Experimental investigation of machinability and surface quality of sapphire machined with polycrystalline diamond micro-milling tool

Ultra-precision machining of single crystalline sapphire was performed using a polycrystalline diamond (PCD) micro-milling tool. Examination of the machining characteristics indicates that a high-quality surface with a nanometre-scale surface roughness can be obtained when the removed chips are thin enough to achieve ductile-mode machining. Although a high-quality surface was successfully machined, the surface roughness gradually deteriorated and the actual depth of the machined groove became shallower as the machining distance increased because of the build-up of material adhering to the surface of the tool. To retain the milling capabilities of the PCD tool, an electrochemical-assisted surface reconditioning process has been proposed. The reconditioning technique was found to be effective in removing the surface contaminant without causing damage to the edges of the tool.