Presentation Information
[P1-64]From Scrap to Bonded Magnet: Exploring Nanocrystalline Recycled Powders in Additive Manufacturing
*Marcelo Augusto Rosa1, Gabriel Maia2, Apuniano Baldarrago1, Maximiliano Martins2, Paulo Wendhausen1 (1. UFSC (Brazil), 2. CDTN (Brazil))
Keywords:
additive manufacturing,fused deposition modelling,recycling,bonded magnet
Bonded Nd-Fe-B magnets are usually fabricated by blending magnetic powders with polymeric binders to facilitate shaping via compression or injection moulding. In recent years, Additive Manufacturing (AM) has been envisaged as a complementary method, due to the possibility of obtaining complex shapes and field configurations without using any mould (1,2). Different AM techniques were explored, mainly Laser Powder Bed Fusion (LPBF), but also Fused Deposition Modelling (FDM), and Stereolithography (SLA) (3,4). The common practice is using commercial powders for that purpose. However, as far as we know, the preparation of AM feedstocks from end-of-life magnets and their use in AM has not been thoroughly addressed, which is the main proposal of this work. Our primary objective is to investigate the fabrication of bonded magnets via AM, using feedstocks composed of nanocrystalline powders obtained from scrap. Recycling has been gaining momentum and most efforts have aimed to obtain sintered magnets via the magnet-to-magnet approach. Reprocessing means pickup of oxygen, leading to a depletion of the Nd-rich phase, which plays a pivotal role in guaranteeing high density and high coercivity in the recycled magnets. But recycling strategies can be rethought towards the fabrication of bonded magnets instead of sintered ones. The scenario is different for bonded magnets because densification is driven by a binder, and high coercivity can be assured by grain refinement techniques, such as the hydrogenation-disproportionation-desorption-recombination (HDDR) process (5). Previous contributions have addressed the use of nanocrystalline recycled powders in the fabrication of bonded magnets using conventional shaping processes. Our contribution focuses on AM processing, more specifically the FDM technique.Nd-Fe-B N35 scrap magnets were subjected to hydrogen processing to obtain nanocrystalline powders. Hydrogen decrepitation (HD) was performed, and then the HD powder was transferred to a glovebox under inert conditions, where it was milled (mortar) and sieved to a particle size <63 µm. Milling was performed to adequate particle size for AM purposes. Laser diffraction analyses revealed a mean particle size of (29+-5) µm for the HD powder. Afterwards, the HD powder was processed via conventional HDDR, which resulted in isotropic particles with mean values of coercivity equal to (750+-75) kA/m and remanence of (705+-14) mT. The HDDR powder was also transferred to the glovebox and milled <63 µm. According to laser diffraction characterization, the nanocrystalline powders presented an average particle diameter of (50+-32) µm. The grain size was assessed by analysing SEM images, revealing an average diameter of (195+-68) nm.To prepare the feedstock for FDM, the nanocrystalline recycled powder was mixed with polylactic acid (PLA) pellets with different vol. fractions of powder (from 5% up to 60%) using a hot mixer setup, where pellets and the powder were heated under vacuum up to 170 °C and then mixed for 30 min. The feasibility of producing filaments for FDM was then explored for each mixture, and it was possible to obtain filaments containing up to 50% in vol. of magnetic load. Such filaments were used to 3D print bonded magnets, reaching average coercivity of (685±21) kA/m.The present work has demonstrated the obtention of ready-to-use AM feedstock for FDM starting from scrap magnets, including the obtention of complex-shape bonded magnets, which may open a variety of new possible applications. The next steps include exploring strategies to increase even further the magnetic load in the filaments and also to develop in situ aligning systems to obtain anisotropic bonded magnets. References: (1) A. Baldissera, et. al. IEEE International Magnetics Conference (INTERMAG), 2017. p. 1. (2) M. Parans Paranthaman, et. al. The Journal of The Minerals, Metals & Materials Society, 2016. vol. 68, no. 7.
(3) R.G.T. Fim, et. al. Additive Manufacturing, 2020. vol. 35, 101353.
(4) G. Maia, et. al. Ready to use Composite FDM Filaments produced with PLA and Recycled NdFeB Nanocrystalline Powder for additive manufacturing of bonded magnets. Accepted Manuscript, IEEE Magnetics Letters, 2025.
(5) M.A. Rosa, et. al. IEEE International Magnetics Conference (INTERMAG), 2024. vol. 60, issue 9, 2100805.
(3) R.G.T. Fim, et. al. Additive Manufacturing, 2020. vol. 35, 101353.
(4) G. Maia, et. al. Ready to use Composite FDM Filaments produced with PLA and Recycled NdFeB Nanocrystalline Powder for additive manufacturing of bonded magnets. Accepted Manuscript, IEEE Magnetics Letters, 2025.
(5) M.A. Rosa, et. al. IEEE International Magnetics Conference (INTERMAG), 2024. vol. 60, issue 9, 2100805.