Simulation of polymer stretch and disentanglement in Fused-Filament Fabrication (FFF)

We utilize the RheoTool package in the OpenFOAM toolbox to simulate the viscoelastic flow of polymer deposition in Fused-Filament Fabrication (FFF). FFF is an additive manufacturing technique whereby polymer filaments are feed through a heated printer head to build three-dimensional structures layer-by-layer. Recent work has shown that the weld strength between layers depends on the interdiffusion of entanglements across the interface and residual stresses arising from flow-induced alignment. We simulate flow-induced conformational changes in the polymer molecules in order to determine how processing conditions influence molecular conformations. The evolution of the polymer microstructure (orientation, stretch, and entanglement fraction) is described by coarse-grained, continuum evolution equations, which we solve numerically within the nozzle as well as within the extruded polymer. We examine different constitutive equations for the polymer and find that models where disentanglement arises from affine-stretch of the molecules overpredict disentanglement at high shear rates. We compare our results to prior analytical theory with simplified dynamics.