Research And Realization Of Axial Force Control Technology In Friction Stir Welding

Friction stir welding has the characteristics of low stress,small deformation,green and low energy consumption etc.,which applies in the welding of aluminum,magnesium,copper and other non-ferrous metals increasingly.However,the mechanical properties and surface quality of FSW joints are very sensitive to the changes of process parameters and welding conditions.A lot of researches and engineering practices show that controlling and reducing the fluctuation of welding load have important practical significances and application values for enhancing the health monitoring level of the main shaft and improving the quality of the joint.This study will be based on the welding force monitoring platform to carry out the spindle downward pressure control method and the platform development work.The main research contents include:Based on the analysis of the existing downward pressure monitoring platform of friction stir welding,the finite element software is used to optimize the mechanical body of piezoelectric force sensor to make it miniaturization further.Two different control schemes are designed by combining the adjustment methods of the spindle speed and feed rate in CNC machine,and the compensation technology of machine coordinate position.They are namely the control strategies based on the downward pressure amount and the adjustable ratio.Then,the test experiments of the spindle downward pressure under different welding parameters are carried out by using the welding equipment.The relationship model between the feed rate and the welding downward pressure is established by referring to the empirical formula of the cutting force and the linear regression method.After that,the fuzzy controller of the spindle downward pressure is determined and designed by comparing with the classical PID method,adaptive control method and intelligent method.Simulink software is used to simulate the ideal friction stir welding process and the actual conditions of the downward pressure control.On the basis of that,the hardware circuit and program of the self-adjusting feed rate of welding equipment are designed,which realize the automatic look-up and fuzzy inference of the control quantity and develop the corresponding software module of the upper computer.Finally,the effectiveness of the downward pressure control method based on the feed rate trimming is verified by performing the downward pressure control tests of friction stir welding at different contour errors,which provides some technical supports for the further development of real time control of welding process.