Theoretical and experimental investigations on rotary ultrasonic surface micro-machining of brittle materials

Many brittle materials, such as single-crystal materials, amorphous materials, and ceramics, are widely used in many industries such as the energy industry, aerospace industry, and biomedical industry. In recent years, there is an increasing demand for high-precision micro-machining of these brittle materials to produce precision functional parts. Traditional ultra-precision micro-machining can lead to workpiece cracking, low machined surface quality, and reduced tool life. To reduce and further solve these problems, a new micro-machining process is needed. As one of the nontraditional machining processes, rotary ultrasonic machining is an effective method to reduce the issues generated by traditional machining processes of brittle materials. Therefore, rotary ultrasonic micro-machining (RUμM) is investigated to conduct the surface micro-machining of brittle materials. Due to the small diameter cutting tool (<500 μm) and high accuracy requirements, the impact of input parameters in the rotary ultrasonic surface micro-machining (RUSμM) process on tool deformation and cutting quality is extremely different from that in rotary ultrasonic surface machining (RUSM) with relatively large diameter cutting tool (∼10 mm). Up till now, there is still no investigation on the effects of ultrasonic vibration (UV) and input variables (such as tool rotation speed and depth of cut) on cutting force and machined surface quality in RUSμM of brittle materials. To fill this knowledge gap, rotary ultrasonic surface micro-machining of the silicon wafer (one of the most versatile brittle materials) was conducted in this study. The effects of ultrasonic vibration, tool rotation speed, and depth of cut on tool trajectory, material removal rate (MRR), cutting force, cutting surface quality, and residual stress were investigated. Results show that the ultrasonic vibration could reduce the cutting force, improve the cutting surface quality, and suppress the residual compressive stress, especially under conditions with high tool rotation speed.