Sheet metal press equalisation device for - workpiece holder

Hydraulic pressure cushion is interposed in the mechanical crank actuated mechanism for holding down the workpiece sheet metal material during the stamping operation in a press. The cushion evens out the variable pressure exerted by the reciprocating crankshaft, which, particularly during its passage through its dead position, exerts virtually no pressure. The piston employed is linked to a low inertia pressure transmitter, a pumping circuit, and an overload device employing a compressed air chamber with a spring loaded valve against which a plunger in a cylinder attached to another plunger in contact with the hydraulic fluid exerts a pressure proportional to the pressure exerted upon the workpiece.