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Give me a good definition of Process Capability…

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  • #43035

    Anderson
    Participant

    I am going to do a presentation at our plant on process capability. I’m looking for a good, solid, short definition.
    I wanna hear yours!
    (please reference any book that you may have quoted)
    Thanks,
    -MikeA
     
     

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    #136174

    TwoCents
    Member

    A little pessimistic, but how about:
    “How bad your process sucks.”  (That’s my own…you can quote me if you want.)

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    #136178

    Paul Richardson
    Participant

    Mike, how about this one. A little longer that the previous suggestion, but more technically accurate.
    Process capability compares the range, or natural tolerance (NT), of an in-control or consistent process to the specifications. The natural tolerance can be described by thinking of the bell–shaped distribution. The natural tolerance would be the +/- 3ó range that includes 99.73% of the data. If the natural tolerance is less than the specification range, then the process is said to be capable of meeting requirements. The tolerance is simply the upper specification limit minus the lower specification limit. A process can either be capable or not. Even though a process may be capable, it may not be meeting requirements.
    Paul

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    #136179

    Openball
    Participant

    Process capability measures the (potential) capability of a process to fulfill operational specifications.

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    #136212

    saphire
    Member

    I like Paul definition. But can I know further how you calculate the natural tolerance? If USL minus the LSL is your natural tolerance, what is the spec range? I just want to know how we define the process is capable through this NT. Previously, I just take the Cpk or Ppk as long as it less than 1.33, I consider it’s not capable enough. Please advice. I’m under training BB trying to get certification. I’ll appreciate your help. TQ

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    #136214

    Zero_Cool
    Member

    TwoCents,
    Have you given your quote with your yellow lit light saber open and in attack mode?? :-)) Carefull with the battery, it might run out of charge.
    Zero_Cool 

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    #136216

    Griswold
    Participant

    Paul stated it very well.  Process Capability, when stable, is the random variation around some centerpoint that the process actually is.  Spec limits is usually something the customer establishes.  Whether are not the process is within those spec limits is another thing.  If they are not, you need to get them there, or the customer goes somewhere else.
     

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