The micro-cracks generated by EDM (RCL circuit) were studied experimentally under various machining conditions. The results are as follows:
(1) The crack length is more largely affected by the source voltage than by both the condenser capacity and the inductance in the discharge circuit, but it is almost unaffected by the charging resistance.
(2) The cracks observed on cemented carbide S2 are always longer than the ones on G2 under the same machining condition.
(3) By a reversed polarity (workpiece: cathode, tool-electrode: anode) the shorter cracks are generated than by a straight polarity.
(4) It can be inferred by the statistical analysis that the distribution of crack length fits the gamma distribution.
(5) The generation mechanism of cracks can not be perfectly explained from a viewpoint of the thermal shearing stress.
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