Gas bubbles entrapment mechanism in the electrochemical discharge machining involving multi-tip array electrodes

This article addresses the gas bubble entrapment issue for the first time when a multi-tip tool array (MTA) is used in electrochemical discharge machining (ECDM). During the simultaneous creation of microholes by the MTA tools, the electrolyte vapor evaporates and condensates on the tool shank. The electrolyte droplet gradually grows in size and then drops, thus, interrupting the electrochemical discharge. The material removal process becomes intermittent, leading to the formation of poor-quality microholes and subsequent breakage of the glass substrate. The ECDM behavior was characterized by analyzing the gas film formation time and the variation in the mean discharge current. The experimental analysis shows that the gas bubble entrapment phenomenon occurs when the average entrapped gas bubble size and electrolyte condensate sizes are larger than the MTA tool electrodes' effective base size and tip length. Increasing the electrode lengths and pitch size reduced the bubble entrapment frequency by >60 %. Increasing the pitch size from 1 mm to 1.5 mm also reduced the bubble entrapment frequency and improved the uniform electrochemical discharges, which is essential to get good quality microholes.