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A three-dimensional unified model is proposed to simulate the weld pool dynamic behavior in swing arc narrow gap vertical GMA welding with allowing for swing feature of arc heat source and joint configuration. Both the moving direction of arc and its inclination are considered by transformation of coordinate system. The model can simulate the weld pool sagging process reasonably. Based on the calculated and experimental results, the mechanism of weld formation in swing arc vertical-up welding is studied. The weld pool size and the peak temperature of liquid metal are reduced largely in the case of swing arc, which leads to the faster solidification of weld pool and is the major factor responsible for suppression of weld pool sagging. Meanwhile, upward component of arc force and the enhanced support force from solidified metal bulge benefits the weakness of downward flow of liquid metal. With increasing the swing frequency, weld cross section geometry tends to be symmetrical and weld bead surface becomes smoother. When the swing frequency is higher than 0.6 Hz, the satisfied weld formation can be obtained. [ABSTRACT FROM AUTHOR]

Challenges in dissimilar materials welding are the differences of physical and chemical properties between welding materials and the formation of intermetallic brittle phases resulting in the degradation of mechanical properties of welds. However, dissimilar materials welding is increasingly demanded from the industry as it can effectively reduce material costs and improve the design. In aerospace applications, Ti-6Al-4V titanium alloy and Inconel 718 nickel alloy have been widely used because of their superior corrosion resistance and mechanical properties. In this study, a single-mode continuous-wave fibre laser was used in butt welding of Ti-6Al-4V to Inconel 718. Investigations including metallurgical and mechanical examinations were carried out by means of varying processing parameters, such as laser power, welding speed and the laser beam offset position from the interface of the metals. Simple analytical modelling analysis was undertaken to explain the phenomena that occurred in this process. Results showed that the formation of intermetallic brittle phases and welding defects could be effectively restricted at welding conditions produced by the combination of higher laser power, higher welding speed and shifting the laser beam from the interface to the Inconel 718 alloy side. The amount of heat input and position of laser beam to improve the Ti-6Al-4V/Inconel 718 weld quality are suggested. [ABSTRACT FROM AUTHOR]