Driven by the need for quality control of complex three-dimensional engineering components such as those by additive manufacturing (AM), X-ray computed tomography (XCT) has been increasingly adopted for industrial inspection in recent years. However, XCT for dimensional measurement is complex and subjected to a number of factors for influencing the measurement results. In order to have a measurement traceability linked to the basic SI unit, related measurement uncertainty needs to be provided for the measured dimensions. This paper presents physical and metrological characterization measurements conducted for an XCT system. Those key influencing factors including sample’s material & shape difference, X-ray tube’s power/voltage & current, beam hardening, geometrical magnification and surface determination and etc. which contribute to the uncertainty, should be quantified respectively. Based on those resulting dimensional measurement results subjected to the key influencing factors, it is found that the maximum dimensional differences between XCT and traceable coordinate measuring machine (CMM) or digital micrometer (DM) measurements generally lie within 10 µm for all samples measured dimensions up to 20 mm. The proposed experimental uncertainty evaluation and budgeting table based on the Guide to the Expression of Uncertainty in Measurement (GUM) are worked out to estimate dimensional measurement uncertainty in dimensional measurement by XCT. It demonstrated that the accuracy of dimensional measurements using XCT could be in the order of micrometres for the assessment and detection of external and internal dimensional structures.
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This research/project is supported by Science and Engineering Research Council (SERC), A*STAR, under its funding programme "Developments of Materials, Processes, Equipment and Standards for 3D Additive Manufacturing" (SERC Grant No.: 142 68 00088).