The Simulation Of TIG Welding Pool Of TC4 Titanium Alloy With External Magnetic Field

The mass and heat transfer process of welding pool would change when the external magnetic field has been applied, the crystalline state of liquid metal also would change,thereby the quality of welding would been affected. In this paper, the TIG welding pool of TC4 titanium alloy was taken as the research object, using FLUENT software and its secondary development platform to study the effects of external magnetic field on flow field,temperature field and the shape of TIG welding pool.Firstly, we should analyze the thermal process of welding, and combine with the theory of fluid mechanics to establish the governing equations, then verified and compared with the experimental results, in addition, set appropriate control parameters, finally, we can build a mathematical model which accord with the actual welding process. The calculated and experimented results show that when the other welding parameters remain unchanged, Single increase welding current, the length, width and depth of welding pool is increased; increase the welding speed alone, the depth and width of pool is reduced, but the length increased.When the uniform constant magnetic field was applied, the flow pattern of liquid metal in the welding pool is similar under the effect of Z-axis and X-axis magnetic field, when the direction of magnetic field is positive, the fluid rotate clockwise, otherwise, rotate counterclockwise, but the center of rotation is different; the outline and temperature field of welding pool deflect according to the direction of rotation accordingly, but the deflected degree of X-axis magnetic field is greater, the value of welding pool parameters of positive and negative magnetic field is equal. When the direction of magnetic field is Y-axis, the outline and temperature field of welding pool is symmetry which is similar to the state of no magnetic field, when the direction of magnetic field is positive, two whirlpool which rotate in opposite direction is formed, otherwise, the fluid center from which liquid metal flow to the pool edge is formed at the front end of the welding pool, the value of welding pool parameters of two direction magnetic field is unequal.With the increase of constant magnetic field strength, the extent of clockwise deflectionof temperature field, especially the high temperature zone, increased gradually, the highest temperature of welding pool is gradually decreased. the length of welding pool increased and the welding width is reduced, despite the welding depth increased, the magnitude of change is negligible. In addition, the flow rate of liquid metal in the welding pool is increased as the increase of magnetic field strength, the fluid convection enhanced accordingly.When the intermittent alternative magnetic field was applied, if the frequency of alternating magnetic field changed alone, with the increase of frequency, the highest temperature of welding pool increases first and then decreases; although the length, width and depth of welding pool has the same trend of increasing first and then decreasing, the alternating frequency at which achieve extreme value is different, when the frequency is 1,5and 3, their peaks can be acquired respectively; the depth/width ratio of welding Pool is maximum when the frequency is 3, and the ratio is minimum when frequency is 5, which means that under the condition of the welding process parameters, the welding quality is the best when the frequency is 3.Based on the results of analysis of alternating frequency, subsequent studies took the intermittent and alternative magnetic field whose frequency is 3and 5 as the research object.When the alternating magnetic field strength increases alone, the highest temperature of welding pool appears the trend of increasing first and then decreasing;the highest temperature of pool is decreased as the increase of the disconnection/connection ratio of magnetic field,the change trend of the shape of welding pool is more complex, the change rule of the depth/width ratio of welding Pool is different when the control parameters vary, under the condition of frequency is 3and 5, the ratio is no longer the biggest and the smallest when the frequency is 3 and 5, therefore, When one parameter of the magnetic field frequency,magnetic field strength, the disconnection/connection ratio changes, other parameters also need to change accordingly, in other words, the control parameters of magnetic field cannot be selected independently, they should be optimized to get the maximum depth/width ratio.