| Aluminum and its alloy suffer the problems of unstable process, bad weld formation, pores(keyhole induced pore mainly) etc. The strategy of dual laser beam and laser beam rotation/oscillation can stabilize the process and refrain the formation of pores. However, they lessen the depth of weld. A new method named laser beam welding with focus rotation and vertical oscillation is employed in this paper, which superpose focus vertical oscillation to beam rotation. A laser welding device with controllable focus movement is designed. Welding test was carried out using this device. The effects of focus movement on weld formation, cross-section and porosity of aluminum are investigated. The weld pool and keyhole behaviors are observed through high speed camera. The influence of laser beam focus movement on weld formation and pores is explained. The melt flow and solidification are analysed.Weld formation is improved by means of focus rotation and vertical oscillation. Weld pool dynamics and keyhole behavior can be controlled by focus rotation and vertical oscillation. Regular and stable melt flow in weld pool results in more stable welding process and better weld formation. Focus rotation enlarges the keyhole and enhances its stability, makes it harder to collapse, so that the formation of keyhole induced pores is restrained. Welding in optimized parameters, focus vertical oscillation increases weld depth and welding efficiency. This is attributed to the change of keyhole behavior. The keyhole depth regularly increases under the effect of focus vertical oscillation and the weld depth increases accordingly, owing to the deepened weld pool overlap in a high enough focus oscillation frequency. The result in this paper shows, due to the stable process, less keyhole induced pores and decent welding efficiency for laser welding of aluminum and its alloy, this method has a promising application prospect for some certain joints, such as lock butt joints, which are not allowed to be penetrated. |
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