CP PROCESS CAPABILITY

Cp Process capability is the measured, inherent reproducibility of the product turned out by a process. The most widely adopted formula for process capability (Cp) is:

Process Capability (Cp) = 6? = Total Tolerance ? 6

Where ? = the standard deviation of the process under a state of statistical control. One of the most commonly used measures for process capability is process capability index (Cpk) is:

Cpk = Lesser of Cpu or Cpl

Where:
Cpu = (Upper Specification - Process Mean) ? 3?
And:
Cpl = (Process Mean - Lower Specification) ? 3?

Interpretation of the index is generally as follows:

Cpk > 1.33 more than adequate
Cpk < 1.33 but > 1.00 adequate, but must be monitored as it approaches 1.00
Cpk <1.00 but > 0.67 not adequate for job.
Cpk < 0.67 totally inadequate.

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