Cp=(55-45)/(6*5.08/2.3259)=0.7631Ca=[50.12-(55+45)/2]/[(55-45)/2]=0.024Cpk=Cp*(1-Ca)=0.7631*(1-0.024)=0.7448Ca: process accuracy. Cp: process precision A++ grade Cpk ≥ 2.0 Very good Can consider cost reduction A+ grade 2.0 ＞ Cpk ≥ 1.67 Excellent Should be maintained A grade 1.67 ＞ Cpk ≥ 1.33 Good Good ability, stable condition, but should be upgraded to A+ grade B grade 1.33 ＞ Cpk ≥ 1.0 Fair Fair condition, the slightest variations in the process factors may lead to defects, and should be upgraded to C grade by utilizing various resources and methods. C Grade 1.0 > Cpk ≥ 0.67 Poor The process has more defects and must be upgraded D Grade 0.67 > Cpk Unacceptable Its capability is so poor that it should be considered to re-design the process
The calculation of the difference between them can be done directly with the SPC software and automatically calculated, no need to calculate manually, you can go to the official website of TAIYO TECHNOLOGY to download the video tutorials.
They also have a free trial version of SPC software on their website, which you can download and try: /jian/SPCMonitor.asp
They also have a free trial version of SPC software on their website.