| With the continuous development of modern process equipment,as well as aerospace,marine engineering,energy engineering and nuclear power industry and other industrial equipment capacity,heavy,large welding structures have been rapidly developed,so the application of thick and super-thick plate welding structure is also more extensive,which reflects from the side of the welding quality requirements are becoming increasingly high.However,in conventional narrow gap welding,the welding arc usually only welds the bottom of the narrow gap bevel,with the heat concentrated only on the bottom workpiece surface,making it difficult to completely heat the side walls,which can easily cause unfused defects on the side walls.Therefore,the development of a new technology to control the fusion of narrow gap sidewalls has been the focus of research in the field of narrow gap welding.In response to the sidewall fusion problems inherent in narrow gap GMAW welding,this thesis presents a new technique-heat transfer regulation for narrow gap cable type seven wire GMAW mechanical stirred molten pool welding.This technique improves the quality of the sidewall fusion by using the cable wire and tungsten stirring bar to generate forced convection heat transfer within the molten pool,accelerating the transfer of energy from the high temperature fluid of the molten pool to the narrow gap sidewall.Unlike other complex mechanical or electromagnetic devices,this technology has the advantages of being a simple device,low cost,easy to operate and can be highly adaptable as high shear rates can be obtained.However,as a new technology,the influence of the stirring parameters on the heat transfer mechanism of the narrow gap cable GMAW mechanically stirred melt pool is not yet fully understood,so numerical simulation techniques combined with process tests are needed to investigate the heat and force production patterns of the arc and the melt pool.First of all,this thesis is the Q235 carbon steel narrow gap cable seven wire GMAW arc numerical simulation analysis,the study of welding current on the narrow gap cable seven wire GMAW arc heat production force impact law,the study concluded that:narrow gap cable seven wire GMAW arc in the welding current of 280 A,300 A,320 A and 340 A,the peak temperature of 20516 K,21226 K,respectively 21915 K,22638 K.In the axial direction,the temperature of the welding arc increases gradually from the workpiece surface to the end of the wire.The maximum temperatures on the workpiece surface were14474 K,14780 K,15027 K and 15207 K respectively.The maximum current densities within the arc are 5.95×10~7A/m~2,6.21×10~7A/m~2,6.57×10~7A/m~2and 6.88×10~7A/m~2respectively,with the peak area of the arc occurring at the end of the cable wire and the current density at the centre of the arc being the maximum,the closer to the centre of the arc the higher the current density,and as the welding current increases the centre of the arc column area The current density in the centre of the arc column increases with increasing welding current.The plasma velocity peaks at 224.29 m/s,248.89 m/s,272.72 m/s and295.63 m/s.The flow rate of the narrow gap arc flows vertically from the velocity entrance to the bottom of the workpiece and then climbs up the side wall from the bottom of the workpiece.And as the welding current increases,the height of the plasma climbing upwards increases.The trend in potential was generally consistent,with the potential increasing faster at 0-0.5 mm from the cathode surface and 0-1.0 mm from the anode tip.The peak pressures at the wire end were 554.81 Pa,634.36 Pa,716.94 Pa and 801.37 Pa.The arc pressure at the workpiece surface also increased with increasing temperature,with peak arc pressures at the workpiece surface of 254.9 Pa,296.8 Pa,338.6 Pa and 378.2 Pa.As the wire height decreased,the wire end The peak current density and temperature field of the arc increase as the wire height decreases,the peak velocity and pressure field of the arc at the wire end decreases and the peak pressure field at the workpiece surface increases.As the height decreases,the current density increases and the temperature rises.After that,based on the thermophysical characteristics of the narrow gap GMAW mechanical stirring melt pool,a double ellipsoidal heat source model,a self-rotating melt drop transition model and a stir bar mechanical motion model were established,and the melt pool fluid flow was simulated using the software FLUENT,and the following conclusions were obtained by changing different welding parameters:keeping the welding current 300 A,the stir bar radius 1.5 mm,the shielding gas flow rate 30 L/min The welding parameters remain unchanged and the stirring speed is kept constant at 1200 r/min,when the stirring rod and cable wire centre horizontal distance are 3.0 mm,4.0 mm and 5.0 mm,the melt depth of the pool is 3.0 mm,2.6 mm and 2.5 mm,the melt depth of the side walls of the pool are 1.1 mm,0.4 mm and 0.1 mm,and the melt width is 11.2 mm,10.6 mm and10.5 mm.As the horizontal distance between the stir bar and the centre of the wire increases,the melt depth,sidewall melt depth and melt width decrease.With the other parameters held constant and a stir bar radius of 1.5 mm,the melt depth was 3.4 mm,3.2mm and 3.0 mm,the side wall depth was 0.4 mm,0.6 mm and 1.1 mm and the melt width was 10.6 mm,11.0 mm and 11.2 mm at stirring speeds of 600 r/min,900 r/min and 1200r/min respectively.As the stirring speed increases,the melt depth decreases and the sidewall melt depth and melt pool width increase.Finally,experiments were carried out on the narrow gap cable GMAW mechanical stirred melt pool with seven wires.The collected arc morphology was compared with the simulation results of the cable wire arc simulation to verify that overall the experimental results and the numerical calculation results matched well.The melt pool simulation results were then compared with the actual experimental results,and the narrow gap melt pool variation pattern obtained using the simulation was close to the actual weld morphology variation pattern,which basically matched the experimental data and proved the accuracy of the model.The numerical simulation method and process parameter settings used are proven to be feasible,and this method can be used for more in-depth research to improve the efficiency and quality of the welding process in practice. |
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