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Trying to Understand Three Sigma and Six Sigma

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  • June 24, 2020 at 1:11 am #248556

    [email protected]
    Participant

    if 99.7 % of the targets are within 3 sigma limits, then how exactly does 6 sigma explains itself? (how does iot affect the USL & LSL)

    are we extending the tolerance levels? or confining the targets to be within the 6 sigma levels?

    moreover is 6 standard deviations greater or lesser than 3 standard deviations in the normal distribution?

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    June 26, 2020 at 2:09 am #248617

    Strayer
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    I’m guessing that you’re conflating the +/- 3 sigma control limits in control charts with customer specification limits.  They’re quite different.  Control  limits, calculated variation from the mean, tell us whether or not the process is under control.  Whether or  not variation is within specification limits is a different question.

    • This reply was modified 6 days ago by Strayer.
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    June 28, 2020 at 4:20 am #248661

    Shamshul othman
    Participant

    I think u are confused abt spec limits and control limits. While they look the same but actually they are world apart. Spec limits are values provided by customer on their product specs. While control limits are guides on your input parameter range for production control purposes. While 99.7% looks good on low volume production, imagine if you are producing 30million pcs of semiconductor permonth, that 0.3% defects  is equal to 900, 000pcs of defect every month.

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    June 29, 2020 at 1:53 pm #248678

    Mike Carnell
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    You need to take this a piece at a time, Start with you last question “moreover is 6 standard deviations greater or lesser than 3 standard deviations in the normal distribution?” If you cannot answer this or understand this then the discussion od control limits and spec limits will never make any sense to you.

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