About computer tomography, standards and automotive sports

The Institute for Production Metrology, Materials Technology, Optics and Photonics PWO at the NTB in Buchs is regarded as a Swiss centre of excellence for application-oriented, production-related precision measurement and testing technology of mechanical and optical components and systems. In the aforementioned fields, including the emerging area of machine vision, the institute conducts applied research and development and performs services and contract work for third parties. Every two years, the national metrology community meets in Buchs in eastern Switzerland. This year, the conference focused on non-destructive dimensional metrology, namely computer tomography.

Technological progress calls for new standards
First, however, the focus was on standards and guidelines. On the same occasion in 2013, a report was given on upcoming changes to ISO 21920-1 (Geometric Product Specifications) and their effects on surface metrology. Prof. Dr.-Ing. Jörg Seewig from the Technical University of Kaiserslautern, who is a member of the ISO standards commission responsible for this amendment, gave a detailed overview of the status of the work and pointed out some of the innovations that the profile standard - expected to come into force in 2020 - will bring with it. Essentially, there will be a number of simplifications (e.g. the definition of parameters such as Rz will be based on profile peaks and valleys, which will lead to statistically smaller scatter) and standardizations (there will be default settings for many parameters). In future, the calibration of the measuring instruments will be practice-oriented according to ISO 25178.

Dr.-Ing. habil Ulrich Neu schaefer-Rube of the Physikalisch-Technische Bundesanstalt PTB in Braunschweig dealt with the ISO standard 10360 (accuracy of coordinate measuring machines). Here, too, adaptations to new developments are to be expected or are already in progress. In particular, the technological possibilities offered by computer tomography for metrology will be incorporated into the revision (ISO 10260-11, in progress). At present, the guidelines of the VDI/VDE (Association of German Engineers) continue to provide information for the implementation of the standard in practice.

Chances and limits of computer tomography
The second session dealt specifically with computed tomography as a method for dimensional measurement. First, Dr. Benja-min Bircher from Metas presented the function of a computer tomograph for industrial applications. The advantages of computer tomography are obvious, especially for the measurement of internal and inaccessible geometries or for the measurement of entire assemblies, such as a watch movement. However, the density of certain materials limits the use of X-rays, and the high data volume - depending on the resolution - must also be taken into account. Classical coordinate measurement is still more accurate, and standards for the industrial use of computed tomography are (still) lacking. However, interest from industry is increasing; the trend is moving towards inline measuring systems, for example, in order to be able to carry out measurements directly on running processes.

Roger Eggenberger from the company Units then demonstrated the concrete benefits of computer tomography. He showed examples of how target/actual comparisons can be carried out on plastic components thanks to the 3D representability of CT images. The evaluation of the deviations can then be used for a tool correction, for example in injection molding. With software support, the CT measurement data can also be used for reverse engineering; CAD data can be derived directly from a 3D representation of a component.

Rolf Kaufmann from EMPA spoke about the limits of computer tomography. Among other things, he mentioned problems that can occur in connection with scattered radiation (from approx. 150 kV). These include, for example, disturbing stripe patterns or restrictions in contrast. As a possible solution he pointed out the computational data correction, with which an equally "recalculated" X-ray image can be produced. Experiments show the suitability of this method, but also its dependence on the material. Also depending on the material, so-called "beam hardening" can occur, caused by energy-dependent absorption of the materials. This problem must also be corrected by calculation and in combination with the correctly selected energy. Overall, the fact that resolution, X-ray energy and sample size correlate must be taken into account, according to the conclusion of the presentation.

Measurement applications
in Industry 4.0 - and in motor racing
Again, the lecture by Dipl.-Ing. François Torner from the TU Kaiserslautern dealt with concrete application possibilities of computed tomography. He classified the method in the classical coordinate measuring technology and showed that CT can be successfully used for measurements of microstructures and roughness. However, the speaker also pointed out that further experiments are still necessary, especially for roughness measurements, since such measurements using CT are still difficult, particularly for large components.

Marco Boccadoro then presented metrological challenges in connection with Industry 4.0 - we have already reported on this in detail in issue 9-2017. The optimal interplay of measurement technology and machine learning means that in the future, manufacturing processes can function with much less human intervention, thus increasing production reliability, was the conclusion of his presentation.

Finally, Hannes Gautschi, Director of After Sales at Toyota AG, "abducted" the audience into the automotive world, specifically into racing. He showed how essential parameters can be recorded on the vehicle using sophisticated measurement technology ("onboard" measurement). By means of data analysis, the optimum values are determined, which can then ultimately be responsible for racing success. He thus showed that measuring devices can make the difference between hundredths of a second.

In the accompanying exhibition, measurement technology specialists presented products and solutions for a number of topics discussed in the lectures.
mentioned areas of application.