Qualification of CT data for areal surface texture analysis

Abstract

The evolution of current manufacturing processes, such as additive manufacturing processes, enables to produce parts with increasingly complex internal and external geometries, to answer functional requirements. This requires an evolution of the measurement methods to analyze the complete part produced. In this context, the use of computed tomography (CT) is increasing. Considering the problem of surface quality control, and also considering the cost of such a measuring system, it becomes necessary to evaluate the capability of tomography techniques to characterize surface geometry despite an inadequate resolution. To this end, the study proposed in this paper aims at assessing the quality of surface roughness characterization by CT in comparison with classical optical measure means. Special attention is given to thresholding, which isnecessary to extract the surface from CT measurements, which are the basis to evaluate roughness parameters. An advanced analysis is also performed to bring out surface typologies that are more appropriate for CT measurements with poor resolution.

Effects of fast x-ray cone-beam tomographic measurement on dimensional metrology

“…Figure 9 quantifies the average error as well as the standard deviation of the errors in the hole plate. We here look at the inner diameter error and its variation for 26 all holes as well as the average relative error and its variation for hole centre to centre distances between hole pairs (6)(7)(8)(9)(10)(11)(12)(13)(14)(15)(16)(17)(18)(19)(20), (20)(21)(22)(23)(24)(25)(26), , , (14)(15)(16)(17)(18)(19), (1)(2)(3)(4)(5)(6) and . For the outer diameters of the step cylinder, we see that the error for all methods varies with step diameter and this is here likely to be due to beam hardening effects, with larger steps showing increasing beam hardening issues in the reconstruction due to the highly attenuating material used (aluminium).…”

“…XCT metrology and quality control [8,18,19] has nevertheless undergone a paradigm shift towards holistic, high-resolution measurements applicable to in-line manufacturing applications where it offers several advantages, including non-destructive evaluation of both internal (e.g. non-accessible features [20]) as well as external geometrical features and surface texture characterization with micrometre accuracy [21,22]. XCT has furthermore the potential to verify parts in assembled states, allowing the detection of manufacturing and assembly induced imperfections, provides simultaneous dimensional and material quality control, and provides complete and high-density point clouds in a relatively short time, all of which are typically not provided by other measurement methods.…”