Process capability, in the context of statistical process control (SPC), refers to the intrinsic ability of a process to produce results in line with specifications. It measures the variability of the process in relation to specified limits, and assesses its ability to produce products or services that meet customer expectations.
The concept of process capability, often measured using indices such as Cp, Cpk, Pp, and Ppk, has emerged as an integral part of the field of statistical process control (SPC). Although several contributors have played a role in the development of these concepts over time, Walter A. Shewhart is often credited with pioneering statistical process control and the concept of process capability.
Assessing the capability of a process is essential to ensure the quality of the final product. A process with high capability is capable of producing results that lie closely within specifications, while a process with low capability may generate results outside acceptable limits.
The most commonly used capacity indices include :
- CpMeasures the potential capacity of a process by comparing the short-term dispersion of results (machine) with product specifications.
- CpkThe focus of the process in relation to the specifications is taken into account, and the actual ability of the process to produce compliant results is measured.
- PpMeasures the potential capacity of a process by comparing the long-term dispersion of results (5M production) with the total width of specifications.
- PpkProcess centricity: Takes into account process centricity and measures the actual ability of the process to produce compliant results.
These indices help organizations to assess the performance of their processes, identify opportunities for improvement and anticipate potential problems. High process capability is crucial to meeting quality requirements, minimizing defects and ensuring customer satisfaction. Continuous improvement of process capability is a constant quest in the field of quality management.