What is the major difference between CP and Cpk?

1. Cp is the simplest indicator of a process capability while Cpk gives a better picture. 2. Cp is also known as the “process potential index” while Cpk is known as “process capability index” or “process performance index”.

What does CP and Cpk tell you?

Cp and Cpk measure how consistent you are to around your average performance. The ‘k’ stands for ‘centralizing factor. ‘ The index takes into consideration the fact that your data is maybe not centered. Cpk tells us what a process is capable of doing in future, assuming it remains in a state of statistical control.

What is the difference between CP Cpk and PP PPK?

Pp, Ppk vs Cp, CPK Cp & Cpk use an estimate for the standard deviation using the R Bar / d2 method. Pp, Ppk are more liberal where Cp, CPK are more conservative. Use Cp & Cpk once the process is in a state of statistical control. Cpk or Ppk is less than CP or Pp.

Is Cpk always less 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.

What is CP Cpk value?

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.

How many Sigma is 1.67 Cpk?

Sigma level table

Why is PPK higher than Cpk?

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.

What is good CP and Cpk?

In general, the higher the Cpk, the better. A Cpk value less than 1.0 is considered poor and the process is not capable. A value between 1.0 and 1.33 is considered barely capable, and a value greater than 1.33 is considered capable. But, you should aim for a Cpk value of 2.00 or higher where possible.

What is CP Cpk formula?

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 minimum Cpk value?

A Cpk value less than 1.0 is considered poor and the process is not capable. A value between 1.0 and 1.33 is considered barely capable, and a value greater than 1.33 is considered capable.

Should I use PPK or Cpk?

Process capability, Cpk, is important because it indicates whether a process potentially can meet a specification. Essentially, it is a prediction of the ability of a process to meet a specification. Process performance, Ppk, is important because it indicates how the actual process performed over a period of time.

What does 1.33 Cpk 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 is the difference between CPK and CPK?

Process Capability Index – Cpk: This is the capability index that accounts for the centering of the process and is defined as the minimum of Cpk upper and Cpk lower. Cpk is a measure of process performance capability. Cpk indicates shifting or closeness of process average from the target or mean value.

When to use CPK and PPK in capability analysis?

In general, if the process is in control and normally distributed (standard assumptions when doing capability analysis), both values should be close. However, since most processes wander around a little bit (and are still in control), an intuitive interpretation is that the Cpk is what you could be doing and Ppk is what you are doing.

What is the relationship between SPC and CPK?

The SPC Cpk measurement shows the relationship of the Six Sigma spread to the specification limits. Cpk represents the lowest value of the capability against the upper or lower specification, showing where within the specification limits the process is producing.

What to do when CPK is less than one?

If Cpk is less than Cp and Cp is greater than one, center the process in the specification. This should make Cpk comparable to Cp. If Cp and Cpk are less than one, there are two actions you can take.