Change in discharge state and effect of machining debris in electric discharge machining of permanent magnets with different initial magnetizing ratio

Abstract

It is difficult to machine permanent magnets by traditional machining because of brittle-material and magnetic force, but EDM can machine permanent magnets easily. However, because magnets have a Curie point, the reduction in the magnetic flux density may occur in EDM where the machined surface becomes high temperature. In previous studies, when 1 mm removal machining was performed for the cylindrical neodymium magnet, the magnetic flux density decreased in the region of several millimeters directly below the machined surface. When the magnet internal temperature was measured individually for several depths, the region where the magnetic flux density decreased was up to about the upper temperature limit. In this study, to improve the accuracy of temperature measurement, three points were measured simultaneously. In addition EDM was performed for the magnet with different initial magnetizing ratio before machining, and it was made efforts in EDM characteristic of the machining. As a result, in spite of the same discharge conditions, it was found that the magnet internal temperature during machining varies greatly due to the difference in initial magnetizing ratio. From the classification of the discharge state, it was found that these differences were affected by the reattachment of the debris to the magnet.