基于三维熔池形态的高速GMAW焊缝咬边缺陷产生机理与抑制措施的研究

With the unceasing intensification of manufacturing competition, the enterprise's demand for development of productivity with increased welding speed is becoming more and more urgent. However, if the welding speed is higher than 1m/min, the appearance of undercut defects will invoke worse weld formation. Desipite this phenomenon will severly affect welding quality and dynamic loading capacity of weld bead, the undercut formatin mechanism during high speed GMAW has not been comprehensively and profoundly revealed yet. Thus this project is aimed at studying the stress state, temperature distribution and convection flow of the liquid metal in the pool for high speed GMAW based on investigation and analysis of 3D weld pool dynamic behaviors. Then the force characteristics in weld pool on transverse/longitudinal direction are analyzed quantitatively under different welding processes, and its effects on weld pool deformation, backward molten flow behavior, and molten metal accumulation at rear are also studied. Hence 3D numberical models which reflect the correlation between molten pool behavior of high speed GMAW and undercut deffects are estabilished. The undercut forming mechanism and its influence factors are revealed and illustrated by the perspective of 3D welding pool behaviors and characterists of force in weld pool on transverse/longitudinal direction. Based on the research mentioned above, the thermal-force condition and fluid flow behaviors in the weld pool will be reformed to suppress the undercut deffects by the means of reasonable adjusting scheme for the consumable electrode arc behavior using extra TIG arc with low current.It will provide a solid foundation for implementing high speed GMAW with high welding speed, strong adaptibility and low consumption.

制造业市场竞争的加剧，迫切要求企业通过提高焊接速度来提高生产率。但当GMAW焊接速度超过1m/min时，焊缝成形变差，产生焊道咬边缺陷，严重影响焊接质量和接头承受动载荷的能力。迄今，高速GMAW焊缝咬边缺陷的形成机制，尚未得到较全面和深入的揭示。本项目基于三维熔池流体动力学形态的分析与测试，深入研究高速GMAW熔池内液态金属的受力状态、温度分布和流动情况，定量分析不同工艺条件下熔池纵/横向受力特性及其对熔池表面变形、后向液体流流态和尾部液态金属堆积等的影响，建立高速GMAW熔池形态与焊道咬边的相关性模型。从三维熔池形态与纵/横向整体受力特性的角度，揭示和阐明高速GMAW焊缝咬边缺陷的产生机制及主要影响因素。采用小电流TIG电弧调控熔化极电弧行为，改善熔池的受力受热与流动形态，抑制焊缝咬边缺陷的产生倾向。为大幅度提高GMAW焊接速度、实现高适应性而低成本的高速GMAW焊接成形奠定坚实基础。

制造业市场竞争的加剧，迫切需要企业通过提高焊接速度来提高生产率。但当GMAW焊接速度超过1m/min时，焊缝成型变差，产生焊道咬边缺陷，严重影响焊接质量和接头承受动载荷的能力。但目前，尚缺乏对高速GMAW焊缝咬边缺陷成形机制的研究。.为此，本课题首先对熔池液态金属流动与后部堆积的3D视觉检测装置进行改进。通过检测，获得了不同焊接速度下熔池上表面流场的流动数据，并对不同工艺参数下（焊接速度、焊接电流、保护气成分等）熔池金属流态对焊缝咬边缺陷的影响展开分析。发现高速GMAW焊接过程中，熔池前部液态金属的横、纵向平均流速比是决定是否产生咬边缺陷的关键性因素，一旦此比值增大，会导致液态金属铺展宽度小于熔池宽度，并滞后于熔池最宽处，从而焊趾处缺乏填充金属，诱发焊缝产生咬边缺陷。. 其次，通过定量、半定量计算不同焊接参数下熔池金属的纵向/横向受力状态以及电弧热分布的影响，提出高速GMAW焊接过程中焊缝咬边缺陷产生临界条件这一关键数据，构建出“工艺参数-熔池液态金属行为-熔池受力受热状态-咬边缺陷产生倾向”之间的定量关系。. 采用低电流TIG辅助调节高速GMAW焊接过程中受力受热状态，焊接速度可达1.5m/min。并根据TIG-MIG焊接过程的特点，基于一定的简化假设，改进复合焊两电弧间相互作用模型，建立不同电弧倾角的自适应电流密度分布模型，并结合少量试验验证，研究了不同焊接参数对电弧偏转角度的影响以及辅助TIG电弧对复合焊传热过程和焊缝成形的影响。研究表明：复合焊过程中，低电流TIG电弧在MIG焊枪前更有利于焊接过程的稳定性；前置的辅助低电流TIG电弧促使熔池前部液态金属有更充足的时间横向铺展，同时热-力重新分布导致焊缝变窄，促使液态金属填充焊趾，抑制咬边缺陷；由于复合焊的热-力重新分布，其熔池中部峰值温度以及高温停留时间反而低于常规MIG焊，有利于抑制焊缝晶粒长大及热影响区晶粒粗化。. 以上研究为大幅度提高GMAW焊速、实现高适应性低成本的高速焊接，提供了理论依据和基础数据。