Near net shape production of radially oriented NdFeB ring magnets by backward extrusion

Abstract

Anisotropic NdFeB magnets find application in electric motors where high flux densities combined with high coercivities are required. Such magnets can be produced by hot deformation of nanocrystalline NdFeB alloys. In particular, the backward extrusion process results in radially oriented ring magnets. The hot working process can be carried out in such a way that the ring magnets obtained after cutting off the top and the bottom are suited for direct use on the rotor in an electric motor. This is possible for a wide range of dimensions, which means that the ring magnets can be produced in a near net shape. Especially, smaller wall depths of the rings are realizable compared with sintered magnets. Major benefits are the simpler rotor construction, a greatly reduced rotor assembly time and simpler magnet retention on the rotor due to greater mechanical integrity of the magnetic structure. After a brief explanation of the backward extrusion process, the used dies and the corresponding rings are presented. Finally, the homogeneity of the magnetic properties and of the deformation process are discussed.