Effect of Weld‐Line Distance From an Obstacle on the Impact Strength of Injection‐Molded Polyamide‐6 and Glass‐Fiber‐Reinforced Polyamide‐6

Weld lines are inherent defects in injection‐molded polymer components, particularly in parts containing multiple gates or internal obstacles that cause the convergence of two melt fronts. This study uniquely combines mold‐flow simulation, mold fabrication, experimental testing, and SEM analysis to systematically investigate how the weld‐line distance from an obstacle affects the impact strength and weld‐line factor (WLF) of unfilled polyamide 6 (PA6) and glass fiber‐reinforced polyamide 6 (PA6‐30GF). Izod and Charpy impact tests are performed on specimens with and without weld lines, and impact strength and WLF are evaluated as a function of weld‐line distance along the melt flow direction at 4, 8, 12, 16, 20, 24, and 28 mm from the obstacle. Results show that impact strength increases by approximately 12%–18% as the weld‐line distance increases from 4 mm to 28 mm. WLF also increases progressively but remains below unity, confirming persistent weld‐line weakness. These findings provide quantitative insight into how weld‐line distance specifically influences mechanical performance, demonstrating that increasing this distance reduces weld line severity but does not completely eliminate its detrimental effect, particularly in fiber‐reinforced systems. The study expands understanding by providing a clear framework for optimizing weld‐line position to improve the toughness of injection‐molded polyamide components.