Multiple Reflections and Fresnel Absorption of Gaussian Laser Beam in an Actual 3D Keyhole during Deep-Penetration Laser Welding

Xiangzhong Jin,Licheng Zeng,Yuanyong Cheng,Yufeng Zou,Honggui Zhang

doi:10.1155/2012/361818

Abstract

In deep penetration laser welding, a keyhole is formed in the material. Based on an experimentally obtained bending keyhole from low- and medium-speed laser penetration welding of glass, the keyhole profiles in both the symmetric plane are determined by polynomial fitting. Then, a 3D bending keyhole is reconstructed under the assumption of circular cross-section of the keyhole at each keyhole depth. In this paper, the behavior of focused Gaussian laser beam in the keyhole is analyzed by tracing a ray of light using Gaussian optics theory, the Fresnel absorption and multiple reflections in the keyhole are systematically studied, and the laser intensities absorbed on the keyhole walls are calculated. Finally, the formation mechanism of the keyhole is deduced.

Highlights

When laser beam with high laser intensity irradiates work piece, the material is vaporized, recoil pressure is produced, and a keyhole is formed in the material
Laser beam can directly enter the keyhole and propagate in the keyhole by means of multiple reflections on the keyhole wall, and the laser energy is absorbed through the Fresnel absorption
Using geometrical optics theory, Jin et al traced a ray of light in the keyhole and calculated the laser intensity absorbed on the keyhole wall in the symmetrical plane including laser beam and welding velocity through the Fresnel absorption

Summary

Introduction

When laser beam with high laser intensity irradiates work piece, the material is vaporized, recoil pressure is produced, and a keyhole is formed in the material. In practical deep penetration laser welding, especially in high-speed penetration laser welding, the keyhole is not rotationally symmetric anymore, but bent and elongated Their results may have great difference from real cases. To study the Fresnel absorption and multiple reflections in the real keyhole during laser penetration welding, in 1995 and in 1997, Semak et al [8] and Katayama et al [9] observed the formation and collapse times of the keyhole from top view with a high-speed camera in case of laser welding stainless steel and aluminum alloy, respectively. Using geometrical optics theory, Jin et al traced a ray of light in the keyhole and calculated the laser intensity absorbed on the keyhole wall in the symmetrical plane including laser beam and welding velocity through the Fresnel absorption. The laser intensity absorbed on the keyhole wall through the Fresnel absorption is calculated

Multiple Reflections in the 3D Keyhole

Results and Discussions

Conclusions