Abstract
This paper presents the results of the CT-STARR (CT-Surface Texture for Additive Round Robin) Stage 1 interlaboratory comparison. The study compared the results obtained for the extraction of areal surface texture data per ISO 25178-2 from five X-ray computed tomography (CT) volume measurements from each of four laboratories. Two Ti6Al4V ELI (extra-low interstitial) components were included in each of the CT acquisitions. The first component was an additively manufactured (AM) cube manufactured using an Arcam Q10 electron beam melting (EBM) machine. Surface texture data was extracted from CT scans of this part. The values of selected parameters per ISO 25178-2 are reported, including Sa, the arithmetic mean height, for which the values from the Nikon MCT 225 metrology CT measurements were all within 0.5% of the mean reference focus variation measurement. CT resolution requirements are discussed. The second component was a machined dimensional test artefact designed to facilitate independent analysis of CT global voxel scaling errors and surface determination errors. The results of mathematical global scaling and surface determination correction of the dimensional artefact data is reported. The dimensional test artefact errors for the XT H 225 commercial CT for length, outside diameter and inside diameter reduced from -0.27%, -0.83% and -0.54% respectively to less than 0.02% after performing mathematical correction. This work will assist the development of surface texture correction protocols, help define surface-from-CT measurement envelope limits and provide valuable information for an expanded Stage 2 interlaboratory comparison, which will include a more diverse range of CT systems and technologies, further expanding the surface-from-CT knowledge base.
Highlights
Additive manufacturing (AM) methods enable the manufacture of components with complex external and internal geometrical features that cannot be manufactured using conventional subtractive techniques, such as grinding, milling or turning
The results from a four-participant interlaboratory comparison investigating the extraction of ISO 25178-2 areal surface texture data from X-ray computed tomography (CT) measurements have been reported
The value of Sa for all metrology CTs was within 0.5% of the mean reference measurement obtained using focus variation (FV)
Summary
Additive manufacturing (AM) methods enable the manufacture of components with complex external and internal geometrical features that cannot be manufactured using conventional subtractive techniques, such as grinding, milling or turning. No corrections were applied to any of the surface texture measurements reported here; there is ongoing work in this field and the isolation and characterisation of global voxel scaling errors and surface determination errors provided by the analysis of a dimensional test artefact included within CT scans of AM surfaces will provide valuable information for the development of AM surface texture data correction protocols. Previous research by the authors into the extraction and characterisation of areal surface texture data from CT data was performed using aluminium AM surface and dimensional test artefacts [15]. An assessment is required of the ability of the technique to remain robust to a variety of materials and a range of machines with differing measurement techniques, envelope sizes and image resolutions This has prompted the development of the interlaboratory comparison ‘round robin’ (RR) reported here [18]. The Stage 1 RR was performed exclusively in the UK, in order to tightly control sample transportation, sample measurement and data analysis
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