Although laser machining and laser assisted machining has been increasingly applied to process silicon nitride ceramics (Si3N4), laser irradiation can cause damage in ceramics due to thermal stress, resulting in microcracks and significant decrease in material strength. The potential subsurface microcracks is one of the most important concerns in ceramic machining. In order to avoid microcracks below the depth of cut, to minimize the deformation of workpiece and achieve temperature high enough at the depth of cut for smooth material removal, finite element analysis (FEA) is applied to analyze the thermal stresses of Si3N4 workpiece. In this study, three-dimensional FEA model is used to study the effects of operating conditions (laser power, laser beam diameter, laser translating speed, tool diameter and preheat time) for laser assisted milling. Both slot milling and face milling operations are considered. It is found that as the laser moves, the location of the largest tensile stress also moves with the laser. The maximum compressive stress usually appears at the center of the moving laser spot on the top surface. Proper selection of laser parameters and machining conditions are needed to achieve temperature high enough at the depth of cut for smooth material removal and yet to avoid potential cracking due to large thermal stress. Laser heating and laser assisted milling experiments will be done and the experimental results will be compared with the simulations.
Keywords: Silicon nitride, Heat transfer, Thermal stress, Laser assisted machining, FEA
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