Restraint of Voids Generated Inside Injection Molded Products by In-Mold Pressing Method

摘要

In recent years, long glass fiber reinforced plastic andcarbon fiber reinforced plastic have begun to be usedfor structural components that require high strength.As a result, thick-walled injection molded productsare being manufactured. However, defects, known asvoids, are generated inside the molded product and decrease the strength of the molded product, posing asignificant problem at molding production sites. Thepartial compression method, which is a type of injection compression molding, is effective in preventing voids in thick-walled injection molding. However,there have been limited studies that comprehensivelyinvestigated the effects of the compression conditionson void prevention in thick-walled injection moldingproducts or the shape and dimension of the moldedproduct, or the issues in the molded product producedby applying compression. The authors have previously proposed the in-mold pressing (IMP) method,which allows the application of partial compressionwithout the use of an injection compression moldingmachine and verified its validity. In this study, we proposed a compression device in which a servomotordriven hydraulic pump actuator is used to propel amovable rod to apply compression to the melt insidethe mold cavity. The IMP method using this devicewas applied to mold thick-walled products with thicknesses of 10 mm and greater, and the effects of compression on the generation of voids inside the moldedproduct and the shape and dimensions of the productwere investigated. The results indicate that the generation of voids can be prevented by application of thismethod. In addition, it was found that marginal deformations, which can pose issues, occur in the moldedproduct when compressive stresses generated insidethe molded product by compression are released afterdemolding.