Study On The Mathematical Model And Multi-fields Coupling Mechanisms Of Laser-Electric/Magnetic Hybrid Welding

Laser-electric/magnetic hybrid welding can combine the advantages and also avoid the disadvantages of single-energy field welding.Therefore,they have great application values in the fields of aerospace,large ship,rail traffic,energy and high machinery welding,etc However,the physical mechanisms in laser-electric/magnetic hybrid welding process are extremely complex.Therefore,the basic theoretical problems in laser-electric/magnetic hybrid welding,such as the influence mechanism of the applied magnetic field on welding process,the coupling behaviors between the laser and the arc,and the multi-fields coupling mechanisms of the laser,the arc and the magnetic field,have not been well understood yet Centered on the above mentioned basic theories of laser-electric/magnetic hybrid welding,supported by a national 973 project,a deep and system study is made using both the methods of numerical simulations and experiments.The major findings are listed as follows?1?A three-dimensional mathematical model which can be used to simulate the solid-liquid-vapor-plasma transient coupling behaviors in laser-electric/magnetic hybrid welding is developed for the first time.The ghost-fluid based multiple-timescales stepping method is proposed.In addition,the in-house parallel computational program is developed.Thus,the difficulties that the multiphase coupling behaviors in hybrid welding are difficult to be accurately calculated for a long time is successfully broken through.Based on the developed model and numerical methods,the coupling dynamical behaviors in the laser-magnetic hybrid welding,the laser-TIG hybrid welding and the laser-TIG-magnetic hybrid welding are numerically investigated.The simulation results are well consistent with the experimental and/or generally accepted literature data?2?The influence mechanism of the applied magnetic field on weld pool behaviors in fiber laser welding of austenite stainless steel is clarified.The effect of the applied magnetic field on the weld pool inside is manifested on the behavior of the electromagnetic brake force impeding the flow of molten liquid.Under the effect of the applied magnetic field,a large thermal electromagnetic force?about 2.0 × 106 N/m3 under a magnetic field of 415 mT?occurs near the solid-liquid interface.This thermal electromagnetic force can cause semicircle and regular thermal electromagnetic convections?TEMC?,which could result in a change of laser weld microstructure.A dimensionless number R_Ti.(R_Ti=??_eSG_TB₀L???_mu_m²?,a ratio of the thermoelectric force to the fluid inertia force)which can character the intense of the TEMC is presented.The RTi can be used to evaluate to the quantitative influence of TEMC on weld microstructure.?3?The coupling dynamics of the three-dimensional keyhole,weld pool and hybrid plasma in fiber laser-TIG hybrid plasma of 316L stainless steel under multiple process parameters are numerically investigated for the first time.The simulated typical flow patterns in weld pool agree well with X-Ray transmission imaging experimental results.It is found that during the welding process,the tail of the hybrid plasma is always in high frequency oscillations with a value of several kHz.In addition,the temperature of the arc plasma tail occurs an obvious decrease?could reach more than 6000 K?,compared with that in single TIG welding.These new findings and their clarified mechanisms can rich the laser-plasma interactive theory.Furthermore,it is also found that under the effect of a laser beam with a power of 2 kW,the input power from arc to weld pool can decrease by a value of 180 W?about 9%?.?4?The dynamical behaviors and their evolution laws of the three-dimensional keyhole,weld pool,and the hybrid plasma in fiber laser-TIG-magnetic hybrid welding of 316L stainless steel are successfully simulated.The mechanism that the high-speed downward spiral movement of the arc plasma is produced and stirs the surface weld pool under the magnetic field of about 20 mT is revealed.Besides,the mechanism that the eddy electromagnetic force?can reach about 1 × 105 N/m3?produced by electric field current stirs the inner weld pool is also clarified.It is found that the lower part of the weld cross section width can increase as a maximum value of about 1.7 times with the stirring effect than that without applying a magnetic field?5?The physical image of the coupling behaviors between the multi-fields in laser-TIG-magnetic hybrid welding is built.The coupling mechanisms of the laser,the arc and the magnetic field on the hybrid plasma and weld pool are clarified.The laser-TIG-magnetic hybrid welding owns special multi-fields positive coupling advantages,except for combining the advantages of single energy field welding.The cooling effect by laser induced vapor plume can decreases the input power of arc?<9%?.When applying a magnetic field of 20 mT,a rotary dragging shear stress of about 60 N/m2 on the surface of the weld pool,and a rotary electromagnetic force of about 105 N/m3 in the inner weld pool within 2 mm depth can be induced.That increases the lower part of the weld cross section width,and promotes the weld pool temperature more uniform and the grain more fine.The positive regulation abilities for the welding process,weld appearance and microstructure and properties in multi-fields hybrid welding process can be improved due to the finding of the multi-fields coupling mechanismsThe above work,on the one hand,can provide a basis for the optimization and control of the hybrid welding process;and on the other,can provide a reference for the modelling of the other hybrid welding processes.