Numerical modelling of the viscoelastic polymer melt flow in material extrusion additive manufacturing

In material extrusion (MEX), it is challenging to accurately predict the steady and transient feeding forces at various polymer extrusion rates when printing island and thin-walled structures involving rapid start/stop or acceleration/deceleration, especially for semi-crystalline polymers. This research presents a non-isothermal viscoelastic Computational Fluid Dynamics model to investigate the steady and transient feeding forces, as well as the phase transition process and viscoelastic behaviour of polylactic acid (PLA), a semi-crystalline polymer, during the extrusion process. The study establishes a relationship between polymer flow and viscoelastic stress, demonstrating that the elastic effect during extrusion is more significant than the viscous effect, particularly at higher feeding rates. Furthermore, the study uncovers critical aspects of PLA melt flow behaviour during the MEX process, laying the foundation for future research and optimisation of MEX printing processes.