This study covers the mirror surface machining by planetary electro discharge machining (EDM). In the process of this EDM, a mirror surface is created in a micro-energy condition where an independent pulse circuit is used, and its gloss is affected by the electrode polarity, storage capacitance, discharging energy and planetary motion.
It has been found as the result of our three-dimensional analysis of a single discharge crater by using a scanning electron microscope and contouring device that the mirror surfacing depends upon the profile of the discharge crater. Also the gloss can be effectively calibrated by the analysis in which the laser diffraction is adopted.
Our study on mirror surfacing by EDM has made clear the following:
(1) In micro-energy conditions using independent pulse circuit where any storage capacitance is eliminated, an extremely flat discharge crater with smaller undulation is obtained when the electrode is negative.
(2) The mirror surface is realized by both the microscopically smooth surface formed by such flat discharge craters as overlapped, and the macroscopic smoothing adopting the elimination of undulation by means of planetary motion.
(3) The gloss of mirror surface has no relation whether or not the workpiece has been subject to heat treatment, but depends upon the small cracks occurring because of the carbide or stressed condition of machined surface due to the composition of material.
(4) The gloss of mirror surface is affected by the capacitance formed between electrodes; as the machining area increase, the gloss will be degraded, and the surface will change from mirror to dull surface.
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