低碳钢CO_2激光焊接光致等离子体屏蔽的实验研究

Experimental Investigation on the Plasma Shielding During High Power CO_2 Laser Welding of Steel

采用20kWCO2激光加工机焊接st37－2钢，研究了辅助气体种类、气体流量以及聚焦激光束的离焦状态对等离子体屏蔽的影响。结果表明，不同辅助气体时等离子体屏蔽临界功率密度存在很大差异，由小到大的顺序为：Ar→N2→CO2→He。He良好的控制等离子体的能力不仅在于He高的电离能不易形成LSC波，更主要地在于He良好的导热性能抑制了LSC波的扩展。增大辅助气体流量或采用负离焦均可以在一定程度上减小等离子体屏蔽对焊接过程的影响。

In this paper,the influences of assistant gas,gas flow rate and laser beam defocusing status to the plasma shielding were investigated by applying a 20 kW CO2 laser materials processing system to weld st37 - 2 steel. The results demonstrate that the critical power density of plasma shielding varies with the assistant gas used. The order of the plasma shielding threshold for different gasses is as following from low to high value:Ar→N2→CO2→He. The high ionization energy and good thermal conductivity of helium, among which the thermal conductivity is the dominant factor, contribute to its excellent specificity to suppress the laser induced plasma which cause the LSC wave can not easy to generate and propagate. Increasing gas flow rate can increase the power density of plasma shielding, and setting the beam focus under the surface of specimen can avoid plasma shielding at high power laser welding.