Powder loading rate impact on the performances of sintered MnZn ferrites fabricated by powder injection moulding

Power electronics’ power density increase mainly depends on size reduction of passive components. Development of compact solutions having two or more magnetic functions (filtering, storage, and signal transformation) on a single-magnetic core or of cores having hollowed structures for thermal integration purposes may require advanced geometries. Ferrites’ conventional fabrication technique (uniaxial compression) presents limitations for the production of cores having advanced geometrical features. Additive manufacturing or powder injection moulding (PIM) are promising techniques that allow for the shaping of magnetics having unprecedented geometrical features. These last fabrication techniques rely on the principle of mixing a powder with a binder system made of polymers to make the parts injectable or printable. The binder system may generally constitute at least 10 wt% of the total formulation’s content (much higher than for the conventional process: 2–3 wt%). The goal of this study was to analyze the impact of the binder amount (11.5, 15.3, 21.3 and 29.6 wt%, what corresponds to a MnZn ferrite powder loading rate of 88.5, 84.7, 78.7 and 70.4 wt%, respectively) inside a formulation designed for PIM. The formulations were made by extrusion, then injected in a pressing machine, debinded and finally sintered at same time (four different PIM samples per batch) in a furnace having partial oxygen pressure control. Our results showed that the power losses were not the lowest ones for the samples having the highest loading rates. The cores fabricated with a loading rate of 84.7 wt% (50 vol%) generated the lowest losses (on the whole frequencies range; between 100 and 1000 kHz/50 mT and temperatures range; between 25 and 110 °C). This behaviour was attributed to lower hysteresis losses (better magnetic phase purity). The power losses of sintered ring-shape cores achieved 88 mW/cm 3 at 500 kHz/50 mT/85 °C. The losses that have been obtained for the parts fabricated by PIM were similar to the ones given by the ferrite powder supplier (conventional fabrication). These results pave the way to the fabrication of advanced cores in applications where a high level of compactness will be required as for on-board-chargers for battery electric vehicles applications.