Additive manufacturing of soft magnets for electrical machines - a review

With growing interest in electrification from clean energy technologies, such as wind power and use of pure electric powertrains in various applications, the demand for next-generation, high-performance magnetic materials has risen significantly. Electrical machine design for these applications is facing challenges in terms of meeting very demanding metrics for power densities and conversion efficiencies, thereby motivating the exploration of advanced materials and manufacturing for the next generation of lightweight ultraefficient electric machines. Additive manufacturing (AM), a layer-by-layer three dimensional (3D) printing technology, opens up new venues of improvements for industrial manufacturing of electrical machines via near-net shape printing of complex geometries, reduction of parts count and production lead time, and conservation of expensive critical materials such as rare-earth magnets as well as nanocrystalline and amorphous soft magnetic composites, allowing their use in only critical regions required by desired properties of the printed parts. The magnetic, electrical, thermal, and mechanical properties of the magnetic materials are also greatly influenced by the selection of the AM method. Among the seven major American Standard Testing and Materials-defined standard modes of 3D printing, selective laser melting, fused deposition modeling, and binder jetting technology dominate the AM processing of soft magnetic materials and their integration in electrical machines. In this work, the state of the art in printability and performance characteristics of soft magnetic materials for electric machines is summarized and discussed. The prospects of soft magnetic materials selection in terms of price, printability, weight, and performance of the electrical machines are also discussed. This review highlights the current status of AM of large electrical machines, AM process selection guidelines, hybrid printing technologies, and the associated opportunities and challenges. An emphasis is put on multimaterial processing that is essential for electrical machines. Hybrid printing technologies that combine multiple AM processes with adequate automation and enable simultaneous multimaterials dispensing, real-time quality control, postprocessing, and surface finish with integrated subtractive computer numeric control machining are the requirements for progressing toward the end-user electrical machines. Published by Elsevier Ltd. This is an open access article under the CC BY-NC-ND license (http:// creativecommons.org/licenses/by-nc-nd/4.0/).