Mechanism of Porosity Formation in Laser Welding.

Abstract

This paper described a model of the porosity formation mechanism and its experimental verification in laser welding. Porosities formed in the molten zone were classified into microporosity and macroporosity according to the porosity size. Moreover, the characteristics of porosities formed in laser welding of the thermal-conductive mode and keyhole mode were investigated. Then, the validity of the proposed mechanism of porosity formation was also investigated experimentally. Based on the proposed mechanism of porosity formation, some ideas for suppressing porosity formation in high-power laser welding were shown. The results are summarized as follows. ( 1 ) Spherical porosities were mainly observed in the thermal-conductive-mode laser welding, whereas keyhole-mode laser welding results in mixed spherical-irregular porosities. Moreover, it was clarified that the formation of irregular porosities was closely related to keyhole formation in keyhole-mode welding. The characteristics of porosity formation were determined by ΔFhr [resultant force of hydraulic pressure and Frf (reaction force by pulsation of liquid surface)] and θ (making angle of Frf and ΔFhr). ( 2 ) The validity of the mechanism proposed for porosity formation became clear through the experiment. ( 3 ) According to measurement of the fluctuation of reflected light, it became clear that the porosity formation depended on the temporal and spatial fluctuations of the keyhole.