Numerical Simulation For Dynamic Behavior Of Weld Pool And Fusion Hole In TIG Welding With Gap

In the limited back welding space and the production of important thin plate structures,one-side welding with back formation technology is required.Due to the stable arc,good weld formation and low application cost,TIG welding is widely used in the production of pressure vessels and pressure pipes,especially thin-walled structural parts with poor accessibility on the back side.It is widely used in the production of pressure vessels and pressure pipes,especially thin-walled structural parts with poor back accessibility.It is one of the most important welding methods used for one-side welding with back formation.In actual welding production,it is often necessary to form fusion holes in one-side welding with back formation technology.Fusion hole is a very important signal for welders to control the penetration of workpieces,and it contains the information about whether the workpiece is penetrated.It is difficult to completely and accurately obtain the characteristics of the internal temperature distribution of the workpiece,the flow of the weld pool and the three-dimensional morphology of the fusion hole solely by experimental means.Therefore,the numerical simulation method is used to reveal the formation mechanism of the fusion hole,quantitatively analyze the fluid flow,heat and mass transfer behavior of the weld pool and the influence of different welding parameters on the behavior of the fusion hole,which has certain theoretical significance and engineering value on optimizing the welding process and promoting intelligent control.A three-dimensional transient mass and heat transfer model for TIG welding with gap was established.Combined with the characteristics of the welding process,the arc heat flux control function is introduced,the total arc heat conservation is considered,a combined heat source model that is adaptive to the free surface deformation of the weld pool is established,and the effect of fusion hole shape on the arc heat flow is considered.Introduce effective thermal control coefficient,indirectly consider the heat loss caused by a small amount of arc heat flux passing through the gap,and establish the arc pressure and electromagnetic force model for TIG welding with gap.ICEM CFD software is used to mesh the calculation model.Through the secondary development of ANSYS FLUENT software,the free surface of the weld pool and the interface of the fusion hole are tracked by the VOF method.The temperature field and weld pool fluid flow for TIG welding with gap are numerically calculated.Analyze the formation process of the fusion hole and its influence on the mass and heat transfer of the weld pool.Fusion hole is mainly affected by arc pressure and surface tension.The appearance of fusion hole intensifies the internal flow of the weld pool,which facilitates the downward flow of fluid metal and promotes penetration.The behavior of the fusion hole is characterized according to the change of the fusion hole width,and the growth stage and critical unstable state of the fusion hole are analyzed.The process experiment was carried out to detect the formation time and width of the fusion hole,and to measure the size of the weld cross section,and compared with the calculation results to verify the accuracy of the numerical model.The effect of different gap size(0 mm,1.3 mm,1.5 mm,1.7 mm)on the behavior of weld pool and fusion hole is calculated and analyzed.The results show that the size of the upper surface of the weld pool with gap is smaller than without that,and the upper surface of the weld pool with gap shows the front low and the rear high.With the increase of the gap size,the depression of the weld pool increases because of the greater demand for fluid metal,and the time for the penetration of the workpiece and the formation of the fusion hole gradually shorten.When the reserved gap is 1.3 mm,there is a stable piercing stage of the fusion hole.The fluctuation range of the fusion hole width at this stage does not exceed 0.15mm.Under the reserved gap of 1.5 mm and 1.7 mm,the fusion hole reaches the critical unstable state after experiencing the growing stage.In this stage,the widths of the fusion hole are increased to 2.78 mm and 2.88 mm,and they will enter the unstable state.Numerical simulation is performed for 1.5 mm gap and 80-95 A welding current for TIG welding.The change of welding current mainly affects the penetration of the workpiece and the formation time of the fusion hole.The time is shortened when the current increases.In addition,the effect of welding current on the width of the fusion hole is determined by the joint action of two aspects.When the welding current is in the range of 80-95 A,there is an extreme point in the width of the fusion hole.