Experimental research on the dynamic behaviors of the keyhole and molten pool in laser deep-penetration welding

Abstract

Both the morphology and temperature are two important characteristics of the keyhole and the molten pool in laser deep-penetration welding. The modified 'sandwich' method was adopted to overcome the difficulty in obtaining inner information about the keyhole and the molten pool. Based on this method, experimental platforms were built for observing the variations in the surface morphology, the longitudinal keyhole profile and the internal temperature. The experimental results of three dynamic behaviors exbibit as follows. The key factor, which makes the pool width go into a quasi-steady state, lies in the balance between the vortex and the sideways flows around the keyhole. Experimental observation shows that the keyhole goes through three stages in laser welding: the rapid drilling stage, the slow drilling stage and the quasi-steady state. The time for achieving a relative fixed keyhole depth is close to the formation time of the maximum pool width. The internal temperatures inside the keyhole and the molten pool first experience a rapid increase, then a decrease and finally go into a quasisteady state. Compared to that in the unstable stage, the liquid-metal uphill formed in the stable stage of laser welding has less influence on the internal temperature.

Effect of Laser-Matter Interaction on Molten Pool Flow and Keyhole Dynamics

“…A. 11 shows a schematic of the experimental setup. In each case, a SS304 substrate about 400 µm thick was processed with a specific combination of laser power and scanning speed.…”

“…The experimental investigations of keyhole dynamics are primarily through visualization of the keyhole shape. Optical imaging has been used most frequently to observe the keyhole dynamics from the top-view [3,5,6,7,8] and side-view [9,10,11]. Alternatively, X-ray imaging provides a unique capability to penetrate non-destructively opaque metals for in-situ observation of keyhole dynamics without disturbing the process [1,2,4,12,13,14,15,16,17].…”

Application of laser-arc hybrid welding of steel for low-temperature service

“…Therefore, X-ray filmography [103, 124, 125] with tracing particles can provide better understanding of the process. Another solution is to apply a sandwich method [126][127][128], where the steel is combined with transparent material, and that allows to study keyhole behaviour with a conventional optical high speed camera.…”

Influence of oscillating magnetic field on the keyhole stability in deep penetration laser beam welding

“…A butt configuration of 25 mm thick structural steel plate (S355J2) and quartz glass was conducted. This experimental setup has also used from several researchers to study the keyhole behavior during the laser welding such as in [19]. A diode laser with a wavelength of 808 nm and a max.…”