Research On Numerical Simulation Of Laser Welding For Thin-walled TC4Titanium Alloy

Titanium alloys are widely used in industry and aerospace military, which havehigh strength, good corrosion resistance, high heat resistance and un-conductedmagnetic characteristics. Laser welding of titanium alloy has the followingadvantages: big depth-to-width ratio, small HAZ zone, low welding deformation andhigh efficiency.This paper studied on laser welding process of TC4titanium alloys with finiteelement software ANSYS which includes Mechanical APDL module and FLUENTmodule. The processes of keyhole forming and vanishing, temperature field of plate,thermal-stress field and deformation of circular tube were simulated. Thesesimulations are significant to realize the processes of laser welding of thin-walledTC4titanium alloy.At first, the process of keyhole forming and vanishing was simulated.Considering the molten pool free surface, evaporation, surface tension, buoyancy andgravity factors, the model used the ray trace heat source to obtain the molten poolflow process. The results showed that when the input of laser energy was relative lowto form blind keyhole, the profile of weld joint was like a ‘bowl’. On the other hand,when the input of laser energy was relative high to burn a keyhole, molten poolflowed clockwise at the bottom of the workpiece under the surface tension force. Theheat spread from the center to the edge of the workpiece resulting in that weld widthincreased at lower surface. At last it formed a ‘drum’. The absorption efficiency of theworkpiece increased as the keyhole depth increased. When the keyhole depth wasgreater than0.44mm, the absorption efficiency of workpiece increased obviously byforming ‘keyhole effect’.Secondly, the temperature field of continuous welding of titanium alloy sheet wassimulated. Comparing to different power and speed, the size of the molten pool andthe duration of high temperature were studied. It turned out that the simulation ofcross sections of weld joints was agreed with the experimental result when cone heatsource model was adopted to simulate the process of laser welding of TC4sheet. Theinitial part of the welding lacked of fusion, and it took a little of time to reach quasisteady state. For example, when the power was1000W and the welding speed was10mm/s, the positions that was1.944mm distant from the initial welding location just penetrated. It took0.53s to reach quasi steady state.Finally, the thermal-stress field and deformation were simulated during laser buttwelding of titanium alloy tube. The influence of the fixture position, power and speedon residual stress and deformation were studied. It turned out that if only welding onecircle along the tube, the initial part of the welding lacked of fusion. Repairingwelding these areas would have less effect of the whole residual stress anddeformation comparing to welding only one circle.