Areal surface texture parameters on surface

L. Pagani, P. J. Scott

Research output: Chapter in Book/Report/Conference proceedingConference contributionpeer-review

2 Citations (Scopus)


Additive manufacturing (AM) techniques enable the manufacture of components with free-form geometries and complex internal and external features. X-ray computed tomography (CT) is increasingly being used to inspect internal features of AM parts. An advantage of the CT process, compared to optical and stylus instruments with limited acquisition slope angles, is the ability to reconstruct reentrant features (undercuts). Processing reentrant features provides an advantage in the computation of surface parameters. If the surface includes many reentrant features, their elimination can lead to a biased estimation of parameters related to the height or the area of the scale limited surface. A unified framework capable of handling free-from surfaces, with generic form surface, reentrant features and unevenly
spaced points, such as those from CT reconstruction, will be proposed. Standard software instruments employed for roughness parameter require evaluation of height data on a rectangular grid. This allows the computation of areal parameters based on discrete methods with good approximation, dependent upon the sample size. The reconstruction from CT volume to mesh allows performance of an adaptive meshing based on the maximum allowable distance between the implicit function (implicit surface defined by a constant grey value) and the final triangular mesh [1]. With irregular meshes it is not possible to perform the integral with the discrete approximation and a bias on the parameters computation can arise. In this paper an approach that approximates a generic mesh based on locally refined (LR) Bspline is proposed [2]. The approach can be applied to a generic form surface because the local stretching of the surface is taken into account. Mesh parameterisation enables to handle undercuts, each acquired point is described as a function of two abstract parameters. In this paper the proposed method will be compared with the discrete (ISO 25178-2 compliant [3]) method implemented in standard software packages [4]. Since filtering techniques based on a general mesh are not yet defined in the standard, the primary surfaces, the surface after removing the form, will be analysed. The areal parameters of a Rubert sample (casting plate 334, nominal Ra of 25 µm) measured with a focus variation (FV) instrument will be evaluated. Two form surfaces will be taken into account: plane and cylinder. Robustness of the discrete method will be finally evaluated with the mesh reconstructed from two CT measurements: the Rubert sample and an AM part.
Original languageEnglish
Title of host publicationProceedings - ASPE/euspen 2016 Summer Topical Meeting
Subtitle of host publicationDimensional Accuracy and Surface Finish in Additive Manufacturing
PublisherAmerican Society for Precision Engineering, ASPE
Number of pages6
ISBN (Electronic)9781887706711
Publication statusPublished - 2016
EventAmerican Society for Precision Engineering & European Society for Precision Engineering and Nanotechnology: Summer Topical Meeting on Dimensional Accuracy and Surface Finish in Additive Manufacturing - Raleigh, United States
Duration: 27 Jun 201630 Jun 2016 (Link to Meeting Details )


ConferenceAmerican Society for Precision Engineering & European Society for Precision Engineering and Nanotechnology
Country/TerritoryUnited States
Internet address


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