Hardened Tooling Steel Selection and Injection Shrinkage Tolerances
Verify tool steel composition and heat treatment phase stability independently to ensure injection shrinkage predictions match finished part tolerances.
Process Capability Cpk
Meaning
Statistical process control indices evaluate how close a manufacturing process operates relative to upper and lower specification limits while accounting for process centering. Calculation formulas incorporate both the overall process spread and the offset between the process mean and nominal engineering design targets. Quality auditors inspect factory production lines by calculating this metric to determine whether processes reliably produce conforming parts without excessive variation.
Values exceeding 1.33 indicate capable manufacturing processes, whereas values below 1.0 indicate unacceptable defect risk.
Mathematical Evaluation
Statistical calculations compare process standard deviation against specified customer tolerance limits. Computing process capability Cpk involves selecting the lower value between the upper specification index and the lower specification index. Process shifts away from nominal targets immediately lower the resulting index value regardless of low overall variance.
Quality Auditing
Sourcing managers inspect factory process control logs during supplier qualification audits. Calculating process capability Cpk across critical product dimensions reveals whether a factory controls machine wear and raw material variation effectively. Consistently low values demand immediate tooling repair or process recalibration.
Defect Prevention
Automated statistical software monitors continuous production data to detect capability degradation before parts fall out of tolerance. Maintaining process capability Cpk above agreed thresholds reduces reliance on manual final product inspection. High capability metrics permit reduced sampling frequencies during incoming batch validation.