基于辅助电弧热力调控的高速TIG焊接熔池行为及焊缝成形缺陷抑制机理

TIG(Tungsten Inert Gas) welding is the main process to manufacture thin-walled stainless steel pipes, while its production efficiency is low, and weld appearance defects such as humping weld and undercut will appear when increasing synchronously welding current and welding speed. By analyzing the macro causes of humping weld and undercut and considering them together, the high speed tandem TIG welding process, a novel high speed welding process with high efficiency and lower energy consumption, is developed by adding an independent TIG arc to thermal- mechanically control the molten pool at its rear formed by the main TIG arc, which can suppress the formations of the humping weld and undercut in the bud. By using binocular vision sensing technology, the TIG arc shape and 3D shape of the molten pool will be obtained by image processing of 3D reconstruction and their coupling in high speed TIG welding process will be analyzed, which can offer the data for the determination of heat source model parameters in modeling high speed TIG welding process. The flow field in molten pool is monitored by Particle Image Velocimetry(PIV) technology which is the most advanced method to determine the flow field of molten pool in welding process. Based on the monitoring results, the mathematical models of high speed single TIG welding and tandem TIG welding are founded respectively to study and compare the heat and mass transfer in their molten pool. The micro mechanisms and quantitative conditions to form humping weld and undercut in high speed TIG welding are revealed and determined. The mechanisms to suppress the formations of humping weld and undercut by controlling the molten pool from both the thermal and mechanical aspects with assisted TIG arc are investigated and known. The effects of the matches of positions and energy between the main TIG arc and the assisted TIG arc on the weld appearance in high speed tandem TIG welding are also analyzed. The high speed tandem TIG welding will be developed and applied to manufacturing the thin-walled stainless steel pipes with high quality, high efficiency and low energy consumption, and the theory of high speed hybrid arc welding is improved in this project. The studies in this project can lay the solid theoretical basis and technical support for the high efficient welding production of thin-walled pipes. So the studies in this project have great theoretical significance and notable engineering application value.

TIG焊是目前工业薄壁不锈钢管主要生产工艺，但其生产效率较低，而通过同比提高焊接电流和速度来提高生产效率，则出现驼峰焊道和咬边的成形缺陷。将驼峰焊道和咬边统筹考虑、根据其产生的宏观原因，提出了列置直流双TIG电弧高速节能焊接新工艺，利用独立的辅助TIG电弧对主TIG焊接熔池进行热-力联合调控，将表面成形缺陷抑制在萌芽阶段。基于视觉传感检测分析揭示焊接速度对TIG电弧与熔池热力耦合影响规律并利用PIV技术测定熔池流场，以此为基础分别建立单、双TIG高速焊接数理模型，研究对比两工艺条件下熔池传热传质行为，全面揭示TIG高速焊中驼峰焊道和咬边形成的物理本质及独立辅助TIG电弧对熔池的热-力调控机制及其对驼峰焊道和咬边的抑制机理，并阐明主辅TIG电弧的位姿和能量匹配对高速焊接表面成形的影响规律，丰富复合电弧焊接理论并为工业薄壁不锈钢管高速焊接生产提供理论支撑，具有重要理论意义和工程应用价值。

钨极惰性气体保护（TIG）焊以成本低、过程稳定、焊缝质量高等优点而成为薄壁不锈钢工业管主要焊接生产工艺，但在高速焊接生产时易出现咬边和驼峰焊道等表面成形缺陷而限制生产效率的提高。本项目通过研究揭示咬边和驼峰焊道形成机理，开发了列置双TIG电弧高速低能耗焊接工艺，并揭示其对焊缝表面成形缺陷的抑制机理。. 根据大电流、高速TIG焊接熔池自由表面发生显著变形的物理特点，提出了随熔池自由表面变形自适应变化的电弧热-力模型，通过数值分析高速TIG焊接温度场、液态金属流动、熔池自由表面变形和液态金属凝固成形等熔池行为，定量揭示了咬边和驼峰焊道形成机理。结果表明，超过80%的液态金属沿熔池两侧向后流动，形成熔池后向流动的侧壁通道，侧壁通道内液态金属离开电弧加热区在数十毫秒内即会凝固，阻碍液态金属后向流动，是咬边和驼峰焊道形成的主要原因。利用π理论及尺度分析法分析了高速TIG焊接驼峰焊道对熔池作用力敏感性、建立了焊接变量-熔池变量-驼峰焊道形成倾向之间的定量关系，获得驼峰焊道形成的临界条件。研究结果不仅丰富了高速TIG焊接基础理论，还为新工艺的开发奠定了理论基础。. 基于高速TIG焊接咬边和驼峰焊道形成机理，提出了直流恒流列置双TIG高速焊接工艺，并数值研究了其抑制焊缝表面成形缺陷形成的机理。结果表明，列置双TIG电弧高速焊接过程中，在辅助电弧的热力联合调控作用下，辅助电弧向前的电弧力抑制了液态金属的后向流动，且形成一个稳定的隆起区域，抑制了焊缝表面成形缺陷的产生；焊接方向温度分布呈现双峰分布，抑制了熔池侧壁通道中液态金属的凝固、延长了熔池存在时间，为尾部液态金属的回流提供充足的时间并使凹陷区保持稳定，从而抑制了咬边和驼峰焊道的形成。为进一步降低焊接热输入，提出了列置脉冲调控控制双TIG（双P-TIG）电弧高速焊接新工艺，试验结果表明，相比恒流双TIG高速焊接工艺，双P-TIG焊接工艺热输入降低了14.5 %。开发的高速低能耗焊接工艺实现了薄壁不锈钢高效低能耗焊接生产。