The computer-aided design and analysis of impulse magnetizing fixtures
The magnetization of the permanent magnet components is a key enabling technology in the production of permanent magnet based electromagnetic devices. Although recent advances in the properties of rare-earth magnets, offer considerable scope for enhanced device performance, in order to realise such improvements, the permanent magnet must be magnetized to saturation. This is a considerably more onerous requirement for the rare-earth materials as compared to the more established permanent magnet materials, particularly if the preferred production route of single step, multipole magnetization of either the part or fully assembled device is to be employed. To enable accurate design of magnetizing systems for such demanding applications, an integrated computer-aided design methodology has been developed. It is based on both analytical and finite element field calculation techniques, and spans the entire design synthesis from initial specification through to the assessment of the performance of the final device into which the magnetized magnet is incorporated. Particular attention is directed towards the role of eddy-currents during the impulse magnetization, and to this end a transient, electric circuit coupled finite element simulation is described. A case study is presented on the relative merits of magnetizing the anisotropic NdFeB magnet of a brushless D.0 motor at various stages during the motor production. A further case study on the magnetization of an isotropic bonded NdFeB multipole rotor highlights the additional considerations that arise in the design of magnetizing fixtures for isotropic materials. Finally, the utility of the methodology in designing a limited range of axial multipole fixtures is demonstrated with a case study on a fine pole-pitch axially magnetized ring magnet.