Research On Influencing Factors Of Backing Wled Formation Using Double-Sided Double Tig For The Thick Plates Of High-strength Steel

High-strength Low-alloy steels thick plates adopt double-sided double TIGbacking welding, double-sided double MAG filling and capping, the procedureeliminates back chipping process which is necessary for conventional thick platewelding and improves welding productivity and welding joint quality. Whatmatters in this process is the backing weld. But in the actual production thechange of relevant parameters of groove makes backing weld root fusiondifficult, so in this paper the influencing factors of thick plates backing weldforming were studied by numerical simulation and experiment.Firstly, the finite element model of thick plates butt backing weld wasestablished. The paper adopts two different heat source models to simulate thetemperature field according to the size of the groove reserved gap. Thereliability and accuracy of the model was verified from the actual weld fusionline and thermal cycling curves in the test compared with results of thesimulation.Then the influence of the groove reserved gap, root face and misaligment ofbutt joint on thick plates backing weld was investigated from the weldingtemperature field. Simulation results show that: the size of the groove reservedgap have a major impact on the backing weld root penetration, when gap wasreserved in the2-4mm the weld of symmetrical X-groove has fine fusion, whenroot face exists at the groove a smaller welding pool renders the backing weldroot fusion more difficult in the same conditions and the allowable thickness ofthe root face that does not affect the backing weld penetration is about1-5mmwith the2-4mm groove gap. when misaligment was between the plates,asymmetrical shape of the backing weld was obtained and the weld deeppenetration is over one side. The maximum amount of the misalignment shoudnot exceed5mm with2-4mm groove gap. When the root face and misalignmentexit at the plates, the total amount can not be out of6mm, otherwise it can notensure the root of the weld penetration.Finally, double-sided double TIG backing weld experiments of thick platesin the flat and overhead position were conducted to analysis the weld forming factors. Experiments results are basically consistent with the simulation results,but also somewhat different: at the symmetrical X-shaped groove, when thegroove gap reserved5mm and above it requires swinging in the welding processwith heat input increases and overhead welding joint forming is not good, so itdoes not be adopted. And the existence of root face can improve the overheadposition welding formation due to reduced the welding pool size with the3-6mm groove gap. The influence of misalignment is agreement with the simulateresults.