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Cp computation

Six Sigma – iSixSigma Forums Old Forums General Cp computation

This topic contains 2 replies, has 3 voices, and was last updated by  Guna 11 years, 12 months ago.

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  • #47625

    AT
    Participant

    When we compute Cp, we divide the range by 3 std deviation. Why is it that 3 standar deviation is used why not 2 or 4?

    0
    #158925

    Mahendra Garg
    Participant

    If we consider 3 sigma in process capability computation, than 99.73% parts fall within specification.

    0
    #158949

    Guna
    Participant

    6sigma is almost 100% coverage of spec limit whereby if the process are centered to the spec mean, u will get Cp  =1. By increasing the sigma range u can improve the process capability as below standard chart. By the time the rejects also can minimized..
     

    USL – LSL
    6
    8
    10
    12

    Cp
    1.00
    1.33
    1.66
    2.00

    Rejects
    0.27%
    64 ppm
    .6 ppm
    2 ppb

    % of spec used
    100
    75
    60
    50

    0
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