水下湿法FCAW气泡内部的熔滴、电弧与水环境持续发生互相耦合的、复杂的化学和物理作用，针对其特殊的熔滴过渡形式对焊缝质量和焊接过程稳定性形成严重制约的问题，本项目从控制熔滴受力的角度，提出一种基于脉冲电流调控的水下湿法FACW熔滴自由过渡新工艺。研究电流快速变化对熔滴形态和动态行为的热-力作用机制，揭示急速降低电流以减弱气体拖拽力和电弧力对熔滴排斥的科学依据，明确熔滴惯性动量与电磁力协同作用控制熔滴下落的机理，研究调节电流降低排斥力保证熔滴沿轴线下落的方法，获得较高频率和较小尺寸的“一脉一滴”过渡模式及脉冲参数设定规则，建立直流/脉冲电流条件下的熔滴过渡数值模型，定量分析脉冲电流作用下熔滴形成和脱落、熔滴受力、电弧形态以及气泡形态演变等物理过程，揭示该新工艺的特点及焊缝成形的规律，初步建立脉冲电流湿法FCAW熔滴可控自由过渡理论架构，为改善焊接过程稳定性和提高焊缝质量奠定基础。

For the underwater wet flux-cored arc welding (FCAW), there exist complicated and coupled physicochemical reactions between the droplets, arc, bubbles, and the water environment. The current repelled droplets transfer and short-circuit transfer seriously restrict the weld formation and welding process stability. From the angle of forces control, a new approach of controlled free flight droplet transfer based on the pulse current is proposed to solve this problem in this project. The mechanisms of the rapid changing current influencing the thermal-force conditions of the droplets are analyzed. The scientific principle of lowering the repelling forces including gas drag force and arc forces in the same time via reducing the current rapidly is investigated. The synergism of inertial momentum and increased magnetic force is studied to push the droplets downward detaching from the wire tip. The repelling forces are reduced to maintain the droplet flight paths coaxial with the wire. Subsequently “One pulse one droplet” transfer mode with higher frequency, smaller size and coaxial flight paths is realized and the responding pulse parameters are acquired. Numerical models for direct and pulse current controlled wet FCAW are both developed. Afterwards, the physical processes including droplets formation and detachment, forces on droplets, arc behaviors, and bubbles evolution, etc. are all investigated quantitatively to examine the pulse current influences. In addition, the main characteristics and weld seam formation mechanism of this new approach are investigated. The preliminary theoretical structures of this new approach are expected to be established. It provides a novel active control method of the droplet transfer and is expected to improve the welding quality, process robustness and stability with practical application value and theoretical significance.