激光快速成形过程熔池行为的实时观察研究

通过建立近距离连续拍摄系统实现了对激光快速成形过程中熔池行为的实时观察,并采用图像分割算法获得了熔池侧视形态,结合熔覆试样的定量金相法获得的熔池前视形态,对熔池进行了定量表征。结果发现,熔池的长度和宽度与光束直径相当,熔池自由表面呈圆弧形并向外凸起,最大熔深处熔池自由表面法向和激光束轴线之间存在夹角,表明熔池向激光束轴线方向倾斜,而熔池在液态存在时间较短,例如光束直径为4mm,光束扫描速度为5mm/s时,熔池在液态存在时间小于1秒。激光熔覆区的高速摄影实验结果发现,随金属粉末的射入,熔池的几何尺寸逐渐减小,熔池后沿不断抬高,最大熔深处熔池自由表面法向和激光束轴线之间的夹角由1度左右逐渐增大到25度左右,导致熔池中局部凝固条件发生改变,从而影响到局部熔覆层的微观组织。

Research on the Molten Pool Behavior in the Process of Laser Rapid Forming through in situ Observation Technique

The close-range continuous photography h as been employed to realize in situ observation on the behavior of the molten pool in the process of laser rapid forming (LRF). The side-view shape of the molten pool is obtained by adopting the image partition technology. The molten pool is characterized quantitatively with the combination of the front-view shape obtain ed by the quantitative metallography. The results show that the length and width of the molten pool is similar to the beam diameter, and the free surface of the molten pool is a segment arc in shape and protrudes outward. There is an angle between the normal of the free surface of the molten pool at the biggest depth o f the molten pool and the laser beam axis, which indicates that the molten pool inclines to the axis of the laser beam. And the lifespan of the molten pool is s hort, for example, when the beam diameter is 4mm and the laser scanning speed is 5mm/s, it is slightly less than 1 second. By using the high-speed photography i t has been found that with the powder particles ejecting the geometric size of t he molten pool gradually decreases, the angle between the normal of the free sur face of the molten pool and the laser beam axis increases from 1 degree to 25 de gree or so, which indicates that the molten pool inclines to a great extent. It results in changing the local solidification condition of the molten pool and th e local microstructure of the cladding layer.