DEFECT DETECTION AND SIZING IN LASER-WELDED ALUMINIUM WELDS, USING LASER-GENERATED ULTRASOUNDS

摘要

Embedded welding defects, such as porosity, cracks,rnare generally observed during laser welding ofrnaluminium. Non Destructive Inspection (NDI) afterrnprocessing could be a way of assuring an acceptablernweld quality. Nowadays, NDI techniques to control therninside of a weld are often limited to X-Rays orrnultrasounds. However, these techniques are expensivern(X-rays) or not contact-less (ultrasounds) limiting thernapplicability. The present paper shows the use of arnLaser Ultrasound (LU) technique to inspect porositiesrnin 2-mm thick sheet lap welds. The LU techniquernimplements a pulsed Nd:YAG laser to generaternultrasounds in the material and a heterodyne Nd:YAGrnlaser interferometer to measure the echo. This contactlessrntechnique improves the NDI flexibility in regardrnof the geometry and surface quality of analyzedrncomponents while increasing the inspection speed.rnFirst experimentations resulted in the detection of 2-rnmm holes drilled in bulk aluminium sheets and thernmeasurement of the shape and size of these defects isrnpossible. On-going investigation shows thernapplicability of the LU technique to detect porosities inrnaluminium laser welds. Finally, the use of signalrnprocessing is also carried out to increase, in a first step,rnthe signal-to-noise ratio and therefore enhances therndefect detection.