Laser welding in a high pressure gas environment

A study was undertaken to investigate the effect of a high pressure gas environment on the laser welding mechanism. This was specifically related to high power CO₂ lasers in the power range between 1.2 and 5 kW. A small high pressure chamber rated up to 150 bar was utilized for the trials. Successful laser welding was completed up to a pressure of 50 bar in the pressurized helium environment. The chamber was modified to incorporate a high pressure transmissive zinc selenide window and internal focusing optics. The initial welds exhibited wide and shallow profiles indicating a loss of keyhole penetration welding. By filming the welding action the problem was found to be the formation of a plasma approximately an order of magnitude larger than in normal atmospheric conditions. The solution was to implement a gas jet system and to use a higher power laser. The resulting welds in terms of penetration and quality were significantly improved.