Real-time X-ray inspection for aerospace applications

Citation

Drake, S. (2003), "Real-time X-ray inspection for aerospace applications", Aircraft Engineering and Aerospace Technology, Vol. 75 No. 4. https://doi.org/10.1108/aeat.2003.12775daf.005

Real-time X-ray inspection for aerospace applications

Real-time X-ray inspection for aerospace applications

Keywords: Aerospace, Aircraft, Components, Inspection

There are many different destructive and non-destructive methods that can be used to monitor and assess the quality of aircraft and aerospace components during the manufacturing process. However, only X-ray inspection allows engineers to monior the ability to penetrate visually opaque metals and ceramics to reveal accurately any imperfections or defects that may be present.

Significantly, X-ray also avoids any interference with the object being inspected. Destructive methods can involve the sectioning or dismantling of objects and assemblies and can therefore, disturb crucial evidence such as faults or defects. X-ray inspection on the other hand provides a clear picture of the situation, without any physical disturbance.

Some of the greatest benefits of modern X-ray inspection systems are available from real-time operation. When struck by an X-ray, a scintillator converts the signal to light which is then detected by a CCD camera or digital panel detection system. Imaging software can then be used to display an image on a standard computer screen for visual interpretation. Advanced software packages can be used to analyse, interpret, manipulate and store images electronically. Those seeking to maintain a permanent record of X-ray images can use highly cost effective CD or DVD media for image storage.

Traditionally, X-ray inspection equipment used film-based technology and the aerospace industry in particular has lagged behind in adopting the benefits of real-time inspection. Electronic real-time imaging systems offer resolutions every bit as good as fine-grain X-ray film without the need for the same radiography skills, a processing laboratory and all the chemicals required for film development. In many production environments, the instant imaging facility of real-time can save valuable time and money over the inevitable delays and expense of film processing.

Images are displayed on screen as positive images, making it much easier to use intuitive skills to interpret images. X-ray film is in negative format – with the image reversed, which inexperienced users find difficult to interpret accurately. However, for those accustomed to looking at negative film, digital images can easily be inverted on screen as negatives if required.

These systems are not only ideal for identifying faults quickly during the initial manufacturing process, but also can be crucial when used for investigating a defect in a finished product that may have been already sold and returned by a customer. Potential issues can be solved in the fraction of time that they would have taken using film-based systems and substantially minimise any inconvenience to customers.

In a production environment, systems can even be designed with Automatic Defect Recognition (ADR) to look for, recognise and create alerts for specifically known or suspected critical faults. This is a potentially huge labour-saving quality application.

One of the latest systems specifically designed for the real-time X-ray inspection of aerospace components is X-Tek's new VENLO cabinet. Offering an attractive combination of high productivity and low cost of ownership, VENLO has been specifically developed to replace film in applications requiring the highest levels of radiographic quality including aerospace engine components, turbine blades, safety critical castings, waxes/ceramic cores, ecm drilling and final inspection phases. It uses a choice of micro and mini-focal X-ray sources and a high resolution, large-area, amorphous silicon X-ray detector.

More than any other factor, resolution determines can be discerned from an X-ray image. Image resolution depends on two key factors: resolution of the image detector and the focus size of the X-ray source, but nowadays image detectors are so advanced, image resolution now depends almost entirely on focal spot size of the X-ray source.

By using a microfocus X-ray source and geometrically magnifying the image by more than 5 times onto an amorphous silicon detector panel, an image resolution of 50 microns is easily achievable, which is much higher than normally required for aerospace applications. For larger components, where microscopic detail is not required, but higher power is required to be able to penetrate greater thickness of dense material such as metal, mini focus systems with focal spots of between 100 and 500 microns are better suited.

Eldim, the Netherlands-based manufacturer of precision-drilled aerospace turbine blades, expects to recoup the cost of an X-Tek VENLO machine solely from saved film and processing costs within the first 12 months of use.

As well as a very rapid return on the capital investment, the company has been able to substantially cut the amount of time taken up by X-ray inspection. When using film, it typically took 5min for exposure and further 15-20min to develop the film for inspection. The real-time X-ray imaging of the VENLO produces an image within 1-2min, offering huge cumulative time savings and speeding up production.

A key feature of the VENLO system is that it produces genuine film quality resolution images, essential for Eldim's own quality control and its aero engine OEM customers.

Commenting on the benefits of the new VENLO machines, Harrie Martens, Quality Engineer at Eldim said: "Using VENLO is going to save us a minimum of EUR 100,000 in film and processing costs in the first year alone. It is quicker to use than film, yet offers the same quality and resolution. X-ray inspection is essential for checking the cooling holes in turbine blades, so the time and cost saving efficiencies of this technology gives us substantial competitive advantage."

The VENLO's state-of-the-art large area, amorphous silicon detector features over seven million elements and can achieve a contrast of better than 1 per cent and a dynamic range exceeding 4,000:1. It has an area of 40–30 cm and even at 50 micron resolution/5X, magnification coverage is 8–6 cm of the component under test.

Standard digital or real-time radiography can satisfy most needs as a quick method of inspecting components, locating and measuring defects and expressing 3D structures in two dimensions. Above and beyond this, computed tomography (CT, "tomos" is the Greek word for slice) allows engineers to assess volumetric data and build up a 3D picture of the internal and external structure of an object under inspection. It is particularly useful for inspecting components during design and development phases as well as for some production testing applications.

CT generates a picture by aggregating the data of multiple X-ray projections taken through a solid object and as little as a quarter of a degree apart. A computer is then able to generate a range of different images in either 2D or 3D. Slice images and rendered views can be exported to standard format image files, and animation fly-bys can be created.

Transparent 3D images can be used to show cracks, inclusions and voids or porosity. As all the data is stored in electronic formats, it is possible to manipulate images at any time after the initial X-ray inspection has been completed. This means old images can easily be revisited and re-rendered to show aspects that may not have been under consideration in the first instance.

CT images are also accurately dimensioned and calibrated, making it possible to measure the size of any anomalies within solid structures with the highest degree of accuracy. CT generated 3D images are also very useful for explaining the nature of material faults or problems to colleagues and suppliers, whereas 2D radiographs need a greater level of skill and experience to interpret accurately.

Digital real-time X-ray inspection technology can now be said to truly reproduce images which are directly comparable with the best quality film techniques. With component testing such as essential part of aerospace manufacture, the potential savings of real-time X-ray in terms of both time and materials are too substantial to be overlooked.

About X-Tek

X-Tek Industrial Ltd designs and manufactures comprehensive and innovative range of X-ray equipment for industrial non-destructive testing. In-house capabilities include mechanical/electrical design, turnkey project management, image processing, ADR and CT. X-Tek industrial has considerable expertise in detector design and its comprehensive range includes amorphous silicon panels, linear array detectors, multi- line detectors and CCD imagers. Standard products include X-ray cabinets, X-ray rooms and constant potential X-ray sources using both sealed and vacuum demountable microfocus tubes. Custom solutions are also available to meet the exact performance requirements of the customers. X-Tek Industrial has extensive X-ray R&D facilities.

X-Tek Systems Ltd is the premier manufacturer of real-time microfocus X-ray inspection equipment and high-resolution vacuum demountable X-ray sources. Its range of high quality microfocus X-ray systems offers high resolution, high-power, low maintenance and low cost of ownership. The X-Tek product range includes low cost bench-top systems, suitable for lightweight components, up to larger units with more complex functions, useful for inspecting electronic assemblies or engineering components in great detail.

Details available from: X-Tek Industrial Ltd. Tel: +44 (0) 1493 600677; Fax: +44 (0) 1493 603347; E-mail: steve.drake@xtekxray.com; Web site: www.xtekxray.com

X-Tek Systems Ltd. Tel: +44 (0) 1442 828700; Fax: +44 (0) 1442 828118; E-mail: paul.ramsay@xtekxray.com

Steve DrakeManaging Director of X-Tek Industrial