TWI Industrial Member Report Summary 368/1988
By I M Norris
Background
During laser welding, a plasma cloud that interacts with the laser beam can form above the weld pool. At high laser powers and low welding speeds the plasma cloud can significantly reduce the power reaching the workpiece in the form of a focused beam and, therefore, limit the weld penetration. Previous work at The Welding Institute has resulted in the development of a series of gas jet plasma control devices for use on the 2 and 5kW lasers that blow a jet of helium gas through a nozzle to disrupt plasma formation above the weld. The use of such devices has resulted in significantly improved welding performance at low welding speeds (< 1 m/min). In the work reported here, a device based on the same principle, has been designed and built for use with a 10kW CO2 laser, and its effect on welding performance has been assessed. The effects of varying nozzle bore diameter, gas flow rate and nozzle position, with respect to the laser beam/material interaction point, have been investigated when making partial penetration melt runs in 18mm thick microalloyed C-Mn steel to BS 4360 Grade 50D and full penetration melt runs in 12mm thick plate of a similar type.