Research on sub-micron EDM with high production

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Firstly, possible factors which influence the limits are discharge crater size, depth of heat affected zone, especially residual stress and material micro-structure were experimentally examined. For the negative effects of residual stress, both residual stress already present prior to machining and residual stress generated by machining itself were investigated using tungsten and cemented tungsten carbide as micro-rod workpiece materials. To determine the effects of material micro-structure, the influence of tungsten carbide grain size on the limits of minimum machinable diameter of cemented tungsten carbide rods was investigated. Comparing the limits between poly-crystal tungsten and mono-crystal tungsten, it was found that micro-machining characteristics were affected significantly by the anisotropy of the mono-crystal tungsten. Then, a new micro electrical discharge machining method using electrostatic induction feeding was developed. This method can reduce the minimum discharge energy per pulse because the influence of the stray capacitance in the circuit can be eliminated. Furthermore, since non-contact electric feeding is possible, this method enables EDM using a high speed rotating spindle. It was found that the gap voltage calculated from the equivalent circuit of this method agreed with the experimental results. Surface roughness of Rz 0.27μm was obtained using a normal electrical discharge machine.