amna77 -- There is considerable data here on that subject (ppk) -- please do a search and I am sure you will find an answer to your question. The calculation is essentially the same as Cpk. I am late for a meeting or I would point you to the threads.
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Mike S. ("Gun Nut")
And they ask me why I drink....
Actully our customer wants PPK formula for 5 piece study, thats why i have to do it. is that true that PPK=(averange-LTOL)/(3*stdDev)?
can someone help me please.
thankyou
I got this definition from GM some years ago:
Ppk: This is the performance index which accounts for process centering and is defined as the minimum of USL - X double bar divided by 3*std Dev or
X double bar - LSL divided by 3* std Dev. Ppk should only be used to compare to or with Cp and Cpk and to measure and prioritize improvement over time.
I never had to use it, so I not 100% it is correct. Hope this helps.
Good explanation of CpK and PpK. amna77 should pay particular attention to the fact that the process must be in a state of statistical control before the calculations are done and Note #1 on page 3 which states:
"As a [rule of thumb] a minimum of 50 randomly selected samples must be chosen for process performance studies and a minimum of 20 subgroups (of sample size preferably of at least 4 or 5) must be chosen for process capability studies."
I noticed the author was a Six Sigma black belt and showed how CpKs were related to the various levels of Sigma. He also referenced to Forrest Breyfogle who is well known for his Six Sigma book. Just another case where an old methodology is probably being re-invented as a Six Sigma tool.
Ppk formula - Can some one please help me - I have attached the sheet.
I noticed the author was a Six Sigma black belt and showed how CpKs were related to the various levels of Sigma. He also referenced to Forrest Breyfogle who is well known for his Six Sigma book. Just another case where an old methodology is probably being re-invented as a Six Sigma tool.
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