【作者】 姜涛；

【导师】 刘佳；

【作者基本信息】 长春理工大学 ， 机械工程， 2021， 硕士

【摘要】 近年来,随着激光焊接技术的快速发展,电、磁辅助激光焊接技术受到了国内外研究人员的广泛重视。在激光焊接中引入电、磁场能够控制等离子体形成和影响熔池流动,从而对焊缝形貌、气孔缺陷、接头强度及焊接过程的稳定性起到改善和促进作用。本文从电场与激光焊接等离子体的相互作用角度出发,解释了电场对激光焊接熔池流动的影响机理;同时针对磁场对熔池流动、焊缝形貌、气孔缺陷的影响机制出发,采用数值模拟与实验相结合的方式揭示了磁场强度对于焊接接头影响的内在联系。主要研究工作如下:(1)搭建了电场辅助激光焊接实验的平台,在电场反接情况下(板材接高电势、激光头接低电势)发现大量自由电子向下运动聚集在匙孔内部,影响匙孔波动行为,导致焊接接头质量不稳定。在此基础上改变电场方向,探究电场强度对焊缝横截面形貌、气孔率以及焊接接头力学性能的影响规律,根据等离子体的带电性质建立了带电粒子在电场中运动的二维模型,从电场对于等离子体运动影响的角度出发来解释电场对焊接接头的影响机制,实际试验与仿真结果表明电场会影响等离子体中自由电子的运动,改变了匙孔上方以及喷嘴处的电子浓度,影响激光的散射和吸收,随着施加电压的增大焊缝熔深、结合面宽度、接头强度呈现出的变化规律相同,均是先增大后减小,焊缝熔宽则随着电压的增大持续增大,同时其焊缝内部气孔率升高。在施加电压为200V时,焊接质量最优。继续增大板材与喷嘴之间的电压后,发现空气被击穿,回路内产生电流,经计算随着施加电压的增加,喷嘴与板材之间电势差降低,因此焊缝形貌、气孔率、拉伸强度以及等离子体特征的变化规律均与施加正向电场时的相反。(2)搭建了磁场辅助激光焊接实验平台,研究了磁场强度对焊缝横截面形貌、气孔率的影响规律,研究表明磁场能够增大焊缝熔深和结合区宽度,减小熔宽,焊缝形貌由“酒杯状”向“V”字型转变,但同时会导致焊缝气孔率升高。基于流体传热和流体流动的理论,建立了磁场辅助激光焊接的熔池流动模型,针对磁场强度对激光焊缝横截面形貌的影响规律,主要从磁场强度对熔池流动行为影响的角度出发模拟了不同磁场强度条件下熔池温度场分布和流场分布,通过实际试验与理论分析可知磁场作用下熔池内所产生的洛伦兹力会抑制熔池的流动,导致焊缝形貌、气孔率发生变化。仿真结果与实验结果吻和较好。更多还原

【Abstract】 In recent years,with the rapid development of laser welding technology,electric and magnetic assisted laser welding technology has been widely valued by researchers at home and abroad.The introduction of electric and magnetic fields in laser welding can control the formation of plasma and affect the flow of molten pool,thus improving and promoting the weld morphology,porosity defects,joint strength and the stability of welding process.In this paper,from the perspective of the interaction between electric field and laser welding plasma,the influence mechanism of electric field on the flow of laser welding pool is explained;at the same time,according to the influence mechanism of magnetic field on the flow of laser welding pool,weld morphology and porosity defects,the internal relationship of the influence of magnetic field intensity on the welded joint is revealed by combining numerical simulation with experiment.The main research work is as follows(1)The experimental platform of electric field assisted laser welding was built.In the case of electric field reverse connection(plate connected with high potential,laser head connected with low potential),it was found that a large number of free electrons moved downward and gathered in the keyhole,which affected the keyhole fluctuation behavior and led to the instability of welding joint quality.On this basis,the influence of electric field intensity on weld cross-section morphology,porosity and mechanical properties of welded joint was explored by changing the direction of electric field.According to the charged nature of plasma,a two-dimensional model of particle motion in electric field was established.The influence mechanism of electric field on welded joint was explained from the perspective of the influence of electric field on plasma motion.The actual test and simulation results were compared The results show that the electric field can affect the movement of free electrons in the plasma,change the electron concentration above the keyhole and at the nozzle,and affect the laser scattering and absorption.With the increase of applied voltage,the weld penetration,joint width and joint strength show the same change law,which first increases and then decreases,while the weld width continuously increases with the increase of applied voltage,and the cross section of the weld increases The porosity increased.When the applied voltage is 200 V,the welding quality is the best.After increasing the voltage between the plate and the nozzle,it is found that the current is generated in the loop.According to the calculation,with the increase of the applied voltage,the potential difference between the nozzle and the plate decreases,so the variation laws of weld morphology,porosity,tensile strength and plasma characteristics are opposite to those of the positive electric field.(2)The results show that the magnetic field can increase the weld penetration and the width of the bonding zone,reduce the weld width,and the weld morphology changes from "wine cup" to "V" shape,but at the same time,it will lead to the increase of the weld porosity.Based on the theory of fluid heat transfer and fluid flow,the molten pool flow model of magnetic field assisted laser welding is established.According to the influence of magnetic field intensity on the cross-section morphology of laser weld,the temperature field and flow field distribution of molten pool under different magnetic field intensity are simulated from the perspective of the influence of magnetic field intensity on the flow behavior of molten pool.The magnetic field distribution can be seen from the actual test and theoretical analysis The Lorentz force generated in the molten pool will inhibit the flow of the molten pool,resulting in the change of weld morphology and porosity.The simulation results are in good agreement with the experimental results.更多还原