微束等离子弧焊电弧三维光谱及其抗干扰解耦

Three-Dimensional Arc Spectrum and Anti-Interference Decoupling in Micro Plasma Arc Welding

针对焊接电弧二维光谱检测温度场研究的局限性,在以共聚焦光路为关键的三维光谱检测系统基础上,检测到了三维电弧内部任意一点的光辐射强度。以电弧内部垂直于光谱检测方向且过电弧轴中心的各点的光辐射强度,通过借鉴Abel逆变换进行抗干扰解耦,恢复了电弧内部任意一点光辐射强度的相对发射系数,以解决所提出的三维光谱检测系统对电弧内部任意一点进行聚焦光谱检测的干扰问题。根据恢复得到的焊炬高度为2 mm的2 A微束等离子弧焊电弧ArⅡ特征谱线(波长为771.308与856.221 nm)的相对发射系数,通过相对谱线强度法,得到电弧的三维温度分布。进一步讨论了由此得到的电弧温度场分布和电弧形态特征,并与数值模拟计算得到的相同条件下电弧温度场进行了比较。研究表明:该研究提出的三维电弧光谱检测系统能够采集到电弧内部三维空间点的光辐射强度,虽然受到共聚焦光路的限制,采集到的电弧径向端面光谱为拖长的非轴对称圆形,但经过抗干扰解耦后的电弧径向光谱图为轴对称;虽然抗干扰解耦后得到的电弧光辐射相对发射系数分布出现一定的离轴最大化现象,但电弧光辐射强度在离轴了的电弧中心处达到了最大值,该最大光辐射强度从喷嘴至工件呈现先减后增现象,与电弧轴中心光辐射强度分布呈"双峰"态一致;并且电弧径向半径从喷嘴至工件是先减小、再保持、然后增大,其形貌为底部呈蘑菇状的准柱形,也符合相对于2 A焊接电流的短电弧(焊炬高度2 mm)的电弧形态;同时,通过电弧三维光谱检测并经过抗干扰解耦间接得到的2 A电弧的最大温度在微束等离子弧焊电弧的温度范围内,且在归一化后与数值模拟的电弧径向温度场分布较为吻合,误差较小。

In view of the limitation in temperature field measurement of welding arc by two-dimensional arc spectral method, the detection of light radiation intensity at arbitrary points within arc based on three-dimensionally spectral acquisition system with confocal optic path as the key is studied. With arc light radiation intensity at each point on the central line(this line was on an arc transverse) perpendicular to detecting direction, Abel Inverse Transform is used for a reference for anti-interference de-coupling, in order relative emission coefficients of light radiation intensity at arbitrary points within arc to be rebuilt. Interference problems resulted from focally spectral measurement at an arbitrary point within arc using the studied three-dimensionally spectral acquisition systemwere solved. According to rebuilt relative emission coefficient about Ar Ⅱ characteristic spectrum(wave length arc 771.308 and 856.221 nm) of arc in micro-plasma arc welding with 2 mm torch height and 2 A welding current, three-dimensional temperature distribution of arc was obtained by relatively spectral intensity. Furthermore, Arc temperature distribution and arc geometry achieved in this way were discussed, and temperature field was compared with the numerical calculation results under same welding conditions. It is shown in the study that the studied three-dimensionally spectral acquisition system can be effectively used to acquire light radiation at a point in arc three-dimensional space. Radially spectral maps were non-axisymmetric with elongation due to a limitation of confocal optic path. However, the radially spectral maps with anti-interference decoupling were axisymmetric. Although the distribution of arc light relative emission coefficients with interference resistance de-coupling appears off-axis phenomenon, light radiation at the off-axis arc center reached maximum. The maximum light radiation at the location from nozzle to workpiece reduced firstly and then increased. This distribution is in agreement with "two-peak" distribution of arc light radiation. Moreover, when the location of arc was from nozzle to workpiece, arc radius decreased firstly, then kept certain value followed by increasing, leading to a quasi-column profile. This arc profile agreed with short arc geometry(height of arc torch was 2 mm) relative to welding current 2 A. In addition, the maximum value indirectly detected for welding current 2 A using three-dimensionally spectral acquisition and anti-interference de-coupling is in the temperature range of arc in micro-plasma arc welding. Furthermore, radial temperature distribution detected in this study is in agreement with the results by numerical simulation for temperature field. The maximum error was only about 0.03.