Enhanced Dimensional Accuracy of Material Extrusion 3D-Printed Plastics through Filament Architecture

Optimization of three-dimensional (3D) print conditions for material extrusion of plastics by fused filament fabrication typically involves trade-offs between mechanical properties and dimensional accuracy due to their orthogonal requirements. Increased polymer mobility improves the mechanical properties by chain diffusion to strengthen the interfaces between printed roads, but flow associated with the high polymer mobility leads to inaccuracies. Here, we describe the application of a model core-shell geometry in filaments to address these trade-offs and understand the material requirements to achieve improved dimensional accuracy. Systematic variation of the core with commercial polycarbonate-based plastics and a common high-density polyethylene (HDPE) shell illustrates that tensile properties obtained with these filaments are relatively insensitive to printing conditions and selection of the core polymer, but the dimensional accuracy of the printed part improves markedly as the glass transition temperature of the core polymer increases. The impact resistance of the core-shell-based parts is dependent on the selection of the core polymer with a significant decrease in impact resistance for the lowest modulus core examined. Although warping can be mostly mitigated with the core-shell filaments, the printed object is generally smaller than the digital source due to large volume change associated with HDPE crystallization. The dimensional accuracy is dependent on the solidification temperature and mechanical properties of the polymers comprising the filament, print conditions, and the local geometry of the object as quantified by layer-by-layer analysis of 3D scanned images of the printed objects. Both processing changes and some structures in the digital object that can degrade the dimensional accuracy are identified through this analysis. The core-shell filament structure represents a model geometry to understand the potential for the printing of polymer blends where separation of solidification temperatures in cocontinuous blends could provide a route to improve performance.