Numerical simulation of the complex flow during material extrusion in fused filament fabrication
Julian Kattinger, Tim Ebinger, Raphael Kurz, Christian Bonten
Abstract
This paper presents a CFD simulation of the non-Newtonian and non-isothermal polymer flow through the nozzle of a fused filament fabrication printer. The modeling approach is based on a melt fraction model which allows to cover the entire flow domain from the solid filament entering the nozzle to the melt state at the nozzle exit. The numerical results were compared with a specially developed setup that allows the measurement of the feeding force required to push the filament through the nozzle. The comparison is carried out over a wide range of filament velocities using different nozzle temperatures and nozzle geometries. It is shown that the assumptions used for the simulation are suitable to predict the melting and flow behavior in the relevant processing range. The model represents both the process region where the filament has sufficient time to melt before reaching the nozzle tip and the region of high filament velocities where there is insufficient time for complete melting. In the latter region, the model predicts that the molten region is reduced to a thin melt film at the tip of the filament as it is pushed against the conical transition zone of the nozzle. Furthermore, the simulation results show that the temperature at the nozzle exit decreases with increasing filament velocity. Based on this modeling approach, melting within the additive manufacturing process of material extrusion can be improved. Furthermore, the findings can be used to optimize the strand deposition.