(396e) Continuum Simulations of Polymer Deposition in Fused-Filament Fabrication (FFF)

We utilize the OpenFOAM tool box to simulate the viscoelastic flow of polymer deposition in Fused-Filament Fabrication (FFF). In FFF, molten polymer extruded from a nozzle is built up layer-by-layer to form three-dimensional structures; the ultimate mechanical properties of the resultant structures depend on the material properties of the polymer as well as the microstructural changes of the polymer molecules induced by the processing history of the melt. Prior theory has examined polymer conformational changes during deposition, however, these theories relied on an “advection” calculation with no dynamics during deposition, suggesting the need for simulations to access the full dynamics. We simulate the non-uniform flow within nozzle and the deposited material; the polymer microstructure is described by coarse-grained, continuum-level structural variables (orientation, stretch, and entanglement fraction). The evolution equations for these structural variables, as well as conservation laws of mass, momentum, and energy, are solved to obtain the polymer conformation, velocity, and temperature within the nozzle as well as within the extruded polymer. We compare different entanglement dynamics schemes, and find that models with shear-induced disentanglement schemes overpredict disentanglement at high shear rates. We investigate the conformational changes induced by regions of local shear and extensional flows within the nozzle. The influence of processing conditions (e.g. volumetric flowrate, print speed, printer height) are investigated; it is found that these processing conditions may be tuned to produce desired conformational changes in the polymer molecules.