Bonded NdFeB magnets produced by selective laser sintering

Martin Mapley

Abstract

The production of complex-shaped bonded NdFeB (neodymium-iron-boron) magnets is a key element in the development of compact and efficient electromechan­ical devices. Due to constraints imposed by current man­ufacturing methods, geometrically complex magnets are high in cost and require long lead times. The use of addi­tive manufacturing techniques for low volume production of complex geometries from a wide range of materials has been shown to dramatically decrease product cost and lead times. This work describes the production and char­acterisation of net-shaped bonded NdFeB magnets using selective laser sintering (SLS) from mechanically mixed powders. Net-shaped magnets, cuboids for geometrical measurements and cylinders for magnetic measurements, wereproducedusingmagneticpowderswithbothflakeand­sphericalparticlemorphologiesmixedwithpolyamide-12. The powder loading fractions, which were based upon the ratio of the bulk density to the theoretical density of the individual magnetic powders, were 38% and 56%/ volume for the flake and spherical powders respectively. The mixed feedstock was processed using an experimen­tal SLS machine equipped with a mechanically tracked 15 W solid state laser emitting radiation at a wavelength of 445 nm. The magnets were shown experimentally to possess a high level of geometrical accuracy (less than 0.15 mm deviation from model data) with magnetic proper­ties comparable to permanent magnets produced using other additive manufacturing methods (residual induc­tion of 284 and 357 mT, intrinsic coercivity of 661 and 735 kA/m for flake and spherical powders respectively). This work has demonstrated the feasibility of producing bonded magnets using SLS, allowing the possibility for the rapid, cost-effective production of geometrically com­plex magnets.