| Gas Metal Arc Welding(GMAW)is one of the most widely used welding methods at present.It boasts the advantages of good quality,high efficiency,low production cost and high automation,etc.In order to further improve the deposition efficiency of the traditional monofilament GMAW,a new GMAW welding method--Cable-type Welding Wire GMAW emerge as the times require,which enjoys the advantages of high efficiency,energys saving and good quality,etc.,and its equipment is simple and easy to realize automation of welding,especially suitable for ships and other large thick plate welding.This thesis employs FLUENT to conduct a numerical simulation of cable-type welding wire GMAW arc as well as the droplet transfer behavior,in order to verify the accuracy of the calculation result,carry out the verification test and conduct high-speed camera shooting to welding arc and droplet transfer simultaneously.This study reveals the mechanism of heat and force production of the arc,the dynamic process of droplet transfer as well as distribution law of welding temperature field,hoping to lay an important theoretical foundation for promoting cable-type welding wire GMAW.According to the relationship that cable-type welding wire contacts resistance,this thesis deduces that the intermediate wire accounts for 13% of the total current,peripheral wire occupies 14.5%,and the anode region is coupled by three kinds of multi-polar regions.Based on the momentum conservation,energy conservation,mass continuity and Maxwell's equations in fluid dynamics,a three-dimensional numerical model of the arc is established.The distribution of current density,temperature field,velocity field,pressure and potential under 400A-600 A current is calculated respectively.The result shows that the current density,temperature field,velocity field,arc pressure and electric potential of the welding arc increase along with welding current.Every 50 A the welding current increases,the highest temperature of its arc will increase 1280-1300 K,and the largest plasma gas flow rate is increased about 37-50m/s.The peak pressure of the arc appears in the anode region,where the intensity of pressure is about 65Pa-90 Pa higher than that in the cathode region.Combined with the measured data,the research shows that during the welding process,the anode region of the arc will be reduced by 2-4V while the cathode region will be reduced by about 15 V.This thesis also calculates the temperature field,velocity field of cable-type welding wire GMAW arc and the distribution of arc pressure under the gas flow of 15-35L/min.Every 10L/min gas flow increases,the plasma gas flow rate of the weldingarc will be increased by 21% to 29%,the maximum pressure in the anode region will be increased by approximately 100Pa-122 Pa,the peak pressure of arc pressure near the surface of workpiece will be increased by about 50Pa-55 Pa,and the radius of its range of action will be increased by about 1.7mm-2mm.The simulation and test result show that the anode region of cable-type welding wire is composed of 7 small anode regions,the arc on the top of welding wire is coupled by several small arcs,which move along with welding arc.The diameter of small arcs expands and thus couples to a large arc,and the large arc acts on the workpiece and the molten pool.This research concludes the physical characteristics of the arc of cable-type welding wire GMAW,which provides a theoretical basis for subsequent research,promotion,production and application.By establishing the three-dimensional droplet transfer numerical model of cable-type welding wire GMAW based on VOF method,this thesis expounds the governing equation of droplet model,force bearing of droplet as well as model solution.This chapter,through the method of experimental verification by high-speed camera and calculation,studies the ways of droplet transfer under 400A-500 A.The result shows that,every 50 A the welding current increases,the size of droplet will be decreased by 9% and 41% respectively from test result,and increased by 11% and 43% from calculation result.The transfer frequency is32 Hz,47Hz,70 Hz from test result,and 40 Hz,58Hz,78 Hz from calculation result The transfer way changes from exclusion transfer into particle transfer,and then into projected transfer.By comparing calculation and test result of high-speed camera,the conclusion shows that the droplet size coincides well with the transfer frequency.This thesis takes advantage of the thermal imager equipment to study the distribution of surface temperature of workpiece after welding.The result shows that the increase of welding current and voltage exerts little effect on the surface temperature of workpiece after welding.Every 50 A the welding current increases,the weld width will be increased by 1.5mm ? 2.5mm and 3.0mm respectively.With the extension of cooling time after welding,the surface temperature of workpiece declines the fastest within 2.0s to 6.0s,and the falling range slightly slows down within 6.0s to 8.0s.The increase of welding speed can lead to that the retention time of high temperature becomes shorter,heat input decreases,and the surface temperature of workpiece also declines accordingly.In the meanwhile,the increase of welding speed can also lead to a significant decrease in weld width. |
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