GB2197813A

GB2197813A - Controlling or adjusting blank holder force during a drawing process

Info

Publication number: GB2197813A
Application number: GB08727815A
Authority: GB
Inventors: Erich Harsch; Hans Engelhardt
Original assignee: Mueller Weingarten AG
Current assignee: Mueller Weingarten AG
Priority date: 1986-11-27
Filing date: 1987-11-27
Publication date: 1988-06-02
Anticipated expiration: 2007-11-27
Also published as: GB2197813B; DD265815A5; FR2607416A1; DE3640507C2; GB8727815D0; DE3640507A1; IT1223162B; FR2607416B1; IT8722774A0; DE3640507C3

Abstract

An arrangement for controlling or adjusting the blank holder force during the drawing process is characterised by the provision of a proportional or servo valve 8, to control and adjust the pressure in the blank holder fitting and thus the blank holder force. This reduces inertia. The arrangement has a hydraulic pump in a hydraulic supply unit 14, an oil container 15a hydraulic cylinder 1 for each pressure fitting of the blank holder, and a pressure transmitter 2 linked to a respective hydraulic cylinder 1, each with an oil piston 3 and an air piston 4 connected mechanically thereto. An additional cylinder 6 is located in the operating direction of the oil/air pistons 3, 4 with piston 7 exposed to pressure on both sides. An overload spray-off pipe 5 leads to the oil container 15. The proportional or servo valve 8 is actuated by a control 12 responsive to sensor 10 in the blank holder, sensor 11 in the tool, and a control line 9. In Figure 5 (not shown), the proportional or servo valve (8) is connected directly to the hydraulic cylinder (1). An overload safety valve (19) has a piston path dependent release. <IMAGE>

Description

Arrangement for the controlling or adjusting the blank holder force during the drawing process.

The invention relates to an arrangement tor the controlling or adjusting the blank holder force during the drawing process.

Mechanical drawing presses with separate ram and blank holder have a hydraulic element in the power flux of the blank holder, which is designed to ensure power adjustment independently of small changes in path caused by the drive of the blank holder or springing of the press stand.

In principle this arrangement is similar to a hydraulic overload safety means. Here too there are hydraulic cushions under the drive fittings. A pressure transmitter is allocated to each fitting, its step pistons exposed to the impact of oil from one side and, by air from the other. The pressure of the four air cushions can be adjusted individually, allowing varying degrees of blank holder force to be applied to the four driving points of the blank holder.

The extent of pre-stressing in the hydraulic cushions determines the elastic behaviour of the blank holder when set on the plate.

The smaller the pre-stress pressure, the more flexible the blank holder, which can thus be fitted snugly on the plate. For rigid power transfer on the other hand, the pre-stressing is set at the equivalent of the stress produced by the operating pressure.

With the standard diagram of this arrangement, it is possible to keep the blank holder force constant throughout the entire drawing process.

There is also a control which allows the blank holder force to be modified as a function of the drawing ram movement, e.g. in such a way that after the drawing bead has been pressed in, it is reduced, or equally so that the specific blank holder force remains virtually constant. The modification of the blank holder force can also be undertaken during the drawing process for each of the four driving points of the blank holder ram separately, and at different times and to different extents, by means of an automatic control using a so-called counter air arrangement ( fine setting).

The disadvantage of the known arrangement for power adjustment on the blank holder is the - inertia of the setting, so that adjustment during the drawing process is scarcely possible, particularly with modern presses with high numbers of strokes.

It is the task of the present invention to create a fast-reacting power setting which can also be used for power control or power adjustment.

To solve this problem, it is proposed according to the invention, with an arrangement of the design described at the outset, to locate proportional or servo valves to control and adjust the pressures in the blank holder fittings, and thereby the blank holder force.

In a special arrangement of this kind, which has a hydraulic pump with filter, a pressure control, an oil container, a hydraulic cylinder for each pressure point (fitting) of the blank holder, and a pressure transmitter linked to a respective hydraulic cylinder, each with an oil piston and an air piston connected mechanically thereto, which at the same time represents an overload safety means through the overflow cbanwel, It is also advantageous for an additional cylinder, with piston exposed on both sides, to be located in the operating direction of the oil / air piston, with pistons exposed to impact on both sides.

Further features for this are described in Patent Claims 3 to 5.

Modifications of the arrangement according to the invention are the subject of Patent Claims 6 to 10.

The invention displays the following advantages : rapid reactivity is assured. As a result of recently developed components, the blank holder force is controllable or adjustable during the drawing process. The control of this arrangement can be taken over by modern press controls or integrated in them.

The invention is described in greater detail by means of a drawing in diagram, wherein 5 different control systems are represented in diagrammatic form.

The arrangement according to the diagram in Figure 1 is used for indirect adjustment of the blank holder force. It consists of a hydraulic cylinder 1 with connected pressure transmitter 2 with mechanically conducted oil piston 3 and air piston 4, whereon a piston 7 acts, controllable via a proportional or servo valve 9, switchable on or off via an additional valve 13, and exposed to impact on both sides. A hydraulic unit 14 supplies the cylinder 1 direct, and via the storage unit 16, the proportional valve 8 also. At the same time the spray-off pipe 5 represents an overload safety means in conjunction with piston 3. The proportional valve 8 is actuated by the control 12 via sensor 10 in the blank holder, sensor 11 in the tool or the control line 9 of the machine.

Figure 2 shows a variation of Figure 1, wherein the hydraulic oil supply 22 for the proportional valve 8 is separate from the remaining hydraulic supply 14.

Figure 3 shows a variation of Figure 2, wherein the pressure transmitter 2 has, in place of the air piston 4, which operates against the storage unit 17, a further hydraulic piston 18.

Figure 4 shows a further variation of Figure 1. The piston 7 is exposed to impact on one side, and operates counter to the air piston 4 or oil piston 18 operating at maximum pressure in Figure 3.

The arrangement according to the diagram in Figure 5 is used for direct adjustment or control of blank holder force. It shows a hydraulic cylinder 1 which is lies in the power flux of the blank holder drive, and is linked to the proportional valve 8 and an overload safety means block 19. The proportional valve 8 is supplied by the hydraulic unit 14 and the storage unit 16, and is actuated via the control 12 with the sensors 10 and 11 and the control line 9.

In addition to the power release, the overload safety valve 19 has a piston path-dependent release through the valve 20 and the cam 21.

Claims

1. Arrangement for controlling or adjusting the blank holder force during the drawing process, characterised in that, proportional or servo valves are provided to control and adjust the pressurcs in the blank holder fittings and thus the blank holder force.

2. Arrangement according to claim 1, which has a hydraulic pump with filter, a pressure control, an oil container, a hydraulic cylinder for each pressure point (fitting) of the blank holder, and a pressure transmitter linked to a respective hydraulic cylinder, each with an oil piston, and an air piston connected mechanically thereto, which at the same time displays an overload safety means through the overflow channel, characterised in that, in the operating direction of the oil/air piston an additional cylinder is located with pistons exposed to impact on both sides.

3. Arrangement according to claim 2, characterised in that the piston of the additional cylinder is exposed to preferably hydraulic pressure, and is activated via a proportional or servo valve which is supplied from a hydraulic aggregate and storage reservoir.

4. Arrangement according to claim 3, characterised in that, the proportional or servo valve is actuated path- or angle-dependently by the press via a control line or by means of sensors located in the tool or blank holder, after comparison with pre-programmed signals from the control.

5. Arrangement according to one of claims 2 to 4, characterised in that, the blank holder adjustment hydraulics (proportional or servo valve with controls) may be switched off or on via an additional valve.

6. Arrangement according to one of claims 1 and 2, characterised in that, the additional cylinder and the proportional and servo valve has its own closed hydraulic circuit with a separate hydraulic unit, which is operated with a medium other than the one in the cy#linder.

7. Arrangement according to claim 1 and 2, characterised in that, the air piston of the pressure transmitter is replaced by an oil piston operating against a storage reservoir.

8. Arrangement according to claim 1 and 2, characterised in that, the additional piston operates only against the piston operating at maximum pressure.

9. Arrangement according to claim 1, characterised in that, the hydraulic cylinder is linked directly to the proportional or servo valve.

10. Arrangement according to claims 1 and 9, characterised in that, a separate overload safety means with known pressure control and additional path control via valve and cam is present.

11. Arrangement for controlling or adjusting the blank holder force during the drawing process, substantially as herein described with reference to the accompanying drawings.