Analysis Of Heat And Fluid Flow Field In Laser Oscillating Lap Welding Of Aluminum Alloy Sheets

Under the background of global warming,saving resources and protecting the environment,lightweight design and manufacturing of automobiles have become an important standard in the manufacturing industry,which can not only reduce fuel consumption and pollution,but also improve the stability of automobiles.6016 aluminum alloy plate is relatively light in weight,high in specific strength and specific rigidity,good in formability and corrosion resistance,and is widely used for manufacturing car body parts.An automobile company used oscillating laser welding technology to weld the lap joint of 60]6 aluminum alloy sheets,and found that it was easy to form crack in welds.In order to optimize the welding process and avoid weld crack formation,it is necessary to deeply study the heat transfer process and molten pool flow behavior in laser oscillating lap welding of thin aluminum alloy sheets.Entrusted by the company,we have carried out relevant research,which is of great significance to promote the development and application of this new welding technology.A numerical analysis model for the thermal process of laser oscillating lap welding of thin aluminum alloy sheets is established.Firstly,the nonlinear transient heat conduction process is analyzed by prefabricating welds and modeling in ANSYS APDL program.The temperature fields under different m-line power,different oscillating frequency and different power modulation process parameters are calculated and verified by experiments.A group of examples is selected to show and analyze the temperature field distribution characteristics of oscillating laser lap welding of aluminum alloy sheets.Then,the numerical results under different m-line power,different oscillating frequency and different power modulation are compared.The temperature fields at the upper surface and cross section of the workpiece and the thermal cycle curves at specific points are extracted.The FLUENT software was applied to establish a numerical model of heat transfer and fluid flow behavior in the molten pool of laser oscillating lap welding of thin aluminum alloy sheets.Considering the main process characteristics,reasonable initial and boundary conditions are set,and VOF method is used to track the dynamic interface of the molten pool.The changes of the thermal field and flow field in molten pool as well as the keyhole behavior&its position in an oscillation cycle during the welding process are numerically simulated.The characteristics of the thermal field and fluid flow field in molten pool under different oscillating amplitudes are compared and analyzed.The numerical simulation results show that a relatively large change in shape and position of the keyhole occurs in one oscillation period.The whole process,from the formation of small molten pool when the laser approaches to the formation of keyhole in the molten pool when the recoil pressure due to evaporation is large enough and the change of the morphology and position of keyhole are quantitatively analyzed.