STUDY ON HIGHER REMOVAL RATE OF CEMENTED CARBIDE BY EDM

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It was found that when a cemented carbide is heated at elevated temperature in the air, a tungsten carbide WC can be decomposed into tungsten and carbon at about 620 ℃. Generally, the machinability with electrical discharge machining (EDM) is governed by thermal than by mechanical material properties. If a cemented carbide can be machined by EDM based on the decomposition of WC, it is possible to machine a cemented carbide at a lower temperature of 620 ℃. In this study, the various experiments were conducted to establish the EDM with higher material removal rate, and the following results are obtained.(1) Explanation of decomposed process for cemented carbides machined by EDM in waterA tungsten carbide can be decomposed into tungsten and carbon under the existence of oxygen. As the EDM will be done using deionized water as a dielectric liquid, the dissolved oxygen (DO) and oxygen generated electrolytically exist in the deionized water. The following results are obtained.(1) Only a tungsten W was detected in the debris through the X-ray diffraction pattern.(2) Carbon separated from WC reacts with oxygen in the deionized water to form carbon dioxide gas.From above results, it was found that when cemented carbides were machined by EDM in the deionized water, tungsten carbide WC could be decomposed into tungsten and carbon.(2) The influence of DO concentration on the material removal rateIn general the maximum amounts of oxygen which can be dissolved in the water is 20 mg/l. The EDM was done in the deionized water where the dissolved oxygen is supersaturated. In the case of the deionized water with higher concentrated DO, the material removal rate is about 30 % higher than that of the deionized water with lower concentrated DO.