What should be the Cp and Cpk value?
We generally want a Cpk of at least 1.33 [4 sigma] or higher to satisfy most customers.
Cpk can have an upper and lower value reported.
If the upper value is 2 and the lower is 1, we say it has been shifted to the left..
What is CP CPK formula?
The equation for Cpk is more complicated: [minimum(mean – LSL, USL – mean)] / (0.5*NT). LSL stands for Lower Specification Limit and USL stands for Upper Specification Limit. Often we describe Cpk as the capability the process is achieving whether or not the mean is centered between the specification limits.
Can CP CPK be negative?
Both Cpk and Ppk can be a negative numbers. It means that, on average, the process is not meeting customer requirements.
How do you read Cp and Cpk values?
The higher the Cpk, the better is the capability of the process to meet its requirements. In the industry, a Cpk of less than 1.66 needs a closer look. A Cpk that’s less than 1.33 needs some action to make it higher, and a Cpk of less than 1.0 means that the process is not capable of meeting its requirements.
What does a Cpk of 1.33 mean?
Cpk = or >1.33 indicates that the process is capable and meets specification limits. Any value less than this may mean variation is too wide compared to the specification or the process average is away from the target.
How many Sigma is 1.67 Cpk?
Sigma level tableTwo sided tableCpk PpkSigma levelPPM out of tolerance1.334.063.3421.504.56.7951.675.00.5738 more rows
What is a good CP value?
By convention, when a process has a Cp value less than 1.0, it is considered potentially incapable of meeting specification requirements. Conversely, when a process Cp is greater than or equal to 1.0, the process has the potential of being capable. Ideally, the Cp should be as high as possible.
What is CPK and how is it calculated?
Cpk is a process capability index used to measure what a process is capable of producing. … The formula for the calculation of Cpk is Cpk = min(USL – μ, μ – LSL) / (3σ) where USL and LSL are the upper and lower specification limits, respectively.
What does CP and CPK tell you?
Cp and Cpk, commonly referred to as process capability indices, are used to define the ability of a process to produce a product that meets requirements. In other words, they define what is expected from an item for it to be usable. …