在大功率激光焊接时，除了通常认为的稳定深熔焊和稳定热导焊外，作者发现在一定条件下还会出现第三种焊接过程-模式不稳定激光焊接，其基本特征是深熔焊和热导焊两种模式随机出现，熔深和熔宽相应地在大小两级跳变.综合研究了焦点位置、激光功率和焊接速度对激光焊接模式及焊缝成型的影响，得到了反映上述三种焊接过程的工艺参数范围的双U型激光焊接模式转变曲线。

We have discovered a third welding Process-unstable-mode welding (UMW)under a certain condition, apart from the already known stable deep penetration welding (DPW) and stable heat conduction welding (HCW) in a high-power laser welding. UMW has a basic feature that the two welding modes (DPW and HCW) appear intermittently with extremely varying penetration depths and welding widths. In this peper, offects of welding parameters (focal cosition, laser power and moving speed) on laser welding mode and weld forming have been comprehensively studied. Double-U curves of laser welding mode transition have been obtained, which can be used to determine the process parameters of the three mentioned welding processes.