A Strategy for Mastering Variation


Deleryd, Mats   (1997, ASQ)   LuleĆ„ University, LuleĆ„, Sweden

Annual Quality Congress, Orlando, FL    Vol. 51    No. 0
QICID: 10620    May 1997    pp. 760-768
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Article Abstract

Process capability studies should be linked with other improvement methods to effectively reduce variation and its effects. The best strategy for dealing with variation is a combination of two ideals: making variation so minor that it does not harm product performance; and making the product so robust that it does not yield to variation. Process capability studies provide the information to support these strategies for quality. In this paper, quality takes on a manufacturing-based definition expressed in terms of product conformance to design or specification. Step one in a process capability study is to identify important characteristics for analysis and then to plan the study. Improvement methods useful in this step are the seven quality control tools, the seven management tools, brainstorming, and Pareto analysis. Step two is to establish statistical control and then to collect data about the controlled process. Control charts are essential for verifying statistical control. Data collection techniques can be short-term or long-term, depending on whether the study is a machine capability study or a process capability study. Step three is to assess process capability. Boxplots and histograms provide visual information, while process capability indexes supply precise measurement of capability. Tools for subsequent improvement actions include design of experiments and failure mode and effects analysis. The final step in a process capability study is to implement the improvement actions.


Variation,Process capability index (Cpk),Manufacturing

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