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  1. Francisco Hernandez

    Francisco Hernandez New Member

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    Has someone some reference to join the criterion of R&R and FMEA?

    When GRR's result is bigger than 10 %, exists some way of defending this value bearing in mind the result of the RPN?

    A spreadsheet of Excel found in Internet shows that when GRR's value does not overcome a value of 37.8 the system of measurement can be used in a reliable way, nevertheless, I do not find a direct reference to any document of the AIAG, someone can help me?
     
  2. Atul Khandekar

    Atul Khandekar Administrator Staff Member

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    Can someone help Francisco with this query ?

    Francisco, can you provide a link to this Excel sheet ?
     
  3. Ganesh Sundaresan

    Ganesh Sundaresan Active Member

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    In my limited exposure to MSA and fairly higher exposure to FMEA, I haven't come across anything like accepting the Measurement System based on RPN relevant to the characteristics being measured. But can it be taken into account? I think that's little fishy and paradoxical because RPN has a Detection number that assumes acceptable Measurement system, doesn't it.
     
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  4. Dave Mahon

    Dave Mahon Member

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    There's that fuzzy area between 10 and 30, where the application MAY be acceptable. I would think you could base this acceptance on a low severity rating.
     
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  5. Atul Khandekar

    Atul Khandekar Administrator Staff Member

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    Well, I found the file. It appears to be a Delphi PPAP file.

    On Sheet 13 it says:

    I am not sure where the 37.8 comes from...or there needs to be an assumption of some 'threshold' RPN value.
     

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  6. Bev D

    Bev D Moderator Staff Member

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    The MSA should determine the detection rating.
    A few cautions:
    - The AIAG guidelines are not mathematically correct in addition to being very fuzzy.
    - The detection rating is too often opinion and not based on a real R&R study.
    - The RPN value is also mathematically corrupt.
    As Dave mentioned, a low severity will make a low detection ability acceptable. so if you are in the 20% or greater AIAG zone, a low severity failure makes that detection level OK. but if the severity is very high and there is no other mitigation then detection is critically important.
    Occurrence is irrelevant. (occurrence and detection are dependent on each other and occurrence is a variable thing...)
    so the RPN itself is not relevant.
    Severity and actual R&R are relevant.
     
  7. DavidD

    DavidD Member

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    I'm always highly skeptical of using the percentage metrics (10% or 30%) for evaluating standard R&R studies as they provide very weak estimates of process capabilities so the percentages are pretty close to useless in practice. Much "better" estimates/understanding of the effect can be gained by using better estimates of the process (long term study data, etc.). I don't have it readily available but the confidence bounds on R&R studies (readilaly available in std sqc books) are huge so it the alpha and beta risks on selecting a bad gage or rejecting a good gage are very significant.

    David
     
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  8. Bev D

    Bev D Moderator Staff Member

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    David those are very valid concerns with the traditional (AIAG, 3X3X10) approach. Fortunately those concerns don't come into play if you use the more robust approach (See my MSA resources in the Resources section under the statistical engineering tab) as advocated popularly by Donald Wheeler.
     
  9. DavidD

    DavidD Member

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    Bev, All,

    Thanks, I'm working on reading your MSA posting and seeing if I can get ahold of Wheeler's papers.

    Do you have any suggestions on putting together a good exercise to illustrate the differences between the different techniques and demonstrate the advantages over using the AIAG method.

    Does anyone else have particular experience using this method w/ Youden plots? What industries are you using them in?

    Thanks,

    David
     

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