Analysis of interfacial force interaction in the internal polymer flow in the hot end of material extrusion additive manufacturing

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Abstract
To better understand the polymer flow physics through the hot end of a material extrusion additive manufacturing process, a volume of fluid multiphase computational fluid dynamics model (CFD) was formulated to integrate the effect of interfacial forces in the air gap between the heating wall and the melting filament. The model was validated by developing a measurement system that captures the extrusion dynamics, which was quantified in terms of feeding force by using two load cells rated at 5 kg and 20 kg as force sensors and a 1 kg load cell to measure extrudate mass. The CFD experimental validation setup presents a detailed method for integrating an inline force measurement system into a commercial 3D printer, requiring minimal modifications to the printhead and gantry head arrangement. The CFD model result, validated against experimental data, follows more closely the measured feeding force of the 5 kg load cell than the 20 kg load cell. The experimental results further show that lower-rated load cells (5 kg) are more precise at low feeding rates, while higher-rated load cells (20 kg) are better for higher extrusion forces. The CFD analysis of the internal flow through the hot end revealed fascinating actionable insights for exploiting interfacial tension effects for the design of the hot end and extrusion system, enabling faster and more reliable printing. The new understanding of the interaction between thermofluid and interfacial tension can inform process parameter control and the design of desktop 3D printers.

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