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Seeing the Forest to Improve Quality May 14, 2014

Posted by Tim Rodgers in Process engineering, Product design, Quality, Supply chain.
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A few weeks ago I listened to a presentation by a quality engineer who gave an overview of his company’s processes for measuring and improving first-pass yield (FPY). He started with a fairly standard graph showing the trend in FPY over time, and later presented a detailed breakdown of the individual defects found at the end-of-line testing of the product. It was a typical Pareto analysis, with a problem solving focus on the defects that occurred most-frequently.

All very straightforward and by-the-book, but it seemed to me that there was something missing. Certainly part of our job in quality is to address the problems that occur most often, but it should also be about detecting trends and implementing preventive action, not just corrective action.

I asked the speaker if he had tried to classify the individual defects into categories of some kind (Answer: no). In this case, for a hardware product, one simple classification scheme would be to group the defects by root cause, such as design, workmanship, supplier, or test procedure. A large number of defects in one root cause category would indicate the need for a more generalized problem solving approach that prevents different, but similar, defects from occurring in the future.

You might get there eventually, if you ask enough “whys” during the corrective action root cause analysis, but too often this results instead in a localized fix to a specific defect. We don’t see the forest for the trees, and we end up chasing individual defects instead of addressing the real causes. It may look good to reduce or eliminate defects one-at-a-time, but in quality we should be working toward defect prevention, and that requires more detailed analysis.

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