Transient, three-dimensional heat transfer model for the laser assisted machining of silicon nitride: II. Assessment of parametric effects

In a companion paper (J.C. Rozzi, F.E. Pfefferkorn, F.P. Incropera, Y.C. Shin, Transient, three-dimensional heat transfer model for the laser assisted machining of silicon nitride: I. Comparison of predictions with measured surface temperature histories, International Journal of Heat and Mass Transfer 43 (2000) 1409-1424), experimental validation was provided for a transient, three-dimensional heat transfer model of the LAM of a silicon nitride workpiece. In this paper, the model is used to elucidate the influence of operating parameters on thermal conditions within the workpiece. Calculations reveal that thermal energy generation in the primary shear zone has a significant influence on the workpiece temperature distribution, while the effects of heat transfer at the tool flank interface may be neglected. Although temperatures at the material removal plane were only moderately influenced by an increase in the workpiece rotational speed, a reduction in total laser energy deposition due to increased laser/tool translational velocity or decreased laser power may preclude the attainment of a minimum material removal temperature corresponding to the softening temperature range of the YSiAlON glassy phase. Due to the comparatively small influence on radial temperature gradients within the material removal plane, the minimum material removal temperature decreased only slightly with increasing depth of cut. However, the amount of laser energy deposition on the unmachined workpiece increased significantly with increasing laser-tool lead distance, yielding an attendant increase in the material removal temperature. For a fixed laser-tool lead, energy deposition at the unmachined workpiece surface increased with decreasing laser beam diameter and increasing power. (C) 2000 Elsevier Science Ltd. All rights reserved.