Investigation on the weldline strength of thin-wall injection molded ABS parts

It is well known that the weldline reduces the mechanical performance of the conventional injection molded parts. Yet, systematic researches and reports on weldline strength of thin-wall molded parts are still insufficient. This study investigates the influence of processing conditions on the weldline strength of thin-wall Acrylonitrile Butadiene Styrene Copolymer (ABS) parts. The relevant parameters include melt temperature, mold temperature, injection speed and packing pressure. Tensile tests on specimens of different thickness (1.0, 1.2 and 2.5 mm) are conducted. Comparisons on 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 higher melt temperature, higher mold temperature, faster injection speed and lower packing pressure would result in better mechanical strengths. Higher melt and mold temperatures not only lower the residual stress but also help the diffusion of molecular chains leading to a higher degree of surface bonding at the weldline interface. On the other hand, high packing pressure leads to higher residual stress formation and reduces the molecular bonding rate. 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.