Study on fluid flow behavior of electromagnetic stirring welding pool
Introduction The research of welding thermal process is one of the premises of welding metallurgical analysis, welding thermo-elastoplastic analysis and automatic control of welding process. The fluid flow and heat transfer behavior of the molten pool in the TIG welding with an external longitudinal magnetic field have an important influence on the weld formation, structure and performance, and welding quality. The melting and solidification process of TIG welding with applied longitudinal magnetic field is very complicated, and the research on fluid flow and heat transfer process of TIG welding with applied longitudinal magnetic field is relatively weak. In this paper, the TIG fixed arc welding with applied longitudinal magnetic field is selected as the research object, and the variation law of the flow field, temperature field and shape of the molten pool in the TIG welding with applied longitudinal magnetic field is explored.
1 Mathematical model In the establishment of its mathematical model, this article makes the following explanations: (1) The fluid flow in the TIG welding bath with an applied longitudinal magnetic field is a laminar flow state of incompressible viscous fluid, and the fluid in the welding bath is Newtonian. The surface of the welding pool is flat. (2) During the TIG welding process with an applied longitudinal magnetic field, energy is transferred from the welding arc to the workpiece. Under the welding conditions with weak magnetic field (BO. 1T) and small welding current (IS200A), the heat flux density of the welding arc is normally Gaussian. The research confirms that the arc current density of the TIG welding arc applied with the longitudinal magnetic field on the anode surface is all distributed in the radial direction. 1 The control equation of the fluid flow and heat transfer process of the molten pool in the TIG fixed-point welding with an applied longitudinal magnetic field is: according to the analysis and calculation, the volume forces in equation (2) are: the flow field and heat transfer of the TIG molten pool with the applied longitudinal magnetic field are an instant For the state axis symmetry problem, the cylindrical coordinate system 0) is selected, and the velocity of the flow field is (k, co), as shown. The excitation coil is installed on the welding torch.
Under this condition, the boundary conditions of momentum and energy in the grate area are shown in Table 1.
Table 1 Boundary conditions of energy and momentum in the calculated area 2 TIG welding puddle fluid flow and heat transfer behavior with applied longitudinal magnetic field 2.1 Weld puddle fluid flow and heat transfer process The welding puddle flow field is shown below.
LD10CS welding pool flow field The LD10CS welding pool temperature field can be seen. Under the effect of negative surface tension temperature gradient, the liquid metal still flows in the radial outward movement direction, and the maximum flow rate appears on the surface of the welding pool; fluid loop The center of the vortex is located in the center of the semi-melted pool; the strong direct current moving along the surface of the molten pool to the edge makes the increase in the width of the welding pool much greater than the increase in depth. Shown is the temperature field of the weld pool at this time. It can be seen that the temperature distribution in the entire welding pool is relatively regular. The temperature near the center of the welding pool is higher and the edge temperature is lower. The axial temperature gradient of the liquid metal in the molten pool is larger than the radial temperature gradient, and the radial temperature change is gentler. The isotherm of the welded molten pool exhibits a wide and shallow characteristic. The flow and heat transfer process of TIG welding pool fluid is the most important difference compared with the ordinary TIG welding process without external magnetic field. Under the action of an applied longitudinal magnetic field, the liquid metal in the TIG welding pool exists around the axis of symmetry (oz The rotation speed of the shaft) is dagger. It is precisely because the liquid in the welding pool has a flow in this direction, which causes a vigorous stirring effect in the welding bath, and this effect has an important effect on the quality of the TIG welding joint with the external longitudinal magnetic field. Therefore, it is necessary to conduct a special study on this movement mode of the welding pool fluid.
It is the isokinetic line of the dagger when the welding time is Is. The direction of the dagger is perpendicular to the plane of symmetry (as shown, it is perpendicular to the plane% /), which does not exist under ordinary TIG welding conditions. It is the result of the applied longitudinal magnetic field and the unique property of fluid flow in the TIG welding culture tank with the applied longitudinal magnetic field. Therefore, the fluid flow behavior of the TIG welding pool with an applied longitudinal magnetic field is more complicated, and the difficulty of numerical analysis is greatly increased.
It can be seen that from the bottom of the welding pool to the surface of the molten pool, the rotation speed of the liquid metal relative to the axis of symmetry. Gradually increase. The constant velocity line is a semi-annular shape, and the maximum value appears near the surface center of the welding pool. The constant velocity line is denser at the bottom of the welding pool, indicating that the axial attenuation gradient of the dagger is more distributed than that of the dagger constant velocity line. For the alloy welding workpiece material, the external longitudinal magnetic field applied to the welding molten pool rotates the TIG welding arc, and at the same time, the molten pool fluid is subjected to the additional electromagnetic force, and the welding tank fluid exhibits agitated motion.
3 Conclusion The transient mathematical model of the fluid flow and heat transfer process in the molten pool of TIG fixed point welding with an external longitudinal magnetic field is established.
This model not only considers the influence of electromagnetic force and other fluid flow driving forces, but also considers the additional electromagnetic force of the applied longitudinal magnetic field to make it closer to the actual application of the applied longitudinal magnetic field TIG welding.
The introduction of an external longitudinal magnetic field has caused a fundamental change in the fluid flow state of the TIG welding pool, which is significantly different from the fluid flow of the ordinary TIG welding pool. Under the action of an external longitudinal magnetic field, the welding pool exhibits a "wide and shallow" shape; from the bottom of the molten pool to the surface, the rotational speed of the liquid metal in the molten pool relative to the axis of symmetry is gradually increased, and the Fluid near the surface of the molten pool. The speed is the largest overall. Isokinetic lines are denser at the bottom of the weld pool, ie. The axial attenuation gradient is large.
The mathematical model and numerical analysis method of TIG fluid flow with the applied longitudinal magnetic field established in this paper can accurately simulate the fluid flow and heat transfer process of the TIG welded pool with the applied longitudinal magnetic field.
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