A new methodology for determining the stress state of the plastic region in machining with restricted contact tools

In rigid-plastic slip-line theory, once the geometry of the slip-line field is established, the stress state of the plastic region (including the prim ary and secondary deformation zones) in restricted contact machining is gov erned by the hydrostatic pressure P-A (at a point on the intersection line of the shear plane and the work surface to be machined) and the frictional shear stress tau on the tool rake face. Based on the recently established u niversal slip-line model and a detailed study of six representative machini ng cases, a new methodology for determining the stress state of the plastic region, i.e. maximum value principle, is presented in this paper. Accordin g to this principle, the stress state of the plastic region can be determin ed by giving both P-A and tau their theoretical maximum permissible values. The theoretical maximum permissible values of P-A and tau can be found by satisfying four mechanical and geometrical constraint conditions under whic h the universal slip-line model applies. A comprehensive assessment factor is introduced in this paper. It is shown that the three machining parameter s investigated in this present study, i.e. cutting force ratio, chip thickn ess ratio, and chip back-flow angle can be simultaneously considered to for m a comprehensive criterion to compare predicted and experimental results. The applicable range of the maximum value principle is also discussed. (C) 2001 Elsevier Science Ltd. All rights reserved.