用minitab分析出来的Xbar-R控制图不好但是过程能力CPK\PPK都很好，这是为什么？

本帖最后由 ZMD520521 于 2013-3-29 11:24 编辑

用minitab分析出来的Xbar-R控制图不好但是过程能力CPK\PPK都很好，这是为什么？求解。。。
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