Study On Twin Wire Indirect ARC Simulation And The Twin Wire Indirect ARC-TIG ARC Hybrld Welding

In traditional gas shielded welding method, the arc is burning between the wire and the workpiece, the workpiece is one of the electrode of the arc, the heat generated by the arc is partly used to melt the workpiece and partly used to melt the wire. Gas shielded twin wire indirect arc welding is a new welding method with high efficiency and energy saving, it features that twin wires connected negative and positive electrode of direct current power source, the workpiece is not connecting to the power source, no current pass through it. The arc burning between twin wires, the heat generated by the arc is mainly used to melt the wires and only a little used to melt the workpiece. This new welding method has the advantages of high efficiency, energy saving and small fusion ratio, has the good prospects for engineering application.The arc is the energy source for welding, the value and distribution of arc temperature, current density, plasma velocity and electromagnetic field determined the welding process and thus determined the energy distribution between workpiece and wires, the melt rate of the wires and the heat input to workpiece, thus affect the weld appearance and finally the quality of the welding joint. Study the arc is a prerequisite to understand the nature of the welding process. At present the research on twin wire indirect arc is still in the initial stage. Study the twin wire indirect arc is important to understanding the heat and the melting mechanism of this new welding method. It laid the foundation of further development and optimization process of this new welding method.Due to the high temperature, it is difficult to measure the arc by the conventional measurement methods, it is more difficult to measure the twin wire indirect arc because its particularity, thus it is necessary to use the numerical techniques to analysis the arc. This paper establish a 1/2 three-dimensional finite element model for twin wire indirect arc which based on magnetic dynamics and Maxwell equations, the model is calculated by finite element analysis software. The results showed that the arc temperature, plasma velocity, current density and electromagnetic force of twin wire indirect arc are higher in upper part of arc column region and lower in lower part of arc column region, and highest in the region which near the cathode and anode in arc column region, relatively lower in the region which is far from the cathode and anode in the upper part of arc column, and lowest in lower part of arc column region. The arc is deflecting to the anode side and similar to a tilted and inverted basket.This paper analyzes arc temperature, plasma velocity, current density and electric potential distribution in twin wire indirect arc with the influence of different welding current, different angles between twin wires and different arc length. The results showed that with the angle between twin wire increase, the arc temperature, plasma velocity and current density increase in upper part of arc column region and decrease in lower part of arc column region, wherein the increment in the region which near the anode is higher than that of near cathode, the arc deflection increase. With the welding current increases, the arc temperature, plasma velocity and current density increase in the whole arc column region, wherein the increment in the region which near the cathode and anode is larger and relatively lower in the region which is far from the cathode and anode in the upper part of arc column,lowest in lower part of the arc column region, the arc deflection also increase. With arc length increase, the arc voltage increased significantly, the arc temperature, plasma velocity and current density increased at a smaller rate, wherein the increment in the region which near the cathode and anode is far larger than that in lower part of lower arc column region, and the deflection of the arc also increase. Change the welding current, welding voltage, the angle between twin wires will not change the arc parameters distribution tendency as:"higher in upper part of arc column region and lower in lower part of arc column region, wherein highest in the region which near the cathode and anode, relative lower in the region which is far from the cathode and anode, lowest in the lower part of arc column region". The arc temperature, plasma velocity and current density is always high in the region which is near the cathode and anode, always maintained at very low levels in lower part of arc column region, which lead higher melting rate of twin wires and lower heat input to workpiece.The transition track of cathode droplet and anode droplet deflection, the distance between the land position of cathode droplet and anode droplet is relatively larger, the volume of cathode droplet is bigger than that of anode droplet, and the droplet transfer frequency of cathode droplet is less than that of anode droplet. The repulsive force on the droplet is the main reason for its deflection. The droplet go through a lower temperature region after they detachment from wire surface, thus the arc transferred less heat to the droplet. The calculate results and test results show that twin wire indirect arc and droplet transfer less heat to the workpiece, this is the main reason for the low heat input of twin wire indirect arc welding.Twin wire indirect arc welding has the advantages of high welding efficiency and energy saving, but also has some limitations. It is easy to cause some defects in welding process, such as low welding penetration, discontinuity weld, faulty fusion in the edge of the weld and weld porosity which hindering the engineering application of this new welding method. This paper studies the forming process, mechanism and eliminating of these defects. The larger weld torch cavity, the long flow time of droplet, the low heat input, the high surface tension of weld pool and the fast solidification speed of weld pool lead the gas in liquid metal is not easy to escape and thus the sensitivity of porosity is high. The low temperature, poor liquidity and high surface tension of liquid metal in weld pool are the main reason for discontinuous weld. More deposited metal and lower heat input to workpiece lead the weld pool is not big enough to hold the liquid metal. The overflowed liquid metal can not melt the workpiece and difficulty to spread is the reason for the faulty fusion in edge of the weld.Due to the limit of inherent thermal properties of twin wire indirect arc welding, change welding process to improve the heat input to the workpiece and elimination the defects has some limitations. In order to solve this problem, a TIG arc was introduced to improve the heat input and elimination the defects.The new welding welding method called twin wire indirect arc-TIG arc hybrid welding. The heat input of TIG arc can adjust individually with the melt rate of twin wires not change. The heat input to workpiece can be flexible adjustment by adjusting TIG welding current, so as to realize the reasonable ratio between deposited metal and heat input. It can not only maintain the advantages of high efficiency and energy saving, but also overcomes the drawbacks of lower heat input. The droplet transfer, arc stability, weld pool shape and weld shape will change after the addition of TIG arc. This paper study the droplet transfer, arc stability, weld pool shape and weld shape of twin wire indirect arc-TIG arc hybrid welding with the influence of relatively position between tungsten and twin wires, the distance between the two arcs, the current of TIG welding and the tilted angle of tungsten. The results show that when the tungsten near the cathode, the angle between cathode droplet and anode droplet increases and when the tungsten near the anode, the angle between cathode droplet and anode droplet decreases. The repulsive force on cathode droplet and attractive force on anode droplet generated by TIG arc is the main factor for this phenomenon. TIG arc can increase the conductivity of twin wire indirect arc by transfer more heat and more metal vapor to the arc plasma, which can stable the twin wire indirect arc. With the TIG welding current increase, the arc stability of twin wire indirect arc increase and with the distance between two arcs increase, the stability of twin wire indirect arc decrease. The weld width is determined by TIG welding current and twin wire indirect arc welding current. The weld penetration depth is determined by the twin wire indirect arc welding when TIG welding current is small. The weld penetration is mainly determined by TIG welding current when TIG welding current is more than 150A. The distance between two arcs has more influence on weld width and smaller influence on weld penetration. The welding speed has more impact on weld penetration than of weld width.