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

X射线计算机断层扫描（XCT）越来越多地应用于复杂三维制造部件的坐标测量。XCT对于激光粉末床增材工艺制造的部件特别有吸引力，因为可以测量内部特征，例如孔隙率或冷却通道。对于XCT应用于质量控制场景，其能力需要通过校准来量化，但迄今为止还没有开发出校准过程。ISO 213委员会正在开发性能验证的规范标准，但不用于校准。在这个项目中，我们将研究一种校准方法，该方法已被应用于表面形貌的光学测量，使用“校准特性”的概念。这些是可以确定的仪器特性，然后在给定任务的给定测量模型中用作标准不确定度项。我们将定义一小部分可确定的XCT特性，这些特性可捕获导致XCT测量不确定度的众多影响因素。这些特性需要易于确定，具有成本效益的材料措施，并在工业环境中。这样的校准框架可能不是完全严格的（例如，一些影响因素将不止一次地对最终的不确定性声明做出贡献），但它是一个非常需要的起始位置，并且增材制造中所需的公差通常不像传统制造中的公差那么高。

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.