激光焊接小孔内部三维可压缩金属蒸汽等离子体动力学数值模拟-材料加工工程专业论文.docx

华中科技大学硕士学位论文 华 中 科 技 大 学 硕 士 学 位 论 文 华中科技大学硕士学位论文 华 中 科 技 大 学 硕 士 学 位 论 文 PAGE IV PAGE IV III III Abstract The physics of deep penetration laser welding process are very complicated, and currently the dynamics of compressible vapour/plasma in keyhole during the deep penetration laser welding are still unclear. Supported by the Natural Science Foundation of China and so on, this thesis theoretically investigates the dynamics of compressible vapour/plasma in keyhole during the deep penetration laser welding by numerical simulation. The major results are listed below: Coupling considers the major important physical factors, such as heat transfer and fluid flow of weld pool, the thermodynamic effects such as evaporation, melting and solidification, and the compressibility of the vapour/plasma in the keyhole, a three-dimensional mathematical model is developed to simulate the dynamics of compressible vapour/plasma in keyhole during the deep penetration laser welding. A code is developed to solve the three-dimension compressible Euler equation with independent intellectual property rights. The software can attain some physical states of the compressible gas at all speeds, including density, pressure, velocity and internal energy and so on, and the result can reach second order accuracy. Meanwhile, some classical 1D, 2D, 3D cases including high speed, low speed and complex boundary condition cases are used to comprehensively validate the code. The dynamics of compressible vapour/plasma in keyhole during the 304 stainless steel deep penetration laser welding is numerically simulated using the model and software. The evolutions of three-dimensional distribution of density, pressure, velocity and mach number field changing with time are attained. A 304 stainless steel fiber laser welding process with laser power of 2kW, welding speed of 3m/min, and spot radius of 0.25mm is simulated and the dynamics of vapour/plasma in keyhole are deeply studied. The results show that, in t