Towards a better understanding of the characteristics of electrolytic plasma discharge and spark discharge in ECDM

Abstract

Abstract Electrochemical discharge machining (ECDM) is an essential process for microstructures fabrication of difficult-to-machine materials. Currently, there are various kinds of ECDM, and plasma-assisted electrochemical machining (PA-ECM) is a new and promising ECDM proposed in recent years. However, the differences between electrolytic plasma discharge and conventional spark discharge are unclear. Therefore, this study aims to systematically explain the evolvement mechanism and characteristics of these two kinds of discharge. From the phenomenology, the electrolytic plasma discharge is saffron color determined by electrolyte and wrapped at the entire immersion surface of the tool electrode, while the spark discharge is white color and only excited at the end of the tool electrode. Electrolytic plasma discharge is generated preferentially to spark discharge, and easily transforms to spark discharge in high electric field strength such as large applied voltage or small inter-electrode gap. The discharge energy and emission spectrum of spark discharge is more significant than that of electrolytic plasma discharge. Especially, the electrolytic plasma discharge does not cause any tool electrode wear due to the low discharge energy (discharge current about 0.5 A), and the resulted surface of the workpiece is smooth. On the contrary, the spark discharge energy is high (discharge current about 9 A), which causes noticeable tool electrode wear and leaves discharge craters and thermal damage on the workpiece surface. Considering the obvious flushing effect of bubble flow during plasma ignition, PA-ECM is an ideal method for functional surface micro-dimple array fabrication without using tube central spray and workpiece mask.