Prediction model for surface shape of YAG wafers in wafer rotational grinding

Abstract

Yttrium aluminum garnet (YAG) wafers are essential for thin disk lasers, requiring extremely low peak-to-valley (PV) values after thinning. Wafer rotational grinding is an efficient thinning method for controlling the surface shape, minimizing the time required for polishing. However, the high hardness of YAG increases grinding forces, which can deform the grinding wheel and compromise the surface shape. This paper presents a novel predictive model for the surface shape PV value of ground YAG wafers to address this issue. Initially, a grinding force model is established by considering material elasticity rebound and the size effect of material hardness. Subsequently, the wheel deformation induced by grinding force is calculated and the results are confirmed with finite element simulation. Furthermore, the effect of wheel deformation on the inclination angle is investigated, and the PV value of the ground surface is calculated. Finally, grinding tests are used to validate the suggested model, and the impact of the grinding settings on the PV value is investigated. The results demonstrate that the PV value of the wafer increases with higher grain size and wheel rotational speed, but decreases with higher workpiece rotational speed and feed rate. Additionally, wafers ground with resin-bond wheels shows lower PV value compared to those ground with vitrified-bond wheels. The experimental results align with theoretical predictions, indicating that the proposed model is accurate. This work improves the understanding for grinding surface shape prediction in wafer rotational grinding and provides valuable guidance for optimizing grinding parameters for YAG wafers.