激光深熔焊时,产生的等离子体降低激光能量效率。等离子体中电子与正离子热运动速度的差别,导致喷嘴和工件间形成一电位差。将喷嘴和工件短路则可产生一等离子体电流。如在该回路中串联一外加电源, 等离子体电流将随外加电源电压增大呈线性增大。加入一垂直于激光束方向的磁场,则带电粒子受电磁力作用而产生偏离激光束的运动。实验采用焊接过程中提升喷嘴的方法,使深熔焊模式转变为热导焊。加人辅助电磁场可使深熔 焊焊缝长度增加, 表明驱除熔池上方等离子体后激光对工件的耦合效率提高。随磁场强度增大,深熔焊长度增大。在外加电压为25 V时,深熔焊长度最大,过低和过高的外加电压都减小深熔焊长度的增加量。

The plasma produced during deep penetration laser welding decreases the efficiency of laser energy. The difference of thermal movement speed between electrons and ions results in a voltage between the nozzle and the workpiece, and an electric current occurs if the nozzle and the workpiece are short circuited. The current increases with the increase of external voltage. The charged particles can be driven away by electric and magnetic fields if the magnetic field is applied in the direction transversal to the laser beam. In the experiment the nozzle is elevated during welding so that the welding mode changes from deep penetration welding to heat conduction welding. The increment of bead length by applying electric and magnetic fields indicates the improvement of energy efficiency if plasma above the melt pool is driven away. With stronger magnetic field, longer bead length is produced. The length of deep penetration weld reaches largest value at 25 V external voltage and decreases when higher or lower external voltage is adopted.