Influence of beam space shape on weld formation in laser keyhole welding

In laser welding of metals with a high power continuous CO2 laser, a so-called keyhole is formed in the material. The keyhole greatly affects the absorption of laser and makes remarkable influence on the weld formation. Based on the energy balance in the keyhole, this paper presents an analytical mathematical model about the quantitative relationship between the weld formation and the welding parameters. The model takes into account of the plasma absorption for laser beam, and involves most of the important welding parameters such as laser power, welding speed, focal position, therm-physical properties of metal and the space shape of focused laser beam. The influence of the space shape of focused laser beam upon the weld formation is specially discussed. The beam space shape is dependent on the laser beam quality, beam formation system and focus position. The analysis shows that, when the focused beam become thinner and the focus depth become larger, the laser weld will be deeper and narrower. The influences of the beam quality, focal length and focus position on the weld formation are analyzed. Through comparison with the experiments carried on various laser processing systems with different focused beam shapes, the theoretical analysis is in good agreement with the experiments.