Thick section laser butt welding of structural steel using a coaxial powder filler nozzle

An assessment has been made of implementing a coaxial powder fill nozzle for the butt welding of 4 and 7 mm thick structural (shipbuilding) grade steel, specifically accommodating the gap width tolerance. The effect of position of focus, powder mass flow, gap width, shielding gas, energy input, and edge cut quality have been examined. The results indicate that a gap of 0.8 mm can be filled, and that the catchment efficiency of the powder is proportional to gap width, thus offering a self regulating of the gap width provided the energy input is sufficient to melt the additional filler material. The effect of the powder on the welding is an enlargement of the plume, which can become critical at high mass flows. Countering this negating effect, the thermal and physical momentum of the powder may aid weld penetration. The welds show no signs of porosity, good cap geometry and tensile testing confirmed the weld strength.