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FMEA in the machining process

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  • #45582

    kamon
    Participant

    Hi
    I’ve always have problem with Occurrence, but it’s hight time to solve it with your help
     
    Example from the machining:
     
    Potential mode failure : let’s say a diameter is out of tolerance – too small and a part cannot be fixed somewhere.
    Potential cause: a broken tool
     
    According to  FMEA reference manual: “occurrence is how frequently the specific failure cause/mechanism is projected to occur” but next in the table there is “probability of failure” so I’m a bit confused.
     
    Which question below best describe occurrence, in your opinion?
     

    How often the tool breaks?
    How often the diameter is too small?
    How often the diameter is too small when the tool is broken? (almost always when an internal diameter is concerned)
    How often the tool breaks and causes the diameter too small?
     Thank you

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    #149322

    Atkins
    Participant

    Occurrence is related to the specific cause (#1, tool breaking), since the undersize diameter could be caused by more than one cause, and each is addressed separately.

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    #149327

    The Force
    Member

    Use #4 because occurrence rating is for the causes or each cause that relates to the failure mode

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    #149331

    Flavius
    Participant

    I agree with Duke’s post, I have the same interpretation of the occurence.
     

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    #149372

    kamon
    Participant

    Thx
    I must admit that agree with you all, but for me #4 is the best
    Probably the example is not good because as I wrote a broken tool almost always causes an  internal diameter undersize.
     
    What if there is three different causes:
    –          wrong tool setting
    –          tool breaking
    –          machine malfunction
    for me the questions should be:
    –          How often  a tool is wrongly set and causes the diameter undersize?
    –          How often  a tool breaks and causes the diameter undersize?
    –          How often  machine malfunction causes the diameter undersize?
    Because wrong tool setting and machine malfunction can cause the diameter oversize as well.
    Am I right?

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