Study On Simulation Of Slender Keyhole Transient Formation Process During Deep Penetration Laser Welding Of Thick Plate

Compared to the traditional welding processes, deep penetration laser welding hasmany advantages, such as the larger aspect ratio (bead depth/bead width), the higherwelding speed, the lower heat affected zone and the lower weld distortion. It has beenwidely used in aerospace, large ships, new energy and other fields. However, the physicalmechanism of the deep penetration laser welding is quite complex, and the currentunderstanding of some important mechanisms, such as holes stability, welding pooldynamics, coupled behaviors of gas/liquid/solid multiphase and common welding defectsis not entirely clear. As the fundamental mechanism of laser deep penetration welding,the research for transient behavior of keyhole has deep significance. Under thisbackground, supported by the National Natural Science Foundation of China (51175165)and National major projects of China (2013ZX04001131), transient formation process ofkeyhole, the behavior of metal vapor and welding pool dynamics during deep penetrationlaser welding of thick plate are studied in the thesis, according to build atwo-dimensional model with Level-Set approach and mixture model. The simulationresults are validated by “sandwich” experiment method. The main innovation and resultsare as follows:(1) A multiphase coupling model is established to simulate deep penetration laserwelding process, important interfacial phenomena, such as recoil pressure,thermocapillary force, surface tension, buoyancy force, convection and radiation, areconsidered and applied to the model. The level-set approach is adopted to track themotion of liquid/vapor (L/V) interface and the mixture model has been employed totrack the solid/liquid (S/L) interface. The initialization phase and transient equationof model are solved by Comsol multiphysics analysis software. And through thesandwich experiment, the simulation results are compared with that of experiment andfound to be in good agreement.(2) Keyhole transient formation process, temperature distribution, velocitydistribution and metal vapor behavior during deep penetration laser welding arestudied. Analysis of bending in the rear of keyhole, wall deformation, welding poorhunch and the effect of metal vapor on the keyhole wall and welding poor are basedon the results of the numerical simulation.(3) The effects of laser power and welding speed on keyhole formation processand metal vapor behavior are analyzed. (4) The effects of recoil pressure, thermocapillary force and surface tension onthe keyhole evolution and welding pool dynamics are studied.In summary, transient formation process of slender keyhole, the behavior ofmetal vapor and welding pool dynamics during deep penetration laser welding ofthick plate could be deeply understood, and these provide some theoretical referencesfor the development of proper laser welding process...