Currently, throughout the automotive industry, a major emphasis is being placed on reducing costs of plastics part manufacturing. For example, manufacturers of plastics parts used for interior trim applications have traditionally painted parts, to improve part aesthetics and cover over such surface defects as weld lines. Part painting can typically add from $.60-$2.00 to the part costs for these applications. Furthermore, due to the loss in mechanical properties found at weld lines, structural integrity can also be sacrificed.
This paper discusses the use of the multi-live feed molding process as a solution to minimize weld lines, improve mechanical properties and part aesthetics, and potentially reduce costs by eliminating steps in manufacturing operations such as painting. Several materials, used extensively in automotive interior and exterior applications, will be examined; acrylonitrile butadiene styrene (ABS), terpolymer, polycarbonate (PC)/ABS blends, syndiotactic polystyrene, and polypropylene. The effect on mechanical properties as well as the surface aesthetics and polymer rheology will be reviewed in this study.