| K-TIG is a new welding process based on the ordinary TIG.It has the advantages of low equipment cost,good process flexibility and high welding quality.It can achieve the effect of one side welding and two sides forming for mid-thick plate,and the production efficiency is greatly improved.At present,the researchers mainly carry out the experimental research on K-TIG welding process.There is no report on the complex physical mechanism of weld pool.In this work,based on CFD software,the K-TIG welding process is simulated,and the heat and mass transfer behavior of keyhole weld pool is analyzed.The results provide theoretical basis for the practical application of K-TIG welding.The main work and conclusions of this paper are as follows:(1)A combined heat source model suitable for K-TIG stationary welding is proposed.The heat source model is composed of two parts:the internal part is the concentrate arc heat source with high energy density and large gradient,and the surrounding part is the free arc heat source with low energy density and small gradient.CSF model is used to convert the surface heat and force into volume heat and force.A stationary K-TIG welding numerical model is constructed,and the temperature field and dynamic flow field of the coupling of keyhole and weld pool are calculated.The simulation results show that under the action of arc pressure and arc shear force,the molten metal of the bottom of the keyhole will flow upward along the keyhole wall as soon as it is melted,and there is almost no molten metal at the bottom of the pool.After reaching the edge of the pool,molten metal flows downward from the inner part of the weld pool under the action of inertia force,and then flows upward again under the action of shear stress after reaching the keyhole wall.The maximum weld pool volume is about 50mm~3.The experimental results show that the heat source model and the numerical model are effective.(2)A combined heat source model for K-TIG continuous welding is proposed.By analyzing the characteristics of continuous welding arc,the external free arc heat source is modified to a double ellipse distribution model,while the internal concentrated arc remains unchanged.The numerical model of K-TIG continuous welding is established by applying velocity to the heat source model and force source model.The simulation results show that relative movement makes the center of heat source deviate from the lowest point of the keyhole;the temperature of the weld pool presents uneven distribution from the front to the back,the isotherms at the front of the molten pool are densely distributed,the isotherms at the rear of the weld pool are sparse,and the high temperature area is large;the molten metal in the rear weld pool circulates under the action of arc force and surface tension.The fusion lines in the cross section,the beginning and end of the longitudinal section of the weld,the full penetration time,the distance of the keyhole offset center and the size of the keyhole are used to verify the calculation results.(3)The thermo-mechanical coupling numerical model of K-TIG welding is preliminarily explored.The parameters of keyhole shape are extracted from the simulation results of stationary welding,and the coupling numerical models of tungsten electrode-arc-anode boundary with different keyhole depth are constructed.The influence of the keyhole shape to the arc is studied.It is found that when the depth to width ratio of the keyhole is greater than 1,the keyhole has a compression effect on the arc;the arc pressure on the keyhole surface is not only related to the maximum flow rate of plasma,but also to the surface shape of the workpiece;the arc shear force decreases with the increase of the keyhole depth,and the distribution trend has little variation. |
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