Cpk Formula How To Use The

Further sampling from the stable system is essential when obtaining meaningful estimates of the process performance for future production.

This is satisfied if the process designed matches the customer need.

Before we move forward let us begin with an example to provide you with a sign of relief that we can achieve at the right process with simple math.

Process Capability Example 1: The ice cream that must be served in an ice cream parlor has to be between -15 degrees Celsius and -35 degrees Celsius.

The process of refrigeration that keeps the temperature has a standard deviation (SD) of 2 degrees Celsius.

And the mean value of this temperature is -25 degrees Celsius.

Cpk Formula How To Use The

Using these inputs obtain the process capability index (PCI) for this process Note In this section do not bother about any technical terms just understand how to use the formula.

In the following section, you will find another example with a detailed explanation of each terminology used.

What is Process Capability It refers to the arithmetical study of the natural process variability of the given responsibilities in consideration.

Cpk This is also used for calculating the ability of the process; it determines how close you are to the given target and how consistent you are around your average performance.

Another way to study the ability of the performance is by finding the Pp and the Ppk.

The Cp and Cpk are used for processes that are old, matured, and are under control statistically.

Whereas the Pp and Ppk are used for the processes that are new and are not possible to determine their statistical control factor.

In this article, we will discuss Cp and Cpk is a process capability study.

Also, if you want to improve the process capability, then you need to apply the right design thinking which is discussed in DFSS (design for six sigma).

Process capability Formula and Calculation The Cp has 2 subdivisions Cp upper that is Cpu Cp lower that is Cpl These can be calculated with the formula Cpu (Process mean - LSL) (3 Standard deviation) where the LSL is the lower specification limit.

Cpl (USL - Process Mean) (3 Standard deviation) where the USL is the upper specification limit.

Now the term Cpk is only the value that is smallest of the above two, that is Cpu and Cpl.

Process Capability Index Formula Cpk is the smallest of the Cpu and Cpl.

Lets take an example Example 2: - The training room temperature during the training must be kept between 18 degrees Celsius and 26 degrees Celsius.

The process of maintaining this temperature has a standard deviation of 2 degrees Celsius.

Answer; - Here USL is 26 and LSL is 18 and the Standard deviation is 2, and the mean is 21.

Cpu (26 - 21) (3 2) 56 0.8334 Cpl (21 - 18) (3 2) 36 0.5 Cpk Minimum of Cpu, Cpl That is Cpk minimum of 0.8334, 0.5 The process capability index Cpk is 0.5 The practical difficulty in conducting process capability study Cp and Cpk values will not be accurate if the processes are not stable, in this case, we need to use Process performance values such as Pp and Ppk.

For a centered process the Cp value will give the correct estimate and for a not centered process, the Cpk value will be the correct value.