Cold Sizing of Cold- and Hot-Formed Gears

Abstract

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.