Optimisation of plasma/plume control for high power Nd:YAG laser welding of 15mm thickness C-Mn steels

摘要

Nd:YAG lasers are now commercially available with power levels up to 10kW, and therefore of increasing interest for welding of thicker sections (e.g. up to 15mm in steel), for example for off-road vehicles and shipbuilding applications. However, because travel speeds for deep penetration laser welding are generally relatively low (<1m/min), plasma/plume formation above the keyhole can cause a reduction in laser power at the workpiece, limiting penetration depth and weld quality. Although this issue has already been extensively investigated for CO_2 laser welding, the results may not be directly transferable to Nd:YAG laser welding since the wavelength of the laser light as well as the plume characteristics are different. This paper reports on an extensive investigation of different nozzle designs, process gases and set-up parameters, specifically for Nd:YAG laser welding of thick section C-Mn steel. Characterisation was performed in terms of weld penetration and quality, for melt runs made at 7.5 and 9kW of laser power. Using the optimised set-up, penetration levels of 15mm could then comfortably be achieved.