| Friction stir welding(FSW)of large thin-walled light alloy has been paid more and more attention.FSW is a kind of solid-phase connection technology.Because of its unique welding advantages,it has been successfully applied to the welding of large-scale rocket tanks in foreign countries.At present,the process control of FSW is mostly based on experience in large launch vehicle,spaceship and other important technical fields.In order to realize the systematization and quantification of FSW technology.Higher requirements are put forward for real-time monitoring and optimization of welding process parameters.Firstly,based on the design goal of friction stir welding robot,the actual welding condition of rocket fuel tank is analyzed,and the system structure and spindle drive of the robot are introduced in detail.Through the derivation of kinematics and dynamics of friction stir welding robot(FSWR),the motion accessibility of the robot and the loading conditions of joints are analyzed.The dynamics simulation analysis is carried out for the most complex melon-flap welding process,and the feasibility of the welding process of the system is analyzed.The heat generation model of the robot end-effector is established,and the heat generation theory of the stirring head at the robot end-effector is analyzed.A finite element model of FSW is established to simulate the welding process under all working conditions.The load field and temperature field of the welding process are analyzed by numerical simulation,and the welding defects can be predicted realistically.The material flow(MF)in the welding zone is analyzed by particle tracking technology,and the material flow law(MFL)in the whole welding process is studied.However,the simulation process found that the temperature input had a significant effect on the MF.In order to better study the MFL and optimize the welding parameters in the welding process,a temperature acquisition system at the end of the robot was designed,which was mainly used to monitor the temperature distribution in the welding zone in real time.The temperature monitoring in the welding zone was completed well through the design of two temperature acquisition systems,and the control relationship between temperature and welding parameters was established.The microscopic analysis of the welding joints revealed similar material flow patterns as numerical simulations.The material flow model(MFM)is proposed by combining the numerical simulation and the test results.The formation mechanism of the welding defects is studied by using the MFM.The analysis of the mechanical properties of the joints combined with the temperature measurement at the end of the robot determined the better welding parameters.Finally,the optimized parameters are applied to the complex curved surface welding of the space storage tank.The FSWR has carried out the welding test for the most difficult melon flap welding condition of the space storage tank.The robot trajectory planning was performed to ensure the welding accuracy.The welding result has obtained a good weld with smooth and compact surface.Therefore,the combination of real-time temperature monitoring method can effectively guide the improvement of friction stir welding process parameters,and provide effective data reference for the welding and application of aerospace fuel tanks. |
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