Simulating the heating procedure of HREE-coated Nd-Fe-B magnets to assess the feasibility realizing GBDP online

To date, the grain boundary diffusion process (GBDP) of heavy rare earth elements (HREEs), such as Dy and Tb, into sintered Nd-Fe-B magnets has been the most efficient approach for improving the coercive force of the magnets. However, conventional GBDP is achieved by loading the HREE-coated magnets in a high-temperature vacuum furnace and performing the essential processes of vacuumizing, heating, holding, and cooling down. This has to be repeated for each batch in mass production, which leads to low production efficiency and a substantial waste of electrical energy during repeated vacuuming and heating. This study proposes a new continuous GBDP production method in which the HREE-coated magnets are arranged precisely in stacked trays, and the trays can be uplifted step-by-step throughout a thermal region at a specific speed, which achieves the heating and holding procedures on the magnets. Here the heating and holding temperature processes of magnets were simulated using the ANSYS software to verify the feasibility of the new approach. The results show that the diffusion parameters such as the heating rate and holding time can be well adjusted to fit the conventional GBDP technologies. The study provides guidelines for the design and operation of a continuous diffusion furnace.