Numerical simulation of the shear rate in the fused filament fabrication process of poly-ether-ether-ketone (PEEK)

Abstract Fused filament fabrication (FFF) is a material extrusion-based process and one of the most popular additive manufacturing processes, widely used for rapid prototyping and manufacturing of polymeric parts. Despite the simplicity of the process, the polymer undergoes complex rheological properties’ transformation in this process. Understanding the rheological properties of the polymer during deposition is of paramount importance to model and improve the quality of the final product. In this study, for the first time, a two-phase flow numerical simulation approach with a Level Set equation has been used to model the shear rate in the FFF process after polymer exiting from the nozzle. The rheological properties of the raw PEEK as the feedstock were measured at low frequency by parallel-plate rheometer, and at high shear rate using an extensional die. Influence of travel speed, inlet velocity, nozzle diameter, and layer height on the shear rate of the deposited bead has been investigated. Obtained results revealed that the inlet velocity, nozzle diameter, and layer height highly influence the shear rate of the bead after exiting from the nozzle, while the influence of travel speed on the shear rate is negligible. Increasing the inlet velocity leads to an increase in velocity field and consequently maximum shear rate during deposition. Polymer melt tends to relax stress and become at steady state after existing from the nozzle rapidly, thus, it is required to reduce the inlet velocity using bigger nozzle diameter or smaller diameter raw filament or increase layer height to reduce the induced shear rate during deposition. Finally, multiple equations have been proposed to predict the maximum shear rate during the deposition based on the printing parameters.