Spring load and geometry respond to material lot, machine setup, heat treatment and measurement. Capability analysis helps expose production risk; it does not replace process understanding.
Verify measurement first
If repeatability is poor, apparent variation may come from instruments or fixtures. Confirm resolution, calibration and operator consistency before analysis.
Stability is a prerequisite
Trends, shifts or special causes make a single Cpk value misleading. Review data over time and remove special variation first.
Monitor true critical characteristics
Working loads, torque, assembly dimensions and contact resistance deserve more attention than many reference dimensions. Select them from function and failure risk.
Use the index to improve
When capability is weak, investigate material, setup, tooling, heat treatment and inspection instead of relying only on final sorting.
References
This article is informed by public standards catalogues and industry engineering resources. Project values should be confirmed by drawings, material certificates and sample validation.