Design Of Narrow Gap GMAW Torch And Research On Vertical Welding Process Characteristic

In recent years, with larger and heavier equipments increasingly used in pressurevessels, nuclear power, marine engineering, oil and gas pipeline industry, applications ofthick plate found a multidirectional way, in which significantly developed anincremental demand of the narrow gap for all position welding. As an important part ofall-position welding methods, vertical welding is not available to avoid the molten pooldripping down away from the influence of gravity if without properly selected processparameters.In order to solve the problem of sidewall fusion and thus ensure vertical weldingjoint quality and production efficiency, a compact welding torch for narrow gap weldingwith a swing arc function was designed. After having found the regulations of theprocess parameters on the welding stability and welded formation, the optimum processparameters in vertical up and down welding methods were confirmed. On the basis ofthis, the single pass multilayer experiment was completed and welded joints withoutdefects were obtained. Moreover, droplet transfer characteristics, arc oval-shape andmolten pool behavior were photographed using the high speed camera devices. Allabove make ready for the realization of all-position welding with the swing-arc narrowgap technology in the future.(1) The circuit system, cooling system and gas protection system of the weldingtorch were designed and optimized. Under the experimental verification, the torch wasproved to be stable and adapt to welding work for a long time.(2) The effects of process parameters such as the air flow rate, welding current,welding speed, swing angle, swing frequency and the sidewall residence time on weldformation were studied. And a preliminary analysis for the different weld characteristicsand causes between vertical up and vertical down welding process was given. Finally, asound welding joint of25mm thickness using material Q235was acquired in verticalposition.(3) The arc behavior and droplet transfer were observed under the high speedcamera system. The results showed the arc and droplet deviated from the axis of thewire due to the effect of centrifugal force when wire swings simultaneously, and thedroplet size decreased, while the transfer frequency increased. Through comparativelyanalyzing the influence of process parameters on the arc shape and droplet transfermode, the reasons of welding formation differences in vertical up welding and verticaldown welding were revealed.(4) The essence of substantial difference between vertical up welding and verticaldown welding was proposed from the perspective of force. Combined with the transferimages collected under different torch angle, the mechanical behavior of droplet and weld pool was analyzed.