A study on the development of milling process for silicon nitride using ball end-mill tools by laser-assisted machining

Silicon nitride is a non-oxide ceramic that represents strong characteristics in high strength, abrasion resistance, corrosion resistance, and thermal shock resistance at high temperatures and that has been widely used in the industry. However, it also exhibits high levels of hardness and brittleness, and machining of silicon nitride is usually implemented using a diamond grinding process. This presents difficulties in machining due to increased machining cost and time, and a machining method to reduce these is needed. Current studies on an alternative approach to the problem have been focused on laser-assisted machining (LAM) methods that facilitate machining by softening a workpiece using a laser heat source. The advantages of a LAM process are decreases in tool wear and cutting force and reductions in catastrophic tool failures and the occurrence of chatter. In this study, a high-power diode laser (HPDL) is used as a heat source for machining of silicon nitride. Machining experiments were carried out using cubic boron nitride (CBN) tools. The proper laser power for the experiment was determined through thermal analysis. A back-and-forth laser-path preheating method was newly proposed to obtain sufficient temperature for softening the silicon nitride. Machining experiments were performed using back-and-forth method and insulation material for protecting heat. The machining of silicon nitride was performed successfully by a laser-assisted milling (LAMill) process using a CBN ball end-mill tool, which is stable at high temperatures. In the machining with applying three times of a back-and-forth laser-path preheating process, tool breakage and gas marks were not occurred at the 170 W for processing a depth of cut of 0.15 mm. It is expected that the results of machining experiments can be used to process the various shape of silicon nitride material.