Additively Manufactured Soft Magnets With Reduced Core Loss

Soft magnetic materials with reduced energy losses are essential for transformers, power electronics and motors. Laser powder bed fusion (LPBF) additive manufacturing (AM) has been used to fabricate topology optimized soft magnets, in which space filling curves and air gaps are used to reduce energy losses. Here, we use LPBF AM to print magnetic toroids out of Ancorsteel and FeSi3.5wt% electrical steel. Dense, thin walled structures were successfully printed using the following-border scanning strategy with an interlayer wait time. The cross-sections of these toroids are made of Hilbert and Peano space filling curves. Complex permeability is characterized up to 1 MHz, and core losses are measured up to 1 kHz. We find that the additively manufactured toroids can be designed to have stacking factors (relative density) up to 81%, cut-off frequencies above 100 kHz, and core loss as low as 0.94 W/kg at 50 Hz. The Peano curve has lower core loss than the Hilbert curve, but also lower cut-off frequency. Our results demonstrate the tradeoffs between the space filling geometry, stacking factor, wall thickness, and area-to-perimeter ratio on magnetic performance.