Patent ID: 7237423

Claim:
Apparatus for stretch forming blanks comprising: a. a punch defining a longitudinal axis and having a first end sized and shaped with chosen configuration, a second end, and a side surface connecting the first end and the second end; b. means for stationarily supporting the punch second end on a bed; c. a plurality of fluid cylinders each having a casing in the press bed, and a piston, each cylinder being pre-charged to a predetermined force; d. a pad between the punch second end and the cylinders pistons, the pad including a ledge that extends transversely from the punch side surface; e. a blank holder surrounding the punch; and f. a draw ring surrounding the punch and having a step, the draw ring cooperating with the blank holder to hold a blank therebetween during a draw stroke during which the draw ring and blank holder advance in a direction parallel to the punch longitudinal axis to bend the blank over the punch first end and such that the draw ring step approaches the pad ledge and ultimately cooperates therewith to create a step-ledge and to bend the blank into a reverse bend at the step-ledge, the draw ring exerting sufficient force on the step-ledge to overcome the predetermined force of the cylinders and cause the step-ledge and cylinder pistons to travel a short distance, so that the blank between the punch first end and the step-ledge is stretched and the blank is stretch formed into a formed piece.