Abstract
Long-fiber polymers offer the advantage of a lower production cost because specific tool designs are required for conventional injection molding equipment to produce long-fiber polymer parts. The use of long fibers allows relatively high fiber aspect ratios to be obtained, thereby enhancing composite stiffness, strength, creep endurance, and fatigue endurance. However, the multigate design of the injection-molded part can result in weldline formation during the molding process, which reduces the structural strength of the molded part. Therefore, in this study, the surface quality, fiber compatibility, and structural strength of long-glass-fiber-reinforced polypropylene (PP/LGF) injection-molded samples were compared in the use versus nonuse of a mold-cavity overflow-well area and the mold-face infrared heating method. The experimental results indicate that the mold-cavity overflow-well area more greatly improved the surface roughness of the PP/LGF molded samples. Moreover, the infrared heating of the mold-face decreased the weldline depth of the samples. Optical-microscopy images and mold-cavity pressure distributions indicated that the weldline tensile strength and the interface compatibility between fibers and melts at the weldline region during the molding stage were higher in the use than in the nonuse of the mold-cavity overflow-well and mold-face infrared heating method.
Highlights
In recent years, fiber-reinforced polymers, which have excellent mechanical properties, have become the preferred composite material for executing lightweight applications in many industries, such as the automotive industry
Samples with weldlines were molded using different overflow-well depths and types of mold-face heating, whereby the surface roughness or the presence of surface-floating fibers was observed after two melts were merged (Figure 4)
A strong surface-floating fiber phenomenon was noticed, which weakened as the overflow-well depth increased (Figure 4b1, b2, c1, c2, d1, d2) due to overflow-well provided an important influence on melt flow during filling stage and provided a better molecular chain entanglement for molded samples
Summary
Fiber-reinforced polymers, which have excellent mechanical properties, have become the preferred composite material for executing lightweight applications in many industries, such as the automotive industry. Due to their advantages such as high strength or stiffness, design flexibility, and ability to be recycled, the aforementioned polymers have been widely used to construct structural parts [1,2,3,4,5,6,7]. Long-fiber-reinforced polymer (Lf-P) composites have attracted considerable research attention due to their desirable features, such as high strength, stiffness, and impact properties, which are superior to those of short-fiber-reinforced polymer composites [10,11,12]. Injection molding is one of the most favorable polymer processing methods because
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