Enhancing tensile strength of injection molded fiber reinforced composites using the Taguchi-based six sigma approach

The paper presents a case study where the targeted tensile strength of injection moldings is required to reduce or eliminate defects and to improve the process capability index C-p and C-pk for an injection molding process. The six sigma methodology, DMAIC (namely, design, measure, analyze, improve, and control), was applied in the study to eliminate defects, improve process, and reduce costs. The Taguchi-based six sigma approach was applied to identify the optimized processing and material parameters that led to the targeted tensile strength of injection moldings. An orthogonal array (OA) L9 was applied in the Taguchi experimental design, with four controllable factors and one non-controllable/noise factor. The four controllable factors identified include the carbon fiber (CF) content of 5 wt%, injection speed of 10 cm3/s, holding pressure of 250 bar, and barrel temperature of 260 degrees C, to meet the targeted tensile strength of injection moldings. A confirmation run verified the optimal parameter settings and the improved process capability index C-p and C-pk. An additional experiment with the CF content of 6 wt% was conducted after analyzing the effects of CF to further reduce defect, and the final results successfully demonstrated the improvement of the injection molding process. The implication of the study is that the six sigma methodology can be effectively used to eliminate defects and improve the process capability of injection molding.