HIGH-POWER LASER-WELDING IN HYPERBARIC GAS AND WATER ENVIRONMENT

A hyperbaric laser welding facility has been constructed and the feasi bility of high power CO2 and Nd:YAG laser welding in both high pressur e gas and water environments, to simulated eater depths of 500 m, has been established. From initial trials on welding through water at atmo spheric pressure, it was found that the different absorption character istics of water to 10.6 mu m (CO2 laser) and 1.06 mu m (Nd:YAG laser) radiation proved crucial. The Nd:YAG laser was totally unsuitable as t he beam was largely diffused in the water, whereas the CO2 beam was re adily absorbed and, using high speed video equipment, was found to for m a high irradiance channel and a dry region around the weld area. Wel ding under a high pressure gas environment produced a highly energized plume which prevented keyhole welding at pressures over 1 x 10(6) Pa. An investigation carried out into the efficacy of a gas jet delivery system to alleviate the extent of the plume showed that argon blown ho rizontally across the weld was the optimum configuration, extending th e welding range up to 5 x 10(6) Pa. A limited investigation into high pressure underwater welding showed porosity to be a problem although s ound welds were produced at pressures up to 2 x 10(6) Pa.