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The keyhole behaviors were observed directly by laser welding experiment with quartz glass. Based on Fresnel absorption of laser beam and multi-reflection combined with volume of fluid (VOF) method, a three-dimensional mathematical model was established to study the role of welding speed on keyhole behaviors and keyhole-induced porosity formation in laser welding of aluminum alloy. The keyhole behaviors and weld pool fluid flow were discussed, and the result shows that, although the welding speed varies, the mechanism of keyhole collapse was similar. However, the keyhole stability at higher welding speed was improved due to reduced weld depth fluctuations, spatter number, keyhole depth to width ratio, and keyhole collapse frequency. Furthermore, the improved keyhole stability impeded the keyhole collapse, and the lower weld depth and solidification rate facilitated bubble escaping from the weld pool easily, which are the main factors for suppression of porosity at higher welding speed. [ABSTRACT FROM AUTHOR]

Hybrid laser-MIG (metal inert gas) welding has not been extensively applied in welding of aluminium alloy with thickness more than 10 mm because of the existence of weld defects and low joint strength. In this study, an original hybrid laser-MIG welding plus MIG welding process was developed. Double-sided hybrid laser-MIG welding method was designed and applied to the welding of 30-mm-thick Al 5083 alloy. The process was then optimized by overlaying a MIG welding upon the weld. Analysis on the weld revealed that the overlaid MIG welding played multiple roles, including making up the bead formations, eliminating the keyhole-induced porosities as well as refining grains. Along the longitudinal direction of the weld, the grains became finer from two fringes to the middle, and the mechanical properties improved accordingly. Compared with MIG welding, the hybrid laser-MIG welding plus MIG welding process showed overwhelming superiorities over the MIG welding, which will be promising in industrial applications. [ABSTRACT FROM AUTHOR]

A novel detection method of penetration status was presented for a high-power fiber laser welding. The metallic vapor and molten pool was recorded by a high-speed camera during welding process. The radiation intensity of metallic vapor, as well as the morphology of molten pool end, was calculated by image processing algorithm as image features. Four image features, the radiation intensity of metallic vapor (RIMV), the area of molten pool end (AMPE), the rear angle of molten pool end (RAMPE), and the aspect ratio of molten pool end (ARMPE), were extracted. The mean value, relative range, variation coefficient, and frequency ratio were computed for the four features to obtain the 16 characteristic parameters. Aiming at penetration status, the characteristic parameters were reorganized to form two complex indicators by the principal component analysis. Experimental results showed that the detection method was potential for online detection on the penetration status in a high-power laser welding process. [ABSTRACT FROM AUTHOR]

It is essential to acquire the electron temperature distribution of plasma plume to determine the laser energy loss caused by laser-induced plasma. In this paper, a set of synchronous high-speed cameras were positioned in different angles to obtain plasma images during CO laser welding process shielded by He-Ar mixed gas. The absorption coefficient and refractive index of incident laser was calculated based on the 3D distribution of laser-induced plasma. The results indicated that the temperature field of plasma core region was nonuniform while the temperature distribution was relatively smooth and uniform for plasma periphery portion. It was found that the shielding gas affected the 3D distribution of plasma, as well as the energy interaction between laser and base material. Laser energy loss caused by plasma increased with argon percentage in the shielding gas. Relatively, laser energy loss caused by refraction is slightly higher than that caused by absorption. [ABSTRACT FROM AUTHOR]