Cp, Cpk, Sp, Spk for a one-sided minimum specification

[bkearns]

Hey folks,

Can anyone out there tell me how to handle the calculations for a spec that is a minimum only? I want to analyze process data where the spec is >= 5 MPa there is no upper and lower spec limit.

Thanks in advance for any help you can offer.
bkearns

 

[Atul Khandekar]

Welcome to the Cove, bkearns!

The issue has been discussed in the forums before, you'll find quite a few threads on Cp/Cpk issues if you do a forums search.

Just to get you started, check out the following threads:
Calculating Cpk on a single sided (unilateral) tolerance
Cp and Cpk for Product with only LSL (Lower Specification Limit)
Determining Cpk on a single sided tolerance dimension

 

[Narfeldt - 2011]

To calculate Cpk use the formula Cpk=(Average-LSL)/(3*sigma). Cp is N/A because you can't compare process variation against specification width.

What is Spk and Sp?