Study On Double-electrode Micro-plasma Arc Welding Three-dimensional Welding

Micro-plasma arc welding has obvious advantages in the welding of medium and heavy plate and the three dimensional rapid prototyping of arc welding.However,the melting rate of welding wire is low,which affects the efficiency.In order to improve the production efficiency of micro-plasma arc welding and realize the decoupling control of the heat of melting base materials and the heat of welding wire,a new method of double-electrode micro-plasma(DE-MPAW)arc welding is proposed based on the experimental study and the theory of bypass coupling arc welding.The feasibility and effectiveness of the proposed method are demonstrated by theoretical analysis and experiments.According to the characteristics of double-electrode micro-plasma arc welding and for the convenience of experimental study,a rapid prototyping test system for double-electrode micro-plasma arc welding is established,which main includes rapid prototyping system,welding system,video acquisition system and thermal signal acquisition system,based on x PC real-time target environment and used to rapid control prototype technology.The influence of some welding parameters on the appearance of weld bead is studied through using the experimental platform to carry out the test of flat plate welding.As a result,with the increase of the total welding current,the width and the height of the weld bead are decreased,and the aspect ratio of the weld bead increases gradually;With the increase of welding speed,the width and the height of weld bead are decreased,the aspect ratio is reduced gradually and its variation trend is similar to the width of weld bead.With the increase of wire feed speed,the width and height of weld bead are increased in the basically constant rate at the start,then the weld width was hardly any increased,the weld height is continued to increase in smaller rate than the beginning,and the aspect ratio has been decreased.With the increase of the ionic gas flow rate,the width of weld bead is increased,the height of weld bead is decreased,and the aspect ratio is increased rapidly.With the increase of the bypass currents,the width of weld bead is decreased,the height of weld bead is increased,and the aspect ratio is decreased gradually.On the basis of the DE-MPAW process test,the deposition rate,the heat input of the base metal and the weld bead forming quality are studied by matching welding parameters.The results show that DE-MPAW not only maintains the advantages of the conventional micro-plasma arc welding,but also improves the deposition rate and decreases the heat input of the base metal.When the other welding parameters remain the constant,the weld penetration and thedilution rate decreases and the weld forming coefficient increases with the increase of the bypass currents.The weld forming quality and the stability of the welding process are greatly affected by the droplet transfer.Thus the metal transfer behavior in DE-MPAW is analyzed based on the principle of statical equilibrium and pictures taken using the high speed camera about the process of metal transfer under different process parameters.The results indicate the frequency of the metal transfer could be decreased and the size of the drop is increased with the increase of bypass current,increased first and then decreased with the increase of wire feed speed and increased with the increase of ionic gas flow rate when the total current is a constant.So bypass arc hinders droplet transfer.Moreover,When the wire is melted at the edge of the plasma arc,gravity is the main force to promote the droplet transfer and because the spot force in the horizontal component force greater than the electromagnetic force in the horizontal direction,the droplet is exclusive transition;When the wire is melted in the center of the plasma arc,the plasma flow force is the main force to promote the droplet transfer.3D rapid prototyping of DE-MPAW is realized by using the 3D motion platform.A vernier caliper is used to measure the height of stack and a CCD camera is used to track 3D welding stacking pocess in real time,to observe and analyze the change of the weld pool and the droplet transfer.Moreover,the influence of welding force and welding parameters on the collapse is analyzed.Experimental results demonstrate that the reseaons of the collapse in the end portion of the weld pass include the flow of molten metal and the lack of the filler metal due to the fact the liquid metal pressed to the rear end of the weld pool can not be returned and the last molten droplet on the wire is not transfer to the weld pool.Especially,the droplet can not transfer stably to the molten pool with the accumulation of stacking wall sinking,and it makes the collapse further exacerbate.The flow of deposited metal is mainly caused by the action of plasma flow force,gravity and electromagnetic force.Welding current,welding speed,wire feeding speed and ionic gas flow rate are the main factors that affect the stack collapse of the 3D rapid prototyping process of DE-MPAW.