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김홍석,조명상,손중식,서태수,김태웅,Kim, Hong-Seok,Jo, Myeong-Sang,Son, Jung-Sik,Seo, Tae-Su,Kim, Tae-Ung 대한기계학회 2001 大韓機械學會論文集A Vol.25 No.8
In order to reduce the time and cost for assembly, automobile speaker grills have been injection molded with door trims or map pockets in one piece recently. However, several defects such as short shots or air traps can easily occur due to the decreased fluidity of the melting polymer according to the excessive heat transfer to the mold. Therefore, it is necessary to optimize the resin feed system and predict possible defects by CAE analysis. However it is not possible to obtain exact analysis results for the speaker grill by using general shell elements since the heat transfer in the thickness direction which is the dominant factor of the filling stage can not be considered. Therefore, there have been several efforts to simulate the injection molding nature of the speaker grill by using shell elements with an effective thickness which is smaller than the actual thickness of the part. Two empirical values have been recommended for the effective thickness in real practice. One is 50∼70% of the thickness of the speaker grill and another is the gap distance between the adjacent holes. In this paper, CAE analyses of a map pocket with a speaker grill were conducted using shell elements with both of these recommended effective thicknesses, and the predicted flow fronts were compared with the findings from injection molding experiments. The commercial code MOLDFLOW was used for injection molding analysis and an 850 ton injection molding machine was used for experiments.
김홍석(Hong-Seok Kim),손중식(Jung-Sik Son),서태수(Tae-Soo Seo) 대한기계학회 2002 대한기계학회 춘추학술대회 Vol.2002 No.5
A polymer such as polypropylene or polyethylene has a unique feature of integral hinge which can<br/> flex over a million times without failure. With advantages of a hinge, time and cost required to<br/> assembly can be eliminated by injecting a whole part as one piece. However, due to the increased<br/> fluidity resistance at hinges, several defects such as short shots or premature hinge failures can occur<br/> with an improper location of gates. Therefore, especially for a part with hinges, it is necessary to<br/> optimize the flow balance before making a mold. In this paper, resin flow patterns according to<br/> various gate positions were observed by CAE analyses of a simple strip part with a hinge. As a<br/> result, we found that gates should be located to minimize flow hesitations at hinge areas in order to<br/> avoid defects. To verify the guideline, a gate system for an automobile junction box was designed by<br/> CAE analyses and injection tryouts were conducted.