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Dimensional surface metrology

Providing confidence in surface texture analysis software

Dimensional surface metrology is ever-present in manufacturing process control, since the topography of a machined surface is often critical to its functional performance. It is accepted practice to use physical artefacts – measurement standards – to calibrate surface measuring instruments such as stylus profilometers or optical 3D microscopes. But how do industrial users and software developers check that their surface texture analysis software is suitable for the task and working correctly?

Surface texture analysis software typically seeks to automate the filtering of raw topography data and the calculation of representative characteristics known as surface texture parameters. The use of a surface texture parameter to characterise numerically the measured topography was proposed many years ago, and several parameters – such as Ra or Sq – have been adopted by standards bodies and are used in industry for this purpose. Users increasingly rely on analysis software to correctly apply the rules and procedures of a range of ISO standards on their behalf. But physical measurement standards do not allow this software to be validated for suitability or performance-verified for evaluating surface texture parameters.

NPL has for some time collaborated with UK and international surface metrology experts to develop candidate software measurement standards ('SoftGauges') and other software tools on behalf of ISO TC213 WG16 (areal and profile surface texture) and wider industry. Development of standards and linked tools must be a coordinated activity, and we invite expressions of interest (and offers of collaboration) from all parts of industry.

The following are some project outputs to date:

  • SoftGauges for the evaluation of profile surface texture parameters (2005)

Two types of software measurement standards to encourage compliance to ISO 5436-2:2000 when testing the software component of surface texture profile instruments. Type F1 standards are reference data: test profiles for which the result of standard calculations is already known. Type F2 standards are reference software: trusted implementations of standard calculations. Both types allow the comparisons needed for testing. Collaboration between the University of Huddersfield, NPL and Taylor Hobson Ltd.

  • SoftGauges for the evaluation of areal surface texture parameters (2011)

Unambiguous definitions and specifications of algorithms for areal filtering and evaluating areal surface texture S-parameters, implemented reference software consistent with those definitions and specifications. Focussed on height parameters (Sa, Sq, etc.), spatial parameters and hybrid parameters. Collaboration between NPL and the University of Huddersfield.

  • Software for the evaluation of areal surface texture function and feature parameters (2011)

Extension of the above activity by the same collaboration to include function parameters (relating to height distribution and material ratio) and feature parameters (relating to high and low points in the topography). Collaboration between NPL, the University of Huddersfield, University of Nottingham and Cranfield University.

A proposed new method for validation of surface texture parameter calculation software, focussing on field surface texture parameters. Surface height functions are defined mathematically, either using Fourier series or polynomials, and are then input into the surface texture parameter definitions to obtain mathematical parameter values. The approach does not depend on interpreting the standard definitions of surface texture parameters for sampled data. Collaboration between the University of Nottingham, NPL and surface metrology software provider Digital Surf.

We have temporarily removed our direct reference software download links while we carry out a periodic review. Please watch this space for more news.

To contact us on any related matter, including to request a download link, please don’t hesitate to contact at the link below, quoting ‘softgauges’.

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