Realisation of a metrological characteristics approach to calibration of X-ray computed tomography

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X-ray computed tomography (XCT) is increasingly being applied for coordinate measurement of complex three-dimensional manufactured components. XCT is especially attractive for components that result from laser powder bed additive processes, as internal features, e.g. porosity or cooling channels, can be measured. For XCT to be applied in quality control scenarios, its capabilities need to be quantified through calibration, yet no calibration process has been developed to date. ISO committee 213 is developing specification standards for performance verification, but not for calibration.In this project, we will investigate an approach to calibration that has been applied to the optical measurement of surface topography, using the concept of "metrological characteristics". These are characteristics of an instrument that can be determined and then used as the standard uncertainty terms in a given measurement model for a given task. We will define a small number of metrological characteristics that can be determined and which capture the multitude of influence factors that contribute to the measurement uncertainty for XCT. The characteristics need to be simple to determine, with cost-effective material measures and in an industrial setting. Such a calibration framework may not be completely rigorous (e.g. some influence factors will be contributing more than once to the final uncertainty statement), but it is a well-needed starting position and the tolerances required in additive manufacturing are not generally as high as those in conventional manufacturing.