Influence of reaction force on the electrode in micro hole drilling by micro EDM

Micro electrical discharge machining (EDM) is widely used to drill micro hole with high aspect ratio in any electrically conductive material regardless its hardness. Due to the electrode wear during machining, the electrode has to be prepared long to compensate the wear length. It is found that the discharge gap of a micro hole by a long and thin electrode is larger than that by a short electrode. Although there is no mechanical contact during EDM, the reaction force generated by electrical discharges causes the long and thin electrode to bend, resulting in the hole diameter larger than the expected. In this paper, a simple model is used to estimate the deflection of electrode in order to explain the large diameter of a micro hole by a long electrode. Experimental results indicate that the theoretical values agree with the real machining results.