DD267926B5 - BACK TRAY CONTROL FOR PULLERS AT PRESSES - Google Patents

Description

For this 1 page drawing

In forming work, which require the holding of the die cushion, it is on double-acting presses, in which the BlechhalterstÖUel the sheet metal position of the drawn part takes, in principle required that the die cushion in the deepest Working position is locked. Even with single-acting presses, this function of the die cushion is required when the drawn part in the lowest working position

by a holddown of great force, z. B. ram pillow, held above the bottom dead center of the press ram addition

The often used in pneumatic cushions hydraulic lock, the outflow of the hydraulic fluid after

prevents the bottom dead center of the press ram from the arranged usually below the pneumatic piston locking cylinder by closing a controllable check valve, is sufficient for the o. g. Applications are not sufficient because the compressibility of the pressure fluid has a springing of the pillow of several millimeters result, causing an unacceptable deformation of the detained in the lowest working position drawing oil.

To compensate for this Kissenauffederung a retraction device is used, which the die cushion and thus the Pillow plate with the force acting on the Un.erwerkzeug pressure pin against the pneumatic ejection force of Kissen zurückzioht. A known solution of this device is shown in DD-WP 82108. Be! This solution is the locking piston on both sides

biased by high pressure by means of nitrogen battery. At the withdrawal time shortly before the bottom dead center of

Press ram, the lower locking piston surface is depressurized by draining a metered amount of pressurized fluid,

whereby the further acting on the upper locking piston surface pressure causes the withdrawal.

Disadvantage of this solution is that large diameters and flow rates required to ensure high performance

are what leads to a very cufwondigen solution due to the high equipment cost of Gesamtoinrichtung.

Another solution, which has found widespread use in modified structural variants, is in the US patent

2 584 339 using the example of a hydropneumatic cushion.

Regardless that in this solution, the check valve and the retraction device are integrated with each other, the Retraction device realized by a pneumatically actuated pressure booster. At the moment of withdrawal, the Compressor pressurized with compressed air, whereby a metered amount of pressurized fluid is displaced into the locking cylinder

and thus causes the withdrawal of the pillow. Disadvantage of this solution is that it requires a large compressed air consumption in pneumatic cushion with large evaluation forces. Another disadvantage is that an impermissibly large pressure drop in the pneumatic space of the pressure booster with increasing Pressenhubzahl (corresponds to increasing required retraction speed) can only be prevented by the fact that the pressure drop of the hydraulic fluid between pressure booster and locking cylinder of

Cushion units larger than functionally required selected (increased air consumption) or the pneumatic room of the Pressure booster with a supply line of very large nominal size (including inlet and outlet valve) is executed. The problem of the invention is to provide a retraction control for die cushions with improved Performance characteristics at high stroke rates, in which the pressure booster is operated without additional separate drive. According to the invention this is achieved by the features described in the characterizing part of claim 1. Further detailed embodiments of the invention are described in the claims 2 and 3. The advantages of the invention consist in an energetically favorable efficiency, i. without air consumption, and low

equipment technical effort.

The inventive solution is shown in a Ausführuiigsbeispiel. The figure shows a schematic sectional view

a single-acting press with the interaction of press ram, ram cushion, tool and pneumatic

Die cushion. During the drawing process, the workpiece 3 in a known manner between the upper tool 2 and the drawing ring 4 of the lower tool. 5

clamped and deformed over the pressure pin 6 and die cushion plate 7 against the pressure applied to the cushion piston 8 pneumatic pressure. The ram cushion 24 acts as a hold-down and ejector on the workpiece. 3

While holding in the tappet flow flows through the check valve 9 hydraulic fluid from the Expansion tank 21 in the locking cylinder 10th Parallel to the ram flow of the Kolbonseitig coupled to the press ram 1 working cylinder 22 is driven and

displaces during the entire ram stroke above the hydraulic pressure line 26 pressure fluid in the pressure booster sixteenth

This is thereby biased against the applied Pneumtjtikdruck. In this case, the differential piston 14 against the on Pressure control device 23 adjusted pneumatic pressure shifted. To reduce the pressure increase or pressure drop when working the differential piston 14 of the pressure booster 16th

pneumatically connected directly to a pressure equalization tank 15.

Shortly before the lower toe point of the press ram, the directional control valve 20 is activated by a crank position-dependent control

switched over, whereby the check valve 13 is unlocked and the pressure booster 1 β is discharged.

Due to the pressure gradient between pressure intensifier 16 and locking cylinder 10 of about 10 ... 50% flows pressure fluid from Differential piston 1'4 via the connecting line 28 in the locking cylinder 10 and pulls with the locking pin 11, the cushion with the Die cushion plate 7 back against the voltage applied to the cushion piston 8 pneumatic pressure. A deformation of the workpiece 3 in the bottom dead center of the press ram 1 against the also euf the workpiece. 3

acting ram pillow 24 is prevented.

By crank position-dependent control is about 30 ... 60 * after the bottom dead center of the press ram 1, the lock · and Throttle valve 12 is opened, whereby the die cushion gets damped in its upper working position. Here is the from the Locking cylinder 10 in the means of pressure control device 25 pneumatically preloaded expansion tank 21 flowing out Pressure fluid throttled pillow path-dependent. During the return stroke of the press ram 1 passes via a hydraulic line 27 between surge tank 21 and Working cylinder 22 hydraulic fluid in the working cylinder 22nd The arranged in this hydraulic line 27 check valve 17 prevents the outflow of hydraulic fluid from Working cylinder 22 to the expansion tank 21st Parallel to the check valve 17, a pressure relief valve 18 and a lockable passage valve 19 are arranged. At the Pillow mode with retraction control is the through valve 19 in the blocking position. Controlled in the pillow control modes

without retraction, ".ungesteuert" and .Ziehkissen out of service ", the through valve 19 is switched to passage, so that the working cylinder 22 operates in the non-pressurized circulation.

Claims (3)

1. retraction control for die cushion on presses, in which the Ziehkissenzylinder with a locking cylinder (10) is in operative connection and the locking cylinder (10) via connecting lines to a pressure booster (16) and a pressure equalization tank (15) is connected, characterized in that a piston side hydraulic working cylinder (22) connected to the press ram (1) via a hydraulic line (26) to the pneumatically actuated pressure booster (16) and via a hydraulic line (27), in which a check valve (17), a pressure relief valve (18) and a through-valve (19) are interposed, is connected to the surge tank (21). 2. retraction control according to claim 1, characterized in that between the pressure booster (16) and locking cylinder (10) a pilot-operated check valve (13) is arranged. 3. retraction control according to claim 1 and 2, characterized in that the pressure booster (16) on the pneumatic side with a pressure equalization tank (15) forms a unit.