Relationship between Thermal Influence and Magnetic Characteristics in Electrical Discharge Machining of Magnetic Materials

Abstract

t is difficult to perform traditional machining, including turning, milling and grinding, of a permanent magnet, which is a functional material, because of magnetic forces. However, electrical discharge machining (EDM), which is a non-contact machining method, has been used for shape machining of magnetic materials. In the EDM process, non-magnetic materials such as copper or graphite are typically used as electrodes. Magnetic materials have a Curie point; therefore, their magnetic flux density reduces when they are heated to a high temperature. Because EDM is a thermal process, it has the potential to control the magnetic flux density of a machined surface. In this study, to clarify the influence of magnetic flux density on a machined surface, the following machining conditions were investigated: (1) the Duty Factor (D.F.) and (2) the input energy of one pulse. A sintered neodymium material was used as the work piece. The magnetic flux density of a cross-section of a machined neodymium magnet was measured. The results showed that the influence of the magnetic flux density was low under low-energy machining conditions. In contrast, for high-energy machining conditions or a high D.F., the magnetic flux density significantly reduced compared to the initial value. These results confirm the importance of machining conditions for EDM of magnetic materials.