Presentation Information
[P1-65]Enhancing the Printability of Nd-Fe-B Feedstocks for Laser Powder Bed Fusion
Marcelo Augusto Rosa1, Apuniano Baldarrago1, Arthur Mascheroni2, José Maria Mascheroni2, *Paulo Wendhausen1 (1. UFSC (Brazil), 2. Alkimat (Brazil))
Keywords:
additive manufacturing,laser powder bed fusion,feedstock,bonded magnet
Over the past decade, Additive Manufacturing (AM) has emerged as a complementary method for producing bonded magnets. Among the various AM techniques, Laser Powder Bed Fusion (LPBF) has shown significant potential, achieving dense bonded magnets with a volume fraction of magnetic particles around 50% vol (1,2). Other techniques such as Fused Deposition Modelling (FDM) were also explored, but in this case, a magnetic load no higher than 22% were obtained (3). In the end, a bonded magnet with high coercivity and high remanence is desired. The coercivity depends fundamentally on the kind of magnetic powder used to compose the feedstock, so it is a fixed parameter (considering that no degradation of the magnetic particles takes place during additive manufacturing). Remanence, on the other hand, depends on particle alignment and the vol. fraction of magnetic particles (4,5). To date, most of the research has concentrated on changing printing parameters to enhance especially the magnetic load of printed magnets. The strategies adopted consisted of optimizing laser processing parameters (scanning speed, hatch space, etc) to eliminate pores and improve the magnetic load. In contrast, this study shifts the focus towards the preparation of feedstocks with enhanced technological properties, specifically targeting the flowability of the particles, the overall magnetic load of the feedstock, its apparent density, and composite particle morphology. These properties collectively contribute to what the literature refers to as printability. The experimental methodology involves the preparation of magnetic powder from end-of-life magnets through hydrogen processing, which includes hydrogen decrepitation followed by the hydrogenation-disproportionation-desorption-recombination process, with the objective of obtaining a coercive powder. Powders with mean coercivities of 737 kA/m were obtained. The resulting powder is then combined with various binders such as PA12, PLA, and PP, in different volume fractions, using a hot mixing technique. The composite chips thus obtained are produced under vacuum conditions using a Winkworth hot blender, with working temperatures exceeding 150°C, depending on the binder used. Subsequently, the composite chips are milled in a knife mill and processed in Alkimat for particle spheroidization. A notable distinction in this approach is the preparation of composite particles, wherein the magnetic particles are embedded within a polymeric matrix, as confirmed by SEM analysis. This contrasts with previous studies where feedstocks were prepared through simple mechanical mixing under room conditions, resulting in a blend of separate magnetic and binder particles. The composite approach offers several advantages, including the prevention of phase segregation—often observed due to density differences between polymeric and metallic particles—and the ability to leverage the processability of the binder to spheroidize the composite particles, thereby enhancing flowability during printing. For polypropylene-based feedstocks, a magnetic load of up to 60% vol. was achieved. Comprehensive evaluations were conducted on all types of feedstocks in terms of flowability, magnetic load, and printability. The findings demonstrate that the preparation of feedstocks with improved technological properties not only enhances the performance of bonded magnets but also offers a novel approach to optimizing the LPBF process. This study paves the way for future research and development in the field of AM for bonded magnets, emphasizing the critical role of feedstock preparation in achieving superior magnet performance. Notably, the most promising results were obtained using polypropylene-based feedstocks, for which the magnetic load was increased to 55% vol. (1) A. Baldissera, et. al. IEEE International Magnetics Conference (INTERMAG), 2017. p. 1. (2) R.G.T. Fim, et. al. Additive Manufacturing, 2020. vol. 35, 101353. (3) 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. (4) M.C. Mapley, et al. Selective laser sintering of bonded anisotropic permanent magnets using an in situ alignment fixture, Rapid Prototyping Journal, vol. 27, no. 4, p. 735 740. (5) K. Schafer, et. al. Laser powder bed fusion of anisotropic Nd Fe B bonded magnets utilizing an in situ mechanical alignment approach. Journal of Magnetism and Magnetic Materials, 2023. vol. 583, 171064.