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

X射线计算机层析成像(XCT)越来越多地被应用于复杂三维制造部件的坐标测量。XCT对于激光粉床添加工艺产生的部件特别有吸引力，因为可以测量内部特征，例如气孔率或冷却通道。要将XCT应用于质量控制场景，需要通过校准来量化其能力，但到目前为止还没有制定出校准过程。ISO委员会213正在制定用于性能验证的规范标准，但不是用于校准。在这个项目中，我们将研究一种已应用于表面形貌光学测量的校准方法，使用“计量特性”的概念。这些是可以确定的仪器特性，然后用作给定任务的给定测量模型中的标准不确定度项。我们将定义一小部分可以确定的计量特性，这些特性包含了导致XCT测量不确定度的众多影响因素。这些特征需要简单易确定，具有成本效益的物质措施，并在工业环境中使用。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影响最终的不确定度陈述)，但它是一个非常需要的起点，加法制造中所要求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.