Abstract The density gradients and flow characteristics of the gas shield during gas metal arc welding (GMAW) of DH36, higher strength ‘construction steel’, were visualised using schlieren imaging. A systematic study was undertaken to determine the effect of shielding gas flow rate, as well as changes in the nozzle stand-off and angle, on the weld quality. The schlieren images were used to validate 2D and 3D magnetohydrodynamic (MHD) finite element models of the interaction between the Ar shielding gas, the arc and the ambient atmosphere. Weld porosity levels were determined through x-ray radiography. Sufficient shielding gas coverage was provided at a minimum of 9 l/min pure Ar, irrespective of relatively large increases in the nozzle stand-off and angle. Using 80% Ar/20% CO2 shielding gas, and 86% Ar/12% CO2/2% O2 shielding gas with flux cored arc welding (FCAW-G), achieved good quality welds down to 5 l/min. The introduction of 12 l/min in production welding has been implemented with no compromise in the weld quality and further reductions are feasible.

中文翻译：

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气体保护金属电弧焊过程中保护气体覆盖的可视化和优化

摘要 DH36 高强度“建筑钢”在气体保护金属电弧焊 (GMAW) 过程中的密度梯度和流动特性使用纹影成像进行了可视化。进行了一项系统研究，以确定保护气体流速以及喷嘴间距和角度的变化对焊接质量的影响。纹影图像用于验证 Ar 保护气体、电弧和环境大气之间相互作用的 2D 和 3D 磁流体动力学 (MHD) 有限元模型。焊缝孔隙率水平通过 X 射线照相确定。无论喷嘴间距和角度有相对较大的增加，在最低 9 l/min 纯 Ar 时提供足够的保护气体覆盖。使用 80% Ar/20% CO2 保护气体，和 86% Ar/12% CO2/2% O2 保护气体与药芯电弧焊 (FCAW-G)，实现了低至 5 l/min 的优质焊接。已在生产焊接中引入 12 l/min，并没有影响焊接质量，进一步降低是可行的。