Process Capability Assessment Model (PCAT)

Process capability assessment entails comparing the performance of a process against its specifications. We say that a process is capable if virtually all of the possible variable values fall within the specification limits.

Process capability is defined as the ability of a process to meet requirements and is typically expressed as an index, Cp. This index is calculated by dividing the tolerance by 6 times the standard deviation of the process. Tolerance is, of course, the difference between the upper specification and lower specification limits. The higher the standard deviation in a process, the lower the Cp and vice versa. When the standard deviation decreases, the process itself has become less variable and the Cp, or process capability, becomes higher. Why does this matter? When a process has a very low Cp, it is unlikely that it will meet the customer’s requirements and it will produce defects.

Process capability is critical to determine if your process has the potential to achieve what it was designed to do all along. Processes that have high capability are instrumental in preventing waste, saving resources, and preventing defects. Process capability is also a key aspect of continual improvement as processes should be regularly assessed and fine-tuned. [1]

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