Characterization and simulation of material distribution and fiber orientation in double gated glass-reinforced polypropylene injection

CAMILA QUINTANA; MARTINEZ GAMBA, M.; ANTO´ NIO SERGIO POUZADA,; PATRICIA M. FRONTINI,

Congreso; International Conference on Polymers and Moulds Innovations; 2014

It is well known that the characteristics of short fiber reinforced thermoplastic injected components depend on fiber orientation. However, the fiber orientation varies through part location and through thickness as a consequence of flow-induced orientation within the mold during the forming stage. This can lead to local variation in the part?s mechanical properties. Special attention should be paid to those parts with welding lines. Indeed, even if fibers can greatly improve the mechanical properties of polymers the may also severely weaken molded parts at their weld lines compared to their bulk strength. In order to improve the technology of short fiber reinforced thermoplastic injection molding, the use of a predictive tool based on computer simulation results very useful determining the correct process conditions which are capable of controlling fiber orientation. In this work, injection moldings with weld lines were produced in glass reinforced polypropylene grades differing in filler content using a two-gated hot runner injection mold. The skin-core microstructure developed during injection molding and fiber orientation was quantitatively analyzed by means of optical microscope and image analysis. In order to predict influence of injection-molding parameters on material distribution and weld lines quality, fiber orientation inside the skin and core layers and fiber orientation distribution within the weld line region, the commercial CFD simulation software Moldex3D has been utilized. The accuracy of the simulation prediction was verified by comparing with the experimental measurements of fiber distribution that were previously made using a polarized light microscopy. The results of micrographic observations of samples cut far from the weld line show the characteristic skin/core layer structure: in the skin region, the fiber orientation is predominantly parallel to the flow direction. In contrast, the core layer contains fibers mainly aligned perpendicular to the flow direction. Simulation results show the filling pattern of the cavity and distribution of fiber orientation. Predicted results agree with the experimental far from the weld line.