Investigation of the Weldline Strength of Injection Molded Nylon 6 Nanocomposite

Abstract

Nylon 6 nanocomposite is usually comprised of montmorillonite-containing silicate layers with good mechanical properties and processability, which have attracted a great deal of interest from researchers. Yet, systematic researches and reports on weldline strength of thin-wall injection molded nano-PA6 parts are still insufficient. This study investigates the influence of processing conditions on the weldline strength of thin-wall Nylon 6 nanocomposite parts. The relevant parameters include melt temperature, mold temperature, packing pressure, and flow rate. Tensile tests on specimens of different thicknesses (1.0 and 2.5 mm) are conducted. Comparisons of tensile strength for single-gate molded specimens (without weldline) with those of double-gate molded specimens (with weldline) are presented. From the experimental results, it was found that weldline specimens molded at faster injection speed and higher packing pressure would result in better mechanical strengths. Effects of melt temperature and mold temperature on weldline strength depend on specimen thickness (1.0 or 2.0 mm). Lower melt temperature and lower mold temperature have positive effects on weldline strength of 1.0 mm thickness parts while lower mold temperature has a negative effect on that of 2.5 mm thickness parts. In addition, part thickness also exhibits significant effect on weldline strength. A regression analysis combined with fitting model seems to correlate process conditions and weldline strength reduction quite well.