Effects of workpiece thermal properties on machining-induced residual stresses - thermal softening and conductivity

Workpiece material properties play a key role in controlling the cutting process, and consequently residual stresses. Different materials may behave totally differently under the same cutting conditions; they may produce different types of chip, surface finish, residual stress, etc. The current work examines the effects of two workpiece thermal properties, specifically thermal conductivity (k) and thermal softening exponent (m), on machining-induced residual stresses, in order to understand their role in controlling the residual stresses induced in different materials, when cut using the same cutting conditions. Finite element analysis was used to model the process of orthogonal dry cutting, using the arbitrary-Lagrangian-Eulerian technique, and then predict the induced residual stresses. In order to isolate the effects of the examined properties (k and m), only one material (stainless steel AISI 316L) was used as the base workpiece material, and different values were assigned to its k and m, one at a time. Values up to four times the original magnitudes were used, covering almost all commercial steels and stainless steels. All other material properties and cutting conditions were kept constant. Surface tensile residual stresses were induced in all cases, and a strong effect was found for both properties. k has mainly affected the thickness of the tensile layer, where higher k resulted in thicker layers; it has also induced higher surface tensile residual stresses. On the other hand, higher m (lower softening effects) has significantly increased the magnitude of surface tensile residual stresses, with almost no effect on the thickness of the tensile layer.