GB1311681A - Punching and stripping mechanism - Google Patents

Abstract

1311681 Punching; strippers PIERCE-ALL MFG Ltd 20 April 1970 [5 May 1969] 18734/70 Heading B3W Hydraulic fluid is supplied to a punch cylinder 1 and 16 a cylinder 5 of a piston 7 driving a spring-biased hold down and stripper member 3 via an adjustable valve 10, 11 with flow and return connections 13 and 15 respectively to a supply tank (not shown). A flow restrictor 20 is provided in the conduit 19 leading to the upper end of the cylinder 1 and a check valve 22-24 in the line 21 leading to the stripper cylinder 5. A return line to the tank has a control valve 27, 28 therein. To initiate a punching operation the valve rotor 11 is moved to the Fig. 2 position in which fluid is supplied to the upper ends of cylinders 1 and 5, the flow restrictor 20 causing greater flow to the stripper cylinder 5 so that the stripper member 3 holds a workpiece 34 against a press table 35 before the punch enters the workpiece. For the return stroke, the rotor 11 is rotated to a position in which fluid is supplied only to the underside of punch piston 8. Due to the check valve 22-24 pressure in the stripper cylinder is maintained until, after the punch has been removed from the workpiece, the valve 27, 28 is opened by, e.g. electrical means including limit switches or through a releasable mechanical coupling (29), (30), Fig. 1 (not shown), with the punch piston-rod 9. The spring 4 raises the stripper member 3 and the valve 27, 28 is closed. Alternatively, the stripper member 3 can be raised hydraulically and/or the punch by spring pressure. The flow restrictor may be omitted, the increase in resistance to the punch before workpiece penetration ensuring sufficient pressure for the stripper member 3 to engage the workpiece before the punch enters the workpiece. Alternatively, the volume of the cylinder 1 and the size of conduit 19 may be selected to ensure that the stripper member 3 engages the workpiece before or at approximately the same moment as the punch 2.