针对中厚钢板传统背衬板手工打底焊接工艺存在的效率低、工序复杂、过程稳定 性差等问题，采用低频率、大占空比的脉冲 TIG 方法来实现无衬板 5mm 大钝边 16MnR钢 的单面焊双面成形． 利用高速摄像详细观察了焊接电弧穿过熔孔的被压缩过程，统计分析 了一定焊接速度下电弧尾焰偏转角度和长度与焊缝熔透的相关性． 实验结果表明:在一定 焊接规范下，电弧熔化钝边形成孔状熔池，穿过熔孔的电弧尾焰偏转角度和长度均与焊接 速度呈负相关，且与焊缝熔透程度约呈现正相关，通过观测电弧尾焰尺寸，可对打底焊时 焊缝的熔透程度做出预判;电弧周期性变化的热力耦合作用增强了熔池液态金属的搅拌 及对流作用，在表面张力、重力、电弧力以及气体吹力的共同作用下，熔孔侧壁上的液态金 属向熔池边缘及底部流动，增强了熔池中的热传导，能有效增加焊缝熔深．

The pulse TIG welding with low frequency and large duty cycle was used to realize single-side welding without subtrate and double-side forming of 16MnR steel plates with 5mm large blunt edge，in view of the low effi- ciency，complex process and poor stability in traditional manual welding with subtract for medium and thick plates backing welding． The compression process of welding arc passing through the molten hole was captured by a high- speed camera． And the correlation between deflection angle and length of arc tail flame and weld penetration at a certain welding speed was analyzed． The results show that a hole-shaped weld pool is formed under a certain para- meters，and the deflection angle and length of the arc tail flame passing through the hole is negatively correlated with the welding speed，and positively correlated with the weld penetration． By observing the size of the arc tail flame，the weld penetration can be estimated，and the stirring and convection of liquid in weld pool is enhanced un- der the thermo-mechanical coupling effect of periodic arc． Under the combined action of surface tension，gravity， arc force and gas blowing force，the liquid metal on the side wall of the welding hole flows to the edge and bottom， which enhances the heat conduction in the weld pool and effectively increases the weld penetration．