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Simplified Sigma Conversion Table

Sigma Table is useful to understand the process capability and the yield. It provides a measurement to understand the quality level.

Sigma
Level
Defects per million
Opportunity
Yield
percentage
1 690,000.0 30.9%
2 308,000.0 62.9%
3 66,800.0 93.3%
4 6,210.0 99.4%
5 320.0 99.98%
6 3.4 99.9997%

Posted By: Kenneth Yu Category: Quality Date: 4 May 2014

What is Cp and Cpk?

Cp is the process capability and Cpk is the process capability index. Process capability does not consider whether the average is on the middle of USL (upper specification limit) and LSL (lower specification limit) while Cpk takes into consideration for this.
Normally to improve the process, we check CP first. If CP is not stable, we will improve it to be stable first and then check for CPK. Formular for
Cp = ((USL-LSL)/(6*standard deviation)
CpU = (USL-mean)/(3*standard deviation) where mean is the average.
CpL = (mean-LSL)/(3*standard deviation) where mean is the average.
Cpk = min(CpU,CpL)

Posted By: Kenneth Yu Category: Quality Date: 3 May 2014

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D&D News/ Update

Simplified Sigma Conversion Table

Update on: 4 May 2014

What is Cp and Cpk?

Update on: 3 May 2014