Study On The Humping Suppression In High-speed Triple-wire Gmaw Process

In the gas metal arc welding(GMAW),hump is a significant defect which limits the increase of welding speed.In the same line energy,the double-wire GMAW can suppress the hump defect to some extent.However,the hump defect occurs again after a further increase of welding speed.In the triple-wire GMAW,a good weld bead can be obtained without any hump defect in a higher welding speed.In recent years,there were some researches on the mechanism of hump formation in single-wire GMAW and hump suppression in double-wire GMAW,but no agreement has been reached yet.As for the mechanism of hump formation in double-wire GMAW and hump suppression in triple-wire GMAW,fewer scholars have studied on these areas.Therefore,based on the computational fluid dynamics software FLOW-3D,a three-dimensional transient numerical model of high speed single / double / triple wire GMAW weld pool is established.The images of the weld pool are captured by a high-speed camera and the weld beads are obtained by the welding experiments.Combining the simulated results and the experimental ones,the following mechanisms are studied in this paper: hump formation in single-wire GMAW,hump suppression in double-wire GMAW,hump formation in double-wire GMAW,hump suppression in triple-wire GMAW.In high-speed single-wire GMAW,hump defects occurs at the welding speed of 1.5m/min.During the hump formation,the molten metal flow backward at a high speed,accumulating in the pool tail,and the liquid channel is formed,elongated,pinching and solidified,which lead to the hump.It is found that the strong backward momentum of molten metal flow in the gouged zone is the major reason for the formation of the liquid channel,the strong backward momentum of molten metal flow in the liquid channel zone is the major reason for the elongation of the liquid channel,and the normal surface tension is responsible for the pinching of the liquid channel.To reduce the backward momentum of molten metal flow is one of the effective means to suppress the hump.In the same line energy,a sound bead can be obtained in double-wire GMAW at the welding speed of 2.1m/min.The analysis shows that there is a "push-pull" flow in the leading weld pool of double-wire GMAW,which can effectively inhibit the backward momentum of the molten metal flow.On the other hand,the double-wire welding pool has good inter-circulation,and the weld pool of the gouged region under the trailing arc has a certain thickness,which have a buffering effect on the droplet impact force and inhibit the backward momentum of molten metal flow.Therefore,the hump defect can be suppressed in double-wire GMAW.In the same energy line,hump defects occurs again at the welding speed of 2.7m/min in double-wire GMAW.It's found that the mechanism of hump formation in double-wire GMAW is similar with the one in single-wire GMAW.In both cases there are two phenomenon: the molten metal flow backward at a high speed;the liquid channel has dynamic actions.In high-speed double-wire GMAW,the welding pool is so long that the arc pressure distributes in the front part of the weld pool,which leads to an uneven deformation of weld pool.The molten metal layer in the trailing wire's gouged region is so thin that the common weld pool has a poor inter-circulation and buffering effect.Additionally,the inhibition of backward flow by the “pull-push” flow cannot transfer to the trailing weld pool successfully.In the meantime,the effect of surface tension on the pinching of liquid channel is not obvious.In the same line energy,a good bead can be obtained in triple-wire GMAW at the welding speed of 2.7m/min.The results show that the "push-pull" flow is also found in the common weld pool.As the arc pressure and droplet impact force are relatively small and have an even distribution in the common weld pool,the triple-wire GMAW common weld pool has a cooperative buffering effect.Therefore,the "push-pull" flow can effectively inhibit the backward trend of the molten metal flow and suppress the hump formation.In triple-wire GMAW,it's beneficial to the formation of a triple-wire GMAW common weld pool with good inter-circulation and even weld width,the obvious “pull-push” flow and a sound weld bead by appropriately increase the current of the leading wire.