Surface extraction algorithm influence on the uncertainty assessment and tolerance compliance of computed tomography measurements

Computed tomography (CT) is progressively assuming an important role in metrology. However, many challenges still remain, especially regarding its measurement uncertainty calculation and, therefore the tolerance compliance. This is even more challenging when it is applied to complex parts, including parts with complex geometries or multi-material parts. In those cases, the use of different surface extraction algorithms may have an important influence in the final measurement result. This paper presents the experimental analysis carried out on two parts with a variety of geometries, one with regular geometries and another one with freeform surfaces. In all the cases two surface extraction algorithms have been applied: one based on threshold and another one on gradient methods. The measured values and the estimated uncertainties are eventually analyzed together with the micro manufacturing tolerances compliance and the U/T ratios are calculated, showing the influence of using different surface extraction algorithms.