The study of the die geometry and the characteristics of a non-Newtonian viscoelastic fluid during extrusion

Plastic extrusion is a typical plastic manufacturing process. After heating, plastic with high resilience and low viscosity, dependent on the temperature, are extruded from the nozzle. The change of the rheological properties will swell the extruded geometry and reduce the deposited surface quality and structure. Thus, the swelling phenomenon of the visco-elastic fluid during extrusion has become a significant area under discussion. This study is conferred on the behavior of the melting plastic extruded from the nozzle in the Fused Filament Fabrication layer manufacturing process. The heating and cooling properties were first discussed with different materials of the extruders, and different die geometries combined with the new nozzle holder were designed and analyzed by the computational fluid dynamic simulation with Arrhenius viscosity model which are temperature dependent. Relationships between different nozzle geometries and swelling angles were also compared. Validations were observed that the analysis results are consistent with experimental results. The larger nozzle outlet divergent angle is, the less difference between extruded plastic diameter and nozzle caliber. As the nozzle outlet angle approaches -10 degree, the diameter dimension of the melting plastic is about 0.394mm which is very closed to the nozzle caliber.