Overview
EN ISO 4351:2023 - Geometrical product specifications (GPS) - Association (ISO 4351:2023) defines the terminology and fundamental concepts of association used in GPS. It specifies how an ideal feature (an associated feature) is fitted to one or more real or extracted input features by means of an association criterion (objective function) possibly subject to association constraints and an optional material offset. This document is a general ISO GPS standard adopted by CEN (EN ISO 4351:2023) and is concerned with concepts rather than GPS syntax or default decision rules.
Key topics and requirements
- Core definitions: clear terms for association, input feature, associated feature, restricted associated feature and related concepts.
- Association criterion: describes that an association is driven by an objective function (e.g., L-function based on signed local deviations, S-function based on size) and may include constraints.
- Objective functions:
- L-function - uses signed local geometrical deviations between input and associated feature.
- S-function - applies to associated features of size (e.g., maximum inscribed / minimum circumscribed features).
- Association constraints: explicit constraint types are defined - orientation, location, material and size constraints - limiting degrees of freedom or enforcing material-boundary relationships.
- Material offset: optional step after optimization to adjust the associated feature relative to the material boundary of the input feature.
- Process description: association is an optimization workflow that can be applied independently to single features or simultaneously to collections of input features.
Practical applications
EN ISO 4351:2023 is used to establish associated geometry for downstream GPS work, for example:
- Defining a datum or reference feature for a geometric or surface texture specification
- Creating an associated toleranced feature or any dimensional characteristic in inspection reports
- Establishing intersection planes, orientation planes, collection planes or direction features for measurement and reporting
- Forming a consistent mathematical basis for CAD/CAM metrology, CMM programming, and inspection software algorithms
Who uses this standard
- Metrology and quality engineers, inspection labs and calibration facilities
- Design, manufacturing and CAD/CAM engineers working with geometric tolerancing
- CMM programmers and metrology software developers implementing association algorithms
- Standards committees and technical publications dealing with ISO GPS
Related standards
Keywords: EN ISO 4351:2023, ISO 4351, GPS, geometrical product specifications, association criterion, objective function, association constraints, material offset, associated feature.
