Development of Laminographic Reconstruction Methods for 3D Industrial Inspection
By G Liaptsis, M Sutcliffe, R Hanna and A Clarke
X-ray computed tomography (CT) is widely used for the non-destructive testing (NDT) of various materials/parts, including developmental components as well as pre-production and production items. CT can provide information to engineers such as the detail of the structure of composites, manufacturing tolerances and deviations (geometrical and volumetric) of complex additive manufactured components, and the presence of defects within finished items destined for assembly. For high image quality, the object under test typically must contain similar density materials and have a low aspect ratio (width-to-depth) to allow similar X-ray penetration in all directions of the scan. With CT scanning becoming more widely known, there is increasing demand for inspection of components that fall outside these criteria, to the detriment of the volumetric data, sometimes to the point where a traditional CT scan cannot meet industry requirements.
This report describes the research, development and deployment of iterative reconstruction algorithms for the acquisition of tomosynthesis/laminographic data. This opens up the opportunity for novel scanning strategies, outside the traditional 360° rotational scanning method, allowing the volumetric inspection of components that are not suitable for conventional CT.
- TWI has developed a clear understanding of the implementation and application of iterative reconstruction techniques for X-ray laminography.
- Two iterative reconstruction techniques, ART and SART, have been successfully implemented.
- The use of efficient 3D computer graphics algorithms and GPGPU computation has been successfully applied to this research to speed up ART reconstruction and eliminate common limitations and artefacts with standard tomographic reconstruction.
- Tomographic projection data acquired from a commercial CT system have been used and reconstructed using the prototype software developed in this research. It was shown to offer very similar performance, in terms of image quality, to that of the commercial FDK-based offering, but has the potential to be a lot more flexible.
- An advantage of the new software is the ability to customise CT inspection solutions. This would not be possible using proprietary commercial solutions.
Cross-sections (orthogonal axes) through a pencil sharpener using proprietary, commercial FDK-based software. Dark grey is aluminium and the brighter regions are the steel blade and screw.
The same cross-sections based on the SART reconstruction algorithm implemented in the new software, which offers greater flexibility and customised solutions while retaining comparable image quality.