What are Cpk and Cmk?
Cpk and Cmk are capability indices for evaluating process and machine capability. In the industrial environment, they are used to manage quality risks systematically and make decisions traceable.
Scientific background
The methodological foundation is based on statistical and process-oriented concepts. Central is the position and spread of a characteristic relative to specification limits. CT data can supplement these systems with internal component information and thereby increase evidence quality.
Relevant key metrics
- Effectiveness of the method against defined KPIs and target values.
- Reaction time between deviation detection and stable correction.
- Sustainability of measures across multiple production cycles.
Standards and thresholds
- Standards: AIAG SPC (SPC-3, Version 2, published Jul 2005), ISO 22514-2:2026 and AIAG MSA (MSA-4, Version 4, published Jun 2010).
- Typical thresholds (in practice): Cmk at least 1.67 (machine capability), Cpk at least 1.33 (series-capable); for special characteristics often Cpk at least 1.67.
- Validity: Limits vary by characteristic class, risk and customer requirement.
Application in industrial practice
- Risk reduction during development and series ramp-up.
- Standardised decision processes across functions and sites.
- Linking quality-related evidence to customer requirements.
Sources and reference date
- AIAG SPC, product code SPC-3, Version 2 (published Jul 2005).
- ISO 22514-2:2026 (Process capability/performance).
- AIAG MSA, product code MSA-4, Version 4 (published Jun 2010).
- Reference date: February 2026.