Laser-Assisted Cylindrical Grinding of Silicon Nitride Ceramics

Abstract

Cylindrical grinding of advanced ceramic materials, like silicon nitride, is a crucial machining process for high-precision industrial applications to achieve a damage-free surface and subsurface where a high grinding efficiency and material removal rates are also desirable. For the first time in the cylindrical grinding process, a laser structuring of Si3N4 workpiece has been employed to structure the material surface prior to the grinding process (as a time-independent process). The laser structuring is to generate controllable damaged zone to reduce grinding forces and temperature and accordingly increase the achievable material removal rate. A series of line structures parallel to the workpiece axis with different structure percentages have been generated on the circumference surface of the samples by a nanosecond laser. The effect of laser structuring on thermal damage zones has been microstructurally analyzed by SEM and EDS. The detected laser-induced thermal damages prior to the grinding process (with different microstructures and chemical compositions) are classified as the recast layer and the heat-affected zone (HAZ). The maximum damage thickness for the recast layer is 2 µm, while for the heat-affected zone is approximately 10 µm. The HAZ thickness could be increased up to 50 µm if the snowflakes are located near the thermal damage zone. The tangential grinding force and the surface integrity, including surface roughness and microstructure of the ground surface have also been investigated in laser assisted cylindrical grinding. The results indicate that laser structuring causes a substantial reduction in the tangential grinding force (up to 75%). Additionally, a damage-free subsurface and even slightly better ground surface quality (compared to the conventional grinding process) could be achieved by the proposed laser-assisted grinding process.

Keywords: Laser-assisted cylindrical grinding, Silicon nitride, Laser structuring, Subsurface damage, Microstructure analysis