Numerical Prediction of the Weld-line-Induced Strength Reduction for Injection-Molded Part

Weld-lines or knit-lines are formed during the mold filling process when the split melt flow fronts meet at the same downstream location. Weld-lines look like cracks on the appearance of plastic parts. Sometimes these visible features are not accepted esthetically in many applications. However, most importantly, the local mechanical strength in the weld-line area could be significantly weaker. It could be one of the most significant problems for structural applications due to the potential failure in the weld-line areas. Hence, how to prevent the weld-lines and guarantee the good quality are the major concerns to part/mold designers. Traditionally, the structure analysis for injection-molded plastic part is to perform CAE analysis based on the assumption of one or several isotropic materials. However, the material characteristic of plastic part is extremely dependent on molding process, such as weaker mechanical strength in weld-line areas. In this paper, a numerical approach is proposed to predict weld-lines strength. Furthermore, through the data link between mold-filling simulation and ANSYS structure analysis, the effects of weld-lines towards part structure are predictable.

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