Transient, three-dimensional heat transfer model for the laser assisted machining of silicon nitride: I. Comparison of predictions with measured surface temperature histories

Laser assisted machining (LAM), in which the material is locally heated by an intense laser source prior to material removal, provides an alternative machining process with the potential to yield higher material removal rates , as well as improved control of workpiece properties and geometry, for dif ficult-to-machine materials such as structural ceramics. To assess the feas ibility of the LAM process and to obtain an improved understanding of gover ning physical phenomena, experiments have been performed to determine the t hermal response of a rotating silicon nitride workpiece undergoing heating by a translating CO2 laser and material removal by a cutting tool. Using a focused laser pyrometer, surface temperature histories were measured to det ermine the effect of the rotational and translational speeds, the depth of cut, the laser-tool lead distance, and the laser beam diameter and power on thermal conditions. The measurements are in excellent agreement with predi ctions based on a transient, three-dimensional numerical solution of the he ating and material removal processes. The temperature distribution within t he unmachined workpiece is most strongly influenced by the laser power and laser-tool lead distance, as well as by the laser/tool translational veloci ty. A minimum allowable operating temperature in the material removal regio n corresponds to the YSiAlON glass transition temperature, below which tool fracture may occur. In a companion paper [1], the numerical model is used to further elucidate thermal conditions associated with laser assisted mach ining. (C) 2000 Elsevier Science Ltd. All rights reserved.