Computed tomography in quality control: chances and challenges

Abstract

Since the first applications of computed tomography for medical diagnostics in the 1970s, the technology has been rapidly adopted for non-destructive testing of casted workpieces or complex assemblies. In 2005, the first coordinate measuring machine with computed tomography sensor has been presented for manufacturing metrology and quality control. Today, there exist numerous different manufacturers as the benefits for metrology are convincing. Computed tomography offers the possibility to acquire a measurement object holistically, that is, the whole volume of the object, not only the surface, with a very high point density of typically several millions of points. Current research and development activities are focused on several different aspects of computed tomography. First, the machine components are analysed and improved with respect to application in metrology. Larger detectors with better resolution or X-ray tubes with smaller focal spots may help in improving the machine's accuracy. Second, algorithms for reconstruction and artefact reduction are developed, especially for metrological purpose. As technical measurement objects feature a greater variety of material properties than in medical diagnostics, different strategies have to be investigated. The most crucial point is that not only the image quality of the radiographies or the reconstructed data is important but also the measurement accuracy plays the decisive role. Finding the interrelation between image quality and measurement accuracy is an important research topic. Third, from a metrological point view, the determination of measurement accuracy and measurement uncertainty for computed tomography measurements is an important task. Methods for experimental and simulationbased uncertainty determination are developed at the time being.

Surface texture evaluation of additively manufactured metallic cellular scaffolds for acetabular implants using X-ray computed tomography

“…As shown in Fig. 2, a sequence of projection is generated from rotating either the X-ray source or the measurement object, resulting in a sequence of 2D greyscale image slices [18]. Thereafter, the 3D volumetric data are reconstructed as a cube of 3D voxels, each voxel is associated with a grayscale intensity.…”

“…In recent years, using XCT for surface texture measurement began to attract researchers' attention, even though the use of XCT for this purpose is still restricted due to the (1) Fig. 2 Basic principle of XCT in dimensional metrology [18] limited resolution of XCT physical system as well as the data analysis capability of its software. Researchers from the KU Leuven University illustrated a comparison study on using tactile, optical and micro-focus XCT methods to measure AM components with different surface roughness [23].…”

Topographic inspection as a method of weld joint diagnostic

“…Inspection by a CT scanner is based on the measurement of radiation absorption which penetrates the object. If the condition of the object penetration is fulfilled, the X-ray CT allows for measurement and control of any butt, filled, edge, point, and plug weld [32,33].…”