In this paper, we describe the improvement of the machining characteristics of sinking electrical discharge machining (EDM) using a tool electrode that has microholes for jetting dielectric liquid over the working surface. The tool electrode was made by diffusion bonding copper plates, on the surface of which microgrooves for jetting the dielectric fluid were formed by electrolyte jet machining. The bonded tool electrode was finished by turning to obtain a hemispherical shape. When dielectric liquid was dripped from the microholes over the tool electrode surface, processing time was shortened and machining stability and accuracy were improved compared with the case of the conventional solid tool electrode.

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Sintered polycrystalline diamond (PCD) is widely employed for cutting tools because of its great hardness and high wear resistance. However, it is extremely difficult to shape PCD micro tools by conventional machining methods. We describe the truing of a PCD micro tool by electrical discharge machining (EDM). The EDM mechanism and the EDM machinability for PCD are discussed. It is confirmed that insulated diamond grains in the PCD can be directly processed by EDM, because they are covered with an electrically conductive layer generated by applying discharge to the binder metal around them. Moreover, a short discharge duration of EDM is effective for improving the material removal rate and the surface roughness of PCD.

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