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An Evaluation of Pre-Control

Summary: In this paper we discuss pre-control, an alternative to statistical control charts for monitoring processes. Pre-control and standard control charts are compared; their different objectives are emphasized and their drawbacks, as well as their advantages, are discussed. We find that pre-control has some value, especially in machining operations where the lot sizes are small, and in situations where one deals with very capable processes. However, in general, pre-control is not an adequate substitute for control charts. In particular, it is not well-suited for processes with poor capability where its use will likely lead to unnecessary tampering. It is also doubtful whether pre-control with its small sample size used for set-up approval is able to identify processes of low capability. There is a real danger that poor processes will slip through this certification stage.

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  • Topics: Statistical Process Control (SPC)
  • Keywords: Capability,Statistical process control (SPC),Precontrol,Control charts
  • Author: Ledolter, Johannes; Swersey, Arthur
  • Journal: Journal of Quality Technology