Numerical Simulation Of Thermo-mechanical Behavior In Laser Deep Penetration Welding Of T-joint

For the Shipbuilding industry, laser-welded sandwich panels offer considerable potential advantages which combine with the characteristics of laser welding technology and sandwich structures. Laser welding technology has some advantages including that the large ratio of depth to width, reduction residual stresses, the low distortion of the finished part. These advantages satisfy the special nature and manufacturing efficiency requirements of sandwich structures, which possess a high stiffness-to-weight and strength-to-weight ratio. This project based on ANSYS parameters design language(APDL), background of light-weight shipbuilding industry, and investigation of thermal phenomena of laser full penetration welding of T-joint using technology of the finite element modeling(FEM).The research status has been studied and the adaptive models of the heat source have been concluded, especially the volumetric heat source model has been established. The temperature profile model in laser welding has been developed and the finite element program to achieve the optimal design. It lays solid foundation for thermal stress-strain simulation of laser full penetration welding. The laser weld bead profile of T-joint has been predicted and thermal stress has been simulated. The conclusions are as follows:The finite element program of temperature profile of laser deep penetration welding has been optimized though considering the solid model, meshing of finite element model and loading heat source model based on APDL. T-joint comprehensive material model has been developed and modeling process took into account the T-joint weld material properties of changing with temperature, the convection of molten pool, latent heat, and the material of radiation. As far as possible make the model close to the actual situation.Nine kinds of body heat source models for a comparative study, in which five of them are new body heat source models. Through contrast analysis showed that double ellipsoid+ cylindrical heat source combination model, cone + cylindrical body heat source improved model and rotating +cylindrical body heat source improved model can accurately simulate the process of laser deep penetration of T-joints, which the simulation results of the temperature field are agreement with the experimental weld. Further the rotating +cylindrical body heat source improved model has been validated and applying this model to simulate the temperature field of laser deep penetration welding of T-joint, the changes in the welding process and cooling process have been studied. The effect of laser power and welding speed on the three-dimensional shape of the weld pool of T-joints was investigated through simulating welding temperature field, which lays solid foundation for thermal stress-strain simulation.In order to predict weld profile of T-joints and optimize the process parameters of the laser deep penetration welding, the statistical models between parameters(laser power(P), welding speed(V) and assembly gap(G)) and the weld bead geometry of T-joints(weld penetration(WP), weld width(WW), weld binding region width(WB)) was established using response surface methodology(RSM). Then the analysis of variance is checked and these mathematical models are validated. So that the determination process of parameters of heat source model of laser deep penetration welding is become simple and effective. The effect of laser welding parameters on the weld-bead geometry indicate that for the weld penetration, laser power has a positive effect and welding speed has a negative effect while the gap growing affects WP just slightly; for the weld width, the welding speed is the most significant factor negatively affecting the WW, then is the laser power positively affecting the WW, and the perturbation of laser powder and assembly gap is positive too; for weld binding region width, all the three factors have effect on WB, and both the laser powder and assembly gap affect positively.The stress in the welding process was simulated using "Birth and Death" technology, the distribution and evolution of stress in the welding process is developed. The results showed that with the movement of weld pool, the stress of the solidified weld increases rapidly from 0, and near the weld zone and the weld binding region with high stress concentration; along thickness stress SY and longitudinal stress SZ are closer and larger than the transverse stress SX, maximum stress occurs in the heat affected zone. Further to the welding residual stresses were analyzed, the distribution of welding residual stresses indicates that the transverse stress of weld surface SX and longitudinal stress along the weld SZ are larger than along thickness stress SY, and exceed the material yield strength so that the deformation is inevitable. For the T-joint, there is also a large residual stress along the thickness direction, the weld binding region with high stress concentration.