The Effects of Extrudate Swell, Nozzle Shape, and the Nozzle Convergence Zone on Fiber Orientation in Fused Deposition Modeling Nozzle Flow

Fused Deposition Modeling (FDM) is a rapidly growing Additive Manufacturing (AM) technology that allows for low cost and intricate three-dimensional parts to be created. FDM parts are created in layers by extruding a bead of polymer melt from a filament fed nozzle onto a platform. Several recent developments aimed at improving the mechanical properties of FDM components have focused on adding structural chopped fibers to the FDM filament feedstock. It is understood that the discrete fibers will orient in response to the melt flow within the nozzle. In addition the fluid expansion effects of extrudate swell at the nozzle exit impacts the melt velocity gradients and therefore the underlying fiber orientation. The local varying fiber orientation directly impacts the mechanical properties of the part, making the fiber orientation prediction during processing a necessary portion of FDM composite part design. A computational approach is presented for determining fiber orientation in the nozzle flow domain taking into consideration the effects of the convergence zone in the FDM extrusion nozzle, the fluid expansion caused by extrudate swell, and nozzle shape on the fiber orientation in the extruded polymer. The polymer melt is modeled as a Newtonian fluid in Creeping flow and includes extrudate swell expansion. Fiber orientation is calculated using the Advani-Tucker (1987) orientation tensors with the Fast Exact Closure from Montgomery-Smith, et. al. (2009) assuming the Folgar-Tucker (1984) isotropic rotary diffusion model for fiber-fiber interactions. The results show that the shear flow prior to the nozzle section causes high alignment in the direction of the flow as is expected. This alignment state is further increased within the nozzle convergence zone. The expansion flow in the die swell region causes a noticeable decrease in fiber alignment in the direction of the flow and an increase in fiber alignment transverse to the flow direction.