Re: cpk
dbulak you said.
Is it possible to determine the cpk value just by having the cp and cr values ?
Atul is right, Cr = 1/Cp and as Taz said Cp= Cpk if centered on target (Cpk is always less or equal to Cp).
The question is if you hace specs and mean also, if such the case,
Cp = (USL - LSL) / (6 * Sigma) or Sigma = (USL - LSL) / (6 * Cp)
Cpk = min ( USL - mean, mean - LSL) / (3 * Sigma)
Cpk = min ( USL - mean, mean - LSL) / [3 * (USL - LSL) / (6 * Cp)]
Cpk = min ( USL - mean, mean - LSL) * (2 * Cp) / (USL - LSL)
If only specs are available, you could use target insteed of mean, I readed somewhere in the Milstd hanbooks (but always document the asumptions ie. on target).
Cpk = min ( USL - target, target - LSL) * (2 * Cp) / (USL - LSL)