The manufacturing process of an injection molded polycarbonate/ poly(butylene terephthalate) automobile bumper was optimized, using Taguchi's method, to eliminate silver streaks on the surface of the product. First, a set of process factors was selected and a preliminary experiment was conducted with an L12 orthogonal array to screen the significant factors, check the validity of the data fitting model, and predict an improved process condition to overcome the filling difficulties. Second, using the selected control factors, a principal experiment was conducted with an L18 orthogonal array to predict an optimal process condition that solve the quality problem. Finally, the predicted process condition was tested on an 2500-ton injection molding machine to confirm the prediction. The results reveal that the main factors that directly relate to the generation of silver streaks are the mold temperature, the fill time, the fill/ postfill switch over control, and the injection rate.
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