Tag: Ppk

One must necessarily understand that the short-term standard deviation reports on the “instantaneous reproducibility” of a process whereas the long-term standard deviation reflects the “sustainable reproducibility.”  To this end, the short-term standard deviation is comprised of the “within group” sums of squares (SSW).  The long-term standard deviation incorporates the “total” sums-of-squares (SST).  Of […]

You may need to be able to determine if your processes are acceptable and capable. Thankfully, there are capability and performance indicators such as Cp, Pp, Cpk, and Ppk that can help you make that determination.

In Part 2 we look at failure rates and material conditions for a surface finish example.

The capability of a process, statistically speaking, is the ability of that process – based on historical performance – to achieve measurable results that satisfy established specifications and statistical limits. In a nutshell, process capability indicates how well a process is able to perform its specified purpose. Why is process capability important? When the capability […]