Study Of Triple-wire Gas Indirect Arc And Its Narrow-gap Welding Process For Thick Plates

With the development of modern industries,the demand for high efficiency welding technology is becoming more and more urgent;especially the need of high deposition rate welding technology for manufacturing large structural parts is becoming more and more urgent.However,with the traditional arc welding,when increasing the welding current to increase the deposition rate,the heat input of the base metal also increases,leading to decreased weld performance.In order to increase the deposition rate while reducing heat input,twin-wire indirect arc welding is a good way.Based on twin-wire indirect arc welding,this paper introduced a third wire and proposed triple-wire gas indirect arc(TW-GIA)welding.During TW-GIA welding the arc shape is controlled by the magnetic field of the third wire and a converged arc shape is obtained,which solves the problem of insufficient heat input resulted by arc divergence during twin-wire indirect arc welding.The stability,arc shape,metal transfer,arc characteristics and deposition rate of TW-GIA welding are studied and analyzed.By employing the TW-GIA welding,narrow-gap TW-GIA is developed for the first time.The main contents of this paper are as follows:(1)Studies on the arc characteristics of TW-GIA.According to the arc stiffness theory,the arc is significantly affected by the the magnetic field of the main wire and the indirect arc will extend along the main wire,making the indirect arc converged.In addition,TW-GIA has multiple wire configurations,which affect the magenetic field distribution.Therefore wire configurations can be utilized to adjust the arc morphology and the arc heat distribution.(2)Studies on the metal transfer characteristics of TW-GIA.The magnetic forces between the three wires significantly affect the metal transfer.Due to the magnetic force of the side wire boosts the metal transfer of the main wire,under the experimental condition,the metal transfer of the main wire is always streaming transfer and dropping along the extension of the main wire.Due to the magnetic force of the main wire repells the side wire,the droplet of the side wire is repelled away from the main wire.(3)Studies on the characteristics of the deposition rate of the TW-GIA.Due to the different connection modes of the power supply,compared with traditional twin-wire welding which also has two welding machines,during TW-GIA,more arc heat is utilized to melt wires and less arc heat is utilized to melt base materials.For instance,during experiments,the base material melting efficiency of TW-GIA is 2.09%?12.43%and the wire melting efficiency of TW-GIA is 61.09%?90.31%,while for the traditional twin-wire arc welding,the base material melting efficiency is 22.15%?27.44%and the wire melting efficiency is 37.690%?46.84%.According to the actual test and reference datas,when the current is 480 A,deposition rate of the traditional twin-wire welding is around 8.04 Kg/h and the deposition rate of TW-GIA is around 25.5 Kg/h,deposition rate increases more than 200%.Compared with twin-wire indirect arc welding,TW-GIA increases applicable range of the deposition rate.(4)Development of narrow-gap TW-GIA process.By using wire distributions to adjust the arc morphology and metal transfer,the arc heat is concentrated on the sidewall of the parent material,thus realizing the sidewall fusion of the narrow-gap TW-GIA welding.When the main wire is vertical downwards,the molten pool accumulates under the main wire,the position of the arc can not be further reduced,the heat of the arc can not act on the root of the weld,and the weld root can not be fused.When the main wire is inclined,the molten pool accumulates behind the main wire,the welding torch height can be further reduced,the arc heat can reach the weld root,complete fusion is realized at the root of the weld.(5)Improvement of the weld bead formation of the narrow-gap TW-GIA by a tungsten arc.Because the deposited metal of main wire accumulates in the center of the weld,without other auxiliary methods,the weld surface of the narrow-gap TW-GIA is convex.During narrow-gap multi-layer welding,the welding torch height can not be reduced due to convex weld surface and the heat can not be applied to the weld root,which can cause incomplete fusion at the weld root and incomplete fusion inter-layers.To solve this problem,the method of adding a tungsten electrode arc after TW-GIA is proposed,according to the phenomenon that a tungsten arc can produce concave surface attributed to the arc pressure.With the tungsten arc,narrow-gap TW-GIA weld bead surface becomes concave.With the increase of tungsten electrode current,the pressure of tungsten arc increases and the concave degree of weld surface obviously increases.