Magnetically loaded polymer composites using stereolithography—Material processing and characterization

Abstract

Additive manufacturing employing stereolithography is an expedient means for manufacturing complex three-dimensional (3D) parts from a range of materials. Smart structures that respond to external stimuli is an active research area in this context. Characteristics of such 3D printed smart structures depend on material formulation, 3D printing equipment and process parameters. This research work utilizes a design of experiment framework to investigate the influence of materials and process parameters on resin curing behavior and dimensions of printed composite parts containing strontium ferrite or neodymium iron boron magnetic filler, while also expanding on the fundamental understanding of printing composites with increased filler loadings. First, a Taguchi-based experimental framework was adopted to evaluate the variations in sample thickness as a function of material and process parameters. It was observed that variations in thickness were dependent on the printing region in the 3D printer. To understand the role of material formulation on the depth of ultraviolet light penetration for curing, a diagnostic print file with varying exposure energy levels was designed, and cured material thickness was measured using a coordinate measuring machine. The obtained data further enabled determining the depth of light penetration and critical energy of polymerization. Magnetic suspensions engineered with filler loadings of 10 wt% and 25 wt% were printed. In terms of mechanical response, tensile properties of neodymium iron boron composites with filler loading of 10 wt% were higher compared to strontium ferrite composites. Magnetic cantilever structures with a minimum dimension of 0.13 mm were fabricated. Magnetic composites printed using a resin with 25 wt% filler loading were printable, but defects were observed. This fundamental research serves as a basis for understanding both material and process parameters to produce 3D magnetic structures through stereolithography based additive manufacturing.