脉冲激光与电弧力协同作用下的小电流CO2焊熔滴可控自由过渡机理研究

A new approach of controllable and free droplet transfer in CO2 gas shield welding with the current less than 100A has been proposed in this project. Mechnically speaking, the synergism of pulsed laser and arc force control is adopted. When the low-power pulsed laser irradiates the droplet, the molten metal vaporizates at some location, generating a steam reaction force which can promote the metal droplet transfer into the molten pool. Simultaneously, the welding current is reduced sharply to decrease the arc speck pressure of preventing the droplet transfer. In this manner, the droplet can be separated from the end of welding wire and transfers into the molten pool without the existence of short circuit. Therefore, the short circuiting transfer process can be transformed into the free transfer process. The new technology of CO2 welding is realized, in which the free droplet transfer with the controllable dimesion and frequency occurs under the current range from 10 to 100A. Afterwards, the mechanism of the laser action on droplets, the mechanism of the current negative impulse, the force analysis of droplets, the dynamic behavior of droplets under the synergism, and the optimal control of droplet transfer are researched by experiments and numerical simulation to prove the feasibility of the technology. The present research in this project is of great researching value, and aims to add to the existing knowledge of welding basic theory, provides a new method of the active control of droplet transfer to realize the CO2 welding with no sputter and low heat input, and provides an innovative welding method for the thin and super thin plates.

本项目提出100A以下小电流CO2焊熔滴可控自由过渡的新思路。从控制熔滴受力的角度，采用脉冲激光和电弧力控制协同作用机制。小功率脉冲激光击打熔滴局部汽化产生一个促进熔滴向熔池过渡的蒸汽反力，同时急速降低焊接电流减小阻碍熔滴过渡的电弧斑点压力，这样，熔滴将脱离焊丝末端进入熔池而不发生短路，从而把CO2焊的短路过渡过程转变为自由过渡，实现10-100A范围内任意电流下熔滴自由过渡尺寸和频率可控的全新的CO2焊接工艺。为证明此想法的可行性，采用实验与数值模拟相结合的手段系统研究激光与熔滴作用机制、电流负脉冲作用机制、熔滴受力分析、协同控制下熔滴动态行为、熔滴过渡最优控制等科学问题。本项目一方面丰富焊接基础理论知识；另一方面为熔滴过渡的主动控制提供了新的手段，能够实现无飞溅、低热输入的CO2焊接，为薄板及超薄板的焊接提供一种全新的焊接方法。因此，具有较大的研究价值。

本项目提出了100A以下小电流CO2焊熔滴可控自由过渡的新思路：采用脉冲激光和电弧力控制协同作用机制，脉冲激光产生促进熔滴过渡的蒸汽反力，电流负脉冲减小阻碍过渡的电弧斑点压力，从而把CO2焊的短路过渡转变为自由过渡。为此，采用实验与数值模拟系统研究了激光与熔滴作用机制、电流负脉冲作用、熔滴受力分析、协同控制下熔滴动态行为、熔滴过渡最优控制等科学问题。. 成功开发了功能完善、操作方便的脉冲激光与电弧力协同作用下小电流CO2焊熔滴可控自由过渡研究实验平台。采用恒流源+变速送丝策略保证了小电流焊接时弧长稳定。. 采用高速摄影研究了小电流（20-100A）CO2焊熔滴长大过程，揭示了熔滴尺寸与电流、加热时间的定量关系，建立了熔滴大小预测方法。. 研究了小电流CO2焊熔滴受力状态，揭示了电流与斑点力定量关系，获得了电弧电流与斑点力的数值曲线。理论计算表明，斑点阻力随电流增加呈平方指数增加。. 采用数值模拟从理论上研究了熔滴动态过渡过程，定量分析了各因素对熔滴过渡影响，证明了激光附加外力和电流负脉冲的电弧力调节对CO2焊熔滴过渡促进作用。结果表明，电流负脉冲迅速降低斑点阻力，熔滴形态由托起变为下垂，同时激光附加外力促进熔滴过渡。. 揭示了电流负脉冲对减少斑点力的作用，获得了电流负脉冲参数的确定原则，优化了负脉冲电流波形，实现了CO2焊电流负脉冲诱导熔滴自由过渡。. 揭示了激光与熔滴作用机理，获得了激光功率与熔滴过渡促进力关系，掌握了激光单独作用下熔滴过渡控制规律，明确了激光波形、功率、焊丝直径等与熔滴临界过渡直径的关系。. 实现了脉冲激光与电弧力协同作用CO2焊熔滴自由可控过渡。实验证明了电弧力-脉冲激光协同控制可以实现小电流CO2熔滴滴状过渡。熔滴临界过渡直径比单一电弧力调控熔滴过渡直径小20%。. 掌握了新方法的工艺特点，研究了过程稳定性、焊缝成形、工件热输入等，实现了1mm薄板良好焊接。. 本项目获得国际学术奖励1项，申请专利2项，发表论文11篇，培养硕士生4名，博士生6名。