超声复合等离子弧的热-力特性及其对熔池穿孔行为的影响机制

Nowdays manufacturing industry has increasingly higher demands for the quality and efficiency of welding processes. For welding of middle-thickness plates in structures, plasma arc welding has potential advantages in low cost and high adaptivity. However, conventional plasma arc welding still has some problems, e.g., insufficient keyholing and penetrating ability, and weak stability of weld pool and keyhole. In this project, low power ultrasound is integrated with plasma arc to produce further enhancing effect on plasma arc and to improve its abilities of keyholing/penetrating and stable weld formation. It investigates the interaction mechanism between the ultrasonic field and the triple-constricted plasma arc, especially the micro-scale behaviors of particles (motion, collision, ionization and recombination) inside the plasma arc, and reveals the influence regularity of ultrasonic vibration on the macro-scale heat-pressure characteristics of plasma arc. The coupled model is developed for multi-physical fields such as ultrasonic field, electromagnetic field, fluid flow field and temperature field in both plasma arc and weld pool. Numerical simulation and experimental measurement are performed together to analyze the physical characteristics of plasma arc as well as the shapes and sizes of both weld pool and keyhole under the conditions with and without ultrasonic vibration. The influence of ultrasonic vibration on transient keyholing behavior of weld pool and weld formation is elucidated. The optimization and matching of ultrasonic variables and welding process parameters are achieved. The expected results will enrich the theory of welding processes, and lay solid foundation for promoting the practical applications of ultrasonic vibration assisted keyholing plasma arc welding in joining middle-thickness plates.

现代制造业对焊接成形的质量和效率提出了越来越高的要求，对于中厚板结构的焊接成形，等离子弧焊接具有成本低、适应性强等优势。但是，常规等离子弧焊接工艺存在穿孔焊透能力不足、熔池与小孔稳定性较差等问题。本项目将低功率超声与等离子弧复合，对等离子弧产生进一步的强化效应并提高其穿孔和稳定成形的能力。研究超声振动能场对等离子弧内粒子运动、碰撞、电离与复合等微观行为的作用机制，揭示超声振动对等离子弧宏观热-力特性的影响规律。建立超声能场与等离子弧/熔池内电磁场-流场-温度场的多场耦合模型；数值模拟与实验测试相结合，通过对比和分析施加超声与否时等离子弧物理特性与熔池-小孔形态的差异，阐明超声振动对熔池穿孔瞬态行为和焊缝成形的影响规律。实现超声参量与等离子弧焊接工艺参数之间的优化与匹配。预期成果将丰富焊接工艺理论，为超声辅助穿孔的等离子弧焊接新工艺在中厚板焊接成形方面的实际应用提供理论依据和技术支撑。

现代制造业对焊接成形的质量和效率提出了越来越高的要求，对于中厚板结构的焊接成形，等离子弧焊接具有成本低、适应性强等优势。但是，常规等离子弧焊接工艺存在穿孔焊透能力不足、熔池与小孔稳定性较差等问题。本项目研发了超声振动辅助穿孔等离子弧焊接新工艺(U-PAW)。U-PAW将超声工具头与钨极联结，通过钨极直接将超声振动作用于等离子弧，使低功率超声与等离子弧复合，强化了等离子弧的热力特性并提高了其穿孔和稳定成形的能力。研究了超声振动能场对等离子弧内粒子运动、碰撞、电离与复合等微观行为的作用机制，揭示了超声振动对等离子弧宏观热-力特性的影响规律。建立了超声能场与等离子弧/熔池内电磁场-流场-温度场的多场耦合模型。数值模拟与实验测试相结合，通过对比和分析施加超声与否时等离子弧物理特性与熔池-小孔形态的差异，阐明了超声振动对熔池穿孔瞬态行为和焊缝成形的影响规律。实现了超声辅助穿孔等离子弧焊接（U-PAW）工艺参数的优化与匹配。. 获得了以下重要结果与关键数据：超声振动在等离子弧介质内传播，提高了等离子弧的热导率，降低了等离子弧的电导率，导致等离子弧收缩。在所采用的工艺条件下，当焊接电流80A和离子气流量2.8L/min时，U-PAW阳极表面上的电流密度峰值由4.57A/mm2增加到6.12A/mm2；热流密度峰值由57.8W/mm2增大到69.1W/mm2；等离子弧压力峰值由1053Pa增加到1380Pa；气体剪切力峰值由62.5Pa增加到67.8Pa。小孔入口长度由6.2mm减小为6.1mm，半宽由3.8mm减小为3.25mm。在8mm厚度不锈钢工件上开展的受控脉冲穿孔U-PAW试验表明，不同基值电流持续时间时，U-PAW峰值焊接电流降低了5%-14%，同时焊接速度提高了20%；不同电流下降时间时，U-PAW峰值焊接电流降低了11%-14%，并且焊接速度提高了10%。说明U-PAW可以使用更低的峰值电流和更高的焊接速度实现稳定的穿孔焊接，从而得到焊缝深宽比更大、热影响区更小的焊接接头。. 本项目研究成果丰富了焊接工艺理论，为超声辅助穿孔等离子弧焊接新工艺在中厚板焊接成形方面的实际应用提供了理论依据和技术支撑。