Processkapacitetsindex

Processkapacitetsindex, often abbreviated as Ppk, is a statistical measure used in quality control to assess a process's ability to consistently produce output within specified limits. It is an extension of the process capability index (Cp) and takes into account whether the process is centered within the tolerance range. Ppk is calculated by considering both the potential capability of the process (Cp) and its actual centering relative to the upper and lower specification limits.

A higher Ppk value indicates a more capable process. A Ppk value of 1.33 or greater is often considered acceptable for many industries, signifying that the process is unlikely to produce defects. A Ppk value of 1.67 or greater is generally considered excellent, indicating a very robust process. Conversely, a low Ppk value suggests that the process is either too variable or not adequately centered, leading to a higher likelihood of producing non-conforming products.

The calculation of Ppk involves determining the distance from the process mean to the nearest specification limit, divided by three times the standard deviation of the process. This ensures that both the spread of the data and its position within the acceptable range are factored into the assessment. Monitoring Ppk over time allows for the identification of process drift and the implementation of corrective actions to maintain or improve quality.