Research On Metal Transfer Behavior In Underwater Flux-cored Wire Wet Welding

With the continuous development of marine industry,requirements for underwater welding technology need to be improved urgently.Based on its simple operation,versatility,good economy and other advantages,the underwater wet welding has been widely used in the field of underwater welding.Owing to the lack of welding protection measures,the underwater wet welding still has many problems,such as unstable welding arc,serious metallurgical loss and poor weld formation.The problems existing in underwater wet welding are closely related to the metal transfer mode.As the existence of water environment and underwater pressure,the process of droplet transfer in underwater wet welding has some particularity.Thus,in this paper,the theoretical research work of metal transfer process in underwater wet welding is carried out.It is believed that this research not only fills up the gap of theoretical research on droplet transfer in underwater wet welding,but also provides theoretical support for the control of droplet transfer behavior in underwater wet welding.Based on the synchronous acquisition system of X-ray image and electric signal,the behavior of droplet transfer in underwater wet welding is observed,and the droplet transfer form in underwater wet welding is divide according to different droplet transfer behavior while the transition condition of droplet transfer mode with welding parameters is also explored.According to the different characteristics of droplet transition,three fundamental transfer mode are found: the globular repelled transfer mode,the shortcircuit transfer mode and the “submerged arc” transfer mode.According to the different size of repelled angle,the globular repelled transfer mode can be divided into wide-angle globular repelled transfer mode and small-angle globular repelled transfer mode.Besides,according to the different stages of short circuiting,the short-circuit transfer mode can be divided into surface tension transfer mode and short-circuit explosive transfer mode.Under the same welding parameter,the metal transfer mode is a mixed transfer mode rather than a single transfer mode,which consists of two or three fundamental transfer modes.With the change of welding parameters,the type and proportion of the basic transfer mode in mixed transfer mode changed correspondingly.Based on the metal transfer static force balance theory,the force model of droplet transfer in underwater wet welding is constructed,and the influence mechanism of welding parameters on the droplet transfer form is explored.Through fluid software FLUENT,the effect of rising bubbles on droplet transfer in underwater wet welding is simulated.In underwater wet welding,there are six forces acting on the droplet,which are the gas dynamic force,gravitational,plasma drag force,electromagnetic force,surface tension,the vaporization force and the gas flow drag force.Different from air welding,due to the cooling effect of the water environment,the plasma drag force weakens and the electromagnetic force hinders the droplet transfer in the underwater wet welding.In underwater wet welding,the gas flow drag force,generated by the interaction between floating bubbles and droplets,is unique force,which hinders and repels the droplet transfer.The welding parameters change the droplet transfer behavior including the metal transfer mode,droplet diameter and transfer frequency by changing the force condition of the droplet.Through the analysis of welding electrical signals,droplet transfer images,welding spatter and the welding,the influence of transfer mode on welding arc stability,spatter,droplet impact behavior and welding appearance are investigated.In underwater wet welding.While the main fundamental transfer mode in mixed transfer mode are shortcircuit transfer mode and small-angle globular repelled transfer mode,the welding arc burns stably with less welding spatters and the weld appearance is uniform because of the stable metal transfer.While the main fundamental transfer mode in mixed transfer mode is wide-angle globular repelled transfer mode or “submerged arc” transfer mode,the welding arc burns unsteadily and welding spatters produce easily with inhomogeneous welding appearance and welding defects such as undercut and overlap.