The fiber laser was used to weld austenitic stainless steel SUS304 sheet at the speed of 24 m/min. The effects of laser power, welding speed and shielding gas on humping tendency have been investigated. The melt flow in the molten pool under different welding parameters was studied by Ti tracer method and CCD visual detection system. The results show that the humping tendency is not sensitive to the laser power. The humping is formed when welding speed exceeds 18 m/min, and goes up with the increasing of welding speed. The humping tendency is completely different as changing the direction of shielding gas under constant welding speed and laser power, and it is reduced when the shielding gas direction follows the welding direction. It can be explained that, with the increasing of welding speed, the melt flow becomes fierce, and the humping tendency goes up. The weld shape turns to the £columnar weld §, when the shielding gas direction against the welding direction; the weld shape turns to the£cup weld § when the shielding gas direction follows the welding direction. The £cup weld § expanded£U area § which gentles the melt flow and reduces humping tendency. Therefore, adjusting the shielding gas direction to expand the £U area §is an effective approach to reduce the humping tendency. KEY WORDS high speed laser welding, humping tendency, melt flow in the molten pool, welding process, austenitic stainless steel
The high-speed camera was used to observe the behavior of the melt flow in the highspeed laser welding process. The humping formation and the effect of the welding speed on the humping tendency have been discussed, and the suppression methods of humping have also been studied. The results show that the humping formation undergoes three stages: nucleation stage, growth up stage and solidification stage. During the nucleation stage, the two side streams flow around the keyhole and subsequently converge at the rear of the keyhole. Finally, the wave motion of the liquid metal, which means the nucleus of the humping, is formed in the converging process. During the growth up stage, the valley of the wave is given priority to solidify, which prevents the peak liquid metal from flowing to the rear of the molten pool. The peak of the wave is filled to expand by the front liquid metal. During the solidification stage, the grown-up peak solidifies from the bottom to top, which lifts the solid-liquid interface upward, declines the contact angle, and makes it difficult for the peak liquid metal to spread. With increasing the welding speed, the distance between the converging position at the rear of the keyhole and the laser beam increases, the temperature of the liquid metal at the rear of the keyhole decreases, the surface tension goes up, the peak liquid metal is hard to spread, the humping is apt to nucleate, and humping tendency is increased. Adopting the laser with small spot diameter is helpful to shorten the distance between convergence position and laser beam, and using the trailing beam of
In this study, the high speed camera is used to observe humping formation process as well as the corresponding behaviour of the keyhole and the molten pool in the high speed laser welding with full penetration. The results show that, as the increasing of the welding speed and laser power, and the decreasing of the defocusing distance, the keyhole and molten pool behaviour changes and the humping is apt to form. Humping formation undergoes five successive physical phenomena: elongate keyhole, the lateral oscillation of the keyhole wall, local closure of the keyhole, swelling initiation and swelling evolution. Elongate keyhole is certain to lead to the lateral oscillation of the keyhole wall. Then the contact of the lateral oscillations is certain to cause the local closure of the keyhole, which gives rise to the swelling initiation. Subsequently, the swelling has two evolving modes which are 'flat out model' and 'be filled up model', and humping will form through the 'be filled up model'. The modification of the keyhole and molten pool behavior can control the swelling initiation and evolution process. Therefore, a trailing beam, adding on the oscillations of the keyhole, can modify the keyhole behaviour and resist swelling initiation. What's more, a trailing beam, adding on the back edge of the swelling, can modify the molten pool behaviour and suppress the swelling evolving into humping. Both of the two methods can suppress humping.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.
hi@scite.ai
10624 S. Eastern Ave., Ste. A-614
Henderson, NV 89052, USA
Copyright © 2024 scite LLC. All rights reserved.
Made with 💙 for researchers
Part of the Research Solutions Family.