Thermo Mechanical Coupling Simulation Of FCB Three-Wire Submerged One-Side Arc Welding Pool

Flux Copper Backing three-wire single side submerged arc welding(FCB),is widely used in plate welding of large and medium plate(8~40 mm)in shipbuilding and Bridge industries due to its high efficiency and economy.But because it contains more than one high heat input source and multiple external force stacked,the temperature field and the dynamic behavior of the molten pool is very complex,some defects appear easily when welding,such as grain coarsening of welding seam and heat affected zone,longitudinal cracks at the beginning and terminal of the weld,transverse cracks inside the weld and small transverse cracks on the back of the weld,these welding defects will cause service performance(such as tensile strength,corrosion resistance,fatigue resistance and structural stability etc.)seriously decline,and ultimately affect the overall stability of the ship and bridge.The welding temperature field and residual stress field of welded joints plays an important role in the macro and micro structure and the formation of welding defects,the experimental measurement is time-consuming,and cannot get the distribution of the temperature field,flow field and stress field,so this paper adopt numerical simulation technique.The main work of this paper is as follows:(1)the current research status of various high efficient submerged arc welding processes and welding numerical simulation is briefly introduced.(2)the pool in the process of single wire welding heat source model and the force model was improved on the basis of previous studies,multiple double-ellipsoid heat source models with different distributed parameters and different load positions is adopted,Considering the effects of electromagnetic force,gravity,surface tension,buoyancy,arc pressure,slag pressure,droplet impact force and flux copper backing on the dynamic behavior of molten pool,a three-dimensional model of FCB three-wire submerged one-side arc welding pool is establi-shed,using CFD software Fluent to perform numerical simulation,the distributionlaw of FCB welding molten pool temperature field and flow field was obtained,the HAZ width of the steel plate surface and the back,macroscopic solidification crystallization mode of weld was obtained too,the simulation results ofthe size and solidification mode of the weld pool agree with experimental data well,the accuracy of the model is verified,providing theoretical and technical support for the research of efficient welding method of FCB.(3)The theoretical knowledge of welding thermal stress and residual stress is introduced,by using ANSYS software,FCB heat source and solder filling process was simulated by using the technology of moving heat source and the technology of birth and death element,indirect coupling method was accepted,the distribution of residual stress in welding by FCB method is obtained,the relationship between the distribution of the FCB residual stress and the defects of different types of cracks is analyzed,it provides theoretical guidance for practical engineering to reduce and eliminate FCB welding defects.(4)the influence of different model sizes(length and width)and process parameters(welding speed and tail wire spacing)on the residual stress distribution of FCB welding is calculated,providing data support for the adjustment of actual FCB welding process.