中文摘要：

针对中厚板铝合金横向焊接的技术需求和瓶颈问题,开展变极性等离子弧穿孔横焊技术的研究。以8 mm厚铝合金板为研究对象,进行常规变极性等离子弧穿孔横焊试验,发现横焊穿孔熔池很难建立。通过横焊穿孔熔池受力计算、熔化金属流动分析,探究问题产生的原因。推导出熔池背面小孔临界半径与表面张力、电弧力和重力之间的关系式。当受力状态满足关系式时,小孔熔池才能闭合、形成焊缝。依据上述理论,提出柔性变极性等离子弧。该电弧在保证穿孔前提下,通过降低电弧压力,增大小孔临界半径,促进了穿孔熔池的稳定建立。利用该技术实现了8 mm板厚2219铝合金的穿孔横向焊接,接头成形优良。焊前预热和表面氧化膜刮削可大幅度降低横焊接头气孔缺陷。

英文摘要：

Considering the imperative need of horizontal welding technology for aluminum alloys with medium thickness and its bottleneck problems, keyhole mode variable polarity plasma arc（VPPA） welding technology is studied. Ordinary VPPA horizontal welding experiments for aluminum alloy thickness 8 mm plates are carried out. It is found that the keyhole is very difficult to be established. The forces acting on keyhole and the fluid flow in weld pool are analyzed to seek the cause of the problem. An inequality equation is induced to describe the relationship of surface tension, arc pressure and the gravity. When the inequality equation is satisfied, the closure of keyhole can be achieved. Based on the above theory, a novel soft VPPA is proposed. Under the keyhole mode welding condition, the decrease of arc pressure makes the critical radius of keyhole on back side larger and promotes the stable establishment of keyhole. Using this novel technology, keyhole mode horizontal welding of 2219 aluminum alloy plates thickness 8mm is achieved and its weld formation is very good. Porosity welding defect can be eliminated mostly by preheating method and scraping oxide film before welding.