Effects of nozzle geometry and extrudate swell on fiber orientation in Fused Deposition Modeling nozzle flow.

Fused Deposition Modeling (FDM) is a rapidly growing Additive Manufacturing (AM) technology using extruded thermoplastics to produce intricate three-dimensional parts from digital data. Adding discrete fibers to FDM filament feedstock improves mechanical properties of FDM parts; however, little is known about processing and tooling effects on fiber orientation defined by velocity gradients within the polymer melt flow. This research simulates axisymmetric FDM extrudate swell extending from the nozzle exit by adjusting the radial location of the free surface to minimize the integrated free surface stress. Fiber orientation within the polymer melt is calculated from velocity gradients evaluated along streamlines in the fluid domain using orientation tensors, the fast exact closure, and isotropic rotary diffusion. Results quantify the influence of nozzle geometry and extrudate swell on fiber orientation in the extruded polymer. Parametric studies of nozzle geometry show sharp contractions in nozzle geometry near its exit significantly increases average fiber alignment.