Process Capability Indices

Tolerance Ratio

Comparing the width of the process spread to the width of the allowed specification reveals the inherent risk of defects. These process capability indices help manufacturers decide if a process requires improvement before starting a production run.

Quality Prediction

Statistical models use the collected data to estimate the number of non-conforming parts per million. A fall in the process capability indices indicates that the tooling is wearing out or the raw material has changed. Regular audits of these values prevent the shipment of faulty goods and reduce the need for final inspection.

Variability Assessment

Long-term data collection reveals how the system responds to environmental changes and different operator shifts. Because process capability indices are sensitive to the sample size, the audit must include enough parts to be statistically valid. A process that appears capable over an hour might fail when viewed over a week of continuous operation.