Transient thermal response of a rotating cylindrical silicon nitride workpiece subjected to a translating laser heat source, part I: Comparison of surface temperature measurements with theoretical results

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 apr Processing Laboratory, I impro ved understanding of governing physical phenomena, a laser assisted machini ng facility was developed and used to experimentally investigate the therma l response of a rotating silicon nitride workpiece heated by a translating CO2 laser Using a focused laser pyrometer, surface temperature history meas urements were made to determine the effect of rotational and translational speed, as well as the Inset beam diameter and power, on thermal conditions. The experimental results are in good agreement with predictions based on a transient three-dimensional numerical simulation of the heating process. W ith increasing workpiece rotational speed, temperatures in proximity to the laser spot decrease, while those at circumferential locations further remo ved from the laser increase. Near-laser temperatures decrease with increasi ng beam diameter, while energy deposition by the laser and, correspondingly , workpiece surface temperatures increase with decreasing laser translation al speed and increasing laser power. In a companion paper (Rozzi et at, 199 8), the derailed numerical model is used to further elucidate thermal condi tions associated with laser heating and to assess the merit of a simple, an alytical model which is better suited for online process control.