Can CPK Be Negative?

Which is better CP or CPK?

Cpk is more widely used than Cp, since it takes into account the mean and the standard deviation in its calculation.

When the average of the process approaches the target value, the gap between Cpk and Cp closes.

When the average of the specification is equal to the target value, then Cpk is equal to Cp..

What is the maximum Cpk value?

1.0The 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.

What does a Cpk of 1.67 mean?

The Capability Index, Cpk. The outcome of a Process Capability study is a single metric, which provides an indication of the ability of a process to consistently provide output which is within required specifications. CPK <1.00 (Poor, incapable) 1.00< CPK <1.67 (Fair) CPK >1.67 (Excellent, Capable)

What is a good CPK and PPK value?

According to Six Sigma philosophy, Cp or Pp and Cpk or Ppk should be greater than 1.50. From a technical standpoint, Six Sigma deems a process being acceptable only after achieving a maximum defect rate of 3.4 parts per million opportunities.

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.

What does CPK stand for?

Creatine phosphokinaseCreatine phosphokinase (CPK) is an enzyme in the body. It is found mainly in the heart, brain, and skeletal muscle.

How many Sigma is 1.67 Cpk?

6 sigmaCp = Cpk = 1.67. The sigma level is now 5 – the specifications are five standard deviations away from the average. The out of specification has decreased to 0.57 ppm. The fourth curve represents that magical 6 sigma level.

What does 6 Sigma mean?

Six Sigma is a quality-control methodology developed in 1986 by Motorola, Inc. The method uses a data-driven review to limit mistakes or defects in and process. … Six Sigma points to the fact that, mathematically, it would take a six-standard-deviation event from the mean for an error to happen.

What is the PPM for 1.33 CPK?

Sigma level tableTwo sided tableCpk PpkSigma levelPPM out of tolerance1.173.5465.2581.334.063.3421.504.56.7958 more rows

What does a negative CPK indicate?

The process mean is closer to the lower specification Explanation: A negative Cpk is an indication that the process mean has drifted over either the upper specification or the lower one. It is not a math error, however it could be. It is impossible to have a negative standard deviation.

What does it mean if CPK is less than 1?

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.

Can CPK be greater than CP?

Cpk represents the difference between the actual process average and the closest specification limit over the standard deviation, times three. By convention, when the Cpk is less than one, the process is referred to as incapable. … The Cpk index can never be greater than the Cp, only equal to it.