Research On Optimization And Control Method Of FSW Process Parameters For Thin-walled Metal Parts Robot

Friction stir welding as a green solid welding technology has been widely used in aerospace and automotive fields.However,there are many technological parameters involved in friction stir welding process,and the coupling relationship is more complex.The weld properties and surface quality are directly affected by the technological parameters and welding conditions.Traditional friction stir welding equipment usually uses gantry CNC welding,the equipment can also achieve a certain degree of automation,but compared to the industrial six degrees of freedom robot,the latter small size,large work space,industrial flexibility,at the same time compared to gantry CNC system low cost,so the robot friction stir welding has become a choice of welding processing.However,due to the high degree of freedom of the robot leads to a certain degree of flexibility,so it is easy to cause the axial and transverse tool deviation under the high process parameters of friction stir welding process.Therefore,in order to ensure the success rate of welding during friction stir welding of industrial robots with high degrees of freedom,more parameter states need to be monitored in the welding process to analyze the relationship between each parameter and the influence of each parameter on welding quality.In this paper,1060 thin-walled aluminum alloy was selected as the test object to explore the forming mechanism of robot friction stir welding,and the welding process parameters were controlled by monitoring and compensating process parameters,so as to achieve stable welding.The main research contents include:(1)Analysis of Robot Friction Stir Welding ProcessBy analyzing the technological parameters involved in the friction stir welding process of the robot,the influence of parameters and the main causes of defects in the friction stir welding process of the robot are explored from the two aspects of stress and heat.The friction stir welding technology based on robot is proposed,and the specimen and the mixing head are designed.Aiming at the specific thin-walled metal specimen and stirring head,the thermodynamic coupling relationship in the welding process is further analyzed,and the kinematics and dynamics modeling of the robot is carried out.(2)Optimization of Robot Friction Stir Welding Process ParametersFirst,the response surface was selected to establish the process parameter analysis based on single factor step change,and the relationship between the tool speed,welding speed and insertion depth and the pressure during the welding process was preliminarily obtained through each group of experiments.Then,the quadratic regression equation between the welding pressure and the three process parameters was established based on the experimental data of each group,and the mathematical relationship between them was obtained.Meanwhile,the influence of the process parameters on the pressure under single and multiple factors was obtained by establishing the response surface and contour analysis.It was concluded that the depth of insertion had the greatest influence on the pressure,followed by the tool speed.The least affected is welding speed.Through the quadratic regression equation established,the ideal parameters of the preset down pressure were obtained.Simulation experiments were established by ABAQUS to verify the rationality of the selection of process parameters from the temperature field.(3)Robot Friction Stir Welding Process Control StrategyIn order to ensure the good maintenance of process parameters in the welding process,firstly,the end pose and displacement compensation based on industrial 6-DOF robots were analyzed,and the robot impedance control strategy based on position adjustment was selected.Through the analysis of the traditional impedance control model,the influence relationship of each impedance parameter on the overall control effect was obtained,and based on this,the adaptive impedance control model was established.The simulation analysis was established by MATLAB,and the tracking compensation was carried out by predicting the robot displacement change trajectory,and the effect was more obvious.(4)Construction of Robot Friction Stir Welding SystemAccording to the technology scheme of robot friction stir welding,the design requirements of platform construction were proposed first.The information exchange between hardware was carried out by using TCP/IP protocol to obtain the end force state of robot in real time.The welding experiment was carried out through the robot friction stir welding platform built by ourselves,and the force signals in two states with the inability to control the actuator were compared and analyzed to further verify the effect of the control system.