Article - CS354514
Why does Creo EZ Tolerance Analysis (EZTA) Statistical: Sigma analysis (Sigma = 6) show the stackup objective is met, but Statistical: Cpk (Cpk = 2) analysis reports objectives are not met in Creo Parametric
Modified: 13-Oct-2021
Applies To
- Creo Parametric 4.0 to 8.0
Description
- Why would Creo EZ Tolerance Analysis (EZTA) Statistical: Sigma analysis with Sigma = 6 show the stackup objective is met, but Statistical: Cpk analysis with Cpk = 2 report objectives are not met
- EZTA shows objective not met after changing the stackup Analysis type from Statistical: Sigma to Statistical:Cpk and returning to stackup summary list
- 6 Sigma is equivalent to Cpk =2, and same result is expected
- For a normal distribution, the physical meaning of Sigma, % yield and DPMO is clear
- For a lambda distribution, like in this case, is it always ok to say that 6 Sigma means the 99.99966 of probability to respect the target (and, that is the same, to have 3.4 DPMO?)?
- If one needs to consider Cpk for a lambda distribution, like in this case, what is the meaning of Cpk in terms of probability for lambda distribution?
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