Effect of Weld‐Line Orientation on the Impact Performance of Injection‐Molded PA6 and PA6 – 30GF

ABSTRACT

Weld lines formed during injection molding are unavoidable defects that significantly reduce the mechanical performance of engineering polymers. This study experimentally investigates the influence of weld line orientation on the impact and microstructural properties of both materials using Moldflow simulation, standardized mechanical testing, and SEM analysis. Plaque samples of PA6 and PA6‐30GF were molded, and specimens were prepared from weld‐line and non‐weld‐line regions for Izod impact and Charpy impact testing. Weld‐line orientations of “90°”, “80°”, “70°”, and “60°” were systematically examined to quantify orientation‐dependent impact degradation. Moldflow simulation accurately predicted weld‐line formation and fiber orientation, while SEM was used to characterize fracture morphology and fiber–matrix interactions. Results show weld‐line formation caused deterioration in Izod impact and Charpy impact strength. PA6‐Unfilled exhibited moderate reductions—10% in Izod impact, 11.8% in Charpy. In contrast, PA6‐30GF displayed substantial losses, including a 35.3% drop in Izod impact strength at a “90°” weld‐line orientation and a 7.69% reduction in Charpy impact strength, attributed to fiber anisotropy and random distribution at the weld line. A progressive increase in impact strength was observed as the weld‐line angle decreased from “90°” to “60°” in both materials.