Advancing Additive Manufacturing of Bonded Permanent Magnets via in-situ Magnetic Field Alignment During 3D Printing

Abstract

Additive manufacturing (AM) via 3-D printing technologies have become a frontier in materials research, including its application in the development and recycling of permanent magnets1,2. The increasing criticality in availability of the rare earth minerals in magnets present a demanding challenge to the losses from conventional or subtractive manufacturing. AM allows for a minimal waste production and re-utilization of recovered rare earths in the magnet processing. In-situ alignment during 3D printing of magnetic materials has opened new horizons for manufacturing of complex permanent magnets3,4. The introduction of functionalized magnetic 3D printing (Fig. 1a) as an AM process yields several unique advantages including rapid prototyping of multi-directionally aligned magnetic systems, and reduced energy requirement due to the elimination of post-production alignment3.In this work, we have developed a mechanism to align magnetic materials using fused filament 3D printer with a novel magnetic field source architecture (Fig. 1b). The work addresses opportunities to integrate magnetic field into 3D printing process to enable printing, and alignment of anisotropic permanent magnets, without requiring further processing. The principle behind the analysis is rotation of magnetic particles in a molten matrix under low magnetic field. The alignment architecture was designed and optimized for weight and applied field.An in-depth finite element modeling and CAD was performed followed by prototyping of the magnetic field source (Fig. 1c-d). Several electromagnetic core models were developed using finite element modeling to obtain a field strength of > 1 T with a magnetic material in the nozzle. The electromagnetic simulations were coupled with thermal analysis to obtain realistic transient thermal profiles. Design modifications were incorporated to improve the thermal performance of the models without compromising the electromagnetic output. The results predict models that could be operated over prolonged durations (> 10 hours) at less than the rated temperature (80 oC) and at the rated current (5 A), while producing field strength of > 1 T. As a future prospective, the model would be implemented as a prototype to be incorporated with the 3D printer.Magnetization vs. field measurements of extruded and printed Sm-Co (15 vol.%) in PLA and Nd-Fe-B/Sm-Fe-N composite (65 vol.%) in Nylon-12, prepared with and without magnetic field, confirmed alignment of magnetic particles (Fig. 2a-b). Field vs. alignment and printer temperature vs. alignment analyses were performed to understand the effects of process variables on the degree of alignment of the samples.Finally, a multiphysics model was developed, that couples fluid dynamics and electromagnetic interactions, to predict the degree of alignment (DoA) of a polymer bonded magnet printed under applied field. The model predicts the flow of magnetic particles in a viscous fluid through a nozzle under applied magnetic field. A particle-fluid interactive flow simulation was performed to model the flow regime of molten bonded magnet. The interactions between the drag, inertial, and magnetophoretic forces were analyzed to predict the particle trajectory. A torque balance was performed between the drag torque, magnetic torque on particles from the applied field, and torque from particle-particle interactions. The analysis was used to predict the degree of rotation of magnetic particles during printing. The simulated DoA of 0.68 compares well with the experimentally obtained for 65 vol.% NdFeB+SmFeN in Nylon-12. For 15 vol.% Sm-Co in PLA, the simulated DoA of 0.86 also compared well with 0.83 obtained experimentally (Fig.2c-d). This process can be used for any permanent magnet composition or hybrid magnets and presents a benchmark for application of this technology in industrial and commercial applications.This work is supported by the Critical Materials Institute (CMI), an Energy Innovation Hub funded by the U.S. Department of Energy (DOE), Office of Energy Efficiency and Renewable Energy, Advanced Manufacturing Office. Ames Laboratory is operated for the U.S. Department of Energy by Iowa State University of Science and Technology under Contract No. DE-AC02-07CH11358. **