Copper–tungsten electrode wear process and carbon layer characterization in electrical discharge machining

Abstract

As one of the earliest non-traditional machining processes, the technology of electrical discharge machining (EDM) is being refined and finding wider and wider application in modern industries. Copper–tungsten alloy electrode is widely used in the field of EDM. It has high melting temperature and excellent electrical and thermal conductivity. Copper–tungsten electrodes developed for electrical discharge dressing of metal bonded grinding wheels are experimentally investigated in this work. L9(34) orthogonal experiment is adopted to explore the electrical processing conditions aiming for a lower tool wear rate. The result shows that the sequence of the discharge parameters that reduce electrode wear rate (EWR) for the copper–tungsten electrode at negative polarity is peak current, pulse duration, duty factor, open-circuit voltage. Analyzing the photomicrograph of machined portions, the wear phenomenon of the electrode occurring both at the edge and at the bottom is revealed under the optimized discharge conditions. In the continuously hole processing, edge and bottom wear is significantly higher after completing the first two holes and slower for the rest. During EDM, thickness and micro-topography of the carbon layer are measured. It is shown that the main constituent of the layer is carbon released from the dielectric and the carbon layer with 15∼20-μm thickness attaching rapidly to the surface of electrode at the initial phase. In addition, the conditions of carbon layer formation on the basis of the temperature distribution theory of the electrode surface are discussed.