Cold sizing of cold- and hot-formed gears

Today's markets require industrial forgers to manufacture complex near net shape or net shape parts at minimum unit costs. One way of meeting this challenge is to combine a cold or hot forming process with a subsequent cold sizing process in order to achieve the desired tolerances. In this context, a closed-die cold sizing process of a straight-toothed planetary gear has been investigated in terms of the occurring elastic die deflection which is a threat to accuracy in this and any other cold forming process. Two strategies have been employed to minimize the elastic die deflection. The first strategy consists in a correction of the die cavity's tooth profile based on the finished part's deviation from its theoretical shape determined through Finite-Element-Analysis (FEA). The key idea underlying the second strategy is an innovative tooling concept which compensates the elastic die deflection by means of a counter pressure generated by an elastomer ring embedded in the lower die. The advantages of this active concept have been confirmed in numerical and experimental investigations.