On account of the inherent features of the thin‐wall injection molding process, a three‐dimensional numerical model, which accounts for wall slip effect and pressure dependence of viscosity (PDoV), was proposed for a more accurate simulation of the fiber orientation in thin‐wall injection‐molded parts of short‐glass‐fiber‐reinforced polymer composites (SGFRPC). First, the fiber orientation was simulated using the three‐dimensional and mid‐plane models, respectively. The comparison between the simulated and experimental results verifies that the three‐dimensional numerical results were in better agreement with the experimental measurements. Secondly, the influences of wall slip effect and PDoV on fiber orientation in thin‐wall injection‐molded parts of SGFRPC were analyzed based on the three‐dimensional numerical model. The results show that the three‐dimensional numerical simulation simultaneously accounting for wall slip effect and PDoV can better predict the fiber orientation in thin‐wall injection‐molded parts of SGFRPC, suggesting the validation of the proposed model. Finally, five main processing parameters, that is, injection rate, melt temperature, mold temperature, packing pressure, and packing time, were also studied in terms of their influences on the fiber orientation in thin‐wall injection‐molded parts of SGFRPC.

It is a critical requirement to have an insight into the mechanism of flow-induced fiber orientation in short-shot water-assisted injection molding (SSWAIM) of fiberreinforced polymer for improving the structural rigidity and service life of molded parts. However, this mechanism is still unclear, which stunts the development of SSWAIM. In this work, the mechanism of flow-induced fiber orientation in SSWAIM parts of short-glass-fiber-reinforced polypropylene (SGF/PP) was clarified through numerical research and experimental verification. The results showed that the difference of fiber orientation distribution at different positions both in the radial direction and along the flow direction between SSWAIM parts and conventional injection molding (CIM) parts was mainly due to the strong flow field caused by the high-pressure water penetration in SSWAIM. Moreover, fiber orientation in the SSWAIM part depended not only on its position both in the radial direction and along the flow direction, but also on the processing parameters. At the front of SSWAIM part, fiber orientation changed greatly in the radial direction and presented an obvious "shell layer-core layer-water channel layer" hierarchical structure across the part thickness, whereas this phenomenon became more inconspicuous with increasing the distance of the selected position from the water injection inlet.Short-shot size is the principal parameter affecting the fiber orientation, and within the range of investigated processing parameters, smaller short-shot size, shorter water injection delay time, higher water pressure, and lower melt temperature could significantly facilitate fiber orientation across the part thickness.