激光深熔焊过程中保护区特征尺寸的数值模拟

小孔效应和小孔的周期性波动是激光深熔焊过程的重要特点。小孔的波动起伏与小孔内气流压力的不断变化密切相关。这一观点通过分析小孔喷发烟流(Plume)高速摄影图像得到了证实。在测定了小孔喷发烟流的速度后,利用流体力学商用软件FLUENT建立了由保护气体、小孔喷发烟流和空气组成的组分模型,模拟了组分气流的质量分数和流场。实验结果表明,小孔喷发烟流的速度并不是一个恒定值,其数值依气流粒子团和小孔出口位置的不同而不同。在小孔喷出气流速度一定的情况下,研究了侧吹气流的流量和输送角度与影响保护区特征尺寸之间的相互关系,给出了氩气保护区和氦气特征保护区随侧吹气流参数改变的变化规律。从组分气流模拟结果看,焊接区组分以辅助气流为主,但其组分质量分数低于0.9。

Simulation of Shielding Zone Characteristic Size during Laser Deep Penetration Welding

Keyhole effect and its periodical fluctuation are important characteristics of deep penetration laser welding processing.The plume fluctuation over laser keyhole arises from the pressure fluctuation of keyhole gas.It is validated by plume behavior obtained from a series of plume images by a high-speed videography system,and the expanding speed of hot gas emitted from laser keyhole in the workpiece is determined.Then,a mathematical model for the simulation of characteristic weld gas shield phenomena during deep penetration laser welding based on a numerical solution of the equations of species,mass,momentum and energy is presented.Important differences are observed between Ar gas shield and He gas shield.All these experiments are also simulated using the 3D hydrodynamic software Fluent.It is seen that the characteristic size of argon gas shield is larger than that of helium gas shield,and the smaller the nozzle inclination angle,the larger characteristic shield size of the assist gas.The effective protection zone will be increased when the flux rate of the nozzle assistant gas is increased.The expansion speed of the plume over laser keyhole is much smaller than 150 m/s.The maximum mass fraction in the species flow zone is smaller than 0.9.