Monitoring of hybrid laser-arc welding of galvanized steels in a gap-free lap joint configuration

Abstract

The stability of the welding process is directly related to the evolution of the highly-pressurized zinc vapor developed at the interface of two metal sheets. A large amount of spatters and blowholes tends to be produced in the instable laser welding process of galvanized steels in a gap-free lap joint configuration. In addition, the corrosion issue arising from the large at the interface of two metal sheets is another concern. Due to the intense laser-induced plume and arc light produced during the laser welding process and hybrid laser-arc welding process of galvanized steels, it is difficult to directly observe the dynamic behavior of the molten pool by human eyes.In this paper, the weld quality of lap joints obtained by laser welding, hybrid laser-GTAW welding in the common molten pool, and hybrid laser-GTAW welding in a separate molten pool, is compared. A high speed camera with the frame rate of 4000 f/ps is applied to monitor the welding process in real-time. With the help of the illumination light, the images of the molten pool are clearly acquired by the high speed camera and the patterns of fluid flow in the molten pool are identified. Mechanism of the formation of spatters is studied based on the captured images of the molten pool. It was found that when the metal fluid flow is stable, the keyhole is kept open, which provides a channel for the highly-pressurized zinc vapor to be vented out from the interface of two metal sheets. Consequently, the welding process is stable and the sound weld is achieved. However, when the fluid flow in the molten pool becomes turbulent due to the instable highly-pressurized zinc vapor, the metal fluid flow in the rear part of the molten pool is immediately transformed into the swirling status and spatially progresses forward to close the keyhole. A large amount of metal liquid is brought out of the molten pool and deposited in the welds. In addition, the relationship between the saturated pressure of zinc vapor and temperature in fusion zone is described by Clausius-Clapeyron equation. Effect of the gap between two plates on the weld quality is also investigated.The stability of the welding process is directly related to the evolution of the highly-pressurized zinc vapor developed at the interface of two metal sheets. A large amount of spatters and blowholes tends to be produced in the instable laser welding process of galvanized steels in a gap-free lap joint configuration. In addition, the corrosion issue arising from the large at the interface of two metal sheets is another concern. Due to the intense laser-induced plume and arc light produced during the laser welding process and hybrid laser-arc welding process of galvanized steels, it is difficult to directly observe the dynamic behavior of the molten pool by human eyes.In this paper, the weld quality of lap joints obtained by laser welding, hybrid laser-GTAW welding in the common molten pool, and hybrid laser-GTAW welding in a separate molten pool, is compared. A high speed camera with the frame rate of 4000 f/ps is applied to monitor the welding process in real-time. With the help of the illumination light...