Earlier detection of manufacturing errors in aircraft components
30-06-2009
The aerospace industry exhaustively tests all aircraft components before allowing them to enter service. Manufacturing errors or damage can be imperceptible to the human eye, however. The National Aerospace Laboratory (NLR) has therefore recently started using a medium-sized 3D C-scan robot to detect such damage. The C-scan is capable of testing various materials, including Glare, metals and composites. The aerospace industry’s increasing use of composite materials was a motivating factor for investing in the C-scan.
The C-scan is comparable to the ultrasound machines used during pregnancy. For aircraft components, the ultrasound waves internally examine the materials for any sign of manufacturing errors or damage. The reflected sound waves are displayed in colourful graphics, rendering any weak points immediately visible. When testing components, there are two methods for combining the high 
frequency sound waves, which are muted when exposed to air. The first method is the immersion technique, whereby components are immersed in large water tanks; the second method is the waterjet technique, whereby sound waves are conveyed via jets of water. A remarkable feature of the NLR C-scan robot is that both of these coupling techniques are combined in this one system, and quick switches can be made between techniques. This renders the C-scan robot suitable for research assignments (immersion), yet also for inspecting medium-sized components for the aviation industry (waterjet technique).
The aerospace sector’s most complex 3D composite products are designed using CAD software. These CAD files help create digital profiles of the various components. Based on these profiles, an ultrasonic probe(s) follows the contours of the component during the measuring process, which is performed in either pulse-echo mode, by means of one ultrasonic probe, or in the through-transmission mode, whereby the sound waves are generated on one side of the component, before being absorbed on the other side of the component. Through-transmission mode requires two ultrasonic probes, which simultaneously receive 11 coordinates.
The NLR’s C-scan research aims to optimise quality levels during the components’ developmental stage, while also ensuring the quality of the manufacturing process. The NLR is actively developing new composite concepts to replace the aerospace sector’s heavier metal components – a process that increases the complexity of the components. All composite components produced by the NLR are designed in accordance with NDT (Non-Destructive Testing) standards. Partly owing to the C-scan robot, new opportunities now exist for developing components and successfully introducing them on the market. Composites are light and strong, possess good mechanical properties and reduce manufacturing costs.
