| Summary: | 碩士 === 國立高雄科技大學 === 模具工程系 === 107 === Rib is a frequently used feature in plastic products design for the purpose to enhance the strength of the plastic products. With the ribs application of many industrial fields, the shape, size design and forming method of various ribs are becoming more and more diverse and important. For example, some of the ribs are designed in a large size, and the traditional injection molding screw holding mechanism cannot improve and reduce the sink mark defects. Therefore, the internal gas-assisted injection molding technology is an effective process that produces plastic products with large ribs. The process injects gas into the thick sections where the internal gas pressure compensates for the shrinkage and keeps the part surface in contact with the cavity wall, thus preventing the sink marks of large ribs. In the other hand, the plastic products with many small ribs, the external gas-assisted injection molding technology is selected to solve the sink mark problem of such products. The external gas holding mechanism is best for plastic products with large surface area and small ribs. In addition, the external gas-assisted injection molding no need many gas-delivery nozzles.
In recent years, there are more and more plastic products with different sizes and complex reinforcing ribs. For this reason, this study proposes an integrated process of internal and external gas-assisted injection molding for fabrication of plastic products with complex ribs. The advantages of this novel integration process can improve the production yield and molding quality of plastic products with complex ribs design.
In this study, a flat plate with large and small ribs structure is designed and developed. The effects of processing conditions on the quality of fabricated plastic parts were investigated. The depth of the sink marks on the surface of each ribs and the gas penetration characteristics were measured and discussed. Finally, comparison of simulation and experimental results for verify the feasibility and uniformity of the novel process.
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