Shewhart developed control charts at Western Electric, AT&T’s manufacturing arm and the high technology of the 1920s. Information technology in the 1920sĪnother consideration is the manufacturing technology for which process capability needs to be achieved. These clever tricks addressed issues we no longer have.įigure 1. In Control Charts, for example, using ranges instead of standard deviations was a way to simplify calculations. Data was recorded on paper spreadsheets, you looked up statistical parameters in books of tables, and computed with slide rules, adding machines or, in some parts of Asia, abacuses (See Figure 1). Tools like Control Charts or Binomial Probability Paper have impressive theoretical foundations and are designed to work around the information technology of the 1920s. When manufacturing professionals talk about SPC, they usually mean Control Charts, Histograms, Scatter Plots, and other techniques dating back from the 1920s to World War II, and this body of knowledge in the 21st century is definitely obsolete. The semiconductor process engineers who apply statistical design of experiments (DOE) to the same goals don’t describe what they do as SPC. In this broad sense, you couldn’t say that it is obsolete, but common usage is more restrictive. In the broadest sense, Statistical Process Control (SPC) is the application of statistical tools to characteristics of materials in order to achieve and maintain process capability.
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