Study on Polishing Method Using Magnetic Levitation Tool in Superconductive-Assisted Machining

Abstract

Superconductive-assisted machining (SUAM) is a polishing method that employs a magnetic levitation tool, which is based on a superconductive phenomenon called the pinning effect. Since the tool magnetically levitates, the issue of tool interference is eliminated. In this study, in order to set up the polishing conditions of the magnetic levitation tool, we evaluated the relation between the flux density distribution relative to the tool position and the holding force acting on the magnetic levitation tool to maintain its initial position, set by field cooling by the superconducting bulk. For the holding force, we measured the attractive, repulsive, restoring, and driving forces. We found that the greater the holding force, the smaller the initial distance between the superconducting bulk and the magnetic levitation tool. The attractive force was found to peak when the levitated tool was displaced 6 mm from an initial position of 9 mm from the bulk, and it became only the self-weight of the magnetic levitation tool at displacements of 30 mm and above, where the pinning effect broke down. We then evaluated the polishing characteristics for SUS304 and A1100P at a tool displacement that results in the maximum attractive force. In the polishing experiment, we employed a water-based diamond slurry because the temperature of the workpiece was close to room temperature. We found that it was possible to polish SUS304 and A1100P while avoiding the effects of magnetization due to the polishing pressure or induced currents that accompany the rotation of the metal plate. The arithmetic average roughness, Ra, of A1100P was relatively high due to the effect of scratches, while that of SUS304 improved from 92 nm before polishing to 55 nm after polishing when polished with grains with a diameter of 1 μm.