![]() ![]() However finding the inconsistency related to question 1 above threw a wrench into this idea - so I came here. Normally I would say "Well a Cpk of X is correlated to ppm defective of XXX PPM," or something along those lines. Why does the normal distribution, with the higher Cpk, also have a higher PPM?Ģ. In review of the same study report, I was asked "Why is a Cpk of 1.33 right for this process?" The other fits a non-parametric curve to the same data.ġb. See the attachments for examples I'm referring to. I've often found that where JMP reports a Cpk, the PPM it predicts does not match with sources I find online (i.e Cpk=1.33 and ppms are 6210 online vs. I have a couple of questions that have been bothering me for too long:ġa. I use the Cpk to justify that the study results are acceptable. So I analyze the resulting data by fitting a curve, and JMP outputs a Cpk and predicted PPM defective. Generally the DOE studies require that we meet a certain Cpk or Sigma-quality level for each run. Where I work, we generally perform DOEs to verify that a machine is capable before we release it to manufacture saleable product. ![]()
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