Calculate Cp , Cpk , Clevel

[sam__gleeson]

What formulas would i need in excel to calculate Cp,Cpk & C"level"....i am new to this example below but here are figures
1. n=5
2. Double X Bar = 15.22
3. Rbar = 0.17
4. specification limit = 15.0 & 15.5
5. calculate Cp,Cpk & C"level"....from figures in 1 to 4 above

Any help appreciated
Sam

 

[davesweep]

Hi,

You'll need an estimate of standard deviation to calculate Cp and Cpk - how you do this is very much dependent on the condition of the data that you have gathered to get your summary statistics. A VERY crude estimate can be made by taking rbar/4.

Cp = USL-LSL/(6*SD)

Cpk = MIN(USL-mean/(3*SD),mean-LSL/(3*SD))

 

[sam__gleeson]

Thanks a heap
My answer for Cp - 1.96 using rbar/4 (SD)
My answer for Cpk - 1.73 ising rbar/4 (SD)

Would the answers be correct above.I used Excel for calculation

With the figures in post#1 how does one calculate Shewhart Constant...i did a search but i am still learning this

Thanks and appreciated

 

[davesweep]

I'm not sure how to calculate d2 (I assume this is what you mean by Shewhart Constant). I think that it's the result of an integration of the distribution curve. If that's the case, it's not straightforward to do in excel. Much simpler to look it up in a table.