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unstable processes

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Viewing 9 posts - 1 through 9 (of 9 total)
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  • November 22, 2004 at 10:51 pm #37635

    jaime
    ★ 20 Years ★
    Participant

    What are the best method for analize process unstable?.

    0
    November 22, 2004 at 11:44 pm #111152

    Ken Feldman
    ★ 10 Years ★
    Participant

    Be careful, what you have suggested is illegal in most US states except Arkansas.  And then only permissable between siblings.

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    November 22, 2004 at 11:55 pm #111153

    Markert
    ★ 10 Years ★
    Participant

    See here, this is how perfectly innocent people get their threads hijacked. We live in an increasingly connected world: what about said behavior elsewhere in the global environment? 

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    November 22, 2004 at 11:58 pm #111154

    Ken Feldman
    ★ 10 Years ★
    Participant

    Phil, given the global opinion regarding the US, I didn’t want to take a chance and offend any of our international posters, except maybe the guys from Chile.  Easy enough to insult RD because he has a sense of humor.  Others I am not so sure of.

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    November 23, 2004 at 1:33 pm #111183

    Bob J
    ★ 10 Years ★
    Participant

    Jaime,
    Plot the data on a control chart….  If you see out of control data points then the process is unstable…
    Best Regards,
    Bob J

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    November 23, 2004 at 4:47 pm #111196

    Bobd
    ★ 10 Years ★
    Participant

    Jaime,
    To follow up on what Bob J said.  Remember, control charts can run multiple tests for being in control or not.  You’ll  have to decide which tests are appropriate.  I think the test for a point more than 3 sigmas from center is a given, but some of the other tests, I think, are a bit more “subjective”, depending on your tolerance.  At least in my experience.
    Hope this helps.

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    November 23, 2004 at 4:57 pm #111200

    Ken Feldman
    ★ 10 Years ★
    Participant

    Control charts don’t allow you to analyze unstable processes as I assume the original poster was asking.  It tells you when instability is occuring.  Root cause analysis, examining components of variation and even a multi-vari chart will allow you to identify the source.  The control chart says it is present the other tools might let you find the source.

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    November 23, 2004 at 6:58 pm #111216

    jaime
    ★ 20 Years ★
    Participant

    Thanks for your comments. I analyze control chart and I know process is unstable. I can’t use Cpk index. So, are there any index I can use for analysis?
    Gracias por su ayuda. La carta de control muestra inestabilidad del proceso y no puedo usar el Cpk como indicador de análisis. ¿Existen otros indicadores o métodos que pueda usar para su análisis?

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    November 23, 2004 at 10:10 pm #111220

    Ken Feldman
    ★ 10 Years ★
    Participant

    Unfortunately, capability analysis requires a stable process for the results to be meaningful.  Start looking for the sources of your instability using some of the tools I mentioned and once the process is stable, then capability will mean something.

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