Comprehensive Thermal Force Analysis And Control Of Friction Stir Welding Of Spatial Curve

Friction stir welding(FSW)is a new type of solid welding process.Its welding joints are of good quality and can achieve one-time penetration on one side.No shielding gas is needed for processing.In recent years,Friction stir welding(FSW)has been applied to the manufacture of carrier tank bottoms.However,due to the structural speciality of the welding curve in the bottom of the box,the instability of the welding heat will affect the weld quality,which has become an engineering problem to be solved urgently.In this paper,according to the characteristics of different welds,it is abstracted as a specific problem.The force and heat physics in the welding process are systematically analyzed by means of simulation and physics experiments.On this basis,a downforce control scheme based on the generalized predictive algorithm is proposed.And through the simulation experiment to compare the presence of control under the pressure changes.The main research contents of this paper are as follows:(1)According to the characteristics of friction stir welding in the bottom curve of the storage tank of the carrier rocket,the weld is analyzed and abstractly designed and related simulation experiments are carried out.A fully thermodynamic coupling model of aluminum alloy friction stir welding is established by the rigid viscoplastic finite element method.The simulation of one-dimensional/two-dimensional welds was realized;thermal and physical fields of welds at different positions,changes in spatial geometry,changes in welding paths,and arc trajectories were analyzed.The results showed that the space curve weld pairs These variations,which are usually present in welding processes,are sensitive and exhibit different thermal phenomena.(2)Welding process experiments and force-heat measurements were performed on typical experimental groups in the experimental design.A thermocouple embedded stirrer head temperature measurement method was designed.The downforce was measured using a piezoelectric crystal-based tool-holder force sensor.The thermal imager was used to measure the temperature of the workpiece exposed to the air surface,verifying the accuracy of the simulation experiment..By observing and comparing the surface quality of the welded joints,the effect of welding force heat on the welding quality was analyzed.From the perspective of the force of the agitating head and the work-heat conversion of the welding process,the thermal equilibrium function of the welding force and the mechanism of force and heat were revealed.(3)Finally,from the perspective of improving the welding quality of the space curve weld,the lower pressure control strategy based on the welding speed adjustment is determined by comparing different control strategies,and the pressure model under block structure and its correction under different working conditions are established.Based on the model,a downward pressure control scheme based on the generalized predictive algorithm is proposed.Experimental tests have proved that this downforce control method has good control accuracy and real-time performance.