Influence of Fibers on the Flow Through the Hot-End in Material Extrusion Additive Manufacturing

Abstract

Advancements in material extrusion additive manufacturing are driven by the need of fast production of high-quality parts. A key innovation was the introduction of short fibers into the built filament, which substantially improve the strength of manufactured components. However, the presence of fibers also affects the viscosity and thermal conductivity of the filament, which are important parameters for the extrusion flow and thus the maximum printing speed. In this paper, we numerically study the effect of fibers on the polymer flow and pressure drop inside the nozzle, which determines the maximum extrusion rate. The thermoplastic polymer flow is simulated with a non-isothermal computational fluid dynamics model and the inclusion of fibers is treated with a continuum approach. The simulations are performed for ABS polymer with short carbon fibers, however, other thermoplastic systems with short fibers (e.g. glass, wood, or nylon) can be integrated into the model. The model provides a virtual window into the process and illustrates that while fibers increase the viscosity of the filament and the pressure drop, they also improve the thermal conductivity and lead to faster melting of the polymer, which has an opposite effect on the pressure drop. Finally, the model quantifies the relationship between the fiber volume fraction and the maximum extrusion rate.