MAG-TIG双电弧共熔池热源打底焊接自由成形研究

Study on the Back Formation of Root Welding by MAG-TIG Twin-arc Welding in Thick Plate

打底焊接是中厚板多层多道焊接中的关键环节,对接头性能有着至关重要的影响。基于船舶制造、海洋工程、重型机械等行业中厚板结构件打底焊接时存在的自动化程度低,生产效率低等问题,本试验采用熔化极活性气体保护焊-钨极氩弧焊(Metal active gas-tungsten inert gas,MAG-TIG)双电弧共熔池热源焊接技术对厚度为20 mm的Q235-B板材进行打底焊接自由成形工艺研究及机制分析,采用高速摄像系统对TIG电弧作用前后电弧等离子体行为和熔池流动形态进行观察。试验结果表明:MAG-TIG双电弧共熔池热源打底焊接时,TIG电弧对MAG电弧有电磁排斥作用的同时还对熔池流动及热量传递有调控作用;结合焊接电弧等离子体行为与熔池流动形态分析发现,打底成形稳定性最佳时,TIG电弧加速焊接熔池中液态金属向后上方流动,促进热量向后传递,使得熔池前端底部及板材钝边处液态金属减少,受力易于平衡及稳定,可获得熔透均匀、连续、稳定的打底背面成形。

Backing welding is a key procedure in thick plate multi-pass welding and has a crucial impact on the performance of weld joints. Due to the low degree of automation and low production efficiency for back welding, among shipbuilding, marine engineering, heavy machinery and other industries, the metal active gas-tungsten inert gas(MAG-TIG) twin-arc tandem root welding process on thick plate with 20 mm is carried out, welding process and weld seam forming mechanism are investigated. Furthermore, arc plasma behaviors and molten pool state are studied during interaction between metal active gas(MAG) arc and tungsten inert gas(TIG) arc plasma. The results indicate that TIG arc has regulation effect on MAG arc heat distribution when arc discharges. Combined with arc plasma behaviors and molten pool state, a result can be found that, when the bead back formation is optimum, TIG arc accelerates the weld pool to flow backwards. Thus the quantity of liquid metal is reduced at the bottom of the molten pool and at the blunt edge of the plate. At this condition, molten pool with balance stress and steady state is obtained, and a sound, uniform and stable surface appearance back weld is acquired.