Study On Arc Rotation And Droplet Transfer Behavior Of Cable-type Welding Wire GMAW

High-efficiency,high-quality and low-energy consumption welding processes are urgently needed because of the rapid industrial development.The gas metal arc welding?GMAW?is a kind of arc welding method using welding wire as consumable electrode,which has many advantages such as high production efficiency,reliable welding quality,low production cost and strong adaptability.There are many methods to improve the welding efficiency,while the process is complex or cost is relatively high.Therefore,the development of high efficiency,high quality,low consumption and easy to operate the melting pole gas welding method and process has become an urgent need of the industry.And it is also the key basic problem to improve welding productivity.To achieve highly efficient,saving energy,and producing high welding quality,the method of cable-type welding wire?CWW?welding has been proposed.It is an innovative welding method with high efficiency,energy saving,and high welding quality,etc,using CWW as consumable electrode.The CWW is comprised of seven welding wires.One is in the center,while others distribute around it uniformly.With the wire continuous feeding and melting,resulting in anode area on 6 periphery welding wire end around the anode area on center wire end synchronous rotation,and forming an autonomous rotating arc.The CWW CO₂ welding can significantly increase the deposition rate and improve the efficiency of the welding production.In addition,it can easily realize low cost,simple equipment and welding automation.This method combined the advantages of CWW structure can make the welding wire melt quickly and easy to form an autonomous rotating arc.In this paper,the welding arc behavior,droplet transition behavior,molten pool flow behavior,weld forming and process performance of CWW are studied through experimental research and theoretical analysis,which can understanding the arc coupling and rotation behavior mechanism.The signal waveforms and corresponding synchronous images experimental system based on the high speed digital camera and electrical signal system were established.The arc behavior of CWW GMAW was studied according to the arc behavior and CWW structure characteristics.The model of arc coupling and rotation of CWW is established,and the coupling mechanism of arc is analyzed;the influence factors of arc arcing behavior and arc shape are studied according to the arc characteristics of different wire ends.Combined with the unique structure characteristics of CWW,this paper analyzes the distribution of CWW current on each branch line,which is advantageous to the increase of the electromagnetic contraction force,which is advantageous to the formation of arc coupling and beam-shaped arc state.Based on the characteristics of CWW and the electromagnetic contraction force,the model of arc coupling and rotation of CWW is established.The arc coupling shrinkage is proportional to the square of the welding arc height,and is inversely proportional to the distance between the wires in the cable type welding wire;the rotating frequency of the arc is proportion to the wire feeding speed,and the screw rise angle and the welding wire radius are inversely related.This paper analyzes the arc ignition procedure for this type of welding based on experiments with three different wire end conditions:an unsmooth wire end,a smooth wire end,and a preheated smooth wire end.Smaller contact areas between the CWW and the base metal led to higher arc ignition currents,and higher wire tip temperatures led to shorter arc ignition times?AITs?with the same chemical composition,diameter,and extension.Based on the characteristics of the welding wire end structures and the contact resistance between the CWW and base metal,a suitable mathematical model of the AIT was developed.The model was validated using experimental arc ignition images.The AITs for the unsmooth smooth and preheated smooth wire ends were 14 ms,20 ms and 11 ms,respectively,essentially consistent with the model calculations.The influence factors of CWW GMAW are analyzed,the arc shape contraction with the increase of welding current,and the arc length increase with the increase of welding voltage and wire extension under the same welding condition.According to the characteristics of CWW,the melting speed model of cable welding wire is established.The droplet transfer mode belongs to repelled transfer,globular transfer and projected transfer when the welding parameters increased.It is found that the welding wires melt together to form a droplet at the same time and gathering each peripheral wire melts together to form a droplet and gradually grows into a transition.The arc behavior and droplet transfer were observed by the electrical signal waveforms and corresponding synchronous images,based on the high speed digital camera and electrical signal system.The results showed that the shape of welding arc changed from bell arc to beam arc with the increase of welding parameter.The droplet transfer mode changed from repelled transfer,globular transfer to projected transfer in turn.Droplet transfer frequency increased from 18.17 Hz to119.05 Hz,while the droplet diameter decreased from 1.5 times to 0.3 times of the CWW diameter.The transition frequency of droplet transfer in CWW increases with the increase of welding current;the effect of arc voltage on the droplet transition is smaller,the droplet size decreases,and the transition frequency changes little;under the same welding parameters,the droplet size and transition frequency are different under different shielding gas.Based on the observation system of the molten pool of CWW,and it is found that the surface of the molten pool of CWW will produce two sides of the weld flow from the arc center to the center of the molten pool.When the molten pool surface flows to the weld sides,the energy of the molten pool center was brought into the flowing base metal and the base metal melts.When the weld flows to the center of the molten pool,the temperature of the liquid metal decreases gradually,so the melting of the base metal decreases.The force of rotational arc can promote the droplet stable transition to the molten pool,and make the molten pool generate steady flow.The arc has a stirring effect on the molten pool,which has advantageous to the heat transfer from the arc and droplet to the molten pool,to promote the gas escaping,which can refine the grains and improve the welding quality.In this paper,the deposited properties and energy consumption characteristics of CWW are analysis under the same parameters.It is found that the welding wire melting rates and deposition rate are 30%higher for CWW CO₂ welding than those for single-wire SAW when the same welding parameters are used.Meanwhile,this process also requires arc energy lower more than 10%when depositing the same weight of metal.Melting the same diameter of 7wire,the arc power of CWW CO₂ welding is only 2.4 times than that of single-wire CO₂welding.This paper analyzes the relationship between welding seam forming and weld parameters of CWW,and it finds that weld width and reinforcement increased with the increase of current.The weld depth of CWW CO₂ welding changed small after the welding current increased to a certain extent.Base on the above analysis,the research of experiment on the butt test plate of 10mm thickness A36 marine steel shows that the number of butt weld lines of CWW CO₂ welding is less than that of single-wire CO₂ welding and the welded joint,which can meet the requirement of standard.The microstructure of CWW CO₂ welding overheated zone is finer than that of single-wire CO₂ welding.The tensile fracture site of CWW CO₂ welding joint is in the base metal,which is higher than that of the single-wire CO₂ welding.The results of bending properties and impact properties are qualified,and the hardness of welding joints is less than 355V.The performeance properities comply with CCS classification society standard requirements.