| Medium and thick plates have been widely used in the fields of shipbuilding,automobile processing and high-pressure vessels.Due to large structure and wide groove,it has certain difficulties in welding.There are two main welding methods for the medium and thick plates:one is multi-pass welding;the other is swing filler welding.Because the multi-pass welding has the advantages of small heat input,effective reduction of deformation and reduction of defect probability,it has been widely used in the welding of medium and thick plate.And in the multi-pass welding process,because layer-layer,track-channel and layer-channel interacts between the two causes the workpiece to form very large temperature gradient,resulting in extremely uneven welding thermal stress and residual stress,which makes the workpiece forming poorly and ultimately affects the assembly and use of the component.In this paper,multi-pass welding of V-grooves is used as the experimental object for plate and pipe,and the multi-pass welding test system is built.The finite element analysis software of COMSOL is used to numerically analyze the temperature and stress field of the multi-pass welding.Its model for medium and thick-walled pipelines and medium-thick plates are established.The effects of temperature,convection,radiation and phase change latent heat on the physical properties of the material should be consider,and change the temperature field and thermal stress field in different directions of the workpiece.The cooling time and the influence of subsequent welds on the high temperature peak temperature and high temperature residence time were analyzed by finite element simulation.The simulation results were compared with the welding test results under the same process conditions.The different V-grooves were also analyzed.The results show that the simulation analysis results have a good coincidence with the welding experiment results.For the flat V-groove,the coupled field of temperature and thermal stress mainly acts on the lateral and longitudinal directions of the workpiece.and has little effect on the angular deformation in the thickness direction.The coupled field of temperature and thermal stress mainly acts on the axial direction of the workpiece,but has little influence on the radial direction for the pipeline of the V-shaped groove;the subsequent weld has an important influence on the peak temperature and residence time of the high temperature.The welding angle deformation decreases with the increase of the cooling time between channels.When the cooling time is 120s,the angular deformation is the smallest,the efficiency is the highest and the weld is best formed.The welding current is 89A-110A,the voltage is 19.5V-20.6V,and the wires are fed.The speed is in the range of 2.8mm/s to 3.6mm/s.When filling the 60° groove,4 layers are required,and the number of layers equals the number of weld beads;and the molding quality is good,when the welding current is 110A?130A,the voltage is 20.6V?21.0V and wire feeding speed are 3.6mm/s?4.1 mm/s,3 layers are required to fill the 60° groove.When it is larger than the welding process parameter range,the welding parameters are too large,which affects the weld formation.It is of great academic value and practical significance to provide a theoretical basis for controlling,adjusting and reducing welding angle deformation in the future. |
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