電気加工学会誌

In pulse electrochemical machining (ECM), it has been found that the low-level voltage of the applied pulse influences the tool electrode wear and the machining accuracy. In order to acquire a higher machining accuracy, the relationship between the low-level voltage and the machining characteristics was experimentally investigated. It was found that a raised low-level voltage not only prevents the tool electrode wear, but also improves the machining speed. Furthermore, it was found that there exits an optimal low-level voltage for improving the machining accuracy. In order to investigate the cause of this phenomenon, the electrolyte in the gap area was modelled and simulated using FEM software. It was found that bubbles generated by applying low-level voltage improve the machining characteristics.

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Cemented carbides are composed of tungsten carbide and cobalt as a binder. Tungsten carbide (WC) can be decomposed into tungsten and carbon at about 620°C in air, and the carbon that separates from WC reacts with oxygen to form carbon dioxide gas. In this study, these phenomena are applied to the electrical discharge machining (EDM) of cemented carbides in deionized water. First, using deionized water as the dielectric working fluid, it is ensured that dissolved oxygen exists in the liquid. Secondly, as EDM is a removal method based on melting and evaporation, the workpiece temperature around the sparking area exceeds the melting point of the material. Therefore, cemented carbides are machined by EDM in deionized water. As a result, it was found that the debris obtained during EDM is composed of tungsten (W) and tungsten oxide (WO₃). Moreover, the carbon that separates from WC reacts with the dissolved oxygen in the gap between the electrode and the workpiece to form carbon dioxide gas. Thus, in the EDM of cemented carbides in deionized water, the removal mechanism based on the decomposition of tungsten carbide is in effect as well as that based on melting and evaporation.

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