Numerical Simulation Of TA15 Titanium Alloy Components During TIG Welding

Thin-walled titanium alloy structures have been increasingly used in new type of aircrafts to improve their technical performance, decrease weight and increase the loading capability. However, serious welding residual stresses and distortion problems have restricted the wide use of such structures. With the development of computer technology, numerical simulation for welding process can be performed using FEM software, which provides support for solving various engineering problems and saves time as well. Therefore, temperature fields and stress-strain fields during TIG welding titanium alloys are simulated using FEM software and the simulated results are verified with experimental tests. Those are essential for studying the stress-strain behavior during welding and characteristic of welding distortion, optimizing the control technological parameters and improving the welding quality for titanium alloy structures. In this study, a three-dimensional finite element model is established to simulate the temperature fields and stress-strain fields of flat plate, T-joint titanium sheets and the airplane wall panel of TA15 titanium alloy during TIG welding.For the titanium flat plate, the stress distribution on the surface of the flat plate is studied. Compressive stresses occur in regions in front of the weld molten pool and heat-affected zone. Metals in the weld molten pool are in the state of zero-stress. Tensile stresses are produced in the metals behind the weld pool and far away from the weld bead. The peak value of the residual stresses occurs in the HAZ.For T-joint titanium sheets, stress-strain behavior during welding in the transverse section of the weld bead is studied. With the approaching of the heat source, weld metals gradually come into the state of plastic deformation. The compressive (negative) plastic strains are produced in the weld pool. Along with the departing of the heat source, the area of plastic deformation is enlarged and the plastic strains increase. At the residual state, the longitudinal residual stresses are much larger than the transverse residual stresses near the weld bead. The peak value of the simulated longitudinal residual stress is about 555MPa, which is lower than the yield limit of titanium alloy at room temperature. The longitudinal residual stresses on the transverse section of the titanium flat plate and T-joint titanium sheets are measured by the cutting slit method. All measured results are lower than the simulated results, which is due to the experiment method and FEM simplification.Based on the simulation of T-joint titanium sheets, temperature fields and stress-stain fields for the airplane wall panel of TA15 titanium alloy are simulated during TIG welding. According to the practical condition used in the company, the residual stress distribution and the characteristics of welding deformation are analyzed under different welding sequences, which can provide guidance to optimize the welding procedure. The analysis results indicate that the peak value of longitudinal residual stresses under end to end welding sequence is smaller. Therefore, the airplane wall panel of TA15 titanium alloy processed under end to end welding sequence can make the subsequent process easier.