Transient thermal response of a rotating cylindrical silicon nitride workpiece subjected to a translating laser heat source, part II: Parametric effects and assessment of a simplified model

In a companion paper (Rozzi et at, 1998), experimental validation was provi ded for a transient three-dimensional numerical model of the process by whi ch a rotating workpiece is heated with a translating laser beam. In this pa per, the model is used to elucidate the effect of operating parameters on t hermal conditions within the workpiece and to assess the applicability of a n approximate analysis which is better suited for on-line process control. From detailed numerical simulations, it was determined that the thickness o f a surface thermal layer decreases with increasing workpiece rotational sp eed and that the influence of axial conduction an the workpiece temperature distribution increases with decreasing laser translational velocity. Tempe ratures increase throughout the workpiece with increasing laser power, whil e the influence of increasing beam diameter is confined to decreasing near- surface temperatures. Temperature-dependent thermophysical properties and f orced convection heat transfer to the laser gas assist jet were found to si gnificantly influence the maximum temperature beneath the laser spot, while radiation exchange with the surroundings and mixed convection to the ambie nt air were negligible. The approximate model yielded relations for calcula ting the radial temperature distribution within an r-phi plane correspondin g to the center of the laser source, and predictions were in reasonable agr eement with results of the numerical simulation, particularly in a near-sur face region corresponding to the depth of cut expected for laser-assisted m achining.