Effect of Nozzle Geometry on Melt Flow Simulation and Structural Property of Thermoplastic Nanocomposites in Fused Deposition Modeling

Abstract

Fused deposition modeling (FDM) is a low-cost additive manufacturing (AM) process which uses thermoplastic materials to fabricate prototype parts from a computer aided design (CAD) model. Melt flow characteristics in FDM liquefier plays an important role in bead spreading architecture and contact angle, which eventually influences inter-bead voids and interfacial bead bonding. This paper focuses in studying the effects of nozzle exit geometries, on melt flow behavior inside the FDM liquefier chamber, void contents, and performance of carbon nanofiber (CNF) reinforced thermoplastic nanocomposites. A computational model for non-Newtonian flow is developed for the melt flow simulation of CNF/Polylactic Acid (PLA) nanocomposites to understand the behavior of FDM process parameters. The rheological properties of CNF/PLA nanocomposites with different weight percentage of CNF (0%, 0.5%, and 1%) have been determined through a standard rheology test. An existing FDM extrusion channel with characteristic dimensions have been modeled in a three-dimensional domain. The melt flow behavior in terms of the pressure drop, nozzle exit velocity profile, and axial temperature profile is studied by varying material property and nozzle geometry. A conceptual star shaped liquefier nozzle has been considered for improved bead architecture with minimum void contents. The results of the numerical simulations are compared with those for the published existing models which shows reasonable agreement. Tensile dogbone specimens have been printed with different liquefier nozzle diameters for mechanical testing. The optical microscopic examination show the presence of triangular and diamond shape void contents in printed CNF/PLA nanocomposites. The FDM printed nanocomposites show improved modulus and yield strength in comparison to neat PLA resin.