Variable pressure drawpress and method

Claim 1

APPARATUS FOR FORMING SHEET METAL COMPRISING: A PUNCH MOVABLE ALONG AN AXIS NORMAL TO THE PLANE OF A WORKPIECE TO BE FORMED AND ESTABLISHING A FORMING ZONE; OPPOSED GRIPPING MEMBERS LOCATED LATERALLY ADJACENT TO SAID FORMING ZONE AND RELATIVELY MOVABLE TOWARD EACH OTHER IN A DIRECTION PARALLEL TO THE AXIS OF MOVEMENT OF SAID PUNCH TO ESTABLISH A GRIPPING ZONE EXTENDING LATERALLY OUTWARD FROM SAID FORMING ZONE FOR SLIDABLY GRIPPING MARGINAL PORTIONS OF SAID WORKPIECE; FLUID PRESSURE MEANS TO APPLY AND MAINTAIN A LIMITED NUMBER OF ZONES OF DIFFERENT CLAMPING PRESSURES AT AREAS SUCCESSIVELY SPACED OUTWARDLY FROM THE FORMING ZONE; AND WEAR PLATE MEANS DISPOSED AGAINST AND COVERING SAID PRESSURE MEANS TO PROVIDE A SMOOTH WEAR RESISTING SURFACE TO ENGAGE SAID WORKPIECE; SAID WEAR PLATE MEANS BEING LOCALLY YIELDABLE IN AN AXIAL DIRECTION AT SAID SUCCESSIVE AREAS TO TRANSMIT DIFFERENT GRIPPING PRESSURES TO THE WORKPIECE CORRESPONDING TO THE DIFFERENT CLAMPING PRESSURES EXERTED BY THE FLUID PRESSURE MEANS.