Numerical Analysis On The Dynamic Behavoir Of Arc And Weld Pool By Rotating Laser +GMAW Hybrid Welding Of T Joints

Fillet joint or T-joint is essential in the application of complex welded structure.Compared with simple joint,fillet joint weld formation is more difficult to control.Compared with traditional hybrid welding,rotation laser-MIG hybrid welding can suppress the welding defect such as keyhole,humps,undercuts,etc.and improve the macrostructure and property of welded joint.Rotation of laser beam makes the physical characteristics of hybrid plasma andand flow in weld pool more complex.When welding parameters do not match well,welding defect occurs more easily.At present,researchers mainly focus on experimental research,but it is difficult to explain the multiphase multiphysics coupling process.Therefore,this project aims to study the transient behavior of arc plasma in hybrid fillet welding with high-frequency circular rotation laser beam for complex joint through the combination of numerical simulation and experimental detection based on the mechanisms of optics,electromagnetic,heat transfer and fluid dynamics.The evolutions of keyhole,thermal and velocity fields as well as their coupling behavior are illustrated and the generation mechanisms of welding defects,including pore,spatter and so on,are revealed,thus realizing the initiative adjustment and control of welding quality and increasing the stability and reliability of hybrid welding for complex joint.Based on the model calculation and experiment,the results are as follows:Considering the optimization of the shape and inclination angle of the welding wire,the numerical analysis arc model of rotating fiber laser + GMAW hybrid welding for T-joint was established.The difference of arc physical characteristics between hybrid welding and single GMAW welding was studied.The effects of rotating frequency and rotating radius on arc plasma temperature,velocity,pressure and metal vapor distribution were expounded.Studies have shown that the T-joint is affected by the geometric characteristics,the arc is more likely to start arcing on the surface of the bottom plate and the vertical plate,the arc deviates from the axis of the welding wire,and the current density at the angle between the bottom plate and the vertical plate has a significant drop;Due to the laser-induced metal vapor,the temperature and the effective current distribution radius at the tail of the hybrid welding arc is reduced from 12064 K to 7670 K,and the current density is more concentrated;With the increase of the rotation frequency of the laser beam,the time of the laser beam acting on the molten pool within a unit time decreases,the velocity of the metal vapor emitted from the keyhole decreases,and the encounter height between the arc plasma and the laser-induced metal vapor decreases;With the increase of the rotation radius,the rotation speed of the laser also increases accordingly.At the same rotation frequency,the action time of the laser on the same position of the workpiece decreases,which affects the keyhole effect caused by the laser,resulting in the decrease of the kinetic energy of the sprayed metal vapor and the decrease of the rise height of the metal vapor.On the basis of obtaining the physical characteristics and dynamic behavior characteristics of arc and photoinduced plume,the numerical analysis model of molten pool for T-joint high-frequency rotating fiber laser + GMAW hybrid welding was established.The instability of pores is the reason for the formation of pores.The hole collapses,the liquid metal is blocked in the middle of the hole,and the gas is involved,forming pores at the root of the weld.With the increase of laser power,the depth of pores increases,and the possibility of increasing the number of pores increases;In the welding of T-joint,with the increase of laser power,clockwise eddy current appears above the keyhole,which plays a positive role in inhibiting the droop of molten pool liquid metal and the formation of the edge at the welding toe of the vertical plate.However,with the increase of laser power,the fluidity of liquid metal increases,and the droop of liquid metal is aggravated by the influence of joint geometric characteristics;When the rotation frequency is 50 Hz,similar to the flow pattern of the laser hybrid welding without rotation,the liquid metal on both sides of the keyhole flows to the bottom of the keyhole along the hole wall.When the rotation frequency is too low,the keyhole moves slowly around the circle.When the keyhole rotates a circle,it is far away from the bubble position in the welding direction,and cannot merge with the bubble,so that the bubble overflows;When the rotation frequency increases to 100 Hz and 150 Hz,the circumferential direction of the keyhole moves faster,leading to the laser energy can act on the same position multiple times.The solidified bubbles can be ’ knocked out ’ again by the holes formed by the recoil pressure.Bubbles that have not yet overflowed are merged with small pores,and the gas inside the bubble overflows,and the pore defects are suppressed.However,if the frequency is too large,the laser beam moves too fast,and the reaction time of steam acting on the same position is too short,the amount of iron vapor melted and sprayed is reduced,and the depth of the keyhole is shallow.