ISO 25178-2:2021

Overview

Standard Reference: ISO 25178-2:2021
Title: Geometrical product specifications (GPS) - Surface texture: Areal - Part 2: Terms, definitions and surface texture parameters

ISO 25178-2:2021 defines the terminology and the parameter set used to describe areal surface texture (3D surface texture) for geometrical product specifications (GPS). The document specifies how areal surface texture parameters are defined and organized for calculation from measured or derived surface data. Parameters are presented as both symbolic and abbreviated forms (for example, Sq, Vmp) and are defined for continuous surfaces while being intended for use on discrete measurement data in verification and inspection.

Key Topics and Technical Requirements

• Terms and definitions: Comprehensive vocabulary for areal texture, geometrical parameters and feature terminology to ensure unambiguous communication of measurements.
• Field (area) parameters: Categorized parameter families used to quantify surface form and texture:
  • Height parameters: root mean square height, skewness, kurtosis, maximum peak/pit heights, arithmetic mean height, etc.
  • Spatial parameters: autocorrelation length, texture aspect ratio, texture direction, dominant spatial wavelength.
  • Hybrid parameters: root mean square gradient, developed interfacial area ratio.
  • Material-ratio functions and derived parameters: areal material ratio, inverse material ratio, material/void volumes, stratified surface parameters and probability-based measures.
  • Gradient distribution and multiscale methods: gradient statistics and fractal/multiscale descriptors such as relative area/length and scale-dependent complexity.
• Feature parameters: Definitions and methods for segmentation, identification and statistics of surface features (peaks, pits), including density, curvature, five-/ten-point heights and additional shape descriptors.
• Notation and implementation guidance: Rules for parameter notation (lower-case abbreviations in documentation, symbols in formulae), and informative annexes covering implementation details and relations to other GPS matrix standards.

Practical Applications and Users

ISO 25178-2:2021 is essential for practitioners involved in:

• Surface metrology and quality control: specifying, measuring and verifying areal surface texture for production and inspection.
• Design and functional performance assessment: relating surface texture to friction, wear, sealing, lubrication and coating performance.
• Manufacturing process development: toolmakers, machinists and additive manufacturing engineers optimizing surface finishing processes.
• Metrology software and instrument manufacturers: implementing consistent parameter calculations and reporting (e.g., Sq, Sa, Ssk, Sku, Vmp).
• Standards bodies, testing laboratories and R&D groups working with GPS-compliant specifications.

Related Standards

• ISO 25178 series (other parts covering measurement, specification and verification)
• ISO 14638 (GPS matrix model)
• ISO 8015 (fundamental GPS rules)
• ISO 14253-1 (decision rules for verification)

Keywords: ISO 25178-2:2021, areal surface texture, surface texture parameters, GPS, surface metrology, roughness, areal methods, Sq, Sa, material ratio, autocorrelation length.