Visual Six Sigma: Making Data Analysis Lean

Chapter 8. Improving a Polymer Manufacturing Process

The British company MoldMat Ltd. manufactures granulated white plastic at a plant in Britain and supplies it to a molding plant in Italy, where it is made into white garden chairs and tables. However, the molding process goes through intermittent phases when its product quality drops, leading to yield losses at both the polymer and the molding plants. When a crisis occurs, teams are formed to tackle the problem, but the problem usually disappears for no apparent reason.

After yet another mysterious crisis occurs and resolves itself, Carl Linton, a young engineer with black belt training in Six Sigma, is tasked to solve the problem once and for all. Together with a small project team, Carl identifies two characteristics (Ys) that are of paramount importance relative to quality and yield: the polymer's melt flow index (MFI) and its color index (CI).

Carl and his team reanalyze data collected by the most recent crisis team. Because suspected relationships between the two responses and eight process factors fail to reveal themselves in this analysis, Carl suspects that measurement variation may be clouding results. Consequently, Carl and his team conduct Measurement System Analysis (MSA) studies on the measured Ys and Xs. The problematic variables turn out to be MFI (one of the two Ys) and filler concentration (one of the Xs).

Once the repeatability and reproducibility issues for these two variables are addressed, Carl and his team ...