Microhole Machining by a Modified Electrical Discharge Machine

摘要

Microholes in hard materials like alloy steels can be machined on modified electrical discharge machine. It employs ceramic guide assembly with small protrusion of electrode for improved rigidity and tube electrode for high pressure pumping of water dielectric for effective flushing of spark gap. The latter not only improves machining efficiency but also the accuracy of the machined hole with high speed rotation of electrode. Here stainless steel specimens were studied for machining efficiency and accuracy. Higher pulse current and ontimes improve machining rate but reduce accuracy. The hole is tapered due to debris concentration along its depth. With electrode rotation this is offset since any straightness error of electrode generates higher diameter at the hole bottom. The accuracy error due to lateral wear of electrode can be offset by increasing the electrode wear or consumption. This is achieved by employing electrode negative polarity.