WO1999054123A1

WO1999054123A1 - Method for operating a hydraulic press

Info

Publication number: WO1999054123A1
Application number: PCT/EP1999/002301
Authority: WO
Inventors: Manfred Breckner
Original assignee: Mannesmann Rexroth Ag
Priority date: 1998-04-07
Filing date: 1999-04-03
Publication date: 1999-10-28

Abstract

The force required to deform a workpiece in hydraulic presses is applied by the piston of a dual action hydraulic cylinder. Initially, the force of pressure falls during the transition from quick movement to the speed of compression as a result of compression of the pressure medium while the pressure builds up. In order to reduce the drop in the force of pressure, the pressure medium is evacuated from a first cylinder chamber (3.1, 4.1) assigned to the direction in which the press is opened over a first distance and fed to a second cylinder chamber (3.2, 4.2) assigned to the direction in which the press is closed. Pressure is maintained in the cylinder chambers in such a way that the forces acting upon the piston surfaces of the cylinder cancel each other out. The first cylinder chamber (3.1, 4.1) is discharged before deformation of the workpiece begins. The pressure that prevails in the second cylinder chamber (3.2, 4.2) exerts a force upon the workpiece, resulting in the deformation thereof.

Description

description

Process for operating a hydraulic press

The invention relates to a method for operating a hydraulic press, in which the force required for the deformation of a workpiece is applied by the piston of a double-acting hydraulic cylinder and this force is transmitted via mechanical intermediate elements from the piston to a press tool, the press tool only after driving through a first distance and the workpiece is deformed while driving through a second distance, as well as a hydraulic press operated according to this method with a synchronous cylinder arranged between the frame and the pressing tool with two cylinder chambers, of which the the first is assigned to the opening direction of the press and the second to the closing direction of the press, and in which the press is closed by lowering the pressing tool.

In a mechanically driven press, the press tool moves between a first, e.g. B. upper end position and a second, z. B. lower end position. If the pressing tool is in the upper end position, a blank can be inserted into the press. Then the press tool is lowered until it hits the blank. During the lowering of the pressing tool from its upper end position until it hits the blank, a path is traveled through without a counterforce acting on the pressing tool. If the pressing tool has reached the blank, the blank begins to deform. During the deformation of the blank, the pressing tool only has a short distance to reach its lower end position. However, a large force must be applied to deform the blank. The required relationship between the distance traveled by the press tool and the force exerted by the press tool on the blank is determined in an eccentric press by a motor-driven disk on which the press tool is articulated so that the rotary movement of the motor into the desired pushing movement of the press tool is formed. In a toggle press, the relationship between the distance traveled by the press tool and the force exerted by the press tool on the blank is determined by the geometry of a toggle lever. With such presses, the course of movement and force are the same for each stroke. The force is built up according to the mechanics of the press. With such presses, high cycle rates can be achieved. However, a change in the relationship between the distance traveled by the press tool and the force exerted by the press tool on the blank - if it is possible at all - requires complex design changes to the press. The press force of a mechanical press depends on the stroke. A slow setting up of the press with a pressing force, which is particularly necessary for test presses (also referred to as “try out” _presses ), is not possible with mechanical presses. In contrast to mechanical presses, hydraulic presses, ie presses in which the pressing force is generated by hydraulic cylinders, allow variable speeds and forces over the entire stroke distance between the upper and lower end positions. In addition, hydraulic presses allow the press to be set at very low speeds with or without pressing force. For these reasons, hydraulic presses are preferably used as test presses. As an alternative to mechanical presses in series production, hydraulic presses are only suitable to a limited extent, since a force drop occurs due to the compressibility of the oil used as pressure medium when changing from rapid traverse to the press speed. If hydraulic presses are to be used not only as test presses but also for series production, the pressure build-up during the transition from rapid traverse to the press speed must be improved. In order to improve the pressure build-up and thereby increase the pressing speed, large drive powers are required. These drive powers are mostly achieved by oversized storage drives with correspondingly long loading times.

The invention has for its object to provide a method for operating a hydraulic press and a press operated according to this method, which reduces the drop in force during the transition from rapid traverse to the pressing speed without requiring an increase in drive power. This object is achieved with regard to the method by the features characterized in claim 1 and with regard to the hydraulic press by the features characterized in claim 7. While the press tool travels the first distance, the piston of the double-acting cylinder is clamped hydraulically, the pressure medium in the cylinder chambers is already compressed. For the build-up of the force acting on the pressing tool, only the pressure reduction of the cylinder chamber associated with the opening process is decisive. The time in which the force required for the pressing process is built up is thus reduced, since a pressure reduction takes place faster than a corresponding pressure buildup. This makes it possible to use a hydraulic press not only as a test press but also for series production with shorter cycles. The force curve and speed curve of the hydraulic press can be realized like a mechanical press. The accident prevention regulations are observed in accordance with the applicable rules.

Advantageous developments of the method according to claim 1 are characterized in the subclaims 2 to 6. Advantageous developments of the device according to claim 7 are characterized in the subclaims 8 to 14.

The method according to the invention is explained in more detail below with its further details using an exemplary embodiment of a hydraulic press operated according to the method according to the invention shown in the drawings. Show it Figure 1 shows a press operated according to the inventive method in a schematic representation

Figure 2 shows the upper part of Figure 1 in an enlarged view.

Figure 1 shows a press operated according to the inventive method in a schematic representation. Three hydraulic cylinders 3 to 5 are arranged between a frame 1 and a press beam 2. The frame 1 carries a table 6 which, in a lower tool, not shown in FIG. 1, receives a workpiece, also not shown, as a blank to be deformed. A press tool 7 is held on the press beam 2. The pressing tool provided with the reference number 7 is the upper tool of the press. The letter F denotes the force exerted by the press tool 7 on the workpiece or the force acting on the press tool. The press beam 2 serves as a mechanical intermediate member between the cylinders 3 to 5 and the press tool 7. The ^' cylinders 3 and 4 are each identical synchronous cylinders. The cylinder 5 is designed as a differential cylinder. Details of cylinders 3 to 5 are described below with reference to FIG. 2. The reference numerals 8 and 9 denote lines which connect two chambers of the cylinder 3 to a first control device 10. Reference lines 11 and 12 denote further lines which connect two chambers of the cylinder 4 to the control device 10. The control device 10 is connected via a line 13 to a tank 14 and via a line 15 to a Pressure accumulator 16 connected. The two chambers of the cylinder 5 are connected via lines 17 and 18 to a second control device 19. A line 20 leads from the control device 19 to a further chamber of the cylinder 3 and a line 21 to a further chamber of the cylinder 4. A motor 22 drives an adjustable pump 23. The pump 23 supplies the pressure accumulator 16 and the control device 19 with pressure medium via a valve device 24. The valve device 24 is connected to the tank 14 via a line 25. A line 26 leads from the valve device 24 to the control device 19. A controllable valve 27 with three positions is arranged between the lines 8 and 9. In the middle position, the valve 27 acts as a check valve, a pressure medium flow being possible only from line 8 to line 9. In the left position, the valve 27 blocks the connection between the lines 8 and 9. In the right position of the valve 27, pressure medium can flow between the lines 8 and 9 in both directions. The middle position of the valve 27 is its rest position, the left ^" and the right position of the valve is a working position. Between the lines 11 and 12 there is a further valve 28 with likewise three switch positions. In the middle position this acts Valve 28 as a non-return valve, pressure medium flow being possible only from line 11 to line 12. In the left position, valve 28 blocks the connection between lines 11 and 12. In the right position of valve 28, lines 11 and Pressure medium flows in both directions 12. The middle position of the valve 27 is its rest position, in the left and the right position the valve is a working position. A suction tank 29 is located above the frame 1 and is connected to the tank 14 via a line 30. Reference number 31 denotes a ventilation device for the suction tank 29. Five chambers of cylinders 3 to 5 are connected to the suction tank 29 via suction valves 32 to 36 and lines 37 to 41.

FIG. 2 shows the upper part of FIG. 1 on an enlarged scale. In Figure 2, the individual chambers of the cylinders 3 to 5 are provided with the reference numerals 3.1, 3.2, 3.3, 4.1, 4.2, 4.3, 5.1 and 5.2. The pressurized surfaces of the pistons of cylinders 3 to 5 are correspondingly referred to as A3.1, A3.2, A3.3, A4.1, A4.2, A4.3, A5.1 and A5.2.

At the beginning of the pressing process, the support beam 2 is in its upper position. The holding pressure acts on the surface A5.1 of the chamber 5.1 of the cylinder 5. This pressure is chosen so large that the force exerted by it on the surface A5.1 is at least as large as the total weight of the press beam 2 and the press tool 7 attached to it. This ensures that the press beam 2 with the press tool 7 is in a safe position. In this position, the chamber 3.3 of the cylinder 3, the chamber 4.3 of the cylinder 4 and the chamber 5.2 of the cylinder 5 are depressurized, that is, for. B. via the control device 19 with the

Tank 14 connected. The valve 27 is in the right switch position, so the lines 8 and 9 are connected to each other. The control device 10 ensures that the Chambers 3.1 and 3.2 of the cylinder 3 via the lines 8 and 9, respectively, are pressurized with the pressure of the accumulator 16 (e.g. 320 bar). The valve 28 is also in its right-hand switching position, the lines 11 and 12 are also connected to one another. The chambers 4.1 and 4.2 are pressurized via lines 11 and 12 with the pressure of the accumulator 16. The forces exerted by the pressures acting on the surfaces A3.1 and A3.2 and the forces exerted by the pressures acting on the surfaces A4.1 and A4.2 cancel each other out.

The downward movement of the pressing tool 7 takes place in two areas. First, the press tool 7 sinks in rapid traverse. Shortly before hitting the table 6, the sinking speed is reduced to the pressing speed. The changeover from rapid traverse to the pressing speed takes place as a function of the output signal of a path converter which is arranged between the frame 1 and the pressing beam 2 and is not shown in the figures for reasons of space.

For lowering the pressing tool 7 in rapid traverse, the chamber 5.1 is depressurized via the control device 19 to the ^' tank 14. Now the dead weight of the press beam 2 and the press tool 7 attached to it predominate. Pressure medium flows from the chamber 3.1 via the valve 27 into the chamber 3.2. At the same time, the control device 10 keeps the pressure in the chambers 3.1 and 3.2 at the storage pressure. Correspondingly, pressure medium flows from the chamber 4.1 via the valve 28 into the chamber 4.2, and the control device 10 also maintains the pressure in the chambers 4.1 and 4.2 on the memory print. As a result of this measure, the pressure medium is compressed both in the chambers 3.1 and 3.2 and in the chambers 4.1 and 4.2, the pistons of the cylinders 3 and 4 are clamped hydraulically at the full pressure. In the pressure-relieved chambers 3.3, 4.3 and 5.2, pressure medium is sucked out of the suction tank 29 via the suction valves 32, 36 and 34.

Before the pressing tool 7 strikes the workpiece held in the lower tool, the pressing tool 7 is braked from rapid traverse to the pressing speed. For this purpose, pressure is built up again in the chamber 5.1 by the control device 19. In addition, the valves 27 and 28 are each switched to the middle position and the chambers 3.1 and 4.1 are relieved via the control device 10 to the tank 14. The pressure in chambers 3.2 and 4.2 is maintained.

Both the pistons of the cylinder 3 and the pistons of the cylinder 4 are now acted upon by a force supporting the dead weight of the press beam 2 and the press tool 7. The usual way of generating a force that supports the dead weight of the press beam 2 and the press tool 7 is to build up pressure in the chambers 3.2 and 4.2 with the chambers 3.1 and 4.1 relieved of the load on the tank 14. However, such a pressure build-up requires more time than the decompression of the pressure medium in the chambers 3.1 and 4.1 provided in accordance with the invention while maintaining the pressure in the chambers 3.2 and 4.2. This measure eliminates the drop in the pressing force that otherwise occurs in hydraulic presses when changing from rapid traverse to the pressing speed. To increase the pressing force 10

Chambers 3.3, 4.3 and 5.2 additionally supplied with pressure medium via the control device 19. The clamping of the pistons of the cylinders 3 and 4 and the decompression of the chambers 3.1 and 3.2 is carried out via the control device 10. The pressing speed and the maximum pressing force are driven via the control device 19 and the adjustable pump 23.

For the retraction of the pressing tool 7, the valves 27 and 28 are switched to the left position. The connections between lines 7 and 8 and between lines 11 and 12 are thus interrupted. The chambers 3.2 and 4.2 are relieved of pressure via the control device 10 to the tank 14. The chambers 3.3, 4.3 and 5.2 are relieved of pressure via the control device 19 to the tank 14. A retraction pressure is built up in the chamber 5.1 of the cylinder 5 by the adjustable pump 23 via the control device 19. This force is normally sufficient to raise the press beam 2 with the press tool 7. However, if an increased retraction force is required, e.g. B. to tear the press tool from the workpiece, an additional force can be generated briefly by building pressure in the chambers 3.1 and 4.1, which supports the retraction force generated by the cylinder 5.

Different designs of the pump 23 and the accumulator 16 make it possible to implement a large number of movement sequences and force profiles.

It is also possible to run the press as a test press at low speed. Due to the central arrangement of the cylinder 5, when the press is full, 11

Safety alone through appropriate pressurization of the chambers 5.1 and 5.2 via the pump 23 and the control device 19 the complete speed spectrum of the press can be run with a pressing force reduced to approximately 5% to 10%. The chambers 3.1, 3.2 and 3.3 of the cylinder 3 and the chambers 4.1, 4.2 and 4.3 of the cylinder 4 are relieved of pressure so that they do not contribute to the generation of force.

In the exemplary embodiment described with reference to FIGS. 1 and 2, the cylinder 5 is a differential cylinder. Instead of a differential cylinder, a synchronous cylinder can be used. It is also possible to use a single-acting cylinder instead of a double-acting cylinder. In this case, the cylinder 5 only serves to hold the press beam 2 and the press tool 7.

In the embodiment described above, the double-acting cylinders 3 and 4 are synchronous cylinders. So that the forces acting on the piston surfaces from opposite sides cancel each other out, the chambers of the synchronous cylinders are each pressurized when the press is lowered. In principle, however, it is also possible to use differential cylinders as double-acting cylinders instead of synchronous cylinders. So that the forces acting on the piston surfaces from opposite sides cancel each other out, the ratio of the pressures supplied to the chambers of the differential cylinder must be kept in accordance with the reciprocal of the pressurized surfaces, so that the product of surface and pressure is equal in each case. 12

In the embodiment described above, the press tool moves in the vertical direction. Alternatively, however, the press can also be constructed so that the press tool moves in the horizontal direction.

In the exemplary embodiment shown in FIGS. 1 and 2, the chambers 3.1 and 4.1 are connected to the tank 14 before the beginning of the deformation of the workpiece in order to relieve pressure, as described above. As an alternative to this, it is also possible to relieve the pressure in the chambers 3.1 and 4.1 in two stages. In the first stage, the pressure medium is first passed from the chambers 3.1 and 4.1 into the chamber 5.2. This pressure medium supply to the chamber 5.2 takes place in addition to the pressure medium supply from the control device 19 via the line 18 described above. The additional pressurization of the chamber 5.2 increases the force acting on the pressure beam 2. Only when the pressure in the chambers 3.1 and 4.1 (from e.g. 320 bar) has dropped to a predeterminable value (from e.g. 200 bar) will the chambers 3.1 and 4.1 be used for further pressure reduction in the second stage connected to the tank 14. At the same time the connection of the chambers 3.1 and 4.1 to the chamber 5.2 is interrupted and thus prevents the chamber 5.2 from being relieved of pressure to the tank 14. The pressure medium supply to the chamber 5.2 now only takes place from the control device 19 via the line 18. The measure of relieving the pressure in the chambers 3.1 and 4.1 first into the chamber 5.2 and only then to the tank 14 results in an even quicker result Force build-up during the pressing process.

Claims

13 Patent claims

1. A method for operating a hydraulic press, in which the force required for the deformation of a workpiece is applied by the piston of a double-acting hydraulic cylinder and this force is transmitted via mechanical intermediate elements from the piston to a press tool, the press tool only when closing after driving through a first distance striking the workpiece and then deforming the workpiece while driving through a second distance, characterized in that

- That pressure medium discharged from a first cylinder chamber associated with the opening direction of the press and a second cylinder associated with the closing direction of the press while driving through the first distance

Cylinder chamber pressure medium is supplied, wherein such a pressure is maintained in the cylinder chambers that the forces acting on the piston surfaces of the cylinder cancel each other, ^' and - that before the start of the deformation of the workpiece, the first cylinder chamber is relieved, so that in the pressure prevailing in the second cylinder chamber exerts a force which causes the deformation of the workpiece on the workpiece.

2. The method according to claim 1, characterized in that the closing of the press is carried out by lowering the press tool due to the dead weight of the press tool and the mechanical intermediate members. 14

3. The method according to claim 1 or claim 2, characterized in that when using a synchronous cylinder both cylinder chambers are acted upon with the same pressure.

4. The method according to claim 3, characterized in that an additional force acting in the closing direction of the press is exerted on the pressing tool by a pressure acting on a further surface of the piston of the synchronous cylinder.

5. The method according to any one of claims 2 to 4, characterized in that the dead weight of the pressing tool and the mechanical intermediate members in the upper end position is compensated by pressurization of a further hydraulic cylinder acting in the opening direction of the press.

6. The method according to claim 5, characterized in that by ^'a force acting in the closing direction of the press of pressure to the other hydraulic cylinder, an additional, acting in the closing direction of the press force is exerted on the pressing tool.

7. Operated according to the method of claim 1 hydraulic press with a arranged between a frame and a pressing tool synchronous cylinder with two cylinder chambers, the first of the opening direction of the press and the second of the closing direction of the press 15

is assigned, and in which the press is closed by lowering the pressing tool, characterized in that

- That the two cylinder chambers (3.1, 3.2) are connected to each other via a valve (27), via which during the

Closing, when passing through the first distance, the pressure medium flows from the first cylinder chamber (3.1) into the second cylinder chamber (3.2),

- That a control device (10) is provided, which maintains the same pressure when driving through the first distance while closing in both cylinder chambers (3.1, 3.2), and

- That the control device (10) before the start of the deformation of the workpiece connects the first cylinder chamber (3.1) to relieve pressure with a tank (14).

8. Hydraulic press according to claim 7, characterized in that the free end of the piston of the synchronous cylinder (3), which is not connected to the pressing tool (7), projects into a third cylinder chamber (3.3) which, when pressurized, has an additional, in the closing direction of the press force acting on the piston of the synchronous cylinder ^'(3) exerts.

9. Hydraulic press according to claim 8, characterized in that the third cylinder chamber (3.3) of the synchronous cylinder (3) is pressurized during the pressure relief of the first cylinder chamber (3.1). 16

10. Hydraulic press according to one of claims 7 to 9, characterized in that a second synchronous cylinder (4) is arranged parallel to the first synchronous cylinder (3) between the frame (1) and the pressing tool (7).

11. Hydraulic press according to one of claims 7 to 10, characterized in that a pressure accumulator (16) is provided to maintain the pressure in the first and in the second cylinder chamber of the synchronous cylinder (3) or the synchronous cylinder (3, 4).

12. Hydraulic press according to claim 11, characterized in that the pressure accumulator (16) from a pump

(23) is fed.

13. Hydraulic press according to one of claims 7 to 12, characterized in that a further cylinder (5) between the frame (1) and the pressing tool (7) is arranged and that the further cylinder (5) is dimensioned so that it the weight of the moving parts holds at acting in the opening direction of the press pressurization of ^'press in the upper end position.

14. Hydraulic press according to claim 13, characterized in that the further cylinder (5) is a double-acting cylinder which holds the weight of the moving parts of the press in the upper end position and in the closing direction when pressure is applied in the opening direction 17

acting pressure increases the forces acting in the closing direction of the press.