This paper describes a new method of surface modification by EDM to create a hard surface on the workpiece. When a metallic material that can make a hard carbide is used an electrode of EDM, hard layer can be made in a certain condition. The process begins with electrode wear by heat of EDM. Then worn electrode material is combineds with carbon which is a constituent of dielectric fluid and becomes hard carbide. The carbide is piled up on a workpiece and becomes a layer.
In this paper, the relation between electrical conditions to form the layer and thickness of the layer is examined. When pulse duration is short, the workpiece tends to be machined and the layer is thin. While pulse furation is long, the workpiece does not tend to be machined and the layer becomes thick.
It is found that this hard layer has high wear resistance. In a experiment to check wear resistance, the surface which is given a hard layer by EDM is found to be three times as resistant as the one without the layer, and it is more resistant than a surface with TiN layer with PVD.
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