基于光谱诊断的氩-氮P-TIG焊引弧的动态电弧物理特性研究

Dynamic Diagnostic of Physical Property in P-TIG Argon-Nitrogen Shielded Arc Plasma with Optical Emission Spectrometry

焊接电弧等离子体的物理特性直接决定了焊接接头的成形形貌,分析双组分保护气体的脉冲钨极惰性气体保护焊(P-TIG)动态电弧物理特性,为深入开展混合气体保护焊的焊缝成形物理过程研究提供理论基础。氩-氮混合气体保护焊电弧具有高热特性可以增加熔深,但在焊接前混合均匀的保护气体,引弧后气体浓度会重新分布,使电弧等离子体物理特性的实时动态变化特点变得复杂。光谱诊断是电弧等离子体物理特性测量的最重要手段,但对双组分气体保护的P-TIG焊电弧特性的研究仍需深入进行,特别是对于易引起缺陷的起弧过程,其动态物理特性亟需深入分析。针对氩-氮混合气体P-TIG焊的引弧过程,以P-TIG焊产生的氩-氮双组分电弧等离子体为研究对象,提出利用窄带滤光片与CCD相结合的高速摄影实验系统采集双组分电弧等离子的动态光谱信息,获取特征谱ArⅠ794.8 nm和NⅠ904.6 nm的P-TIG焊电弧光谱强度动态分布;提出利用双元素双组分标准温度法计算P-TIG焊引弧过程中距离钨极下方1,2,3和4 mm位置处电弧等离子体的动态温度及浓度,定量分析80%Ar+20%N 2保护的P-TIG焊从引弧至电弧稳定过程的电弧等离子体物理特性实时分布。实验结果表明,80%Ar+20%N 2保护的P-TIG焊电弧强度、电弧温度及浓度的变化均与脉冲电流的变化同步,焊接电流在3 ms内达到稳定状态,而电弧等离子体的强度、温度及浓度需要更长时间达到平衡状态。从起弧到电弧等离子稳定燃烧的过程中,基值期间和峰值期间的电弧等离子体强度均呈现先升高再降低的趋势;由于阴极的热传导及电流密度的变化,使得电弧等离子体轴向位置的峰值温度及基值温度均出现迅速升高再缓慢降低的现象;由于粒子间碰撞及摩擦力的影响,使得电弧等离子体的峰值及基值期间氩的浓度均呈迅速减小再缓慢增加的趋势,且氩的浓度均低于焊前浓度。

The welding property was decided by the physical characteristic of the arc plasma,and the dynamic property of two-element arc plama which was produced by pulse tungsten inert gas welding(P-TIG)with hybrid shielding gas was analyzed,which provides a theoretical basis for further research on the physical process of weld in hybrid gas shielded welding.Argon-nitrogen arc plasma was used to improve penetration since it has high thermal property,but demixing during welding complicated its physical characteristic.Spectral diagnosis is the most important means to measure the physical characteristics of arc plasma,but the further research on the arc characteristics of P-TIG welding with hybrid sheilding gas is still needed,especially during the arc ignition time.In this paper,an argon-nitrogen arc plasma produced by P-TIG welding during arc ignition is studied,the high-speed camera experiment system is proposed to collect the dynamic spectrum information of arc plasma,and the dynamic intensity of ArⅠ794.8 nm and NⅠ904.6 nm under P-TIG welding arc was obtained;temperature and concentration of 1,2,3 and 4 mm under tungsten during arc ignition were calculated by Fowler-Milne method;and the physical characteristics of 80% Ar+20% N2 shielded P-TIG welding arc plasma were quantitatively analyzed.The results show that the change of arc intensity,temperature and concentration is synchronized with the current.The welding current reaches a stable state within 3 ms,while the intensity,temperature and concentration of the arc plasma take longer time to reach equilibrium state.From arc ignition to steady burning,the arc intensity presented a trend of increasing first and then decreasing during the base and peak period.As a result of changes in heat conduction and current density of the cathode,the peak temperature and base temperature in the axial position of arc plasma increase rapidly and then decrease slowly.Due to the impact of particles collision and friction,the concentration of argon decreases rapidly and increases slowly during both the peak and the base period of arc plasma,and is lower than the original value.