In-Line Inspection of Friction Stir Welds Using Laser Ultrasonics

Friction Stir Welding is widely used for joining of aluminum components. Current post-process quality control techniques often cannot keep up with the production flow. Thus, there is a need for an in-line inspection technique that can qualify parts as they are produced. If flaws are detected immediately, corrective actions can be taken, thereby avoiding scrap and saving otherwise wasted production time. We have applied laser ultrasonic testing for in-line weld inspection. In this method, a pulsed laser beam generates ultrasonic waves inside the weld region. The waves interact with internal defects and then return to the surface, where signal perturbations that characterize the defects are detected by a separate laser receiver. The output signals are processed using advanced algorithms that can be programmed for automated real-time measurement. We have performed extensive laboratory and production testing to evaluate our technique. Test samples were aluminum sheets containing linear friction stir butt welds. Sheet thickness ranged from 3 mm to 10 mm. The defects of interest for this study were elongated voids, lack of penetration, and porosity defects. We were able to detect voids below 0.3 mm in cross-section at process speeds.

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