of the voltage U applied to the directional control valve 12 as a function of the time t for a working cycle comprising working stroke A and return stroke R. Starting from the situation shown in FIG. 1 at the beginning of the working stroke at the first point in time t1, the directional control valve 12 is controlled with a first voltage U1. Hydraulic fluid is applied to the first working chamber 9 via the directional control valve 12 in accordance with the opening width of the directional control valve 12 corresponding to the first voltage U1, the system pressure being present at the input of the directional control valve 12. The ram 2 is accelerated by the hydraulic fluid entering the first working chamber 9 and by the force of gravity S acting on the ram 2. In the further course, the voltage U applied to the directional control valve 12 is increased according to a ramp up to a second voltage U2.

[0100] The initial first voltage U1, the ramp and the second voltage U2 are regulated or adjusted by the regulating unit 23 in such a way that the setpoint speed required or desired for the respective forming process, that is to say the desired impact energy, is reached at a second point in time t2. The voltages U1 and U2 and the ramp may, for example, be taken from a table of values for setpoint speeds or impact energies, in particular specifically for a predefined work cycle, or may be set accordingly.

[0101] Corresponding tables of values may be obtained, for example, by simulation and/or testing of the percussion hammer. In a simulation, for example, parameters such as the weight of ram 2 and of the components moved with ram 2 (e.g. piston rod 5, piston 7, tool 3), the technical data of the hydraulic cylinder 4 (e.g. total stroke, pressing surface) and the operating parameters of the hydraulic circuit 8 (e.g. system pressure, properties of the hydraulic fluid, temperature) may be used.

[0102] Besides a ramp, i.e. a linear function of time, other functions, in particular non-linear ones, may also be considered.

[0103] After the setpoint speed is reached at the time tS, the directional control valve 12 in the forging hammer 1, which in the embodiment according to FIG. 1 comprises the suction valve 25, is closed. At this point in time, hydraulic fluid may flow into the first cylinder chamber 9 via the suction valve 25. After the forming, the return strokes carried out as described above.

[0104] After the ram 2 has been braked at the upper reversal point, the regulating unit 23 may regulate the hydraulic circuit 8, in particular the directional control valve 12, for a subsequent work cycle, the work cycle being able to be executed in accordance with the movement, regulation, and control sequence described above.

[0105] FIG. 3 shows an opening diagram of the valve 27 (return stroke valve) during a working cycle (R, A) of the forging hammer 1. The valve 27 is closed during the working stroke A and is opened after the forming (time t2), as a result of which the first working chamber 9 is connected to the hydraulic tank 13. As a result, during the return stroke, the hydraulic fluid may flow out of the first working chamber 9 via the third connection 21 and, after the piston 7 has passed over the third connection 21, via the throttle 28 into the hydraulic tank 13.

[0106] FIG. 4 shows schematically an example of the structure of a second embodiment of a forging hammer 1. In FIG. 4, identical or functionally identical components and elements are designated with the same reference signs as in FIG. 1.

[0107] In contrast to the forging hammer 1 of the first embodiment, the forging hammer 1 of the second embodiment has no suction valve and accordingly also no suction tank. In the forging hammer 1 of the second embodiment, in order for hydraulic fluid to be able to flow into the first working chamber 9 in the braking phase after the setpoint speed has been reached, the regulating unit 23 is configured in such a way that it does not completely close the directional control valve 12 after the setpoint speed has been reached. The regulating unit 23 controls the directional control valve 12 in such a way that sufficient hydraulic fluid may flow in and the pressure prevailing in the first working chamber 9 remains above the cavitation pressure of the hydraulic fluid. As in the first embodiment, the braking action is achieved by the system pressure present in the annular space of the second working chamber 10.

[0108] In particular, the directional control valve 12 may be regulated in such a way that the pressure in the first working chamber 9 is considerably lower than the system pressure but is above the cavitation pressure. With such a control of the directional control valve 12 in the movement phase, essentially the same braking effect may be achieved as when using the suction valve 25, with the braking being effected, as has been mentioned, by the system pressure present in the annular space of the second working chamber 10. The volume flow of the directional control valve 12 may be regulated, for example, such that the pressure in the first working chamber 9 is between 2 and 6 bar, above the cavitation pressure of the hydraulic fluid.

[0109] The control of the directional control valve 12 in the movement phase in the second embodiment of the forging hammer according to FIG. 4 may take place, for example, on the basis of the pressure detected by the first and/or third pressure sensor 15, 22, respectively.

[0110] The use of the directional control valve 12 in the operating mode according to the second embodiment has the advantage over the operating mode of the first embodiment that directional control valves generally have shorter reaction times than suction valves, and therefore cavitation may be avoided with higher certainty. Particularly in the transition phase from the acceleration phase to the movement phase of the working stroke, the short reaction times of directional control valves offer an advantage over suction valves, which react comparatively slowly. However, it is particularly advantageous against formation of cavitation that the directional control valve 12 may be continuously adjusted from the acceleration volume flow to the post-flow volume flow, e.g. according to a linear or non-linear other function, without having to be completely closed in the meantime. Accordingly, the hydraulic fluid flow cannot be interrupted, and cavitation is substantially or completely avoided.

[0111] FIG. 5 shows, by way of example and schematically, a voltage applied to the impact valve 12 of the second embodiment of the forging hammer 1 as a function of the time for a working stroke A. As can be seen from FIG. 5, the directional control valve 12 may be controlled analogously to the first embodiment in the acceleration phase of the working stroke A until the setpoint speed is reached at the time tS. However, in the operating mode according to the second embodiment, the directional control valve 12 is not completely closed when the setpoint speed is reached, but instead is controlled, for example according to a linear function, in such a way that hydraulic fluid may continue to flow into the first working chamber 9. As has already been mentioned, the control is configured in such a way that the pressure in the first hydraulic chamber 9 is above the cavitation pressure of the hydraulic fluid. Since the directional control valve 12 is not completely closed after the setpoint speed has been reached in the braking phase of the working stroke A, it is also possible to prevent the hydraulic fluid flows from stalling.

[0112] FIG. 6 shows a position and speed diagram of the ram 2 during a working cycle of the forging hammer of the first and second embodiments. More specifically, FIG. 6 shows the profile of the position X of the ram 2 and the speed V of the ram 2 as a function of the time t. The first to third times t1 to t3 correspond to those of FIGS. 2, 3 and 5.

[0113] From the first time t1, the ram 2 is accelerated by appropriate control of the volume flow of the directional control valve 12, the control in the present example being such that the speed V increases linearly until the setpoint speed Vsoll is reached. With the proposed invention, however, other speed-time curves, i.e. not just linear curves, may also be implemented.

[0114] Once the setpoint speed Vsoll has been reached, the hydraulic circuit 8 is controlled according to one of the operating modes described above, the movement phase of the working stroke A, in which the ram 2 moves at a substantially constant setpoint speed Vsoll, is not shown resolved over time in FIG. 6.

[0115] In the present example, the control in the movement phase (braking phase) takes place in such a way that the setpoint speed Vsoll is reached just shortly before the forming point, such the suction phase in the operating mode of the first embodiment or the post-flow phase in the operating mode of the second embodiment is advantageously shortened.

[0116] The position X of the ram 2 changes corresponding to the linear speed change according to a parabolic function from the initial position 0 over the stroke H executed in the work cycle.

[0117] During the forming process, at the second time t2, the ram 2 is decelerated and moves back to the starting position 0 on account of the rebound energy and the above-described return stroke control via the hydraulic circuit 8.

[0118] For the return stroke, the hydraulic circuit 8 is regulated as described above, with the ram 2 in the present example experiencing a linear change in speed V during the return stroke. At the top reversal point at the third time t3, the ram 2 has zero speed.

[0119] Since the retraction surface of the piston 7 is an annular surface and is therefore smaller than the pressing surface of the piston 7, the acceleration of the ram 2 during the return stroke R is less than during the working stroke A. In FIG. 6, the braking process in the region of the upper reversal point is not shown in a time-resolved manner.

[0120] Instead of the directional control valve 12, a controllable pump, for example a servo pump, may also be used. With such a pump, the volume flow may be adjusted and varied, in particular controlled, as described above, analogous to the directional control valve 12.

[0121] The described embodiments of a forging hammer 1, in general of a correspondingly configured forming machine with appropriate control, have in particular the following advantages.

[0122] By using valves or pumps with an adjustably variable volume flow, it is possible to change the supply of hydraulic fluid comparatively gently, and abrupt changes may be avoided. This affords in particular the advantage that cavitation may be avoided, which cavitation may be caused by a sudden change in the volume flow, for example by a stall in the hydraulic fluid flow due to the inertia of the hydraulic fluid.

[0123] The regulation or control of the hydraulic circuit that is possible with the proposed forming machine makes it possible, with a predefined setpoint speed or impact energy or energy preselection, to extend the acceleration phase to just shortly before the impact of the ram 2 or tool 3 on the workpiece, or to accelerate the ram 2 in a targeted manner to just shortly before it hits the workpiece, so that the suction phase, in which undesired cavitation may occur, and the post-flow phase may be shortened to a minimum or optimized. For example, the hydraulic circuit may regulate the forming machine and control the volume flow such that, at low setpoint speeds or low forming energies, the acceleration of the ram 2 set over the entire stroke is lower than at high setpoint speeds or high forming energies.

[0124] When using a path measuring unit 24 in combination with directional control valves 12 or pumps that may be controlled comparatively quickly and on the basis of comparatively short reaction times of such actuating units, the working stroke may be traversed in a targeted and regulated manner.

[0125] Furthermore, advantages with regard to the construction of the hydraulic circuit 8 may be achieved with the proposed forming machine. In particular, it is possible to dispense with the comparatively complex impact valves that are used in forging hammers 1 known from the prior art. In embodiments without a suction valve 25, as is the case in the second embodiment according to FIG. 4, structural simplifications may be achieved insofar as the suction valve 25 and the reservoir 26 and associated hydraulic lines and components may be omitted.

[0126] A hydraulic forming machine is made available, more particularly a forging hammer 1, for workpiece forming, comprising a hydraulic cylinder 4 for driving a ram 2 configured for workpiece forming, and a hydraulic circuit configured for operation of the hydraulic cylinder 4, wherein the hydraulic circuit 8 has a valve 12 and/or actuator with an adjustably variable volume flow via which a first hydraulic working chamber 9 of the hydraulic cylinder 4, used to accelerate the ram 2 during the execution of a working stroke A for workpiece forming, may be provided with hydraulic fluid. The hydraulic circuit 8 is configured to adjust and vary the volume flow of the valve 12 or actuator, depending on a setpoint speed Vsoll of the ram 2 to be achieved in an acceleration phase of a working stroke A, and to optimize the subsequent movement phase of the working stroke A.

[0127] The operating modes of the forging hammers 1 of the two described embodiments have in particular the advantage, which may be achieved more or less equally in each case, that cavitation in the hydraulic fluid may be avoided after the setpoint speed has been reached. This is achieved in particular by the fact that the ram is accelerated in a regulated manner, such that the movement phase, i.e. braking phase, of the working stroke that follows the acceleration phase is optimized, in particular as regards the occurrence of cavitation.

[0128] In the case of forging hammers known from the prior art, the hydraulic circuit comprises a hydraulic fluid reservoir, the suction tank, which is connected to the first working chamber via a suction valve. In these embodiments, the suction valve, which is designed as a non-return valve, opens above a certain pressure ratio between suction tank and piston chamber and hydraulic fluid. In the forging hammers known from the prior art, acceleration in the acceleration phase of the working stroke is always carried out with maximum pressure and volume flow. For high setpoint speeds, this results in long acceleration phases and short braking or suction phases. By contrast, in the case of low setpoint speeds, this results in shorter acceleration phases and longer braking or suction phases. Since the suction is generally critical in terms of cavitation, especially in the case of comparatively long suction phases, and the suction phase depends on many factors that are difficult or impossible to influence, such as manufacturing tolerances of the components of the suction valve (spring stiffness, friction of the running surface, mass, etc.), temperature of the hydraulic medium, properties of the fluid itself, filling level in the suction tank or container (geodetic pressure), etc., the known forging hammers are to be viewed rather critically with regard to functional reliability (e.g. cavitation).

[0129] Based on this, it is a finding of the underlying invention that, by suitable regulation/control of the acceleration phase, the suction may be optimized with regard to functional reliability (embodiment according to FIG. 1) or even completely eliminated (embodiment according to FIG. 4). The latter permits, for example, cavitation-free operation.

[0130] According to one aspect of the invention, the suction may be minimized or optimized. The maximum pressure (e.g. the system pressure, in particular the maximum pressure that is or may be made available by the hydraulic system for charging the hydraulic cylinder to execute a stroke) may then always be applied to the actuator, and the volume flow and thus the acceleration pressure in the first working chamber may be adapted to the setpoint speed. This means that, for example, an almost identical acceleration path may always be set, regardless of whether a high or low setpoint speed is to be achieved. In this way, the braking distance or suction phase may be minimized as far as possible, such that the associated lack of functional reliability is minimized. The optimization of the braking distance or of the suction phase may in particular take into account the inertia, e.g. of the hydraulic fluid column or of the suction valve with its components, in such a way that the suction phase is always greater than the reaction time of the system. The proposed invention thus permits an optimization of the braking distance or of the suction phase in order to increase the functional reliability. The braking phase or the ratio of acceleration phase to braking phase may be adjusted using the method according to the invention. It may thus be ensured that the time needed for setting the volume flow required to avoid cavitation, or the stroke required for this purpose, are available.

[0131] According to a further aspect of the invention, the suction may be eliminated, or a cavitation-free drive may be implemented. Here, the hydraulic fluid is supplied via the impact valve during the braking phase, and therefore no suction valve and suction tank are required. The volume flow required to avoid cavitation-critical pressure is fed to the first working chamber via the impact valve. For this purpose, the impact valve is preferably pressure-controlled from the end of the acceleration phase, i.e. the opening cross section and the associated volume flow are changed in real time depending on the conditions in the piston chamber. In particular, it is possible to avoid a situation where the impact valve is suddenly closed after the end of the acceleration phase. Rather, the impact valve may be closed continuously until the (pressure) regulation of the impact valve begins. The parameters required to control the impact valve may be determined or fed back, for example, by a pressure sensor installed on the first hydraulic working chamber. A stalling of the hydraulic fluid column or cavitation and their damage are thus substantially or completely avoided.

[0132] Overall, it can be seen that the object on which the invention is based is achieved.

LIST OF REFERENCE SIGNS

[0133] 1 forging hammer [0134] 2 ram [0135] 3 tool [0136] 4 hydraulic cylinder [0137] 5 piston rod [0138] 6 cylinder tube [0139] 7 piston [0140] 8 hydraulic circuit [0141] 9 first working chamber [0142] 10 second working chamber [0143] 11 pump unit [0144] 12 directional control valve (impact) [0145] 13 hydraulic tank [0146] 14 brake valve [0147] 15 first pressure sensor [0148] 16 first connection [0149] 17 second connection [0150] 18 second pressure sensor [0151] 19 pressure reservoir [0152] 20 safety valve [0153] 21 third connection [0154] 22 third pressure sensor [0155] 23 control unit [0156] 24 path measuring unit [0157] 25 suction valve [0158] 26 reservoir [0159] 27 valve [0160] 28 throttle [0161] A working stroke [0162] R return stroke [0163] S force of gravity [0164] U voltage [0165] t time [0166] G speed [0167] X position [0168] H stroke [0169] O open position