关于PPK和CPK
一直以来对这个问题挺困惑的，就是为什么PPK是有偏移长期过程能力指数CPK是有偏移短期过程能力指数？PPK代表的是初始过程能力指数为什么成为长期的过程能力指数了呢？CPK是稳定过程能力指数怎么就成了短期的过程能力指数了呢？望各位大虾给与解答。
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xn58 (威望:6) (海外 北美) Quality Engineer
赞同来自: Tiny 、路漫漫_309 、杨敏823 、tracy2342
Cpk is focused on stable process which means there is no specific viaraion. Only commom viaration is existing however you can't control it.
PPk is focused on unstable process. If you don't have any evidence to say your process is stable, you can not apply Cpk.
As to the formula, for Cpk, you have to put your data into group and then calculate the average of range.
for Ppk, you don't have to group your data, take all data as a whole and calculate the standard deviation.