Understanding the vibration-assisted extrusion of thermoplastic polymers in fused filament fabrication

Vibration-assisted extrusion is an emerging technique designed to mitigate high hydraulic resistance and poor thermal homogeneity during the processing of viscoplastic materials. However, the complex coupling between dynamic excitation parameters and the non-linear rheological response of polymer melts remains insufficiently elucidated. This study presents a systematic numerical investigation into the thermo-hydraulic characteristics of the Fused Filament Fabrication (FFF) hot-end, utilizing the Souza Mendes and Dutra (SMD) regularization model to accurately capture the shear-thinning and yield-stress behaviors of PE/PLA composites. The results reveal a critical trade-off between vibration amplitude and frequency. While increasing the amplitude monotonically reduces the extrusion force by activating the shear-thinning effect, increasing the frequency beyond a critical threshold induces a saturation in the thermal response. Specifically, high-frequency pulsation is associated with a persistent, unyielded cold core, while the downstream thermal response is interpreted as transport of an upstream-established thermorheological state rather than sustained local transverse mixing. Consequently, a numerical regime characterized by high amplitude and low frequency is identified via quadrant analysis as a favorable combination among the cases tested for minimizing extrusion resistance while maximizing core thermal uniformity. Furthermore, sensitivity analyses demonstrate that the simulated thermo-hydraulic response is strongly dependent on intrinsic material properties: a low power-law index promotes flow enhancement, whereas a high consistency index acts as a viscous damper that suppresses radial vorticity penetration. These findings clarify that the simulated thermo-hydraulic response is governed by the kinematic barrier associated with vorticity confinement, thereby providing a mechanistic basis for future experimental evaluation of vibration-assisted extrusion.