Investigating the effect of beam parameters on joint formation in laser beam welding of T-joint in structural steel

An empirical study on laser beam welding of T-joints in 6 mm structural steel has been investigated. The role of power density on formation of the weld geometry and resulting microstructures has been studied. Autogenous laser beam welding is seldom the first choice in production floor environment over laser-arc hybrid welding because of high sensitivity to joint gap fluctuations. Without alloying elements of filler wire, the microstructure of the joint is dependent only on the thermal cycle of the process. Exceptional brightness of high power fiber laser beam and process stability at high power levels open new possibilities for beam manipulation. The use of processing lenses with long focal length for vastly improved depth of field allows to avoid damage to optical components. Altering the spot size on the surface is simple and straightforward method for controlling the energy input and power density of the beam. Likewise, changing the beam delivery fiber to suit certain application is also a cost efficient solution for beam manipulation compared to change of the welding head. In this study, a 10 kW fiber laser equipped with optical fibers having 200 µm and 600 µm core diameters was used to produce full penetration T-joints in horizontal position. The welding process was observed with high speed camera to study the effect of beam power density on the process stability, formation of the weld profile and quality of the welds. The cooling rate was measured from both sides of the weld and microstructural evolution of the joints is then characterized. The data obtained aims to contribute to existing knowledge base and to broaden the application areas of autogenous laser welding.