R

Recently i am working in the smt production line which use np

chart to monitor the defect level. but i was requested to help

determine the Cp and Cpk for the process.

if i am not wrong for x-bar,R chart the formular are:

Cp = (USL-LSL)/(6 x sigma)

Cpk = min ((USL-mean),(mean-LSL)) / (3 x sigma)

but for the SMT production line there do not have any USL or LSL

so how we calculate the Cp and Cpk...??

pls advise. thank you