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1) Process capability PC refers to the capability of process processing quality. This ability indicates the degree of process stability. When the process is controlled, the distribution of features is normal. The stability of the process can be measured by standard deviation. The smaller the standard deviation, the more stable the process and the higher the process capability. Because in the controlled process, 99.73% of the eigenvalues are scattered in (? -3,? +3), so the process capability is defined as: PC=6.

(2) Process capability index is used to measure the degree to which the process meets customer requirements. Customer requirements can be expressed by specification limits. 6SQ blog space] z7yQ? qX？ F

The customer's requirements for specifications can be two-way, that is, within X in (LSL, USL). If the width of the specification limit is T=USL-LSL and the specification center is M=(USL+LSL)/2, then when the specification center M and the process center? Conformity is to define the process capability index as the ratio of customer requirements to process capability;

Sometimes the customer's request is one-sided. If the customer requires that X must be greater than LSL, the process capability index is defined as:

If the customer requires that X must be less than USL, the process capability index is defined as:

When the customer's requirements are bilateral specifications, the process center? Not necessarily consistent with the specification center m, then the actual process capability index is represented by Cpk:

Cpk=min{CpU，CpL}