Study on Dynamic Behaviors of Weld Pool and Keyhole in Laser Deep Penetration Welding

In order to accurately simulate the dynamic process of keyhole formation during laser deep penetration welding, a ray tracing method based on Particle level set method is proposed to describe the multiple reflections Fresnel absorption effect of keyhole wall on laser energy, and a three-phase unification mathematical model of laser keyhole welding is established to combine the effects of three dimensional transient keyhole and transient weld pool. Dynamic process of keyhole formation and its corresponding temperature and flow field distributions are obtained by numerical modeling of laser deep penetration welding process of 30CrMnSiA steel. The results shows that the depth and shape of keyhole have an obvious characteristic of periodic changes and a phenomenon of high frequency oscillations in process of laser deep penetration welding, and the high frequency oscillations of keyhole is the main factors of laser welding instability and defects forming. Through comparative analysis of the images of weld pool and keyhole obtained by the dynamic monitoring system and the macrograph of welding seam, the results show that the experiment result is in accordance with the simulation one approximately and the simulation method and the mathematical model can accurately simulate the dynamic process of keyhole formation during laser deep penetration welding.