+ Reply to Thread
Results 1 to 3 of 3

Thread: Bimodal data and Ppk?

  1. #1
    Points: 6, Level: 1
    Level completed: 11%, Points required for next Level: 44

    Posts
    1
    Thanks
    0
    Thanked 0 Times in 0 Posts

    Bimodal data and Ppk?




    Hi,

    Hoping someone here can help me with a query.
    I completed destructive testing analysis from a manual process today.

    The product i'm looking at has several features which must meet acceptance criteria of Ppk >1.33

    When I ran the data for one feature it resulted in a bimodal model. The data is showing across people there is a distinctive difference due to technique. (It's a process heavily dependent on operator input so not unrealistic to expect this result)

    My query is, all specifications are met but due to the bimodal model the Ppk criteria cannot be achieved. Is there another way to calculate Ppk based on a bimodal model with P value >0.05 ?

    Thanks in advance!

  2. #2
    TS Contributor
    Points: 12,227, Level: 72
    Level completed: 45%, Points required for next Level: 223
    rogojel's Avatar
    Location
    I work in Europe, live in Hungary
    Posts
    1,470
    Thanks
    160
    Thanked 332 Times in 312 Posts

    Re: Bimodal data and Ppk?

    hi,
    no, this is a clear sign that your process is not standardized and hence not capable. The point of the Ppk measure is to show that your process stays reliably within spec - and due to operator dependence you cannot do that.

    It is not clear from your post whether the problem comes from the measurement error or the process itself - but this does not really matter, unfortunately.

    regards

  3. #3
    TS Contributor
    Points: 14,811, Level: 78
    Level completed: 91%, Points required for next Level: 39
    Miner's Avatar
    Location
    Greater Milwaukee area
    Posts
    1,171
    Thanks
    34
    Thanked 405 Times in 363 Posts

    Re: Bimodal data and Ppk?


    rogojel is correct. You have a mixture of different process streams. The correct approach is to adjust the means of the different streams to a common target to eliminate the bimodal effect. Once that is done, you may then calculate the appropriate capability index.

+ Reply to Thread

           




Posting Permissions

  • You may not post new threads
  • You may not post replies
  • You may not post attachments
  • You may not edit your posts






Advertise on Talk Stats