Investigation of the effects of pre-cross-linked thermoset molding compounds on weld line strength in injection molding

In this study, epoxy molding compounds (EMC) filled with glass beads were fabricated with a twin-screw-extruder (TSE) and tempered before further processing to generate different degrees of cross-linking (0–15%) in the compounds. After that, the compounds were injection-molded into tensile samples with and without weld lines to investigate the influence of pre-cross-linking of compounds on the weld line strength. Both the referent fracture strength and the weld line strength were improved with the increase of pre-cross-linking in compounds. Especially, cavities in the weld line area were reduced presumably due to the improved venting with the increased viscosity. For the resized samples without notches, their weld line strength are higher than those with notches. The in-mold pressure of more pre-cross-linked compounds can be hold longer than less pre-cross-linked compounds. This could lead to a better compensation of the material shrinkage. This might be the reason for the improved weld line strength for more pre-cross-linked compounds.