Minimum energy criterion applied to the orthogonal machining of polymers

The paper deals with the orthogonal machining characteristics of anisotropic and normal stress sensitive polymers. Tensile and compression tests were carried out to define the mechanical properties of the chosen polymers, nylon and polycarbonate. The deformation during cutting is assumed to occur under plain strain conditions and a suitable yield equation is chosen to describe the material yielding behaviour. For the cutting process, a single shear plane model is assumed and the minimum energy criterion applied to the appropriate yield criterion to develop a representative shear angle relationship, which depends on the mechanical state of the chosen polymer. Orthogonal cutting tests were carried out varying three main parameters; cutting speed, tool rake angle and depth of cut. Measured forces and shear angles are compared with the values predicted from the theoretical analysis and an excellent correlation is obtained. It is concluded that, for the assumed mode of deformation, the minimum energy criterion applied to a representative yield equation is justified in explaining polymer behaviour under orthogonal cutting conditions.