GB2115734A

GB2115734A - Pneumatic drawing device

Info

Publication number: GB2115734A
Application number: GB08301627A
Authority: GB
Inventors: Markus Reihle; Helmut Jans; Egon Feirer; Erwin Sauter
Original assignee: Maschinenfabrik Mueller Weingarten AG; Mueller Weingarten AG
Current assignee: Maschinenfabrik Mueller Weingarten AG; Mueller Weingarten AG
Priority date: 1982-01-23
Filing date: 1983-01-21
Publication date: 1983-09-14
Also published as: IT1160453B; FR2520271A1; DE3202134C1; GB8301627D0; IT8319204A0; GB2115734B; FR2520271B1

Abstract

The invention relates to a pneumatic drawing device with a pressure cheek 1 guided in the press bed and supported by at least one pneumatic cylinder 7, which cooperates with a hydraulic locking or retaining device 25 active at the bottom of stroke of cheek 1. In order to increase the number of strokes of the machine and to reduce the noise level when ejecting the workpieces in a device of this type, a pin plate (2) supports ejector pins (3), whereas acting on the lower side is at least one piston rod (4) guided through the pressure cheek (1) of additional compressed air cylinder(s) (5) incorporated in the pressure cheek base. These additional compressed air cylinders receive a pressure which is exactly sufficient to lift the workpieces into the conveying plane by the ejector pins. Thus, while the pressure cheek 1 is retained at the bottom dead centre, the pin plate with the press ram (not shown) once more travels upwards directly after the drawing operation. Subsequently, the pressure cheek may then travel upwards slowly and only needs to have reached the upper dead centre shortly before the beginning of the next drawing operation. <IMAGE>

Description

SPECIFICATION Pneumatic drawing device with a pressure cheek guided in the press bed.

The invention relates to a pneumatic drawing device with a pressure cheek guided in the press bed and supported by at least one pneumatic cylinder, which pressure cheek cooperates with a hydraulic locking or retaining device active at bottom dead centre.

For retaining the metal sheets at the time of drawing and for ejecting the finished workpieces, so called pneumatic drawing pads are provided in the press beds. Various constructions of these drawing pads are known (characteristic construction). They consist essentially of a controlled or uncontrolled pressure cheek which is in one piece or divided several times. In the case of uncontrolled pads, the pressure cheek is pushed by means of the pressing or ejector pins by 1 x the drawing depth to the bottom dead centre and as the ram ascends returns automatically and simultaneously to the top dead centre. At the time of the descent and ascent of the pressure cheek, the pad force is approximately the same in both directions. Particularly with thin-walled workpieces, the danger arose that the workpieces may be pushed by the ejector pins against the upper tool and damaged in this way.

For this reason there has been a change towards using controlled pads. In this case, as with an uncontrolled operation, the press ram pushes the pressure cheek back to the bottom dead centre. Then, at the bottom dead centre, a hydraulic locking device is actuated, which retains the pressure cheek at the bottom dead centre, while the ram travels back in the direction of the top dead centre. Only when the ram is at a distance of approximately 1 2 times the drawing stroke from the bottom dead centre is the locking device once more released, whereupon the pressure cheek then travels back with the drawing part into the upper position, which equally corresponds to the conveying plane.

Due to this construction, the workpiece was also treated carefully at the time of ejection, but this resulted in a lower number of strokes, since the workpiece arrives in the conveying plane with some delay and must be advanced to the next drawing stage before the ram arrives for the next drawing operation.

Starting from the afore-described controlled construction, it is the object of the invention to retain the pressure cheek likewise at the bottom dead centre, but to achieve a greater number of strokes.

This is achieved according to the present invention in a pneumatic drawing device of the afore-described type due to the fact that lying directly on the pressure cheek is a pin plate of the same surface area, the upper side of which supports the ejector pins, whereas acting on the lower side of the latter are piston rods guided through the pressure cheek and belonging to additional compressed air cylinders incorporated in the pressure cheek base. The pressure head for the additional compressed air cylinder may thus be adjusted by means of a pressure-regulating device.

A particularly advantageous construction of the invention is seen in that the piston rod of the pneumatic cylinder of the pressure cheek is extended downwards from the pneumatic cylinder and comprises a further piston, which travels in a hydraulic cylinder arranged coaxially and can be retained at the bottom dead centre by supplying pressure oil from one side.

Due to the fact that a separate pin plate is now provided, which is actuated by additional compressed air cylinders, a considerably lower pressure for the ejection of the workpieces can be pre-set, irrespective of the pressure for the drawing pad.

In practice the drawing force is separated from the ejection force, i.e. when drawing a thin-walled part, a relatively great drawing force is required and pre-set, in comparison with only a low ejection force. Due to this, the workpiece may ascend immediately with the ram and be raised into the conveying plane, while the pressure cheek is retained at the bottom dead centre.

Furthermore, the number of strokes of the ram can be increased, since the ram may prepare for the next stroke while the pressure cheek is still travelling to the top dead centre, since the workpiece has already left the tool chamber. The pressure cheek only needs to be at the top dead centre when the ram is once more moving downwards and the new drawing operation has not yet begun. This produces a substantial decrease in the otherwise normal, considerable noise level.

The invention is described in detail with reference to the drawings, which show one embodiment in slow steps.

Figure 1 shows two different positions A and B of the pneumatic drawing device according to the invention, in a longitudinal section through the press bed and Figure 2 shows two further positions D and C in the same sectional view.

In the drawing, only the press bed 10 with the clamping plate 1 1 belonging to the press are shown, whereas the tool and the remaining parts of the press have not been shown since the invention does not relate to them.

The actual drawing device consists essentially of the pressure cheek 1, which is supported by means of the piston rod 6 and piston 8 in a compressed air cylinder 7. Mounted loosely on the pressure cheek 1 is a pin plate 2 of equal surface area, whose upper side 2a supports the ejector pins 3. Acting on the underside 2b of the pin plate 2 are the piston rods 4 of additional pneumatic cylinders 5, which are mounted for example on brackets 13 of the pressure cheek base. Instead of the two pneumatic cylinders 5 illustrated, if necessary, more or, however, only a single pneumatic cylinder may be arranged centrally.

The piston rod 6 is extended beyond the pneumatic cylinder 7 in a downwards direction and in the lower end region 6a comprises a further piston 8, which is guided in a hydraulic cylinder 9 supplied with pressure medium at one side. The retaining device for the pressure cheek at the lower pressing point designated generally by the reference numeral 25.

The operation of the apparatus is described with reference to positions A to C. In position A, the pressure cheek 1 and pin plate 2 are located in the upper initial position, in which case the ejector pins 3 project upwards from the clamping plate 11. In this case, the retaining device 25 is open and the piston 8 is located in the upper position.

The ram now arrives and the actual drawing operation begins. In this case position B is adopted. The pressure cheek 1 with pin plate 2 have been pressed by way of the ejector pins 3 by the ram (not shown) to the bottom dead centre.

The part is thus drawn and the locking device 25 is locked due to the fact that the hydraulic chamber 14 is closed off by a valve cone 15. In this position, during the descent of the piston 8, pressure oil passes from the container 16, through the pipe 17 and the non-return valve 18 into the cylinder 1 9.

Due to the closing-off of the hydraulic chamber 14 and the plunging of the piston rod 20 into the hydraulic chamber 14, a pressure in the downwards direction is produced in the cylinder chamber 19, due to which the piston 8 is retained reliably in the lower position.

Then, the ram again rises, but the pressure cheek 1 remains in the bottom dead centre position. Since the compressed air cylinders 5 are supplied by a compressed air container 21 with a pressure exactly necessary for the ejectors, the pin plate 2 travels upwards with the ram and in this case lifts the finished drawn part into the conveying plane. The position C has now been reached.

Now the retaining device 25 becomes uncontrolled and the piston rod 20 of the piston 26 returns with the valve cone towards the left, due to which the liquid from the cylinder chamber 19 is forced back through the bore 22, through the hydraulic chamber 14 and the pipe 23 into the oil container 1 6. which is acted upon by compressed air 24. Position D is now reached, which in practice corresponds to the initial position A.

The speed of the pressure cheek at the time of the ascent may thus be pre-set so that the latter only arrives back in its initial position shortly before the beginning of the next drawing operation. Noise is thus reduced and the number of strokes can be increased, since the drawn part has already been raised into the conveying plane by the pin plate with the ascent of the ram and has been discharged from the tool chamber. Whereas the pneumatic pressure in the pneumatic cylinder 7 is always the same, the pneumatic pressure for the compressed air cylinder 5 can be adjusted so that the force is just adequate to lift the finished workpiece from the tool.

Claims

1. Pneumatic drawing device with a pressure cheek guided in the press bed and supported by at least one pneumatic cylinder, which pressure cheek cooperates with a hydraulic locking or retaining device active at the bottom dead centre, wherein lying directly on the pressure cheek is a pin plate of the same surface area, the upper side of which supports the ejector pins, whereas acting on the underside are piston rods guided through the pressure cheek, which piston rods belong to additional compressed air cylinders incorporated in the pressure cheek base.

2. Drawing device according to claim 1, wherein a pressure-regulating device is arranged in the compressed air supply line for the additional compressed air cylinders.

3. Drawing device according to claims 1 and 2, wherein the piston rod of the pneumatic cylinder of the pressure cheek is extended downwards from the pneumatic cylinder and comprises a further piston, which travels in a hydraulic cylinder arranged coaxially and can be retained at the bottom dead centre due to a supply of hydraulic oil from one side.

4. A drawing device substantially as herein described with reference to and as illustrated in the accompanying drawings.