Model analysis of feedstock behavior in fused filament fabrication: Enabling rapid materials screening

This research presents a rapid screening process for analyzing the extrudability of polymeric materials for filament extrusion based additive manufacturing (AM) by predicting extrusion failure. This rapid screening process can further suggest optimal Fused Filament Fabrication (FFF) processing conditions for a specific material. Annular backflow and filament buckling, which are the two primary failure modes during extrusion in FFF, are considered in this study. The screening method focuses on model analysis of annular backflow while simultaneously considering a previously developed model for filament buckling and includes the introduction of a non-dimensional number (Flow Identification Number, or FIN) that predicts a material's propensity to backflow based on a rheological analysis and the system geometry. Annular backflow was modeled by calculating velocity profiles and determining the normalized net flow magnitude. The backflow and buckling models were experimentally verified with acrylonitrile butadiene styrene, low density polyethylene, and sodium sulfonated poly(ethylene) glycol. We empirically validated that the FIN was able to accurately predict backflow and that the potential to backflow and, by extension, propensity to fail during extrusion, is most sensitive to fluctuations in filament diameter and the material's shear thinning behavior. Our results demonstrate the importance of printing in the shear thinning regime to reduce the effect of processing conditions on the extrudability of a polymer.