Chain discharging behavior induced by gas film expansion and its influence on the electrochemical discharge machining (ECDM) process

Spark discharge behavior governs the material removal rate and surface quality during the electrochemical discharge machining (ECDM) process. Most of the studies indirectly inferred the spark discharge behavior from recorded current waveforms or machined results. So far, the dynamic process of spark discharges and its instantaneous effects have not been revealed. In this research, an in-situ observation-based discharge analysis was conducted using high-speed image technology to characterize spark discharges. As a result, the spark discharge cycle can be divided into three stages: bubble generation, gas film formation, and spark discharge occurring. By analyzing images of the gas film and sparks, the effects of applied voltage and inter-electrode gap on the gas-film dimension, discharge intensity, discharge location, and discharge uniformity are obtained. The phenomena of the chain discharges caused by expansion and morphology of the gas film are discovered for the first time. The chain discharges induce continuous transfer of the discharge locations, which affects the material removal region and shape evolution of the workpiece. The chain discharge as a new phenomenon can help us to understand the mechanism and analyze the processing results of ECDM.