Study On Temperature Field And Flow Field Of Friction Stir Welding Based On Ultrasonic Softening

Friction stir welding(FSW)has been widely used in light metal welding since the invention of the British Welding Institute(TWI)in 1991.However,due to the characteristics of its own technology,it needs a lot of axial pressure,and the mixing tool needs to withstand great resistance to advance in the welding.In order to improve the above problems,a new welding technology,Ultrasonic Vibration Friction Stir Welding(UVFSW),has been developed to improve the problem of FSW during welding by adding ultrasonic vibration to the needle.In this paper,the 6061-T6 aluminum alloy was used as the research obj ect,and the effects of ultrasonic vibration on the temperature field and flow field in the welding process are studied by using Fluent software.In order to understand the influence of the ultrasonic vibration in the welding process,a mathematical model of the friction stir welding was established firstly,and then,a mathematical model based on the ultrasonic softening effect of ultrasonic vibration friction stir welding was established by introducing a softening coefficient,which analyzed the influence of the ultrasonic vibration on the axial stress,yield stress,viscosity and heat source model in theory.Then,according to the mathematical model,the heat source model was applied to the shaft surface,the pin side and the pin bottom by using the User Defined Function(UDF)program,and the "Moving Reference Frame+Sliding Mesh Model" was selected to simulate the steady state of the friction stir welding process and get the distribution of the temperature and the plastic material flow near the mixing tool.On this basis,the axial vibration is applied to the stirring pin by using(UDF)program.Meanwhile,the "Spring Smoothing Model" in the "Dynamic Mesh Model" of Fluent software is selected to realize the numerical simulation of ultrasonic vibration friction stir welding.,The influence of ultrasonic vibration on the heat production rate,temperature field and plastic material flow in the process of welding is studied through comparative analysis.Finally,the influence of the vibration amplitude,vibration frequency,shoulder radius and the shape of the stirring pin on the heat generation rate,temperature field and flow field in the welding process is studied by using single variable method.The research work in this paper has important theoretical guiding significance and reference value for revealing the physical mechanism of ultrasonic vibration friction stir welding process,optimizing the structure design and the choice of vibration parameters.