Test-pieces are collected by a robot and placed on a rotatable fixture. The steering knuckle is wetted, magnetised and sprayed with powder from a nozzle. After draining, a rotating cylinder directs UV-laser light onto the component, which is fixed while the optical cylinder rotates and scans the whole test surface with the laser beam. The optical signals are received and processed, and an alarm is activated if a fault is detected. Finally, the component is transferred to a robot, which is supplied with information from the control system as to whether a fault has been detected and accepts or rejects it accordingly.
Magnetic particle inspection is a widely tested NDT method. A metallic test component is exposed to an electromagnetic field and sprayed with white spirit containing a fine suspension of 'iron filings'. If there is a crack at or near the surface, the magnetic powder is attracted there by the field, which 'leaks' from the crack and holds the powder in place. In order to make the powder more easily visible, it is treated chemically to make it fluorescent in UVlight. Until recently, the process of inspecting components to detect these powder marks has been carried out manually; indeed, to make the powder more visible, and thus improve the ease of defect detection, it is treated chemically so that it fluoresces in UV-light. The operator, therefore, usually sits in a darkened area shining a UV-lamp onto the test pieces. The cracks are clearly visible, but they can still be missed, presumably because of the monotonous nature of the work in the darkened room. With automatic inspection, these working conditions are avoided while component quality control is improved.
The component under test is illuminated with a UV-laser via several rotating mirrors, so that even geometrically complex parts can be tested. The mirrors are adjustable in order to make it possible to ignore unimportant areas of the test piece. Light emitted from the surface of the component under test is detected and the detector signal transmitted to a computer programmed with acceptable deviation levels for comparison with a reference component. Tolerance levels can vary for different areas of the same test-piece: they may for example be higher on bottom section than on adjacent unmachined areas.
Abstract Source:
Book of Abstracts, 7th European Conference on Non-Destructive Testing, 26-29 May 1998, ISBN: 87-986898-0-00
Full-Text Source:
Proceedings of the 7th European Conference on Non-Destructive Testing, 26-29 May 1998, ISBN:
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