Investigation of laser-assisted cylindrical grinding of silicon nitride ceramics with controlled damage zone

Cylindrical grinding of advanced ceramic materials, like silicon nitride, is a crucial machining process for high-precision industrial applications. The goal is to achieve a damage-free surface and subsurface while ensuring high grinding efficiency and desirable material removal rates. For the first time in the cylindrical grinding process, a laser structuring of the Si3N4 workpiece has been employed to structure the material surface before the grinding process. The structuring process is conducted as a time-independent process. The laser structuring aims to generate a controllable damaged zone, which reduces grinding forces and temperature. This reduction subsequently leads to an increase in the achievable material removal rate. A series of line structures parallel to the workpiece axis with different structure percentages has been generated on the circumferential surface of the samples using a nanosecond laser. The influence of laser structuring on thermal damage zones has been microstructurally investigated through SEM and EDS analyses. The thermal damages caused by the laser before the grinding process (exhibiting different microstructures and chemical compositions) are categorized as the recast layer and the heat-affected zone (HAZ). The maximum damage thickness for the recast layer is 2 µm, whereas the thickness of the heat-affected zone is approximately 10 µm. The HAZ thickness could increase up to 50 µm if the snowflakes are placed in close proximity to the thermal damage zone. The study also explored the tangential grinding force and the surface integrity, including characteristics like surface roughness and microstructure of the ground surface in laser-assisted cylindrical grinding. The results indicate that laser structuring substantially reduces the tangential grinding force (up to 75 %). Moreover, the proposed laser-assisted grinding process could achieve a damage-free subsurface and even slightly better ground surface quality compared to the conventional grinding process. This study introduces a novel approach by predicting the grinding allowance through material analysis, aiming for a damage-free surface and subsurface.