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  • #39868

    glarety
    Participant

    Dear All,
     
    Average/Process mean =0.3mm
    Standard Deviation = 0.065
    Upper specification limit (USL) =0.5
    Lower specification limit (LSL) =-0.5
     
    If a process is centered in mean=0.3…Cpk value is 1.03
    If the same process is centered in nominal value+0…Cpk value is 2.56
     
    What is the conclusion that I can make from the Cpk value?
     
    Help needed
     
    Regards
    glarety
     

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    #122377

    J.RAVICHANDRAN
    Participant

    Dear Glarety
    Cpk deals with the distance of process mean from the nearest spec level (USL or LSL), I think the way you calculated Cpk is wrong. You cant get two Cpk values at a time.

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    #122379

    glarety
    Participant

    Dear Mr Ravi,
     
    I agree that I shouldn’t get 2 Cpk value but now I need to compare the both values and suggest to the manufacture whether they need to focus on hitting the mean reducing or nothing to meet the typical Six sigma quality target for the given value.
     
     
    Average/Process mean =0.3mm
    Standard Deviation = 0.065
    Upper specification limit (USL) =0.5
    Lower specification limit (LSL) =-0.5
     
     
    So I checked the Cpk value of mean=0.3 and nominal=0(I think this is wrong, not sure)
    What I need to do the check whether this process meets the six sigma quality target??????
     
    If a process is centered in mean=0.3…Cpk value is 1.03
    If the same process is centered in nominal value=0…Cpk value is 2.56
     
    I totally have no idea what to do. I am a novice in this field. Please guide me.
     
     
    Regards
    glarety

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    #122383

    magesh
    Participant

    looks to be very simple.
    contact me in [email protected]

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    #122385

    Whitehurst
    Participant

    Sorry to barge in instead of Ravi Cpk = Min ( Cpl and Cpu )
    I think you have calculated the cpk value wrongly.
    Joe

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    #122386

    J.RAVICHANDRAN
    Participant

    Dear Glarety
    The expected (nominal) value of your process is 0, you have Cpk of 2.56 whose estimated std dev is 0.065.  But there is a huge shift in your process average(from 0 to 0.3) and it is close to the USL of 0.5, obviously your process is not that capable. Here you have Cpk of 1.03 though there is a huge shift because your std dev is fortunately just 0.065 which is far less in case of a six sigma process.  Note that your Cpk when nominal is taken is greatly 2.56 as it is just 2 in case of a six sigma process.
    All you need is to reduce your process mean and bring it close to 0.
     

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