高功率光纤激光焊接SUS 304 不锈钢板的过程中，熔池由于受力不平衡出现下掉，并在试件底部流动堆积，从而形成底部驼峰。采用高速摄像和“三明治”试件焊接新方法，分别从不同角度拍摄熔融金属的流动情况并从侧面直接观测小孔和熔池的变化过程。结果表明，孔内熔融金属流动的不连续和小孔前沿孔壁凸起向下移动，以及孔内金属蒸气压力导致小孔底部熔池形成多个熔滴；底部熔池表面张力和熔池的流动导致熔融金属不断向后流动从而汇聚形成驼峰；底部驼峰的形成影响熔池的流动状态，是导致焊缝表面塌陷的原因。

In the process of high power fiber laser welding of SUS 304 stainless steel plate, the dynamic pool endures imbalanced force and is very unstable. The pool is prone to droping down. The pool is droping down, which makes a flow accumulation at the bottom of the specimen, and a root humping forms. By using highspeed camera and“sandwich”new welding method, the pictures of the flow of the molten metal from different angles are taken and the longitudinal keyhole and the dynamic pool are observed. The results show that the molten metal flow is not continuous in the keyhole, the moving downward shelf on the front of the keyhole wall and the pressure of metallic vapor inside the keyhole lead to a plurality of droplet in the bottom of the pool. The surface tension and the flow of melt pool cause the backward flow of the molten metal. With the accumulation of molten metal, the root humping is formed. The root humping influences the flow state of melt pool, which results in the undercut on the weld surface.