Fused filament fabrication of Nd-Fe-B bonded magnets: Comparison of PA12 and TPU matrices

The present study reports the development of a new filament for Fused Filament Fabrication (FFF) of bonded magnets based on thermoplastic polyurethane (TPU). The performance of the newly developed filament was compared to a filament based on polyamide 12 (PA12), which represented the benchmark material for the production of bonded magnets. Filaments based on TPU and PA12 filled with melt-spun Nd-Fe-B particles (up to 92 wt%) were prepared using a twin-screw extruder, and test specimens were manufactured using a low-cost desktop FFF 3D printer. TPU based bonded magnets exhibited better magnetic performances, less warpage, and more robust processability compared to PA12 based bonded magnets, while the latter provided higher flexural modulus, flexural strength, and higher stiffness at elevated temperatures. It was found out that the best magnetic properties were measured on specimens manufactured from TPU filled with 92 wt% of Nd-Fe-B particles, where remanence (Br) was 532 mT and energy product (BHmax) was 47,5 kJ/m3. The developed method enables robust FFF Additive Manufacturing (AM) of TPU - Nd-Fe-B particles` bonded magnets using low-cost desktop 3D printers with magnetic properties comparable to the injection moulded (IM) bonded magnets, which is mentioned for the first time in the scientific literature.