Surface integrity of die material in high speed hard machining, part 2: Microhardness variations and residual stresses

The main objective of this paper is to investigate the quality and integrit y of the surface produced during high speed hard machining (HSHM) of D2 too l steel in its hardened state (60-62 HRc). Polycrystalline Cubic Boron Nitr ide (PCBN) tools are used in this study. The results obtained from the micr o-graphical analysis of the surface produced are presented in Part 1 of thi s paper. In Part 2 micro-hardness and residual stress analyses are presente d. Microhardness measurements are conducted beneath the machined surface. X -ray diffraction analysis is performed to obtain the residual stress distri bution beneath the surface. Analytically, a 3-D thermo-elasto-plastic finit e element model is developed to predict the residual stresses induced in th e workpiece surface. In the model the cutting zone is specified based on th e tool condition (i.e., sharp or worn). The finite element analysis demonst rates the significant effect of the heat generated during cutting on the re sidual stress distribution. The results illustrate the possibility of minim izing the high tensile residual stresses produced in the workpiece surface, by selecting the appropriate depth of cut. A good correlation between the analytical and predicted residual stress is obtained. [S1087-1357(00)00804- 2].