Development of a critical friction model for cross wedge rolling hollow shafts

In the manufacturing community, there has been a significant movement towards forming hollow shafts with the cross wedge rolling (CWR) process. This trend has presented the engineering community with a significant challenge because all of the current failure models for the CWR process have been based on the rolling of solid billets. In the present investigation, an analytical model has been developed for determining the minimal friction required at the tool workpiece interface to achieve rolling (critical friction) in the cross wedge rolling of hollow shafts. By means of the explicit dynamic finite element method and specialized experiments, the accuracy of the analytical model was evaluated for the rolling of hollow 6061 T6 Aluminum billets. Based on the numerical and experimental results, trends for the variation of the critical friction as a function of CWR process parameters were subsequently ascertained and discussed with respect to excess slip failure.