Process capability refers to a statistical measure of the inherent process variability of a given characteristic.
Organizations use a process-capability study to assess the ability of a process to meet specifications.
Process capability is important because when the capability of a process is understood and documented, it can be used for measuring continual improvement using trends over time, prioritizing the order of process improvements to be made, and determining whether or not a process is capable of meeting customer requirements.
Monitoring process capability allows organizations to understand and evaluate the manufacturing process performance. Once the process is evaluated, it can be adjusted as needed to assure products meet the design or customer’s requirements.
The two primary capability indices for measuring capability are Cp and Cpk.
Cp shows whether the distribution can potentially fit inside the specification, while Cpk shows whether the overall average is centrally located.
If the overall average is in the center of the specification, the Cp and Cpk values will be the same. If the Cp and Cpk values are different, the overall average is not centrally located. The larger the difference in the values, the more offset the overall average.
Cpk can never exceed Cp, so Cp can be seen as the potential Cpk if the overall average is centrally set.
Process capability was first introduced in Statistical Quality Control Handbook by the Western Electric Company (1956).
Want to learn more? Tonex offers Mastering Process Capability: Understanding Cp and Cpk, a 2-day course where participants learn the concepts of process capability, performance, and their differences.
Participants also learn to calculate Cp, Cpk, Pp, and Ppk and interpret the results as well as learn to distinguish between existing processes in statistical control and new or uncontrolled processes.
For more information, questions, comments, contact us.