Patent ID: 7231799

Claim:
An apparatus for producing a workpiece with internal teeth from a cup-shaped preform having a substantially cylindrical side wall and a cup base at one axial end of said sidewall, said apparatus comprising: a press bed plate; a mandrel axially fixedly mounted on said bed plate, said mandrel having an external profile corresponding to the internal teeth to be produced on the workpiece; an annular punch surrounding said mandrel, said punch being moveable axially relative to said mandrel so that the punch can engage an axial end face of a preform disposed on said mandrel with an inside surface of said cup base contacting said mandrel; a press ram movable to advance toward said base plate; a forming tool in the form of a drawing ring axially fixedly mounted on said press ram, said drawing ring surrounding said punch and having an area of reduced inner diameter for reducing the diameter of the cylindrical sidewall of the preform on the mandrel during an advancing movement of the press ram and drawing ring and causing material of the cylindrical side wall to flow into the external profile of the mandrel; and a counter holder mounted on said press ram; said counter holder being moveable axially relative to said drawing ring so that the counter holder can engage an outside surface of said cup base of the preform on the mandrel; wherein said annular punch and said counter holder exert opposing axial forces on the preform to produce compressive stress in the cylindrical sidewall of the preform during the advancing movement of the press ram and drawing ring.