Numerical analysis of screw swirling effects on fiber orientation in large area additive manufacturing polymer composite deposition

Abstract

Large Area Additive Manufacturing (LAAM) polymer deposition employs a single screw extruder to deliver pelletized feedstock resulting in significantly higher flow rates as compared to conventional filament-based extrusion additive processes. Swirling kinematics in LAAM melt flow that result from the screw rotation generate unique particle alignment patterns within the fiber-filled polymer during deposition processing. This paper investigates the effect of the single screw swirling motion on the resulting fiber orientation in a short fiber polymer composite extrudate. An axisymmetric non-Newtonian viscoelastic flow is simulated with the finite element method, where the flow nearby the extruder screw tip, within the printing nozzle, and a short section of free extrudate compose the flow domain. Fiber orientation tensors within the flow domain are evaluated using the Wang-O’Gara-Tucker Reduced Strain Closure (RSC) fiber orientation diffusion model with the orthotropic fitted closure. The results indicate that swirling kinematics yield a longer flow path for fibers to travel and orientate within the flow domain, yielding orientation tensor results that are notably different as compared to a non-swirl event. The predicted principal elastic constant from the swirling flow and non-swirling flow models exhibit 21% difference, and those from the swirling model using the RSC closure shows a good agreement with reported experimental data for a similar material system.