Process Optimization of a Novel Soft Magnetic Composite Inductor Cores

The purpose of this study is to develop a processing method to reduce the porosity of toroidal inductors, whose cores are composed of soft magnetic composites (SMCs) with 65 vol.%, 75 vol.%, and 85 vol.% iron nitride (γ′-Fe4N) and to validate the results with a COMSOL™ model. Using hot-pressing as the main process of manufacture, fourteen samples were fabricated and eight were wound with Litz wire. Four samples of 75 vol.% and four samples of 85 vol.% were fabricated by mixing the Fe4N powder and epoxy at 150°C and initially pressing at 56.6 MPa and 175°C. In a second step, the samples were pressed overnight at 56.6 MPa and 193°C. The optimized processing method increased the density of each toroidal inductor sample by about 7%, increased mixing time, and produced markedly improved surface uniformity. Finally, the COMSOL™ model of the inductors requires further adjustments to better reflect the measured inductance due to wire gauge and construction. By the completion of this project we fabricated a sample which achieved an inductance of 368.8 μH and a density of 5.15 g/cm³.