MACHINE PRESS

Abstract

A machine press is provided in which at least one hermetically sealed hydraulic drive unit is switchable from a working mode, in which a base pressure above ambient pressure is continually exceeded, into a rest mode. To this end, in parallel with a pressure converter, to the high-pressure side of which a pressure store and a raising working chamber of a cylinder piston unit are connected, a bypass is provided, having a first blocking valve that is controllable by a control unit and, in its blocking position, blocks the through-flow direction from the high-pressure side of the pressure converter to the low-pressure side. Furthermore, the low-pressure side is connectable to a lowering working chamber via a second blocking valve controllable by the control unit. The pressure output of the hydraulic unit is connectable to the raising working chamber via a third blocking valve controllable by the control unit.

Claims

1. A machine press comprising: a lower die as well as an upper die (1) that can be lowered and raised by means of a hydraulic linear drive, wherein the hydraulic linear drive comprises at least one hermetically sealed hydraulic drive unit (2) and a control unit acting thereon and, in a working mode, a base pressure higher than the ambient pressure is exceeded constantly and everywhere within the hydraulic drive unit (2), wherein: the hydraulic drive unit comprises at least one hydraulic cylinder-piston unit (3) acting on the upper die (1), a hydraulic assembly (7), a pressure accumulator (8) and a pressure transformer (9); the at least one hydraulic cylinder-piston unit (3) comprises at least one lowering working chamber (11) as well as at least one raising working chamber (10); at least one raising working chamber (10) as well as the high-pressure side (H) of the pressure transformer (9) is connected to the pressure accumulator (8); the hydraulic assembly (7) can be fed from the low-pressure side (N) of the pressure transformer (9) in order to pressurize at least one lowering working chamber (11); the at least one hydraulic drive unit (2) can be switched from the working mode into an idle mode; for this purpose a bypass (12) having a first stop valve (13), which can be controlled by the control unit and in its blocking position blocks at least the flow direction from the high-pressure side (H) of the pressure transformer (9) to its low-pressure side (N), is provided in parallel with the pressure transformer (9); furthermore the low-pressure side (N) of the pressure transformer (9) can be placed in communication with the lowering working chamber (11) via a second stop valve (15) that can be controlled by the control unit; and the pressure outlet (16) of the hydraulic assembly (7) can be placed in communication with the raising working chamber (10) via a third stop valve (17) that can be controlled by the control unit.

2. The machine press of claim 1, wherein the at least one hydraulic drive unit (2) has at least one double-acting hydraulic cylinder-piston unit (3).

3. The machine press of claim 2, wherein the at least one hydraulic drive unit (2) has exactly one double-acting hydraulic cylinder-piston unit (3).

4. The machine press of claim 1, wherein the second stop valve (15) and the third stop valve (17) form a unit (14) comprising a mode-of-operation selector coupled with a valve in such a way that, in a first valve position (working mode), the pressure outlet (16) of the hydraulic assembly (7) is in communication with the lowering working chamber (11) and the communication of the lowering working chamber (11) with the low-pressure side (N) of the pressure transformer (9) is interrupted, and in a second valve position (idle mode), the pressure outlet (16) of the hydraulic assembly (7) is in communication with the raising working chamber (10), as is the lowering working chamber (11) with the low-pressure side (N) of the pressure transformer (9).

5. The machine press of claim 4, wherein the first stop valve (13) is integrated into the unit (14) comprising a mode-of-operation selector and valve in such a way that the bypass (12) is opened in idle mode and in working mode it is blocked at least in the flow direction from the high-pressure side (H) of the pressure transformer (9) to its low-pressure side (N).

6. The machine press of claim 1, wherein the hydraulic assembly (7) is of non-reversible construction.

7. The machine press of claim 1, wherein the hydraulic linear drive comprises two hydraulically decoupled drive units (2) of identical construction acting in parallel on the upper die.

8. The machine press of claim 7, wherein the two drive units (2) can be moved in parallel, synchronously volume-controlled manner to the upper dead point during the transition from the idle mode into the working mode.

9. The machine press of claim 1, wherein a calibration routine can be executed on the at least one drive unit (2) for adjustment of a pressure level present at a reference point in the pressure accumulator (8).

10. The machine press of claim 9, wherein a displacement transducer (18), which senses the position of the piston (19) of the associated pressure transformer (9), is allocated to the pressure transformer (9) of the at least one drive unit (2).

11. The machine press of claim 1, wherein at least one pressure transducer (20), the measured values of which can be conveyed to the control unit, is allocated to the pressure transformer (9) of the at least one drive unit (2).

12. The machine press of claim 1, wherein the torque of the motor of the hydraulic assembly (7) is evaluated in the machine controller as an indicator for the hydraulic pressure in the pressure accumulator (8).

13. A hydraulic linear drive, especially for a machine press, for moving a driven part along a working axis in a first movement direction and a second movement direction opposite to the first movement direction, comprising a hermetically sealed hydraulic drive unit (2), in which, in a working mode, a base pressure higher than the ambient pressure is exceeded constantly and everywhere, wherein: the hydraulic drive unit (2) comprises at least one hydraulic cylinder-piston unit (3), a hydraulic assembly (7), a pressure accumulator (8) and a pressure transformer (9); the at least one hydraulic cylinder-piston unit (3) comprises at least one first working chamber (10) that is active with respect to the first movement direction as well as at least one second working chamber (11) that is active with respect to the second movement direction; at least one first working chamber (10) as well as the high-pressure side (H) of the pressure transformer (9) is connected to the pressure accumulator (8); the hydraulic assembly (7) can be fed from the low-pressure side (N) of the pressure transformer (9) in order to pressurize at least one second working chamber (11); the at least one hydraulic drive unit (2) can be switched from the working mode into an idle mode; for this purpose a bypass (12) having a first stop valve (13), which can be controlled by the control unit and in its blocking position blocks at least the flow direction from the high-pressure side (H) of the pressure transformer (9) to its low-pressure side (N), is provided in parallel with the pressure transformer (9); furthermore the low-pressure side (N) of the pressure transformer (9) can be placed in communication with the second working chamber (11) via a second stop valve (15) that can be controlled by the control unit; and the pressure outlet (16) of the hydraulic assembly (7) can be placed in communication with the first working chamber (10) via a third stop valve (17) that can be controlled by the control unit.

Description

BRIEF DESCRIPTION OF THE DRAWING

[0020] The present invention will be explained in more detail hereinafter on the basis of a preferred exemplary embodiment illustrated (schematically) in FIG. 1. This drawing illustrates one of the two hydraulic drive units acting independently on an upper die of an inventive machine press. Incidentally, an illustration and corresponding explanation of the machine press will not be presented, because it is not pertinent for understanding of the present invention and because the present invention can be implemented in connection with any desired machine presses known as such from the prior art (e.g. DE 102009052531 A1 and DE 102012013098 A1, the complete disclosure content of which is made subject matter of the present disclosure by reference).

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0021] The machine press illustrated in the drawing in what is the definitive detail section here (see above) comprises a lower die and an upper die 1 that can be lowered and raised by means of a hydraulic linear drive. This hydraulic linear drive comprises two hermetically sealed hydraulic cylinder units 2 acting on upper die 1 and a control unit acting on them.

[0022] Each hydraulic drive unit 2 comprises a double-acting hydraulic cylinder-piston unit 3 with a cylinder 4 and a piston 6 connected to upper die 1 via a piston rod 5, a hydraulic assembly 7, a pressure accumulator 8 and a pressure transformer 9. Piston 6 separates the raising working chamber 10 from the lowering working chamber 11. In working mode, drive unit 2 operates as can be inferred from DE 102012013098 A1. In particular, pressure is constantly admitted to raising working chamber 10 via pressure accumulator 8 and, in fact, to such a pressure level that upper die 1 is preloaded in its upper dead point. The lowering movement is achieved by pressurizing lowering working chamber 11 by hydraulic assembly 7. Via pressure transformer 9, which is connected on the high-pressure side to pressure accumulator 8, the system is constantly pressurized with an initial pressure; thus a base pressure that at least exceeds the ambient pressure prevails constantly and everywhere in the system during working mode.

[0023] The drive unit is illustrated with a single lowering working chamber 11. Obviously, however, this may also be splitwith the advantages that can be inferred from DE 102012013098 A1into a first working sub-chamber, which is used for (rapid) lowering of upper die 1 in rapid traverse, and a second working sub-chamber, whichtogether with the first working sub-chamberis used for (slow) lowering of upper die 1 in pressing operation. In this case the second working sub-chamber is in communication with low-pressure side N of pressure transformer 9 via a feeder valve (see DE 102012013098 A1).

[0024] In contrast to the situation in the prior art, hydraulic drive unit 2 illustrated in the drawing can be switched according to the invention from the working mode into an idle mode. For this purpose, a bypass 12 containing a first stop valve 13 is provided in parallel with pressure transformer 9. This is constructed as a proportional 2/2-way valve with a blocking position, in which the flow direction from high-pressure side H of pressure transformer 9 to its low-pressure side N is blocked (via a non-return functionality) and a passing position, in which high-pressure side H and low-pressure side N of pressure transformer 9 are short-circuited. First stop valve 13 is constructed as a solenoid valve, which can be controlled by the control unit.

[0025] Also provided is a unit 14 comprising a mode-of-operating selector and valve, which is constructed as a proportional 4/2-way valve and unites two stop-valve functionalities in itself. And, in fact, low-pressure side N of pressure transformer 9 can be placed in communication with lowering working chamber 11 via a second stop valve 15, which can be controlled by the control unit; and pressure outlet 16 of the (non-reversible) hydraulic assembly 7 can be placed in communication with raising working chamber 10 (as well as pressure accumulator 8) via a third stop valve 17, which likewise can be controlled by the control unit. By virtue of structural and functional integration of second stop valve 15 and third stop valve 17 into unit 14 comprising a mode-of-operation selector and valve, these two stop valves are actuated in coupled relationship and, in fact, in such a way that, in a first valve position (working mode) shown in the drawing, pressure outlet 16 of hydraulic assembly 7 is in communication with lowering working chamber 11 and the communication of lowering working chamber 11 with low-pressure side N of pressure transformer 9 is interrupted, whereas, in a second valve position (idle mode), pressure outlet 16 of hydraulic assembly 7 is in communication with raising working chamber 10, as is lowering working chamber 11 with low-pressure side N of pressure transformer 9. If first stop valve 13 is switched to its passing position in idle mode, pressure equalization exists both between high-pressure side H and low-pressure side N of pressure transformer 9 and between raising working chamber 10 and lowering working chamber 11 of cylinder-piston unit 3. Upper die 1 is lowered into an idle position, in which it is braced on stops (or is held there once it has been moved actively into the lowered position). Freely moving piston 19 of pressure transformer 9 moves so far in the direction of high-pressure side H that low-pressure side N receives all hydraulic fluid from pressure accumulator 8. When the membrane of pressure accumulator 8 constructed as bladder accumulator then reaches the stop, the rest of the system is suddenly depressurized.

[0026] In order to change the machine presswhile raising upper die 1 into its upper end position (determined by the upper dead point of piston 6)over from idle mode into working mode, hydraulic assembly 7with unchanged operating position of unit 14 comprising mode-of-operation selector and valve, but with first stop valve 13 switched to the non-return blocking positionis started up. Raising working chamber 10 is pressurized from hydraulic assembly 7 and gradually filled, in which case the hydraulic fluid forced out of lowering working chamber 11 in the process, i.e. during the raising of upper die 1, passes through bypass 12 into pressure accumulator 8, to the extent that it is not conveyed via hydraulic assembly 7 to raising working chamber 10. Beginning from the end of raising of upper die 1, i.e. when pistons 6 reach their upper dead point position, hydraulic assemblies 7 are fed from the respective low-pressure side of the associated pressure transformer 9. The hydraulic fluid transported from hydraulic assembly 7, to the extent it is not conveyed to the expanding high-pressure side H of the pressure transformer in a manner corresponding to the movement of piston 19 of pressure transducer 9, is forced into pressure accumulator 8. The corresponding filling of pressure accumulator 8with continuing movement of piston 19 of pressure transformer 9 in the direction of its low-pressure side Ntakes place until the pressure level predetermined by the machine controller (i.e. especially the nominal pressure on high-pressure side H) is attained (calibration). Now the two stop valves 15 and 17 are also reversed by the controller, so that they again occupy their operating position illustrated in the drawing and corresponding to the working mode of the machine press.

[0027] As long as the attainment of the predetermined pressure level on the high-pressure side is not being derived from the torque of the motor of hydraulic assembly 7, a pressure measurement takes place. In this way high-pressure side H and/or low-pressure side N of pressure transducers 9 of the two drive units 2 can be assigned to pressure transducers 20, the measured values of which can be conveyed to the control unit. On the basis of these measured values of pressure, and as an alternative to the preferred derivation of the pressure level from the motor torque (if applicable including a torque limitation that can be predetermined by the machine controller), the two drive units 2 can be calibrated as well as hydraulically matched as explained in the foregoing, and so on this basis the same and ideal pressure level is present on the high-pressure side at the upper dead point of both drive units 2.

[0028] The sequence described in the foregoing for the changeover from the idle mode into the working mode results directly from the fact that the piston-area ratio between low-pressure side N and high-pressure side H of the pressure transducer is greater by a multiple (i.e. by a factor between 4 and 8) than the piston-area ratio between lowering working chamber 11 and raising working chamber 10. A pressure step-down ratio of the pressure transformer between 50:1 and 100:1 and a piston-area ratio of lowering and raising working chambers between 8:1 and 20:1 have proven particularly suitable for a typical use. For other geometries, the sequence could be achieved if necessary by an auxiliary valve, which hydraulically blocks the pressure transformer until upper die 1 has been completely raised.

[0029] For the raising of upper die 1 from its idle position (see above) during the changeover from the idle mode into the working mode of the machine press, the two drive units 2 are operated in parallel, synchronously volume-controlled manner. Hydraulic assemblies 7 are operated with identical transport rates, by virtue of appropriate activation of their motors M by the control unit. As a result, no danger of tilting exists.

[0030] For monitoring of the system, displacement transducers 18, which sense the position of piston 19 of the corresponding pressure transformer 9, are assigned to pressure transformers 9 of the two drive units 2. Since, as explained hereinabove, a correlation exists between the position of piston 19 of pressure transformer 9 and the pressure on the high-pressure side at the top dead point position of piston 6 of corresponding drive unit 2, a particular pressure level on the high-pressure side can also be inferred from the position of piston 19 of pressure transformer 9, although temperature influences do exist in this respect. In order to allow for these in the machine controller, it is possible, as illustrated, for example, on low-pressure side N of pressure transformer 9, to provide temperature sensors 21, preferably distributed at various positions within the system.