Laser-material interaction and process sensing in underwater Nd:YAG laser welding

Abstract

Process monitoring is one key problem for the quality assurance of underwater laser beam welding (LBW) which is growing importance with the requirement on the maintenance and repair of nuclear facilities. In this paper, the laser-material interaction and the sensing technology of welding process with infrared optical sensor was discussed. It was found that a kind of plasma with strong ultraviolet emission and strong shielding effect to laser beam forms if the high-power laser beam irradiates to even several millimeters deep water. So a gas-shielding nozzle was used to form local dry cavity. The relationship between the detected optical signals and the weld quality under various shielding conditions of local dry cavity was studied. The result shows that the detected signal well reflects the status of the local dry cavity and the optimal shielding condition could be determined from the amplitude of the signal.Process monitoring is one key problem for the quality assurance of underwater laser beam welding (LBW) which is growing importance with the requirement on the maintenance and repair of nuclear facilities. In this paper, the laser-material interaction and the sensing technology of welding process with infrared optical sensor was discussed. It was found that a kind of plasma with strong ultraviolet emission and strong shielding effect to laser beam forms if the high-power laser beam irradiates to even several millimeters deep water. So a gas-shielding nozzle was used to form local dry cavity. The relationship between the detected optical signals and the weld quality under various shielding conditions of local dry cavity was studied. The result shows that the detected signal well reflects the status of the local dry cavity and the optimal shielding condition could be determined from the amplitude of the signal.