制程能力指数：是一种表示制程水平高低的方便方法，其实质作用是反映制程合格率的高低。
CPK=CP*（|1-CA|）
Ca (Capability of Accuracy)：制程准确度;
Cp (Capability of Precision) :制程精密度;
注意: 计算Cpk时，取样数据至少应有20组数据，而且数据要具有一定代表性。 A+≥1.67无缺点考虑降低成本
A1.33≤Cpk<1.67状态良好维持现状
B1.0≤Cpk<1.33改进为A级
C0.67≤Cpk<1.0制程不良较多,必须提升其能力
DCpk<0.67制程能力较差，考虑整改设计制程 Cpk, a measure of process capability in Six Sigma
In process improvement efforts, the process capability index or process capability ratio is a statistical measure of process capability: the ability of a process to produce output within specification limits. The concept of process capability only holds meaning for processes that are in a state of statistical control. Process capability indices measure how much "natural variation" a process experiences relative to its specification limits and allows different processes to be compared with respect to how well an organization controls them.
Estimates what the process is capable of producing, considering that the process mean may not be centered between the specification limits. (If the process mean is not centered, overestimates process capability.) if the process mean falls outside of the specification limits. Assumes process output is approximately normally distributed.
In the long term, processes can shift or drift significantly (most control charts are only sensitive to changes of 1.5σ or greater in process output), so process capability indices are not applicable as they require statistical control. 硬度也在一个范围，就跟尺寸一样，尺寸一般CPK可以在1.67。这个硬度在1.0是什么概念？ 过程能力指数(CPK)要达到1.67(机加工)也很难，能达到1.33(百万件60件不合格)已经就不错了，如果说一个企业(cpk)的过程能力>1.33有可能就是办公室数据。热处理的cpk要达到1.0也是很难的，影响因素很多。ppk(初始能力)有时也难达到，客户如有要求，也只能用办公室数据对付(造假)。 热处理的硬度用这个CPKPPK来管控不适用·不过既然是客户要求·你就在作业文件里编制进去·要求品质部门跟踪管控就可以了·不然审核的时候，客户的技术要求你没有完全转化又是一个严重的不符合项·
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