Stepped extrusion die assembly

An extrusion die assembly for forming by extrusion an annular part generally symmetrical about an axis,

• said annular workpiece being hollow and thereby defining an inner surface and an outer surface, with each said surface being coaxially disposed about said axis, and
• said workpiece having a generally uniform length along said axis extending from a leading end to a trailing end,
• a first die member,
• a second die member,
• said first and second die members being coaxially disposed relative to one another and reciprocal relative to one another,
• each said die member having an extrusion forming surface contiguous with a respective one of said inner and outer surfaces of said workpiece, with said workpiece being disposed between the relatively reciprocal first and second die members,
• one of said die members including means for extruding a radially projection profile in said workpiece, said profile being of uniform configuration including depth and volume throughout its axial length from the leading end of said workpiece to the trailing end thereof,
• said means including a series of successively axially spaced die profile segments, each die profile having a leading end and a trailing end, the leading end thereof increasing radially in substantially equal proportion from one die profile segment to the next successively arranged die profile segment, whereby as each die profile is successively traversed across said workpiece from one segment to the next segment, said profile will be formed in said workpiece in uniformly successive stages;
• and
• means for maintaining the axial position of the workpiece at the leading end thereof fixed relative to said other die member as the leading end of any one of said die segments axially traverses said workpiece in the direction of the workpiece leading end, whereby axial extrusion of the workpiece is limited to the direction towards the trailing end of said workpiece and said die segment.