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Michael Patton1 Declan Brown1 Nathan Stenger1 Pat Ryan2 Brittany Nelson-Cheeseman1

1, University of St. Thomas, St. Paul, Minnesota, United States
2, sSpectrum Tech, LLC, Minneapolis, Minnesota, United States

The application space for additive manufacturing (AM) has grown significantly through the use of high-performance composite materials. While the mechanical, thermal, optical, and electrical properties of AM polymer composites are being actively studied, the magnetic properties of AM parts have seen much less attention. Even so, AM magnetic composites have a chance to impact a variety of industries that make magnetic components, such as transformer cores, electric motors, and electromagnetic interference shielding. Recent work in magnetic polymer composite AM has shown that the structural print settings for a fused deposition modeling (FDM) process influence the magnetic properties of the printed part [Bollig17]. However, the structural hierarchy present in these AM composites complicates a simple analysis of how these differences arise. Further investigation of the structure-property relationships is required to understand exactly how and why these property changes arise. Here, a variety of samples were investigated to disentangle how the macroscopic sample shape and the mesoscopic filament infill orientation affects the magnetic properties. A magnetic filament consisting of polylactic acid (PLA) polymer and 40 wt.% iron was used to print the 3D magnetic samples via FDM. The array of samples systematically covered different aspect ratios (length, width), overall geometry (rectangular vs. ellipsoidal), and two filament print orientations (long axis alignment vs. short axis alignment). In-plane magnetic hysteresis loops were collected with a vibrating sample magnetometer (VSM) to determine what effects these macroscopic and mesoscopic structural factors had on the magnetic properties. Since previous research demonstrated that the 2D layering of FDM led to an out-of-plane magnetic hard axis, only the in-plane magnetic properties as a function of structure were probed in this work. The samples were measured with the field applied along the longitudinal and transverse directions, and the resulting hysteresis loops were used to compare the magnetization, magnetic moment, and susceptibility for the various structural factors. The results show that the macroscopic shape (aspect ratio and geometry) of the sample has a prominent effect on the magnetic properties. The longitudinal (long) axis of the sample yields a higher saturation magnetization (Ms) than the transverse (short) axis, and shapes with ellipsoidal edges yield a higher Ms than rectangular shapes. The mesoscopic orientation of the printed filament within the sample had a subtler effect; magnetic susceptibility increases in the direction that the filament was printed. Knowledge of how these structural factors within the FDM structural hierarchy affect the magnetic properties of printed parts is helpful for designing parts with optimized performance. Further preliminary studies into magnetic annealing before, during, and after part printing will also be discussed.

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