Clarification of EDM Phenomena by Spectroscopic Analysis

概要

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In electrical discharge machining (EDM), workpiece is machined using heat of the arc-plasma generated in the discharge gap after dielectric breakdown. The characteristics and behavior of the arc-plasma during a single discharge have a great influence on the formation of the discharge crater. In order to improve the machining accuracy and surface roughness of the workpiece, it is quite necessary to research on plasma behavior and its characteristics. In this study, light intensities radiated from the plasma which are considered to reflect the material removal behavior were measured using a spectrometer under different machining conditions. It was found that the starting moment when light intensity was detected had a time delay after the dielectric breakdown. It is because of the time needed for the material to be evaporated before its temperature reaches the boiling point. Besides, the time delay increases accordingly by slowing down the rise speed of the discharge current because of lower heat flux flowing into the surface of the workpiece. In addition, heat conduction analysis was conducted to compare the time delay calculated with the experimental ones. It was found that plasma expanded in a rapid speed within about 180ns right after dielectric breakdown and remained constant with the diameter of about 20µm after that under a roughing condition of micro EDM.