The effect of processing factors on weld lines in injection moulded nylon 6 nanocomposites

The effect of process factors on weld lines of nylon 6 nanocomposites was investigated. Eight process factors were evaluated: injection pressure, holding pressure, holding time, back pressure, screw rotational speed, cooling time, melt and mould temperatures. A modified L₁₆ orthogonal array of the Taguchi method with three levels was designed to run injection moulding experiments using a smaller number of samples to determine the most influential parameters. The experimental results were analysed by sensitivity test signal-to-noise (S/N) ratio and analysis of variance (ANOVA). The results show that the principal process factors for single end-gated tensile samples are different to those of double end-gated samples when the weld line occurs. The important process factors of the single end-gated samples are injection pressure and mould temperature, whilst for the double end-gated samples are mould temperature and melt temperature. The temperature factor plays an important role in processing to heal the weld strength by promoting the ability of polymer molecules to diffuse across the weld line boundary, enhancing interfacial strength at the weld region.