Experimental Evaluation of the Laser Assisted Machining of Silicon Nitride Ceramics

Abstract

Abstract Laser assisted machining (LAM), in which a workpiece 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 and lower manufacturing costs for difficult-to-machine materials such as structural ceramics. To assess the feasibility of the LAM process, experiments were performed on silicon nitride workpieces for a wide range of operating conditions. Data for cutting forces and surface temperatures indicate that the lower bound of the material removal temperature for avoidance of cutting tool and/or workpiece fracture corresponds to the YSiAlON glass transition temperature (920–970°C). As temperatures near the cutting tool increase to values above the glass transition temperature, the glassy phase softens, facilitating plastic deformation and, correspondingly, the production of semi-continuous or continuous chips. The silicon nitride machined workpiece surface roughness (Ra = 0.39 μm) for LAM at the nominal operating condition was nearly equivalent to a value associated with the grinding of silicon nitride using a diamond wheel (Ra = 0.2 μm). Examination of the machined surfaces and chips reveals no detectable sub-surface cracking or significant changes in microstructure, respectively. Relative to grinding, the most significant advantage of LAM is its ability to achieve much larger material removal rates with high workpiece surface quality and reasonable levels of tool wear.