辅助气体对CO_2激光焊接光致等离子体屏蔽的影响

Influence of Assistant Gases on the Shielding Thresholds of Laser Induced Plasma During High Power CO 2 Laser Penetration Welding

采用２０ｋＷＣＯ２激光加工系统焊接低碳钢，研究了辅助气体对等离子体屏蔽临界功率密度的影响。研究结果表明，辅助气体不同时等离子体屏蔽临界功率密度由小到大的排列顺序为：Ａｒ→Ｎ２→ＣＯ２→Ｈｅ。Ａｒ作为辅助气体时，等离子体屏蔽的临界功率密度可以低至１．８５×１０６Ｗ／ｃｍ２。辅助气体对等离子体屏蔽临界功率密度的影响主要取决于气体的导热性和解离能，相比而言，气体电离能的影响是次要的。采用Ａｒ作为辅助气体时，等离子体屏蔽临界功率密度低的原因主要在于Ａｒ的导热性能差，激光支持的燃烧波（Ｌａｓｅｒ－ｓｕｐｐｏｒｔｅｄＣｏｍｂｕｓｔｉｏｎＷａｖｅｓ—ＬＳＣ）波容易过热和扩展。

The influence of assistant gases on the thresholds of laser induced plasma shielding was studied by using a 20 kW CO 2 laser processing system to weld low carbon steel. The results demonstrate that the critical power densities of laser induced plasma shielding for different assistant gases are in the order from low to high values as following: Ar→N 2→CO 2→He. The plasma shielding threshold could be as low as 1.85×10 6 W/cm 2 when argon was used as the assistant gas in our experiment. The influence of gas on the threshold of plasma shielding depends mainly on the thermal conductivity and dissociation energy of gas, while the influence of ionization energy is the secondary compared to the thermal conductivity and dissociation energy. The low power density of plasma shielding in argon is dominantly due to the poor thermal conductivity of argon which causes that the LSC wave can easily overheat and propagate.