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Magnetic Paste as Feedstock for Additive Manufacturing of Power Magnetics

Inductors and transformers are ubiquitous in switch-mode power converters. Additive manufacturing or 3D printing of these components has the potential to drastically accelerate their design and prototyping. However, there are very few reported activities claiming successful fabrication of power magnetics by 3D printing, mainly due to the lack of suitable feedstock materials for printing platforms. Toward this effort, this paper develops two types of magnetic paste material as the feedstock for a commercial paste-extrusion 3D printer: (1) a low-temperature (< 200 °C) pressureless curable powder-iron paste; and (2) a high-temperature (> 900 °C) pressureless sinterable nickel-zinc (NiZn) ferrite paste. For both types, the magnetic properties (relative permeability and core-loss density) after heat treatment were found to be comparable or better than the corresponding commercial products, which often require pressure for fabrication. Shown in Fig. 1 (a) and (b), the powder-iron material had a relative permeability of 35 and a core-loss density of 110 mW/cm3 at Bpeak of 10 mT and 1 MHz. The core-loss density was 33 percent lower than that of a commercial powder-iron core from Micrometals with the same relative permeability. Shown in Fig. 2 (a) and (b), the ferrite material had a relative permeability of 72 and a core-loss density of 200 mW/cm3 at Bpeak of 10 mT and 5 MHz. The loss density is almost 50 percent lower than that of a commercial 4F1 core with a relative permeability of 80. These feedstock materials allow full advantage to be taken of the 3D printing platform's flexibility, thus allowing the design and prototype of high-performance, uniquely-shaped magnetic cores.

Image of plots of relative permeability versus frequency of our powder-iron core and that of a Power Conversion Material-8 core from Micrometals, and plots of core-loss density versus flux density at 1 MHz of powder-iron core and that of a Power Conversio
Fig. 1. (a) Plots of relative permeability versus frequency of our powder-iron core and that of a Power Conversion Material-8 core from Micrometals and (b) plots of core-loss density versus flux density at 1 MHz of powder-iron core and that of a Power Conversion Material-8 core from Micrometals.
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Image of plots of relative permeability versus frequency of our NiZn ferrite core and a commercial 4F1 core and plots of core-loss density versus flux density at 5 MHz of our NiZn ferrite core and a 4F1 core.
Fig. 2. (a) Plots of relative permeability versus frequency of our NiZn ferrite core and a commercial 4F1 core and (b) plots of core-loss density versus flux density at 5 MHz of our NiZn ferrite core and a 4F1 core.
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