Does chip formation minimize the energy?

It has frequently been assumed that the process of chip formation as it occurs during machining minimizes the work done during machining. This assumption has been the starting point of the classical analysis by Merchant as well as many others. In this paper, we investigate the question of work minimization in machining by finite element simulation in two different cases: The first is that of an idealized machining process for an perfect plastic material. It is shown that, as expected by theoretical investigations, the shear plane angle does not adjust itself to minimize the work done. In a second case, a more realistic process is studied where thermal softening leads to the formation of segmented chips. It is shown that chip segmentation is consistent with a minimization criterion i.e., that continuous chips formed under identical conditions would need a larger cutting force than the segmented chips actually observed.