热丝填充对穿孔型等离子弧焊电弧形态、小孔形态及熔池流体动力学的影响机理研究

High efficiency, high-quality and low consumption is an ugent requirement for the current welding technology. Filling hot wire during keyhole plasma arc welding is a novel welding technology which is consistent with this trend of high efficiency, high-quality and low consumption. However,the influence mechanism of filling hot wire on welding arc behavior,keyhole behavior and fluid dynamics in weldpool during plasma arc welding remains unclear. Especially after filling hot wire,the keyhole behavior will be more sensitive to the change of welding process parameters,and the adjustable range of process parameters is limited. Based on the heat transfer principles and fluid mechanics principles, the influence mechanism of filling hot wire on welding arc behavior, keyhole behavior and fluid dynamics in weldpool are studied deeply by combination of numerical simulation with experimental validation. The quantitative relationship between "welding process parameters - the dynamic process of droplet transfer - keyhole behavior - fluid dynamics in weldpool - weld appearance" then will be established. The controlled pulse key-holing strategy technology is carried out in order to improve the welding quality. Research results will be helpful to describe accurately the dynamic process during keyhole plasma arc welding with filling hot wire,and results will have an important role in promoting in-depth understanding of the phenomena and laws of the welding process. At the same time,this study will provide a lot of basic data which can enrich the physical mechanism of welding heat transfer and mass transfer,and can improve its welding process reliability and stability.Therefore, this research has the important academic value and the practical significance.

高效、优质、低耗是当前制造业对焊接技术提出的迫切要求。热丝填充穿孔型等离子弧焊正是符合这一趋势的高效、优质、低耗的新型焊接工艺。但热丝填充后对穿孔型等离子弧焊的电弧形态、小孔形态及熔池流体动力学的影响机理仍不明确。尤其是热丝填充后，小孔对工艺参数的变化将更加敏感，可调裕度小。本研究拟通过数值模拟与试验验证相结合的方式，依据传热学及流体力学原理，深入研究热丝填充对电弧形态、小孔形态及熔池流体动力学的影响机理，建立"焊接规范参数-熔滴过渡-电弧形态-熔池与小孔形态-焊缝成形"之间的定量关系，开展高焊接质量的"热丝填充受控脉冲穿孔"焊接工艺研究。研究结果对于精确描述热丝填充穿孔型等离子弧焊接动态过程，深入理解焊接过程中所发生的现象和规律将具有重要推动作用，同时能提供大量的基础数据，丰富焊接传热、传质物理机制，提高其生产可靠性和稳定性。因此，研究具有重要学术价值和实际意义。

热丝填充穿孔型等离子弧焊是一种高效、优质、低耗的新型焊接工艺，但热丝填充对K-PAW的电弧形态、小孔形态及熔池流体动力学的影响机理仍不明确。.（1）开展了系列热丝填充K-PAW焊接工艺试验，获得了热丝规范参数对焊缝形貌参数和抗拉强度的影响规律，建立了热丝填充K-PAW的BP神经网络智能预测模型，焊接电流、电弧电压和焊接速度作为输入层，焊缝熔宽、焊缝熔深、焊缝余高和拉伸强度作为输出层，能方便地预测出焊缝形貌数据和抗拉强度，预测数据最大误差不超过±10%。.（2）研究了焊接电流、等离子气流量、钨极内缩量、喷嘴孔径等对K-PAW电弧形态及传热传质的影响规律。研究发现增大焊接电流，等离子弧焊接中的电弧温度、电流密度、电弧压力、等离子流速等均增大。焊接电流120A~160A时，电弧轴向电流可达108A/m2，而径向电流密度仅有106A/m2，焊接电流增大20A可增加电弧最高温度约2000K，等离子流速可增大10%-20%。等离子气流量对电弧的温度场影响不大，主要是使用等离子体流速增大。缩小喷嘴孔径，可明显增大等离子弧焊轴线速度，提高电弧最高温度与轴向温度。.（3）研究发现SIMPLEC、COUPLED等不同算法对K-PAW的电弧温度场和电弧形态的结果几乎无影响；等离子电弧对应的马赫数均小于0.3，雷诺数小于临界雷诺数2000，验证了等离子弧焊电弧不可压缩性和流动为层流。.（4）建立了热丝填充K-PAW的焊接熔池、小孔、熔滴耦合的三维瞬态模型，研究了焊接电流、送丝速度、送丝位置对小孔、熔池热场与流场的瞬态影响过程，研究发现热丝填充对小孔有明显的填充作用。0.5m/s、1.0m/s送丝速度下，熔池前方添加预热焊丝时，穿孔时间分别较不填丝焊延长7.82%、16.35%。穿孔过程中小孔壁上的最大流速及最大压力因熔滴带来的动量、热量而增大。.（5）优化了K-PAW热源模型，获得了二次变化的能量修正系数和二次衰减的电弧压力修正系数。研究发现熔滴搭桥过渡时，送丝速度为0.5m/min时，熔滴过渡频率为0.165s/滴，熔滴直径为2.47mm；送丝速度为1.0m/min时，熔滴过渡频率为0.128s/滴，熔滴直径为2.01mm。计算结果和实验结果吻合良好。.本研究获得了热丝填充对电弧形态、小孔形态及熔池流体动力学的影响机理，丰富和发展了焊接传热传质物理机制，具有重要学术价值和实际意义。