工艺因素对熔池小孔特征行为的影响

Influence of technological factors on dynamic behavior of welding pool and keyhole in deep penetration laser welding

为了准确地模拟出激光深熔焊接中小孔的动态变化过程,根据小孔内激光能量的传输过程和吸收机制,采用光线追踪法来描述小孔对激光能量的多重反射吸收作用,建立了基于光线追踪的热源模型,分析了工艺因素对30Cr Mn Si A钢激光深熔焊接过程中瞬态小孔的深度振荡和熔池流动行为的影响。结果表明,激光焊接过程中熔池的小孔深度呈周期性变化并伴有高频振荡特征,而小孔的振荡是焊接不稳定性和缺陷形成的重要原因。而随着激光功率的增大,小孔深度增大,小孔深度达到相对稳定状态的时间缩短。小孔深度达到相对稳定状态时,小孔振荡的幅度随激光功率的增加而增大。在对不同工艺条件下熔池的温度场、流场和小孔的动态演化过程对比的基础上,进一步探索了焊缝气孔的形成机理,并提出了减少焊缝气孔和增强小孔稳定性的新思路。

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 was proposed to describe the multiple reflections Fresnel＇s absorption effect of keyhole wall on laser energy,and heat source model was developed based on ray tracing method. The effect of different welding parameters including laser power and welding speed on the depth oscillations of the transient keyhole and the fluid dynamics of the transient welding pool were studied in laser deep penetration welding process of 30 Cr Mn Si A steel. The results show that the depth and shape of the keyhole have an obvious characteristic of periodic changes with high frequency oscillations in the process of laser deep penetration welding,and the high frequency oscillation of the keyhole is the main factor of laser welding instability and defects forming. With the laser power increasing,the keyhole depth increases and the time reached steady state decreases. The oscillation range of the keyhole increases with the laser power increasing when the keyhole depth reaches steady state. Moreover,the transient evolution of the temperature field and fluid field of the welding pool and the keyhole process are analyzed under the action of different parameters, and the mechanism of porosity formation is also investigated,a new method of controlling the stability of keyhole is proposed.