Metal additive manufacturing in the commercial aviation industry: A review

Pore formation and its mitigation during hybrid laser/arc welding of advanced high strength steel

During laser or laser-arc hybrid welding process of aluminum alloy, laser power waste and keyhole fluctuation are drastic due to the shielding effect of dense plasma. Consequently, small weld penetration depth and numerous weld porosity defects are produced. In the present work, Ar-He shielding gas mixture was used to improve the weld quality of fiber laser-metal inert gas (MIG) hybrid welded aluminum alloy. The influences of Ar-He shielding gas mixtures with various He volume ratios on plasma temperature, electron density, weld penetration depth and porosity defect were investigated, respectively. The He volume ratio enough for improving the weld penetration depth and suppressing the porosity defect was 50%. The effective laser power density increased with the increasing He volume ratio, which contributed to the increase of weld penetration depth. The weld porosity defects were suppressed efficiently, since the stability of the keyhole was improved while using Ar-He shielding gas mixture.

The influences of Ar-He shielding gas mixture on welding characteristics of fiber laser-MIG hybrid welding of aluminum alloy

Various kinds of multi-electrode welding processes are used to ensure high productivity in industrial fields such as shipbuilding, automotive manufacturing and pipe fabrication. However, it is difficult to obtain the optimum welding conditions for a specific product, because there are many operating parameters, and because welding phenomena are very complicated. In the present research, the heat source characteristics of a two-electrode TIG arc were numerically investigated using a 3D arc plasma model with a focus on the distance between the two electrodes. The arc plasma shape changed significantly, depending on the electrode spacing. The heat source characteristics, such as the heat input density and the arc pressure distribution, changed significantly when the electrode separation was varied. The maximum arc pressure of the two-electrode TIG arc was much lower than that of a single-electrode TIG. However, the total heat input of the two-electrode TIG arc was nearly constant and was independent of the electrode spacing. These heat source characteristics of the two-electrode TIG arc are useful for controlling the heat input distribution at a low arc pressure. Therefore, these results indicate the possibility of a heat source based on a two-electrode TIG arc that is capable of high heat input at low pressures.

https://iopscience.iop.org/article/10.1088/0022-3727/44/21/215202/pdf

Numerical analysis of the heat source characteristics of a two-electrode TIG arc

...................................................................................................................... iii TIIVISTELMÄ ................................................................................................................... v ACKNOWLEDGEMENTS ............................................................................................. vii LIST OF PUBLICATIONS ............................................................................................... x AUTHOR’S CONTRIBUTION ........................................................................................ x LIST OF ABBREVIATIONS AND SYMBOLS ............................................................. xi PART I: OVERVIEW OF THE DISSERTATION ...................................................... xii

Usability of laser–arc hybrid welding processes in industrial applications

In carbon dioxide (CO2) laser—gas metal arc hybrid welding, a shielding gas is supplied to isolate the molten metal from the ambient air, suppress the laser-induced plasma, remove the plume out of the keyhole, and stabilize the metal transfer. In this study, a shielding gas consisting of helium, argon, and CO2 was used, and its effects on the composition of the welding phenomena, such as behaviours of laser-induced plasma generation, molten pool flow, and droplet transfer in gas metal arc welding, were investigated. High-speed video observation was used to investigate the welding phenomena inside the arc regime. Consequently, helium was found to have a dominant role in suppressing laser-induced plasma; minimum helium content at a laser power of 8 kW was suggested for laser autogenous and hybrid welding. Argon and CO2 govern the droplet transfer and arc stability. A 12 per cent addition of CO2 stabilizes the metal transfer and eliminates undercut caused by insufficient wetting of molten metal.

H. B. Chae

Papers

The effect of shielding gas composition in CO2 laser—gas metal arc hybrid welding