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In this report, various materials(tungsten, cemented carbide, high-speed steel, and polycrystalline diamond) were machined by micro-electric-discharge-machining. Then, their surfaces were evaluated by SEM observation, surface roughness measurement, residual stress measurement and X-ray diffraction analysis. The following are the results of the experiment; 1) Few layers were affected in the cemented carbide and the polycrystalline diamond, but many layers were affected in the machining of high-speed steel and tungsten. Moreover, the cemented carbide and polycrystalline diamond showed the tendency to have a smooth surface roughness when they were machined in the finishing condition. 2) When electric discharge machining was performed on the minute stick material, the tensile stress on the end and the compression stress on the side were existed. 3) The cutting hole experiment was performed with a drill made of cemented carbide. But extra burr existed around the hole, it was possible to drill a copper plate.

The purpose of this report is to evaluate thermal fatigue characteristics of EDMed surface, which attribute to prolonging the life of die steels and stability of the quality of the product.EDMed surface treated with shot-peening, gas-nitriding and laser irradiation were evaluated for thermal fatigue by use of microphotographic observation and a X-ray residual stress measurement.As a result of these tests, it was found that tensile stress on the EDMed surface can be changed to compression stress by applying the various surface treatments, thus improving the thermal fatigue characteristics. Furthermore, the maximum crack length in the cross sectional area after the fatigue test was remarkably shorter, increasing the ability to withstand heat checking and thus proved to be an effective method for improving the EDMed surface.