Fuente: Journal of applied polymer Lugar: RESEARCH ARTICLE This study investigates the effect of weld-line distance from an obstacle on the impact strength and weld-line factor (WLF) of PA6 and PA6-30GF injection-molded components. Mold-flow simulation, mold fabrication, and experimental impact testing (Izod and Charpy) are systematically combined with SEM analysis. Results reveal that increasing weld-line distance significantly improves impact strength and WLF, although weld-line weakness persists, particularly in fiber-reinforced systems.

ABSTRACT
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.