ISO 20170:2019

Overview

ISO 20170:2019 - "Geometrical product specifications (GPS) - Decomposition of geometrical characteristics for manufacturing control" provides principles and tools to decompose GPS measurement results so they can be used to control manufacturing processes. The standard explains how a univariate GPS characteristic (a single scalar tolerance result) can be transformed into a multivariate collected characteristic - a set of measurable components (size, form, orientation, location) that map to manufacturing process parameters and the manufacturing datum/coordinate system. The objective is to derive correction values for process adjustment and to enable meaningful statistical analysis of production capability. Note: micro-geometry (surface texture) is not covered.

Key topics and technical requirements

• Decomposition concept: Transform a univariate GPS characteristic into a multivariate set tied to manufacturing kinematics and datum systems.
• Collected characteristic: Combination of the global (univariate) result and its decomposed multivariate components used for control and analysis.
• Independent components: Separation of measurable deviations into size, form, orientation (angular deviations Rx, Ry, Rz) and location (linear deviations Tx, Ty, Tz) in linear or angular units.
• Coordinate system alignment: Define a manufacturing coordinate system derived from the specification datum system (may require supplemental datum definitions) so components correlate with machine axes and process parameters.
• Measurement and reporting: Components must be measurable and reported; the procedure describes decomposition steps and presentation of results.
• Statistical use: Decomposed components support meaningful capability indices and process studies (e.g., decomposing a hole position into X/Y to reflect machine X–Y axis capability).

Practical applications and users

Who benefits:

• Process engineers and machine tool setters - convert inspection results into actionable correction values.
• Quality and metrology engineers - perform statistical process control and capability analysis using components that reflect actual kinematics.
• CAD/CAM and manufacturing engineers - align design tolerances with machine capabilities and datum strategies.
• Inspection/measurement teams - prepare collected characteristic reports that support corrective actions.

Typical uses:

• Translating nonconformance results into specific machine adjustments.
• Decomposing position tolerances into axis-aligned errors for root-cause analysis.
• Feeding decomposed components into SPC systems to compute meaningful capability indices.

Related standards

• ISO 1101 (geometrical tolerancing)
• ISO 14638 (GPS matrix model)
• ISO 8015 (fundamental GPS rules)
• ISO 14253-1 (decision rules)
• ISO 25378 (zone characteristic definitions)

Keywords: ISO 20170:2019, GPS, geometrical product specifications, decomposition, collected characteristic, manufacturing control, process correction, metrology, capability analysis.