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Hi
Our manager have asked us to work out a quality control index. We thought that Cpk or Ppk would be good choices, but some problems arose!
1. I have searched in the Cove and could find some articles discussing differences between Cp, Cpk, Pp and Ppk, but they were not so clear. In some cases, it is said that we have to collect more that 60 samples. But our company is producing just 10-20 products a year!!! and we have about 40 collected data.
2. As mentioned above, we are producing 10-20 products a year. Therefore, we have actual sigma, not sample sigma. then, we can't use Cp/Cpk indices. Is this true?
3. Management needs one and only one number as the measure of quality. Can we summarize Ppk? (normal summation or average, weighted sum, products of Ppks, etc.)
Thanks
Our manager have asked us to work out a quality control index. We thought that Cpk or Ppk would be good choices, but some problems arose!
1. I have searched in the Cove and could find some articles discussing differences between Cp, Cpk, Pp and Ppk, but they were not so clear. In some cases, it is said that we have to collect more that 60 samples. But our company is producing just 10-20 products a year!!! and we have about 40 collected data.
2. As mentioned above, we are producing 10-20 products a year. Therefore, we have actual sigma, not sample sigma. then, we can't use Cp/Cpk indices. Is this true?
3. Management needs one and only one number as the measure of quality. Can we summarize Ppk? (normal summation or average, weighted sum, products of Ppks, etc.)
Thanks
Therefore, we really need to minimize the number of our decision factors, especially some critical ones.