In-situ alignment of anisotropic hard magnets of 3D printed magnets

Abstract

3D printing of permanent magnets has recently received considerable attention [1,2]. In previous work the realization of isotropic magnets was demonstrated using fused filament fabrication, which results in the fabrication of polymer bonded magnets, with properties very similar to state-of-the-art magnets fabricated by injection molding [1]. In Ref [3] the easy axis of the printed magnet was aligned by printing the magnetic filament on magnetized hard magnets. Within this talk we will present a significant step forward by producing magnets where the easy axis can be locally aligned in-situ during the printing process. This is realized by redesigning the printer nozzle of a fused filament fabrication printer (FFF) so that permanent magnets can be placed next to the nozzle. The magnetic strayfield of the permanent magnets is optimized so that it aligns the easy axis of anisotropic ferromagnetic particles inside a paste-like compound material when it is in the melted state. Two different magnetic materials are investigated: (i) Strontium hexaferrite inside a PA6 matrix (Sprox® 10/20p), fill grade: 49 vol% and (ii) Sm2Fe17N3 inside a PA12 matrix, fill grade: 44 vol%. In the presence of the external alignment field, the Sr ferrite particles inside the PA6 matrix can be well aligned as shown in Fig. 1, where the hard axis hysteresis loop (blue) and easy axis hysteresis loop (orange) is shown. The ratio of the remanence of the hard axis loop and the easy axis hysteresis loop is 2.2, which shows a significant alignment. No significant alignment for Sm2Fe17N3 could be achieved, where the ratio of the easy and hard axis remanence is just 1.15.The results show the feasibility to fabricate magnets with arbitrary and locally defined easy axis, since the permanent magnets (or alternatively electromagnet) can be mounted on a rotatable platform. Hence, highly optimized magnets can be produced such as Hallbach arrays which can not be produced by any other method.  Hysteresis loops in hard and easy axes of a hard magnetic ferrite (Sprox) measured with the VSM. The 3d printed magnetic material is aligned in-situ during the print process by permanent magnets next to the printer nozzle.