Comparison on gas bubble and pulse trains of deep-cavity electrical discharge machining with/without rotary ultrasonic assistance

Fundamental observation of bubbles and debris in deep-cavity electrical discharge machining (EDM) with an ultrasonic spindle aimed at achieving higher machining efficiency is proposed and compared. Various discharge pulse trains for EDM, rotary EDM (R-EDM), ultrasonic vibration-assisted EDM (UA-EDM), and rotary ultrasonic EDM (RU-EDM) are investigated. Their effects on the removal efficiency, machining stability, and the tool wear rate are studied as well. It is found that EDM in deep cavity is actually discharged in the gas bubble most of the time except the short period at the very beginning stage. The main bubble at EDM tool jumping is maintained with a constant volume. And, the volume results in the boundary height of the bubble at the next EDM stroke. In which, ultrasonic vibration of sufficient strength was found to split main bubble quickly and improve the material removal rate at about 49 % through much higher frequency of pulse trains. Appended with rotation, the rotary ultrasonic vibration EDM can improve the tool wear rate but reduces the MRR in compared with conventional EDM.