Study of Self-Acting Gas Film Aided Electrochemical Discharge Drilling

Electrochemical discharge machining (ECDM) is usually used to machine　non-conductive brittle materials such as glass, but it still has a lot of problems such as the machined depth, the machining rate and the taper. In this study, a hollow tube electrode was conducted and the air was injected through it. The electrolyte in the hole would be disturbed by the injected air and flow deep into the hole. The purpose of the paper is to investigate the effect of the injected air during electrochemical discharge drilling process. The experimental results showed that the injected air would affect the local thickness of the gas film around the side of the electrode and made it unstable. As a result, the unstable gas film made sparks hardly take place around the side of the tube electrode, and the reaming and the taper would be less as compared with that when machining without injecting air into the tube electrode. But the surface roughness inside the wall would be worse because sparks around the side of the electrode could not appear uniformly. Injecting air into the hollow tube electrode contributes to form much evener gas film under the bottom of the electrode, so sparks under the electrode would be much stronger and take place in a larger area. Besides, injecting air into the hollow tube electrode would induce a scavenging effect, and the machining time would be reduced. The electrolyte in the hole would be disturbed by the injected air and penetrates into the hole much deeper; the machined depth could be increased at the same time. In conclusion, injecting air into the hollow tube electrode could improve the machined depth, the machining rate and the taper.