Modeling and experimental investigation of gas film in micro-electrochemical discharge machining process

• A physics-based gas film model was developed, including single bubble formation and gas film evolution.
• Thickness of gas film in ECDM was estimated, and was validated from experiments.
• Transient behavior of gas film formation was observed. The reason that bubbles fail to collapse into gas film under low electrode voltage was revealed.
• Experiments were carried out to validate the model developed in the paper. Experimental results showed high consistency with theoretical predictions.
• Critical voltage and current, which are essential process parameters in ECDM, were investigated through the model.

Electrochemical discharge machining (ECDM) is a promising machining technology that effectively machines non-conducting and brittle materials, featuring good material removal rate, flexibility, and accuracy of machining. ECDM makes use of the electrochemical discharge phenomenon to trigger the discharging by the gas film surrounding the tool electrode. As the fundamental of electrochemical discharging, gas film is essential to the machining quality and efficiency. However, modeling of gas film in electrochemical reaction is not well established. This paper presents analytical modeling of the gas film, involving bubble growth and departure on electrode, gas film evolution, and electrolysis characteristics. Experiments were carried out to compare models to the actual discharging phenomenon. High speed camera imaging demonstrated the formation of a gas film on the tool electrode. The range of thickness of gas film found in experiments indicated good consistency with the range of film thickness estimated from analytical models. Experiments on critical voltages and currents further revealed the characteristics of the gas film in electrochemical reaction.