Computer-aided design of magnetizing fixtures for the post-assembly magnetization of rare-earth permanent magnet brushless DC motors

A computer-aided design (CAD) methodology for the design of post-assembly impulse magnetizing fixtures for radial-field brushless DC motors is presented. The design methodology has been applied to an air-cored fixture for the post-assembly magnetization of a four-pole external rotor brushless DC motor. Its rotor is constructed from a stack of sintered radially anisotropic NdFeB ring magnets/ss and a solid mild steel core which will tend to act as a short-circuit to the applied magnetizing field and have induced eddy currents which inhibit the penetration of the magnetizing field into the magnet. The post-assembly magnetization of a three-phase brushless DC motor with an exterior rotor equipped with sintered NdFeB magnets has been shown to be feasible, albeit resulting in a slight decrease in performance compared to a motor constructed from premagnetized magnets. However, the post-assembly magnetization of interior rotor topologies is considerably more demanding. Nevertheless, the CAD facility for the design of post-assembly magnetization fixtures has been shown to agree well with results from the practical fixture considered