First steps of the melting of an amorphous polymer through a hot-end of a material extrusion additive manufacturing

The melting of an amorphous polymer filament through the hot end of a material extrusion process is addressed using computational multiphase fluid dynamics coupled to heat transfer. Only the flow through the heat block is investigated. The air gap between the filament and the interior of the extruder is accounted for. The polymer/air interface is implicitly tracked by a level-set method. The system of equations is solved using a finite element method with a time-marching method. Three extrusion velocities are investigated. For the lowest velocity, after the contact of the polymer with the extruder on the nozzle, the air gap disappears with time. The transient regime lasts a few tens of seconds. For the two larger velocities, even if the air gap is more and more reduced with time, it persists for a long time. The extension of the air gap increases with the velocity. The feeding force needed to push the filament is obtained by the integration of the tension on the surface of the extruder. After a transient regime driven by the heat transfer, a steady-state regime is observed for the three velocities. Roughly, the feeding force increases linearly with the extrusion velocity. A good agreement is found with experimental results for the two smallest velocities.