Laser Gas Metal Arc Hybrid Welding Research Articles

Effect of leading and trailing torch configuration on mixing and fluid behavior of laser-gas metal arc hybrid welding

The paper introduces the results of mixing and fluid flow studies for full penetration laser-gas metal arc (GMA) hybrid welding with GMA leading and trailing torch configuration. The material used was austenitic stainless steel with the thickness of 10 mm. The joint configuration was butt joint without gap. It was found that the molten pool at the root side is a longer time in the molten state than the pool at the weld surface. Compared to autogeneous laser welding, the addition of GMA makes the upper bead wider. This effect is more prominent in the case of GMA trailing compared to the case of GMA leading. The simulation results also show a similar trend of bead shape change in the case of GMA leading and trailing configuration compared to the experimental ones. Mixing behavior of filler and base metal is also evaluated and compared by both experimental studies and simulations. In GMA leading configuration, the mixing is more pronounced in the upper part of the weld cross section, while in GMA trailing, the mixing is more efficient in the whole cross section compared to GMA leading case. Simulation results support this difference in mixing behavior. Laser is the main source that provides full penetration and forms a molten pool on upper and root surface. The direction of wire feeding affects the mixing behavior. In GMA leading configuration the wire droplets impinge in front of the laser beam and in the front edge of the molten pool, whereas in GMA trailing configuration, the wire droplets impinge behind the laser beam where the molten pool is fully developed. This causes the difference in mixing.

Numerical simulation of keyhole behaviors and fluid dynamics in laser–gas metal arc hybrid welding of ferrite stainless steel plates

The fluid dynamics in weld pool and keyhole behaviors in laser–gas metal arc hybrid welding play a dominant role in affecting the weld quality of ferrite stainless steel plates. In this study, a transient model is developed for numerical simulation of the keyhole dynamics and heat transfer & fluid flow in hybrid weld pool. The heat, mass and momentum transfer due to droplets as well as the interaction between laser and arc are taken into account. The formation, expansion and sustainment of keyhole in weld pool are numerically simulated, and the transient variation of keyhole is demonstrated in three stages. The weld pool and keyhole shapes and sizes, and the fluid flow and thermal field in hybrid weld pool are quantitatively analyzed. The model is validated by hybrid welding experiments on ferrite stainless steel plates. It lays foundation for optimizing the process parameters in hybrid welding.

보호가스 종류에 따른 고출력 레이저 용접특성

Laser-gas metal arc hybrid welding has been considered as an alternative process of gas metal arc welding for offshore pipe laying. Fiber delivered high power lasers which enable deep penetration welding were recently developed but high power welding characteristics were not fully understood yet. In this study, the influence of shielding gas composition on welding phenomena in high power laser welding was investigated. Bead shapes, melt ejection and dropping were observed after autogenous laser welding with 100% Ar, Ar-20% CO2, Ar-50% CO2, and 100% CO2 shielding gas. Process parameter window was widest with Ar-50% CO2 shielding gas and the penetration was deepest with 100% CO2 shielding gas. The melt dropping was not observed when Ar-50% CO2 or 100% CO2 shielding gas was supplied.

Prevention of porosity by oxygen addition in fibre laser and fibre laser–GMA hybrid welding

Prevention of porosity in partial penetration fibre laser and fibre laser–gas metal arc hybrid welding is investigated. It is found that modulation of laser power prevents porosity formation in fibre laser welding, but that this method is not effective in hybrid welding. However, the addition of a small amount of oxygen to the molten pool can prevent porosity formation in both fibre laser and hybrid welding. This is attributed to stabilisation of the keyhole. During welding, oxygen reacts with dissolved carbon to form carbon monoxide (CO) in the keyhole. The CO partial pressure in the keyhole prevents the intense interaction between laser beam and molten metal, thus stabilising the keyhole. The role of CO formation is confirmed by the enhancement of porosity suppression with increased carbon content of the base metal.

Influence of oxygen on weld geometry in fibre laser and fibre laser–GMA hybrid welding

The effect of oxygen on weld geometry during keyhole mode welding has been investigated by adding a small amount of oxygen to the shielding gas during fibre laser and fibre laser–gas metal arc hybrid welding. The results indicate that the penetration depth increases and the weld width decreases with increasing oxygen concentration. This effect is attributed to the formation of a deeper keyhole when oxygen is present. The addition of sulphur up to 1500 ppm in the molten pool has no significant effect on the penetration depth. This behaviour indicates that the Marangoni convection and surface tension are not the main reasons for the deeper weld penetration when oxygen is added to the shielding gas. The increase in the penetration depth owing to oxygen addition is consistent with the formation of CO by reaction between dissolved carbon and oxygen. Rapid generation of CO in the keyhole expands the keyhole and results in deeper weld penetration.

激光气体金属电弧复合焊接高强钢板的焊缝形成和电信号分析

激光气体金属电弧复合焊接高强钢板的焊缝形成和电信号分析

Corrosion properties of Nd:YAG laser–GMA hybrid welded AA6061 Al alloy and its microstructure

The paper presents the corrosion behaviour of the Nd:YAG laser–gas metal arc (GMA) welds of AA6061-T6 alloy. The laser–GMA hybrid welding enhances the corrosion susceptibility of AA6061 alloy. The surface morphology observation and composition analysis were investigated by the scanning electron microscopy (SEM) with energy dispersive X-ray (EDX) spectroscopy. An increasing of the precipitate phase is observed in the weld fusion zone (WFZ). The WFZ suffers more severe pitting and cracks are associated with pitting. It is proposed that the increased precipitate phase increases the galvanic corrosion couples and results in the aggravation of pitting and cracking in the WFZ.

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

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.

Use of Synergistic Effects in High Power Laser-GMA Hybrid Welding for Manufacturing of Thick Walled Structural Pipes

In the manufacturing thick structural pipes recently a new process has been developed. This Paper describes this newly discovered process called Laser Hybrid welding. In laser hybrid welding two processes i.e. laser welding and Gas Metal Arc (GMA) welding are combined together to create synergistic effects. In laser GMA hybrid welding of plates with thicknesses of up to 20 mm, the problem of pore formation and of centre rib defects occurs frequently which have, up to now, not yet been subject to detailed scientific analysis. It was the objective of this research work to reduce these weld defects by weld parameter investigations (of a geometrical and also metallurgical nature) or to even avoid them completely. It was investigated to determine the extent to which shielding gas composition, (root) gap width and misalignment of the joining partners affect the techno-mechanical properties. For this purpose, the welds were subjected to non-destructive test methods (viz. visual inspections and X-ray examinations) and also to destructive test methods (viz. transverse sections hardness measurements, tensile tests and notch bending tests). The synergistic effects have been discussed in the light of the mechanical and metallurgical characterisations of the weldments. Optimum process parameters have been evolved which could tolerate up to 0.4mm root gap and 0.8mm of misalignment without causing any centreline cracking. Combinations of helium and argon gas shielding have been found to produce porous free welds. It has been concluded that it is possible to replace submerged arc welds by laser GMA hybrid welds in the manufacturing of longitudinally welded pipes.