Correlation Between Fiber Orientation and Geometrical Shrinkage of Injected Parts Under the Influence of Flow-Fiber Coupling Effect

Fiber reinforced thermoplastics (FRP) have been widely used in automotive industry. However, how does the flow-fiber coupling effect influence the micro fiber orientation and further affect the geometrical shrinkage of the final part that is not fully understood yet. In this study, a complex center-gated plate has been applied to study the influence of the flow-fiber coupling effect on the fiber orientation variation and the geometrical change through numerical simulation. Then the practical verification through the micro-computed tomography (micro-CT) and image processing technology was carried out. Results show that in the presence of the flow-fiber coupling the required spruce pressure will be higher compared to no coupling case. In addition, the melt flow front pattern will be changed from “convex-flat” to “convex-concave” under the influence of this coupling. Moreover, in the presence of the flow-fiber coupling effect, the wider core width for fiber orientation tensor in the flow direction (A₁₁) can be obtained from upstream to downstream regions for the same model. However, in the downstream region (i.e. in the FR), the flow-fiber coupling effect is more significantly due to the action of less shear rate in that region. Finally, through the measurement of the left–right asymmetrical shape of the FR for Model I (or Model II), the reason is that the flow-fiber coupling effect will switch the fiber orientation from the flow direction (A₁₁) dominate to the cross-flow direction (A₂₂) dominate. This asymmetrical fiber orientation distribution will further create that asymmetrical shrinkage shape of final part. The correlation between fiber orientation and geometrical shrinkage can be achieved.