On-line laser ultrasonic for control of robotic welding quality

Currently, no methods are available for direct on-line determination of weld pool penetration during the robotic arc welding process. This is a serious impediment to autonomous welding processes. Traditional ultrasonic techniques are often used for the off-line inspection of welds, however these techniques require contact with the workpiece and may not be used in high temperature or moving processes. They are unsuitable for on-line weld penetration measurement. On-line generation of ultrasound requires a noncontact source. The use of lasers for ultrasound generation, with electromagnetic acoustic transducer (EMAT) reception, overcomes these limitations.; The first objective of this research is to develop an optical fiber array for the laser generation of ultrasound. Mounting a laser head to a welding torch would be impractical, therefore a flexible method of delivering the laser light to the workpiece is required. In the approach taken, a hexagonal bundle of seven optical fibers is placed in front of the laser beam. The light incident on the bundle is transmitted through the fibers. At the workpiece, the fibers are arranged in a line parallel to the weld with their ends close to the surface. A line source of ultrasound is created on the workpiece.; The second objective of this research is to apply laser generated ultrasound to the measurement of weld penetration in a robotic arc welding process. Laser ultrasonic measurements are made in simulated solidified and liquid weld specimens with varying weld penetration depths. The time-of-flight of the received ultrasound has a direct relationship with penetration depth. Due to the high temperatures in real welds, the effect of increased temperatures on ultrasound in the simulated solid and liquid welds is studied. This laser ultrasonic system has other uses. Other NDE applications such as thickness measurement and crack detection are also studied.