What does a Cpk of 1.67 mean?
This means that, for the control limit that is closer to the specification limit (be it the upper or lower control limits), the distance between the process average and that specification limit is at least 1.67 times the distance between the process average and that control limit..
What does PPK stand for?
PPKAcronymDefinitionPPKPunt, Pass, and Kick (NFL youth program)PPKProfessional Protection KitPPKPalm Portable KeyboardPPKPublic Private Key16 more rows
What is PP and PPK value?
Pp and Ppk It measures how well the data might fit between the spec limits (USL, LSL). It doesn’t care if the process is centered within the limits only if it would fit if it was centered. Ppk is the performance centering index. It measures how well the data is centered between the spec limits.
How do you calculate process mean?
Process center = (USL+LSL)/2, and the process mean is the average or mean of the process data points. While we talk about σ within, it reflects the Rbar/d2 or Sbar/C4.
How many Sigma is 1.67 Cpk?
Sigma level tableTwo sided tableCpk PpkSigma levelPPM out of tolerance1.334.063.3421.504.56.7951.675.00.5738 more rows
Why is PPK higher than CPK?
theoretically Ppk can’t be greater than Cpk. However, it is possible to get Ppk larger than Cpk due to measurement problems (poor resolution or chunky data particularly if you use the Range to estimate the standard deviations) and if you have almost no between subgroup variation…
How do you calculate PPK and CPK?
If we look at the formulas for Cpk and Ppk for normal (distribution) process capability, we can see they are nearly identical: The only difference lies in the denominator for the Upper and Lower statistics: Cpk is calculated using the WITHIN standard deviation, while Ppk uses the OVERALL standard deviation.
What is a good PPK value?
For stable processes and normally distributed data, a Cpk value ≥ 1.33 should be achieved. For chronically unstable processes with output meeting specification and a predictable pattern, a Ppk value ≥ 1.67 should be achieved.”
Should I use CPK or PPK?
Another way to look at the difference is that Cpk is used for a subgroup of data, while Ppk is used for the whole process. Cpk is typically used while processing in the ideal conditions to identify if the process is capable of meeting the specifications.