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tracking process capability w/ unilateral tolerance

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  • #43239

    Lugbill
    Participant

    I have a question that I know I have the answer to somewhere, but I am drawing a blank. How do you track process capability with a unilateral tolerance? If, for instance, I have a minimum spec for a weld nugget size, how do I track process capability? Cp and Cpk only come into play with upper and lower specs correct?

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    #136914

    Savage
    Participant

    When you only have one specification, forget about Cp or Pp. Instead use the Z value (or Cp-upper / Cp-lower) that you have for calculating Cpk. In other words, Cpk becomes either:
    (USL-X-bar) / (3*sigma-r-bar) or
    (X-bar-LSL) / (3*sigma-r-bar)

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