17IND08 AdvanCT: Advanced Computed Tomography for dimensional and surface measurements in industry

• Forschungsstelle: METAS
• Projektnummer: F-5111.30099

Schlüsselwörter (Englisch)

Computed tomography, dimensional measurements, surface texture measurement, traceability, measurement uncertainty, simulation, error correction, standardisation

Kurzbeschreibung (Englisch)

Computed tomography (CT) is an aspiring contact-free measurement method which allows the complete geometry of objects to be determined. This includes the inner and outer geometry and the surface texture, all of which are typically not fully accessible by other measurement methods. There are a broad range of applications for CT, which include macro- and microfabrication, the automotive and telecoms industries, and additive manufacturing.

To support dimensional metrology in advanced manufacturing in the future, this project will develop traceable CT measurement techniques for dimensions and surface texture. Open issues regarding traceability, measurement uncertainty, sufficient precision/accuracy, scanning time, multi-material, surface form and roughness, suitable reference standards, and simulation techniques will be addressed through the project’s objectives.

Over the past few years, CT has increasingly been used for dimensional measurements of both the inner and outer geometry of workpieces, such as cavities and parts in mounted assemblies, which originate from macro- and microfabrication, the automotive and telecommunication industries and additive manufacturing, etc.

Despite the rapidly increasing number of applications in industry, the measurement errors of most CT systems are considered to be too high and need to be reduced substantially, by a factor of 2 – 8, to the order of 10 μm even when mid-size parts (approx. 1000 cm³) are measured. The traceability of the results is yet to be established and methods to determine the measurement uncertainty also need to be developed. The time required to perform CT measurements and data evaluation need to be reduced from hours to minutes if CT is to be more widely used in industry.

Guidelines and standards, such as standardised test procedures and specifications, are required for a fair and competitive market and to support users of industrial CT. The German standardisation committee VDI/GMA 3.33 has developed a few guidelines (VDI/VDE 2630-series) on dimensional measurements using industrial CT. At the moment, an international standard defining acceptance and reverification tests for CMS using the CT principle is under development by ISO TC213 WG10, which will become part of the ISO 10360-series. This project will provide input to standardisation bodies regarding inline CT and multi-material measurements.

This is a joint research project carried out in the framework of the European Metrology Programme for Innovation and Research (EMPIR) (see:http://www.euramet.org/research-innovation/empir/). The EMPIR initiative is co-funded by the European Unions's Horizon 2020 research and innovation programme and the participating states. METAS is one of the project partners in the project.

Projektziele (Englisch)

The specific objectives of the research are:

1.  To develop traceable and validated methods for absolute CT characterisation including the correction of geometry errors by 9 degrees of freedom (DoF). This will include the development of reference standards, traceable calibration methods and thermal models for instrument geometry correction, as well as the correction of errors originating in the X-ray tube and the detector in order to improve CT accuracy.
2. To develop improved and traceable methods for dimensional CT measurements with a focus on measurements of sculptured / freeform surfaces, roughness, and multi-material effects including supplementary material characterisation.
3. To develop fast CT methods for inline applications based on improved evaluation of noisy, sparse, few, or limited angle X-ray projections, reconstruction methods. This will be undertaken using a reduced number of projections from well-known directions and include enhanced post-processing.
4. To develop traceable methods for uncertainty estimation using virtual CT models and Monte-Carlo simulations. Batch simulation and evaluation capacities will be improved. The determination of accurate model parameters is necessary for a reliable uncertainty estimation and this will therefore be performed for different CTs and it will be systematised. Corrections for several artefacts will be developed. Uncertainty will be estimated by Monte-Carlo based simulation and verified using the calibrated standards developed in WP1.
5. To facilitate the take up of the technology and measurement infrastructure developed in the project by the measurement supply chain (accredited laboratories, instrumentation manufacturers), standards developing organisations (e.g. ISO TC213 WG10, VDI-GMA 3.33 Technical Committee Computed Tomography in Dimensional Measurements) and end users (e.g. plastic manufacturers, automotive, telecommunication, medical and pharmaceutical industries and metrology service providers).

METAS contributes to WPs  1, 2, 4 and 5.

Abstract (Englisch)

Computed tomography (CT) is a contact-free measurement method which allows the complete geometry of objects to be determined. This includes the inner and outer geometry and the surface texture, all of which are typically not fully accessible by other measurement methods. There are a broad range of applications for CT, which include macro- and microfabrication, the automotive and telecom industries, and additive manufacturing. In order to support future dimensional metrology in advanced manufacturing, this project developed traceable CT measurement techniques for dimensions and surface texture. In addition, current issues regarding traceability, measurement uncertainty, sufficient precision/accuracy, scanning time, multi-material, surface form and roughness, suitable reference standards, and simulation techniques were addressed by this project. Within the framework of the project, significant progress was made in increasing the accuracy and traceability of CT measurements. New fields of application were opened up through the CT measurement of roughness and the reduction of scanning time.

Umsetzung und Anwendungen (Englisch)

The project enabled METAS to position itself in the field of dimensional computed tomography. With METAS-CT, we operate one of the most accurate CT systems in the world, which meets the requirements for research and services with the lowest possible measurement uncertainties. Hardware and software for the very complex, simulation-based MU estimation have been built and are being optimized within the METAS CT 4.0 project. Through the project, further R&D projects could be acquired: EMPIR NanoXSpot, H2020 MANUELA and Innosuisse GlassPCB. In addition, very good contacts were established with various research institutions and NMIs using CT.
More than 20 preliminary studies and measurement services were performed for customers and METAS internally. The external orders were in the areas of connectors, watch industry, additive manufacturing and functional polymers. Internally, METAS mainly performed services for the high-frequency and hydrometry laboratories.