万瓦级光纤激光焊接过程中小孔内外等离子体研究

Plasma inside and outside keyhole during 10kW level fiber laser welding

为了进一步深入了解超高功率光纤激光深熔焊接过程中等离子体特征,试验拍摄了深熔小孔内外等离子体形态,并采用光谱仪检测分析了光纤激光致等离子体光谱信号.利用检测得到的等离子体光谱信号,计算研究了等离子体的电子温度、电子密度、电离度以及等离子体压力特征,并分析了在小孔内不同深度处及孔外等离子体的变化规律.结果表明,孔内等离子体呈现不均匀分布特征,孔外金属蒸气远多于等离子体.等离子体光谱分析显示,光纤激光致等离子体辐射出的谱线较少,即电离程度较低.进一步的计算结果同样证实了光纤激光致等离子体处于弱电离状态,但等离子体电子密度仍然处于较高水平,且等离子体瞬态压力可达到数百个大气压.

In order to understand in depth plasma behavior during ultra-high power fiber laser deep penetration welding, the plasma inside and outside the keyhole is observed, and the spectrum of fiber laser-induced plasma is measured and analyzed. Based on the measured data of plasma, the electron temperature and electron density, ionization degree and pressure are calculated, and the characteristics of plasma parameters at different values of keyhole depth and outside the keyhole are investigated. The results indicate that the distribution of plasma inside the keyhole is uneven, and the vapor plume is much bigger outside the keyhole. The spectrum of plasma show that the fiber laser-induced plasma is weakly ionized and radiates a few spectral lines. The further calculation results also confirm that the plasma induced by fiber laser is in a weakly ionized state. However, the electron density of plasma still stays in a high level, and the transient pressure of plasma is up to hundreds of times as large as atmospheric pressure.