iSixSigma

Cp and Cpk

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  • #46908

    Nwajei
    Participant

    If Cp is =1 and Cpk =0.333
    Sixsigma =13
    Process mean= 12
    How can I determinate the USL and LSL?

    0
    #155755

    CP
    Participant

    Use the formulas.  However, there is not a unique solution.  There are multiple solutions, e.g., both these give the Cp and Cpk you are looking for.

    LSL
    1.1645
    9.8355

    USL
    14.1645
    22.8355
    Formulas:
    Cp = (USL-LSL)/6Sigma
    Cpk = min(Cpu, Cpl)
    Cpu = (USL – Mean)/3Sigma
    Cpl = (Mean – LSL)/3Sigma

    0
    #155756

    OMER
    Participant

    Hi Frank,
    LSL and USL are your customer specifications !
    Omer

    0
    #155763

    walden
    Participant

    The scenarios Cp provided are the two possible choices. To determine the LSL and USL, you need to know if the calculated Cpk is the Cpk(lower) or Cpk(upper).
    If this is a test or homework question, please inform the proctor or instructor to be more specific in the future.

    0
    #155766

    Rpaul
    Member

    Very vague question.
    If you are looking to find Specification limits, going backwards, from your given values of Cp, Cpk, mean etc., you need to have your values of the control limits also. If this is not a statistical ‘trick’ question, your USL/LSL will be given by the customer.
    By the way; What exactly do you mean by Sixsigma = 13??
     

    0
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