Question: How Do You Calculate CPK And PPK?

What is a good CPK?

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 Cp of 1.5 mean?

A Cp of less than one indicates that the process spread is greater than the specification. This means that some of the data lies outside the specification. … So a Cp of 1.5 means the process can fit inside the specification 1.5 times. A Cp greater than one is obviously desirable.

Are CPK and PPK the same?

If we look at the formulas for Cpk and Ppk for normal (distribution) process capability, we can see they are nearly identical: The only difference lies in the denominator for the Upper and Lower statistics: Cpk is calculated using the WITHIN standard deviation, while Ppk uses the OVERALL standard deviation.

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 PPK number?

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 PPK of 1.33 mean?

meeting customer requirementsPpk < 1.33. The process is substandard for meeting customer. requirements. Process improvements must be given high.

What if CPK is less than 1?

By convention, when the Cpk is less than one, the process is referred to as incapable. When the Cpk is greater than or equal to one, the process is considered capable of producing a product within specification limits. In a Six Sigma process, the Cpk equals 2.0.

Is CPK always higher than PPK?

The automotive confusion aside, Ppk will always be greater than Cpk since Ppk is long term capabliity and Cpk is short term capability. The only way that Cpk will be greater than Ppk (other than a misuse of the terms and formulas) is under the conditions stated in a previous post.

Can CPK be lower than PPK?

In short, Yes, Ppk can be larger than Cpk. … Cpk uses three pieces of information to calculate the index: The mean or average of the data that was collected. The upper and/or lower specification.

What is minimum Cpk value?

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. An estimate for Cpk = Cp(1-k).

What is CP CPK?

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. … Specifications are normally defined in terms of nominal (+/-) tolerances or ranges (low to high.

What is the formula for PPK?

Process Mean close to USL If your Process Mean (central tendency) is closer to the USL, use: Ppk = [ USL – x(bar) ] / 3 s, where x(bar) is the Process Mean.

What is PPK and CPK?

So the key takeaway is that Cpk is the potential of a process to meet a specification (short term) while Ppk is how the process actually did (long term). Another way to look at the difference is that Cpk is used for a subgroup of data, while Ppk is used for the whole process.

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 is Cp and Cpk formula?

There are really two parts; the upper and the lower denoted Cpu and Cpl respectively. Their equations are: Cpl = (Process Mean – LSL)/(3*Standard Deviation) Cpu = (USL – Process Mean)/(3*Standard Deviation) Cpk is merely the smallest value of the Cpl or Cpu denoted: Cpk= Min (Cpl, Cpu)