Numerical Simulation And Experimental Study Of (Temperature Field、Stress Field) In Ultra High Strength Steel Slab Structure MIG Welding

The heavy vehicle tower is a typical box-type structure, which is made up of several 20-60mm thick high-strength steels and tower head. Based on positioning fixture, the turret is welded by multi-pass PMIG welding process, and manufacturing dimensional accuracy is also demanded, so the welding deformation should be strictly controlled. In this thesis, the previous researches on welding numerical simulation were summarized first; then, the multi-pass welding simulations of turret roof and side plates connection were successful done; and the deformation laws of turret roof during welding were analyzed, the deformation laws of side plates connection under different welds orders and different constraints were researched; in the end, the turret structure welding procedure tests were conducted to verify the calculations of welding temperature field and stress field.The heat source model in turret PMIG welding was studied, the second development of double ellipsoid heat source model was done, and the heat energy distribution function was optimized by checking the melting effect. Upon the starting of turret roof welding, the welding center area temperature was rose to 2256℃ immediately, and the weld pool was shaped as "pear"; the weld pool temperature was gradually decreased with the heat source advancing, the isotherm contours rendered nearly oval shape whose long axis was in the direction of welding; showed by the stress and strain contours, the main stress distributions were the arc starting point、the central area of welds and the crater point.The weld stress field distribution of turret sides was studied, and the heat、deformation laws in side plates welding under three welds orders% three constraints were researched. The results showed that:the heat distribution was more evenly in sequential program Ⅲ, the deformation after welding was small, and the residual stress distribution was the best, the highest stress of welds was 896.5MPa, and the stress values in concentration area was in 239-418MPa; program V was a good constraint scheme which synthesized the deformation and residual stress distribution, the deformation of welds and the surrounding areas was in 0.228-0.452mm in the final welding moment, the welds were deformation concentrated areas, the residual stress values in welds were in 376.0～484.9MPa, and the residual stress area was significantly reduced after the clamp was released, while,the stress field distribution was optimized.The turret structure welding procedure tests showed that:the thermal cycle curves trends of points which were selected were consistent with the calculation model, the percentage errors of peak temperature、temperature rising speed and temperature cooling speed all meet the requirements; the comparison of weld pool behaviors showed that the weld width and penetration in the second pass were basically consistent with W2 in the calculation model, the residual stress values which were tested by blind-hole method were also near the calculation values, and the deformation trends in plates were the same with simulation results.In summary, the calculated precision in this thesis meets the requirements, and the models have been verified, the models in the paper could provide the guidance for welding process optimization.