Injection molding control parameter assessment by nested Taguchi design of simulation experiments: a case study

Abstract. Injection molding of a polypropylene (PP) food packaging container is studied using a dedicated simulation program. Three successive Taguchi designs of experiments (DoE) are performed to identify the influence of control factors and to adjust their levels for optimal result. These are nested, each one narrowing down the decision space of its predecessor. In the first design (L27), seven control factors were considered: polymer material in terms of MFI, melt and mold temperature, maximum injection pressure, filling time, maximum packing pressure and packing time. Part weight, clamping force and a fictitious factor related to premature solidification of the material during packing were quality factors. In the next DoE (L27 again), for fixed material, the four most important process factors determined before are examined in more detail, adding cycle time as an extra quality factor. Dependence of results on melt temperature proved to be strong, so a third DoE (L9), examined a narrower temperature range. Calculation of S/N ratios and analysis of variance (ANOVA) led to optimization of control parameters through a weighted objective function.