Manufacturing and Characterization of Soft Magnetic Composite Filaments for Additive Manufacturing

Abstract

Additive manufacturing (AM) is becoming an alternative to traditional manufacturing methods [1]. In the most extended AM method (fused deposition modeling, FDM), a polymeric filament is extruded above its melting point for its deposition into thin layers. There is a high interest in the use of composite filaments, formed by a polymeric matrix with functional fillers, for the AM of functional parts [2]. The quality of the FDM printed parts is highly dependent on the uniformity of the filament diameter. In the case of composite filaments, a homogeneous distribution of the fillers is also crucial to have a reproducible and uniform functionality. Homogeneous soft magnetic PLA composite filaments for FDM have been recently reported, in which a customized feedstock of polymeric capsules filled with the functional fillers is employed [3]. Fig. 1 shows that composite filaments exhibit a soft magnetic behavior. Additionally, they all have a demagnetizing factor of ~ 1/3 (spheres, according to the shape of the gas atomized powders) regardless of the concentrations of fillers (up to 52 wt. %, corresponding to 12 vol. %). The addition of the fillers causes a remarkable shift in the thermal degradation temperature of the polymer. Increasing filler content produces an abrupt drop in the complex modulus of the polymer above its glass transition, which shifts to lower temperatures according to the peak of tan(δ) (Fig. 2). A decrease in the viscosity in liquid state is also observed, which causes a reduction of the extrudability and printability of the filaments for filler contents above 30 wt. %. The reduction of the viscosity of the composites requires the lowering of the temperatures for their extrusion and printing with respect to the typical ones for PLA.Work supported by AEI/FEDER-UE (grant PID2019-105720RB-I00), US/JUNTA/FEDER-UE (grant US-1260179), Consejería de Economía, Conocimiento, Empresas y Universidad de la Junta de Andalucía (grant P18-RT-746), and Army Research Laboratory under Cooperative Agreement Number W911NF-19-2-0212.  Fig. 1. Magnetization vs. magnetic field for the raw maraging steel powder and composite filaments.  Fig. 2. (a) Complex modulus and (b) tan(δ) of raw PLA and composite filaments.