Multi‐response quality improvement by non‐parametric DOE methods

Quality management principles promote the systematic elimination of problematic areas of products before they reach the marketplace. It is a rare fact that a product is as good as optimising just a single quality trait of it. A practical and economical method is presented in this work for placing statistical significance on non‐linear multiresponse‐to‐factor relationship during screening experimentation with unreplicated and saturated fractional factorial designs. A technique is developed on a simple additive rule for multiple ranked responses all of which are tested synchronously against a group of product or process parameters. The developed hypothesis is tested based on the multi‐level nonparametric method proposed by Jonckheere‐Terpstra. Advantages exhibited are the minimal computational effort and convenience in usage while relaxing strict normality assumptions. The theoretical developments are illuminated by a case study on a recently posed problem in the ever‐popular area of small‐component plastic injection moulding.