What does CP and CPK stand for?
The CP (coefficient of process capability) and CPK (coefficient of Index) are both statistical parameters that are useful for determining our manufacturing process’ stability.
There are two main ideas here: measuring the variation of our processes (the smaller the better) and determining how centered the processes are (how close the mean is to the central line between the upper and lower limits defined for each process).
While your process performs with a minimum variation, it may be off the optimal target and reach one of the High or Low limits. It is indicative of a high Cp index, and a low Cpk index. Alternatively, your process is on average exactly at the optimal target, but with a high level of variation. The Cpk will also be low, but the Cp will be high in this scenario. Cpk is higher only when your process meets the optimal target consistently with minimum variation in manufacturing.