A numerical study of the effect of viscoelastic stresses in fused filament fabrication

A computational model for simulations of fused filament fabrication (FFF) – often also called fused deposition modeling (FDM) – that includes viscoelastic stresses, is presented. The flow of a viscoelastic polymer filament from a nozzle, the deposition of the filament onto a substrata or previously deposited filaments, and the cooling and solidification of the filament, are captured using the one-fluid formulations, where a single set of equations is written for all the fluids and phases involved (polymer and air). The governing equations are solved on a regular stationary grid and the boundary between the polymer and the air is followed using connected marker points. The model is based on an earlier development where the polymer stresses were assumed to be Newtonian. The method is tested by simulating the extrusion of a polymer from a nozzle and the predicted swelling compared with results from the literature. The method is then used to simulate three filaments deposited on top of each other and the fabrication of an object consisting of a filament deposited perpendicularly on top of several filaments. The effect of including viscoelasticity on the extruded filament size and shape are discussed.