Numerical Simulation Of Weld Pool Thermodynamics Behavior In Swing Arc And Parameters Optimization

As a low cost,high efficiency and easy automation welding technology,swing arc GMAW is widely used in the welding field.Nowadays,most researches on swing arc GMAW have mainly focused on the form of droplet transition and microstructure and mechanical properties.However,the dynamic thermodynamic behavior of weld pool during the process of swing arc GMAW is rarely reported.Therefore,the numerical model of swing arc GMAW is established by ANSYS FLUENT to simulate the swing arc GMAW of different welding trajectories in the paper.The thermodynamics behavior of weld pool under different welding trajectories is studied and analyzed.It provides theoretical support for the subsequent optimization of welding process parameters.This paper selects Q235 low carbon steel as the base metal.Based on the ANSYS FLIUENT,we need to select the two-phase flow model,melting solidification model and the energy equation,use the VOF model to capture the stacking interface of high temperature liquid metal at the base metal,and simplify the metal transfer process through periodic dripping high temperature liquid metal with a certain initial velocity.We also need to consider the changes of viscosity,specific heat,thermal conductivity when the temperature of base metal changes and load the arc pressure,electromagnetic force,surface tension,buoyancy and gravity of the molten pool during welding.CSF model is used to convert surface forces(arc pressure,surface tension)into volume forces.The reliability and accuracy of the numerical model are verified by welding experiments.It is found that the longitudinal flow trend of liquid metal in the weld pool is larger than that of transverse flow.The temperature gradient is larger and the reinforcement is higher during solidification shrinkage.However,when using Z shape trajectory or triangular trajectory,the transverse flow trend of liquid metal in the weld pool is larger than that in the linear shape and the width of the weld pool is wider.Through the distribution of temperature field and flow field in the longitudinal section,we can find that the bottom temperature is higher and the vortex of bottom region is larger.Because of large current in the first trajectory,it makes vortex in the bottom of the weld pool.The current is small in the second trajectory and has little effect on the inside of the weld pool,which mainly promotes the flow of metal on the surface of the weld pool.More metal is accumulated on the sides,which is helpful to avoid undercut.Since there are many welding parameters in swing arc GMAW,it is difficult to explore the law of welding parameters on weld forming.In order to further explore the application of triangular trajectory when using ship welding,the parameters of welding are optimized by response surface method.Large current,small current,swing width and residence time are selected as variables,weld width,penetration depth and reinforcement are taken as response values,and we can analyze with Design Expert software which is used to obtain the functional relationship between response value and parameter variables.Compared with the small current,swing width and residence time,the value of large current has the greatest influence on weld penetration and is positively correlated with it.The small current,swing width and residence time all promote the weld width to a certain extent,and the large current value is positively correlated with the weld width value in a certain range,and negatively correlated with the weld width when beyond this range.The value of reinforcement is mainly affected by the value of large current.The reinforcement of the weld seam in triangle trajectory welding is negative,which can increase the capacity of enduring the dynamic load and can be used in special welding occasions.