Engineers from Daimler Chrysler are borrowing from the medical world to develop technology that detects faults in vehicle components.
Computer Tomography (CT), a routine method of medical diagnosis, is being used by DaimlerChrysler to transilluminate vehicle components. The cross-sectional images obtained allow faults to be precisely located and analysed.
The company is using the non-destructive technique to investigate sample and prototype components. If weak points can be detected at an early stage of component design, development times can be shortened and cost reduced.
The process can also be used to investigate damage due to intensive use and to examine components from in-company and external suppliers as foundries.
The computer tomography process is preceded by radioscopy, the classical x-ray procedure. For many automotive manufacturers, this is the standard method of testing components. However, since x-ray images give only a 2D representation, depth information is lacking and reliable fault analysis is often not possible by this means.
Computer tomography is more precise. In a fan-shaped array of beams with a thickness of a half to one millimeter, x-rays penetrate the object of investigation. During the measurement, the component rotates in 1440 individual steps; this corresponds to four measurements for each degree of rotation. A line detector records the intensity distribution.
A binary CT image is initially produced, which shows the gray values supplied by the line camera as a function of the angle measured. The computer reconstructs the image to produce the definitive cross-section, which indicates the precise position of the fault.
Daimler Chrysler was the first automotive manufacturer to use this method. The system comprises a combined radioscopy/CT unit, which is unique throughout the world in the automotive sector. In this apparatus, weighing 30 tons, x-ray and CT images can be successfully recorded without the system having to be reset.
Radioscopy is first used to determine the level within the component at which the fault is located. By means of computer tomography, the appropriate cross-sectional image is then produced – without destroying or even damaging the object of investigation.
With two x-ray tubes operating at differing acceleration voltages, components with a wall thickness of upto 150mm can be examined. Objects measuring upto 210mm across can currently be investigated, but this value can be doubled if each half of the object is measured separately.
In the next generation of computer tomography, the series of two-dimensional images will be replaced by three-dimensional ones; engineers from DaimlerChrysler are already working on 3D tomography and are aiming to produce their first 3D CT images by the end of this year.
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