A Study on Factors Influencing the Accuracy Evaluation of Dimensional X-Ray Computed Tomography with Multi-sphere Standards

Abstract

Industrial X-ray Computed Tomography (XCT) is one of the available choices for measuring parts’ internal and external geometries. However, there are still several challenges that limit the current XCT technologies from being widely spread as a dimensional metrology tool. In the study presented in this paper, multi-sphere standards were developed and used for the evaluation of the accuracy of dimensional measurements performed with an open-ended 450 kV XCT system of 0.4 mm focal spot. Normally, the multi-sphere standard refers to a combination of several ball rods of various heights, where a ‘ball rod’ is understood as a ruby sphere mounted on a rod that is usually made of carbon fiber or ceramic. The main purpose was to determine if the rod’s material, the spatial distribution of the ruby spheres, and/or the selection of test lengths (i.e., the center-to-center distance between two ruby spheres) influence the determination of the maximum permissible sphere distance error (MPESD) attributable to XCT data. The experimental data suggested ceramic is more suitable as a rod material than carbon fiber, and also, the spatial distribution of the ruby spheres has no obvious influence on the accuracy evaluation of dimensional measurements. However, the selection of test lengths will significantly affect the accuracy evaluation results. In particular, the results of dimensional measurements showed that the evaluation of the MPESD with multi-sphere standards for the XCT system used in this study can be expressed as MPESD = ± (159 + L/800) μm.