Numerical and experimental study of bubble behavior in ultrasonic vibration-assisted EDM

Abstract

It is well known that the movement of electrical discharge-generated gas bubbles plays a crucial role in debris exclusion, especially in the EDM (Electrical Discharge Machining) process of the micro-hole with the high aspect ratio. Applying ultrasonic vibration to EDM machining is thought to be an effective method to restrain debris accumulation and enhance bubble removal. In this paper, the effect of the ultrasonic vibration of the tool on the bubble behavior in EDM is investigated using a high-speed camera. The computational simulation of bubble behavior is studied by employing the VOF (Volume of Fluid) method with the proposed two-dimensional model of the flow field with liquid, and gas phases for the discharge gap. Bubble observation results show that machining debris scatters in the bubble's boundary and utilization of ultrasonic vibration of the tool will significantly improve the expansion bubbles exclusion in the discharge gap. It is also found from the numerical study that more vibration cycles will be necessarily needed for the bubble discharge from the gap outlet as the machining depth increases. Main Cause suggested for bubbles moving toward the gap outlet may be the periodic oscillation induced by the ultrasonic vibration. Furthermore, as demonstrated by the simulation results, the bubbles move along the edge of the electrode surface in the dielectric fluid.