The Research Of Behavior Of TIG Weld Pool Based On Free Surface Deformation

As the process of TIG welding are stable, easily controled, can automatically remove the workpiece oxidation film, suitable for all position welding and the welding quality is high and so on, it has been widely applied in industrial production. It is the ideal method for welding all kinds of non-ferrous metal and alloy, stainless steel, high temperature alloy, ultra high strength steel. As the welding production mechanization, automation and intelligent level enhances unceasingly, the requirement of welding efficiency is more and more high. Increase the welding current and welding speed is the most commonly used method to improve the welding efficiency. But the increase of welding speed can bring some welding defects. One of the most important is the bad weld formation and the phenomenon of undercut. In order to improve the weld formation of high speed welding, it firstly should understand the mechanism of poor weld. The flow behavior of the molten pool has very important effects on weld forming, while the deformation on the surface of the weld pool not only can cause the change of the current and heat flow density distribution acting on the weld pool, but also can lead to the change of heat transfer environment inside of the liquid metal, so it will affect the molten pool surface morphology, mechanical properties and surface quality of the weld and the joint. Therefore, using numerical simulation technology study the behavior of TIG weld pool based on the free surface to reveal the distribution law of flow field and temperature field, in order to provide theoretical basis for the production process of undercut and hump bead. It has great practical significance for better control the welding process, improve welding method, welding quality and welding efficiency.This paper used the finite difference method and the FLOW-3D software and its secondary development, under the condition of considering the free surface, established a fixed point and moving three dimensional transient model of TIG welding pool, the welding molten flow field and thermal field were analyzed, in order to deeply understand the fluid flow and heat transfer process inside of the weld pool and to provide theoretical basis for getting high quality low carbon steel TIG weld.The classic gaussian heat source distribution patterns of TIG welding heat source model was used in this paper. The convective heat and radiation, artifacts and outside pool of evaporative cooling were considered, and the buoyancy which drives the liquid metal to produce movement, the electromagnetic force and surface tension gradient, etc. Condering the calculation accuracy and computational efficiency, the non-uniform grid were used.Firstly, the flow field and thermal field and the evolution behavior of the free surface of fixed-point TIG welding weld pool was studied under the three kinds of conditions of the same time and different welding current, the different current and the same welding time, and the different surface tension temperature coefficient. The results showed that:when the current was same, the longer the heating time, the greater depth width ratio of molten pool, and the free surface deformation was larger; when the current was different, the larger the currrent, the free surface deformation was larger; when the surface tension temperature coefficient was different, the greater the surface tension temperature coefficient, the temperature gradient was smaller, the depth width ratio of molten pool was greater.Secondly, the flow field and thermal field and the evolution behavior of the free surface of moving TIG welding weld pool was simulated under the three kinds of conditions of the same current and different welding speed, the different current and the same welding speed, and the high-speed TIG welding. The results showed that:when the current was same, the higher the welding speed, the temperature gradient was larger, and the molten pool depth width ratio is smaller; when the welding speed was same, the higher the current, the temperature gradient was larger, and the molten pool depth width ratio was smaller, the free surface deformation was larger; when the current was great and the welding speed was high, the temperature gradient was large, and the molten pool depth width ratio was small.Lastly, the large current and high-speed TIG welding was numerically analyzed, and the formation mechanism of hump bead was studied, the influence of welding process parameters on hump bead was also studied.The above conclusions were summarized, and put forward the outlook for future work.