Mar 5 2024
The statistical quality profession has a love/hate relationship with the Gaussian distribution. In SPC, it treats it like an embarrassing spouse. It uses the Gaussian distribution as the basis for all its control limits while claiming it doesn’t matter. In 2024, what role, if any, should this distribution play in the setting of action limits for quality characteristics?
Oct 27 2023
“Today’s manufacturing systems have become more automated, data-driven, and sophisticated than ever before. Visit any modern shop floor and you’ll find a plethora of IT systems, HMIs, PLC data streams, machine controllers, engineering support, and other digital initiatives, all vying to improve manufacturing quality and efficiencies.
That begs these questions: With all this technology, is statistical process control (SPC) still relevant? Is SPC even needed anymore? Some believe manufacturing sophistication trumps SPC technologies that were invented 100 years ago. But is that true? We the authors believe that SPC is indeed relevant today and can be a vitally important aid to manufacturing.”
Source: QualityDigest
Mar 12 2021
The literature on quality defines process capability as a metric that compares the variability of its output with tolerances. There are, in fact, two different concepts:
Oct 5 2020
20 years ago, Honda stood out through its reputation for quality. Outsiders were studying Honda’s approach and Youtube now offers several videos shot at that time about it. Today, quality is no longer the differentiator among carmakers that is used to be but the practices of a company like Honda — past and present — remain a worthwhile object of study.
Sep 26 2020
The post on Does Toyota Use SPC? elicited many comments on LinkedIn. Some suggested that it was scoping SPC too narrowly when contrasting it with Toyota’s approach. In fact, SPC as referenced in the post is the body of knowledge described in the American literature on quality and taught in professional courses.
As to why Toyota is not using SPC, the answer is simple: SPC is about process capability and the quality problems Toyota addresses in 2020 are not due to lack of process capability. In industries that lack process capability, modern data science outguns the old SPC toolkit but that is a different discussion. The most vital question raised in the comments was why we have been not learning Toyota’s approach to quality. In the past 30 years, American industry has learned “Lean Six Sigma” instead.
The comments also enriched the public sources of information cited in the post with corroboration by current and former employees of Toyota.
Jun 15 2024
True And False Alarms in Quality Control
The SPC literature does not consider what happens when an organization successfully uses its tools. It stabilizes unstable processes so that disruption from assignable causes becomes increasingly rare. While this happens, the false alarms from the common causes remain at the same frequency, and the ratio of true to false alarms drops to a level that destroys the credibility of the alarms.
This is a signal that further quality improvement can only be pursued with other tools, typically the conversion to one-piece flow to accelerate the detection of problems and, once human error becomes the dominant cause of defects, error-proofing. This article digs into the details of how this happens with control charts.
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By Michel Baudin • Quality • 4 • Tags: Control Chart, False Alarm, Quality, SPC, True Alarm