GB1429226A - Drawing apparatus for sheet metal working - Google Patents

Abstract

1429226 Cupping L SCHULER GmbH 12 June 1973 [12 June 1972] 27906/73 Heading B3Q In a drawing press having a back-up holder which recedes into a die during a drawing stroke, a residual pressure less than that applied to it during a drawing stroke is applied to the holder during at least part of a return stroke so as to avoid damaging the drawn work. In one form, Fig. 1, the back-up holder 17 within the die 5 also functions as an ejector, a punch 1 co-operating with the die to cut-out the workpiece 18 and having a blank holder 3 operated by fluid or spring pressure. The holder 17 is operated by a piston 7 in a cylinder 6 to which oil from a reservoir is supplied through a valve 10, 11, the slide 10 of which is moved by a piston 9 in a cylinder 8. A one-way valve is placed between the reservoir and the valve 10, 11 and a pressure relief valve is located in a passage between a port 15 in the cylinder 6 and the reservoir. At the end of a working stroke, Fig. 2 (not shown), the valve-slide 10 is reset by movement of the piston 9 to the right, thus isolating cylinder 6 from the reservoir during part of the return stroke of the die, Fig. 3 (not shown). A spring-pressed plunger 22 in the slide 10 maintains a residual pressure of 2-6 atmospheres in the cylinder 6 during this part of the return stroke. The residual pressure generator may, alternatively, be located in the cylinder wall or in a remote position and be connected to the cylinder by a pipe; it may be constituted by a pump or reservoir. During the last part of the stroke of the die, Fig. 4 (not shown), piston 9 resets the valve to supply reservoir oil to cylinder 6 for ejecting the work. As applied to drawing a cap with an end depression, Fig. 5, the back up holder is in the form of a second blank holder 30 which remains in a receded position (Fig. 6) in the die 5 during ejection of the work by a separate cam-operated ejector 32. An annular piston 7 operates in the cylinder 6, the connection of which to the reservoir through the valve 10, 11 is interrupted at the beginning of a drawing operation.