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. One of the main reasons is the lack of suitable feedstock materials for printing platforms. In this effort, we developed two types of magnetic paste material as the feedstock for a commercial paste-extrusion 3D printer: (1) a low-temperature (< 200°C) pressure-less curable powder-iron paste; and (2) a high-temperature (> 900°) pressure-less sinterable NiZn ferrite paste. Of each type, the magnetic properties (relative permeability and core-loss density) after heat treatment were found to be comparable or better than its corresponding commercial products, which often require pressure for fabrication. 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% lower than that of a commercial powder-iron core from Micrometals with the same relative permeability. 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% lower than that of a commercial 4F1 core with a relative permeability of 80. With these feedstock materials, one can start taking full advantage of the flexibility of the 3D printing platform to design and prototype high-performance, unique-shaped magnetic cores.