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Need Help with Conversion from PPM to Cpk and Vice Versa

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  • September 26, 2019 at 8:28 am #242396

    hazwan
    Participant

    Hi all, i am reviewing FMEA table for occurrence. I’ve aligned Occurrence table per the FMEA AIAG 4th Edition, i converted the occurrence to ppm as my company using ppm (semiconductor business) .They also need Cpk information. How do I convert certain number of ppm to its equivalent Cpk? Pls educate me. I have tried google and found many many tables and each conversion table is not the same with the others.Pls help me.

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    September 30, 2019 at 5:15 am #242476

    Mohamed Asif Abdul Hameed
    Participant

    I have enclosed standard table for PPM to Cpk conversion. Hope this helps.

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    October 2, 2019 at 12:01 pm #242513

    Douglas Mader
    Participant

    You can’t convert PPM directly to Cpk since you don’t know which tail to assign portions of the PPM to.

    The best you can do is assume that the distribution is centered and then split the PPM among the two tails.  This would be equivalent to converting to Cp, not Cpk.  The table you see above assumes centering and calls it Cpk rather than just saying it is Cp.

    Or, if you want to be conservative, you can assign all of the PPM to one tail and call it worst case Cpk.

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