Nozzle geometry effects on exit orientation of short fiber composites

Abstract

A problem in Fused Deposition Modeling (FDM) additive manufacturing processes with short carbon fiber filled suspensions is that the resulting part does not have isotropic properties. Nozzles used during processing tend to align fibers in the direction of flow with a very high degree of anisotropy. An effort is made here to design a nozzle which promotes a homogenous distribution of the carbon fiber orientations throughout the part. This homogeneity results in isotropic mechanical properties which can be better-suited for design and analysis. Fiber orientation analysis is performed via Autodesk Moldflow Insight 2017 using their injection molding simulation workbench. Various iterations of nozzle designs are compared with a baseline nozzle design. The nozzle designs are analyzed as an axisymmetric two-dimensional cross-section using a modified form of the Folgar-Tucker equations specific to Moldflow. These two-dimensional cases are compared to the three-dimensional model which uses the traditional Folgar-Tucker equations. The analysis will primarily compare the fiber orientation tensor component along the flow of the nozzle since the flow tends to align the fibers in the direction of the flow in the convergent and narrow zones of the nozzle.