Process Capability - How much percentage of tolerance?



In a automotive manufacturing process, to achieve 1.67 Cp, how much percentage of tolerance i must have to use. Can any one help me out??

Bev D

Heretical Statistician
Super Moderator
It's 60%. The inverse of the index gives the proportion of the tolerance 'consumed' by the process. If you look at the formula you will see that it is a measure of the tolerance divided by a measure of the process spread. So 1/1.67 = .6. Which is 60%

But remember the Xpk indices include the SD of the process AND the location of the process average in relation to the tolerances.


Trusted Information Resource
Basically what be said. You can set your working limits at 60%. But it could be better or worse depending on your SD.
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