In many injection molding optimization experiments, molded product shapes are evaluated using molding conditions as control factors. This study concerns the stability of plasticizing units, using the screw shapes that are essential for injection molding machines as control factors. In this study the function of a plasticizing unit was defined by the proportional relationship of melted resin weight to the product of the screw revolution time and speed, and the plasticizing interval was used as a noise factor. Analysis of an L18 orthogonal allay expeitment disclosed interactions among some of the control factors. Additional experiments and analysis were therefore performed on the control factors whose effects showed valley-like S/N curves. As a final result, an approximately 8-db S/N gain was obtained.
