Optimization Of Welding Process Of Bridge Steel Q370qE Based On Residual Stress Control

Prediction of welding residual stress and deformation has become an important problem in many manufacturing processes.In the process of welding cooling,the shrinkage of weld metal is limited by the base metal,and large tensile stress and deformation are often accumulated in the weld.The whole welding of bridge structure includes T-type welding joint,cross welding joint and box girder.The analysis of three-dimensional stress and distortion of different structures is a complex problem.In this paper,aiming at different welding structures of low alloy structural steel q370 q E,the temperature field,stress field and distortion field of different welding joints are analyzed by using the finite element simulation software SYSWELD.The main research contents and results are as follows:(1)The finite element models of different joints are studied.The finite element model of T-joint and cross joint is studied by experiment and simulation.The finite element model of double ellipsoidal heat source of Q370 q E steel T-joint is established.The model parameters are set as total heat input Q=24.1Kj/cm,weld pool length a=22.6mm,half weld width b=8.4mm,and weld depth c=10.2mm.The thermal cycle curve is relatively consistent,and the welding residual stress error is less than 15%.The finite element model of double ellipsoidal heat source of q370 q E steel cross joint is established.The model parameters are set as total heat input Q=21.8kj/cm,weld pool length a=22.6mm,half weld width b=8.4mm and weld depth c=10.2mm,the thermal cycle curve is relatively consistent,and the welding residual stress error is less than 10%.(2)The evolution of welding temperature field and stress field of different joints was studied.The numerical simulation process of welding temperature field and welding stress field is analyzed by using the welding finite element analysis software SYSWELD.The results of temperature field and stress field are obtained and analyzed through the determination of geometric model,mesh division,heat source and heat exchange coefficient,and the definition of material attribute.The evolution of welding residual stress and welding deformation of T-type welding and cross welding are analyzed.Finally,the evolution rules of temperature field and stress field are obtained.The results of temperature field show that when the heat source of weld passes a certain node,The temperature of this joint increases.As the heat source moves forward,the high temperature range gradually expands.After the welding,the weldment begins to cool down.the temperature of each joint tends to room temperature,and the multi pass weld often experiences multiple welding thermal cycles.The stress field results show that the weld center of each pass is greatly affected by the heat source,and the temperature cools fast,and the weld shrinks violently The heat affected zone is less affected by the heat source,the temperature cooling is slower,and the residual stress is relatively small.(3)The welding residual stress and deformation of cross welding were studied.In cross welding,the welding sequence has a significant effect on the size,distribution and angular deformation of residual stress,while the welding direction has little effect on the residual stress and angular deformation.In different welding sequences,the peak stress is the smallest when welding diagonally in turn,which can reduce the peak stress by about 20%.After one group of diagonally welded at the same time,another group of diagonally welded at the same time,the welding angle deformation is the smallest,and the z-direction distortion is within±0.5mm.With the increase of welding speed,the change range of longitudinal residual stress of the weld increases,the change of transverse residual stress is not obvious,and the welding distortion increases.(4)The welding residual stress and distortion of box girder are studied.The welding residual stress and distortion in different welding sequences are simulated,and the distribution of residual stress and distortion in each welding sequence is obtained.The results show that the welding distortion is the smallest.In the case of single-layer welding of four welds of box girder structure,the welding sequence has little influence on the size and distribution of residual stress,with the peak stress around 300MPa;in the case of double-layer welding of eight welds of box girder structure,the peak welding residual stress is the smallest when the first four welds are welded in diagonal sequence,and then the second four welds are welded in the same way,with 324 MPa.