Question

R2.82: If two processes have the same value of Cp but process one has a Cpk value of 1.33 and process two has a Cpk value of 0.67, what can be said about these processes?

A. The second is better centered than the first

B. The first is not capable, the second is

C. The first is in control, the second isn’t

D. The first is better centered than the second

Answer 1

R2.82: C is the right answer

Cpk is called process capability index. It is a statistical tool used for measuring the ability of the manufacturing process to produce better output as per customer's said specifications. If it is more than 1.33, then the process is said to be capable, in good control indicating sigma level 4 and is expected to meet the specifications. In any industry, if

Cpk < 1.66= Requires a closer look

Cpk < 1.33= Requires some action to make it higher

Cpk < 1.0= Not capable to meet the requirements and is not in control

So, according to the above explanation, the first process is in good control indicating Cpk 1.33 which is a good value and the second process, Cpk Value 0.67 is poor and is not in control.

Options A, B are wrong because they are telling the second process is good and capable, which is wrong as per Cpk definition.

Option D is wrong because a comparison can happen between two Cpk values when they first at-least meet the requirements. As the second process completely failed to meet requirements, the first process cannot be compared to the second process