Reducing cutting force in rotary ultrasonic drilling of ceramic matrix composites with longitudinal-torsional coupled vibration

Drilling of ceramics matrix composites (CMCs) still faces challenges such as low efficiency and severe delamination. Reduction in cutting force is beneficial for improvement in drilling efficiency and suppression of delamination. Conventional rotary ultrasonic drilling (Con-RUD) using longitudinal vibration is regarded as a superior method for drilling CMCs. This study was devoted to establishing a novel RUD method utilizing longitudinal and torsional coupled (LTC) vibration to further reduce the cutting force. Helical flutes were produced on diamond core tool to generate LTC vibration. Machining tests showed that the LTC-RUD is beneficial for reduction in cutting force by more than 50% compared to Con-RUD.