Overview
ISO/TR 22514-9:2023 is a Technical Report from ISO on statistical methods in process management focused on process capability and performance when product specifications are defined by geometrical product specifications (GPS) rather than simple linear tolerances. The report explains how to calculate process capability indices (PCIs) for features described by geometrical tolerances, modifiers and collective requirements such as Maximum Material Requirement (MMR) and Least Material Requirement (LMR). It reflects modern measurement realities (e.g., point‑cloud data) and supports organizations that must demonstrate process capability for parts with GPS on engineering drawings.
Key topics and technical requirements
- Scope and purpose: Guidance for calculating PCIs when specifications are given as geometric tolerances or linear size with modifiers.
- Statistical foundations: Treatment of location, dispersion, reference limits and reference intervals, and the independency principle used in capability calculations.
- Geometrical product specifications: Definitions and handling of linear sizes with modifiers, ISO tolerance classes with modifiers, and envelope requirements (Taylor principle).
- MMR / LMR / RPR: Definitions and how to combine size and geometrical tolerances into Maximum Material Virtual Size (MMVS) and Least Material Virtual Size (LMVS) to represent collective functional requirements (MMR and LMR). For external vs internal features the virtual size is adjusted by the geometrical tolerance.
- Capability calculations for geometrical tolerances: Methods for form, orientation, location and run‑out tolerances; examples (flatness, roundness) and approaches when inverse distribution functions are known.
- Measurement considerations: Recognition of point‑cloud and other digital measurement outputs; guidance on sample size and distribution identification.
- Supporting annexes: Distribution identification, distributions for geometrical tolerances, recommended number of measurement points, and a process‑improvement case study.
Practical applications and who uses it
- Manufacturing engineers and quality engineers calculating process capability where drawing requirements include GPS, MMR or LMR.
- Metrology teams working from CMMs or point‑cloud scanners to convert geometric measurement results into capability statistics.
- Design and product engineers validating manufacturability (assembly ability, minimum wall thickness) through capability metrics.
- Suppliers and auditors producing capability evidence for acceptance of batches with GPS-based specifications.
Related standards (context)
Keywords: ISO/TR 22514-9, process capability, geometrical product specifications, MMR, LMR, process capability index, geometrical tolerances, point cloud measurement, capability statistics.