Hyeon-Myeong Kim

Gate location design in injection molding of an automobile junction box with integral hinges

Abstract Polymers such as polypropylene or polyethylene offer a unique feature of producing an integral or living hinge for automobiles, which can flex over a million times without causing a failure. However, due to increased fluidity resistance at hinges during molding, several defects such as short shot or premature failure can occur with the improper selection of gate locations. In this paper, a design guideline was induced by investigating resin flow patterns depending on several gate positions obtained by numerical analyses of a simple strip with a hinge. The analyses of the simple strip part showed that the resin at the hinge did not flow until the other side of the strip was filled. Once the resin at the hinge did not flow for a long time enough to be solidified, defects such as short shots or hesitation marks formed. For a practical application of the design guideline determined, four gate systems for an automobile junction box were designed. It was found that the properly determined gate location leads to better resin flow and shorter hesitation time. Finally, injection molding tryouts using a mold that was designed by one of the proposed gate systems were conducted. The experiments showed that hinges without defects could be produced by using the designed gate location to assure the induced design guideline to be reasonable.

Modified looping technique for remeshing of forming simulations with free surface folding

In finite element simulations of forming processes with a complex geometry, free surface folding phenomenon is likely during simulations when die design or the size of initial billet is inappropriately determined. In such cases, free surface geometry becomes so acute that mesh generation may be impossible with a conventional looping technique automatically. In order to solve this kind of problem, looping technique was modified to generate boundary elements for the acute geometry with a better mesh quality. The developed technique was implemented to the in-house bulk metal forming simulation program CAMPform and applied for forming simulations of ring gear forging and nosing in which surface folding defects occur. It was found that folding phenomenon was successfully handled with the currently developed algorithm and suitable process conditions to eliminate the free surface folding were determined through numerical simulations.