A large-sized cover part for air cleaner was injection molded with ABS resin, and its incomplete filling defect was analyzed using commercial Moldflow software. To investigate the effect of processing temperature on incomplete filling defect, tensile properties, weight loss, and phase separation behavior of ABS resin were evaluated. The tensile properties of dumbbell samples were not changed up to 250°C and decreased significantly thereafter. SEM micrographs indicated no significant changes in the status of polybutadiene rubber phase below 250°C. These different test results indicated that ABS resin little affected the thermal decomposition in processing temperature range. The Moldflow simulation was performed using measured thickness of molded cover and actual mold design with the defects. As expected, the cover part showed unbalanced filling and incomplete sections. To improve these defects, two possible cases of hot runner system have been simulated. When applying modified 5-gate system, the maximum injection pressure was decreased approximately 5.5% more than that of actual gate system. In case of 6-gate system, the maximum injection pressure reduced by 23%, and the injection pressure required to fill is well within the range of the molding equipment. The maximum clamping force of 6-gate system was also significantly reduced than that of actual and 5-gate system. 1. Introduction Injection molding is one of the most commonly used manufacturing processes for the fabrication of plastic parts in net shape with excellent dimensional tolerance [1]. A wide variety of products are manufactured using injection molding, which vary greatly in their size and complexity [2–5]. Examples of common, everyday products that require plastic injection molding include automobile bumpers, mobile phone housings, television cabinets, compact discs, toys, and lunch boxes are all examples of injection-molded parts. This process requires the use of an injection-molding machine, raw plastic material, and a mold. A plastic material is melted in the injection-molding machine and then injected into the mold, where it cools and solidifies into the final part. The most commonly used thermoplastics are polystyrene, polypropylene, polyvinyl chloride, and acrylonitrile-butadiene-styrene (ABS) [6–9]. ABS resins are among the most versatile thermoplastics in the styrenic polymers. The primary features and benefits of ABS are derived from the tree building blocks. Thermal stability and chemical resistance are derived from acrylonitrile, while butadiene provides impact resistance and
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