Comparative study of weldline strength in conventional injection molding and rapid heat cycle molding

Rapid heat cycle molding (RHCM) is a special molding process capable of producing molded plastic parts with high surface quality and improved weldline strength and appearance. This study investigated the influence of the weldline on the tensile strength of RHCM and conventional injection molded (CIM) components. The test specimens with and without a weldline were cut from RHCM and CIM parts for scanning electron microscopy (SEM) imaging to characterize the structure and dimensions of the weldline and tensile testing. The tensile testing results showed that the weldline reduced the tensile strength, but RHCM decreased the tensile strength reduction effect of the weldline. There was no distinguishable difference between the two molding processes for the tensile strength of specimens without a weldline. In addition, a thin surface layer of material containing the V-notch at the weldline was removed from the RHCM and CIM parts to examine its effect on the tensile properties. The thinned-out specimens with a weldline showed improved tensile strength, and specimens without a weldline showed decreased tensile strength, compared to specimens with the original full thickness.