Effect Of The Front Trailing Ultrasonic Impact Treatment On Welding Residual Stress And Deformation

Welding as an important part of advanced manufacturing technology,has played a very important role in industrial production.However,large residual stress and deformation in the welded structure,caused by local non-uniform heating in the welding process,have a harmful impact on the use of welding structure and life expectancy.In recent years,ultrasonic impact technology in improving the fatigue strength of welded joints,and controlling welding residual stress and deformation has been widely used.In this paper,based on the ultrasonic impact technology and welding with the impact of rolling with the press,a front trailing ultrasonic impact treatment method is put forward,which implemented real-time ultrasonic impact on the weld or weld toe area behind the molten pool to control welding residual stress and deformation,to improve the microstructure and hardness of the weld.The impact head of the ultrasonic impact device is non-rigid connection with the horn,and the impact frequency of the impact head is less than that of the horn.In order to make better use of the ultrasonic impact equipment,and also in order to provide fundamental data for the SYSWELD numerical calculation,the frequency of impact head are measured.In this paper,high-speed camera method is used to record and collect impact process of impact head.The impact frequency of the impact head is obtained by MATLAB software.The results show that the impact frequency of the ultrasonic impact equipment is mainly about 50HZ under different parameters.The effect of the front trailing ultrasonic impact treatment on the welding deformation,the micro structure and the hardness of the welded joint was studied on the 3mm Q235B sheet.The results show that when the impact distance is 45mm,that means impact at high temperature,the effect of controlling the welding deformation is the most obvious,the deformation is reduced 43.3%compared with that of conventional welding.Compared with the conventional welding,the front trailing ultrasonic impact treatment plays an important role in grain refinement,and the weld grain is thinner.Moreover,it can also increase the hardness of the weld.The smaller the impact distance,the better the effect of grain refinement and hardness increasing is.The effect of the front trailing ultrasonic impact treatment on the welding residual stress was studied on the 8mm Q235B plate.It is found that the larger the impact distance is,the better the effect of controlling the residual stress is.The force load model is established by SYS WELD.The magnitude of the force load,the impact frequency,the distance between the force load and the heat source can be adjusted.The results of simulating of ultrasonic impact on the stressless plate show that the established force load model is reasonable.The mechanism of the force load model is analyzed.The front trailing ultrasonic impact treatment on the area near the weld toe of 8mm plate is numerical simulated.The simulated results show that the effect of welding residual stress is the most obvious impact at low temperature,and the residual tensile stress is converted into residual compressive stress in some areas.As the impact temperature increases,the effect of controlling the residual stress is weakened.The calculated results is consistent with experiment results measured by blind hole method.The preliminary research is also done on simulation of the front trailing ultrasonic impact treatment with the force load frequency of 50Hz and the calculated results are compared with the experimental results.Although the front trailing ultrasonic impact treatment is still in the research stage,it will be widely used in the future because of its unique advantages and comprehensive performance.