★ Bubble behavior and its surrounding fluid are investigated in ultrasonic assisted EDM. ★ Boundary integral equation method was used for the numerical solution. ★ Velocity and pressure around the bubble were shown for ultrasonic vibration of the tool. ★ The fluid behavior is studied for various situations of the tool at the moment of electrical discharge. ★ High velocity and pressure observed near the annular jet of the bubble.
In electrical discharge machining due to the electrical current, very small bubbles are created in the dielectric fluid between the tool and the workpiece. Increase of the number of bubbles and their growth in size generate a single bubble. The bubble has an important role in electrical discharge machining. In this paper the effect of ultrasonic vibration of the tool and the velocity fields and pressure distribution in the dielectric fluid around the bubble in the process of electrical discharge machining are studied numerically. The boundary integral equation method is applied for the numerical solution of the problem. It is shown that ultrasonic vibration of the tool has great influence on the evolution of the bubble, fluid behavior and the efficiency of the machining in EDM. At the last stages of the collapse phase of the bubble, a liquid jet develops on the bubble which has different shapes. Due to the different cases, and a high pressure region appears just near the jet of the bubble. Also the fluid particles have the highest relative velocity just near the liquid jet of the bubble.