Investigation of effects of injection molding parameters on residual stresses in traditional plastics (polyethylene, polypropylene, polystyrene)

Plastic injection moulding is a process where polymer melt is injected into amould cavity, and solidifies to form a plastic part. In the injection molding ofplastic parts, the processing conditions have critical effects on the residualstresses of the molded parts. In this study the effects of the molding conditionson the residual stresses and curvature radius of injection molded traditionalplastic parts were experimentally investigated. Six factors and three levels ofeach factors were examined. These factors were the injection pressure, the melttemperature, the mold temperature, the packing pressure, the packing time andthe cooling time. Taguchi experimental setup was used to reduce the number ofexperiments. The rectangular in shape flat parts were molded using highdensity polyethylene (HDPE), polypropylene (PP) and polystyrene (PS). Thelayer removal technique was used to measure the residual stresses. Thedeformations after that layer removal of the parts were measured using animage based measurement system.The results showed that the melt temperature had the greatest influence on theresidual stresses of molded parts, followed by mold temperature, injectionpressure, and cooling time.