Study on the effects of bending ultrasonic vibration electrode on EDM characteristics via bubble observation

The application of ultrasonic vibration to electrodes has significantly enhanced the efficiency of electrical discharge machining (EDM) in micro-hole processing. However, when the aspect ratio of a micro-hole exceeds 6, the high-frequency vibration at the electrode tip becomes insufficient to effectively agitate the working fluid within the discharge gap, thereby limiting the rapid removal of debris and bubbles. In this study, inspired by the acoustic black hole immersed sonoreactor, a cylindrical electrode was vertically mounted at the end of a bolt-clamped Langevin type transducer (BLT). The cylindrical electrode was designed to incorproate a bending vibration mode, enhancing both the bending wave and its wave number. Under resonant conditions, the electrode exhibited multiple vibration antinodes distributed along the narrow bubble removal path. We characterized the influence of these antinodes on bubble dynamics in the discharge gap by high-speed imaging technology. We demonstrate that these vibration antinodes effectively inhibit bubble coalescence and significantly expedite bubble removal. This study provides valuable insights into electrode vibration modes selection for improving the efficiency of deep micro-hole EDM and reducing abnormal discharges, substantially broadening the possibilities for further increasing the aspect ratio of micro-holes in EDM.