Effect of reverse current on tool wear in micro-electrical discharge milling

Abstract

An RC-type pulse generator is useful in micro-electrical discharge milling due to its small discharge energy. However, when using this kind of generator, the current between the tool and the workpiece oscillates because of the stray inductance of the circuit. This causes current to flow from the tool to the workpiece in reverse direction to the main discharge current. When the reverse current flows, tool polarity is changed which intensifies tool wear. In this research, the reverse current is eliminated by connecting a MOSFET to a normal RC-type pulse generator. As a result, tool wear was reduced and geometrical accuracy was increased during machining of stainless steel using cemented carbide tool. Tool wear was further reduced through the use of deionized water with low resistivity. However, the use of low resistivity water decreases tool wear but can also reduce geometrical accuracy. The combination of using a MOSFET with low resistivity water therefore reduces tool wear while maintaining geometrical accuracy. The addition of the MOSFET to the RC circuit reduced the relative wear ratio by up to 67%. Thus, removing the reverse current is effective in reducing tool wear in various machining conditions.