Method and apparatus for forming a can shell

A method of forming a cup-shaped circular can shell from a flat metal sheet within a mechanical press, the shell including a center panel connected by an annular panel wall to an annular countersink having a generally U-shaped cross-sectional configuration and with the countersink connected to an annular crown by an inclined annular chuckwall, the method comprising the steps of

• forming an air reservoir chamber within a die center piston supporting a die center punch,
• forming an annular air piston chamber between the die center piston and an outer pressure sleeve,
• positioning within the air piston chamber an annular piston integral with an inner pressure sleeve,
• connecting the air reservoir chamber to the air piston chamber with a plurality of circumferentially spaced air spring passages within the die center piston,
• supplying controllable air pressure to the air reservoir chamber and to the air piston chamber through the air spring passages,
• blanking a disk from the sheet,
• gripping an annular portion of the disk with controlled pressure between an annular die core ring and an opposing annular outer pressure sleeve,
• initiating the drawing of a cup from a center portion of the disk with a die center punch insert within the die center punch disposed within the inner pressure sleeve,
• continuing the drawing of the cup until the inner pressure sleeve clamps an inclined annular portion of the cup against the die core ring and forms an inclined inner wall for the annular crown,
• continuing the drawing of the cup with the die center punch insert cooperating with an opposing panel punch to complete the cup while a contoured outer surface on the die center punch surrounding the die center center punch insert cooperates with a contoured inner surface on the die core ring to form the annular chuckwall of the shell, and
• reversing the direction of the panel punch and the die center punch while continuing to clamp the annular portion of the cup between the inner pressure sleeve and the die core ring to form the center panel, the panel wall and countersink with surfaces on a peripheral portion of the panel punch.