ASQ - Statistics Division

Shewhart Charts – Mini Paper Taken from the Spring 1993 Newsletter

Abstract: This paper examines the claims made by proponents of traditional Shewhart control charts and proponents of Pre-Control. Sources for further readings and study are suggested. The published supplier quality requirements of Chrysler, Ford and General Motors are examined regarding acceptance of each of these methods. The place of both tools in variation reduction and continual improvement is considered. Finally, as opposed to a rejection of classical control charts or a rejection of Pre-Control, an approach is presented which suggests the use of both tools in the manufacturing environment. "Does it work?", "Can I use it?" and "When should I use it?" are discussed. The paper suggests that control charts are overused, and that Pre-Control is not a replacement for control charts. Pre-Control is instead another tool with its own proper fields of application.

Keywords: X-bar and R chart - Individuals and moving range chart - Median and range chart - Pre-control - Statistical process control - Process improvement

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Studying the SPC chart
--FN Cheah, 03-14-2012
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