How is Cpk value calculated?
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. A process with a Cpk of 2.0 is considered excellent, while one with a Cpk of 1.33 is considered adequate.
How Cp and Cpk is calculated?
A perfectly centered process will have Cp = Cpk. Both Cpk and Ppk relate the standard deviation and centering of the process about the midpoint to the allowable tolerance specifications. An estimate for Cpk = Cp(1-k). and since the maximum value for k is 1.0, then the value for Cpk is always equal to or less than Cp.
What is the formula for the Process Capability calculated?
The process capability is thus, defined as the ratio of the voice of the customer and voice of the process: Cp = (USL-LSL)/6σ.
What does Cpk value of 1.33 indicates?
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 to calculate the CPK of a set of data?
The following formula is used to calculate the CPK, or process capability index, of a given set of data. CPK = Min [ (USL – mean/3 * std.), (mean-LSL/3*std.)] CPK is defined as the process capability index and is a measure of the ability of a process to produce objects to a customers specifications. First, determine the upper and lower limits.
What is the meaning of the CPK index?
Process Capability Index (Cpk) Definition: Process capability index (cpk) is the measure of process capability. It shows how closely a process is able to produce the output to its overall specifications.
Which is the minimum value for CPK and PPK?
The minimum value of “k” is 0 and the maximum is 1.0. A perfectly centered process will have Cp = Cpk. Both Cpk and Ppk relate the standard deviation and centering of the process about the midpoint to the allowable tolerance specifications.
Why is CPK not a good measure of process capability?
In our April publication, we explained why a Cpk value by itself is not sufficient for defining process capability – and that is if your data are somewhat normally distributed. If your data are not normally distributed, then forget it. Cpk, applied to the raw data, is pretty much worthless as a measure of process capability.
