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Abstract
The phenomena during inclined laser irradiating on the metal surface were investigated to imitate the behaviour on the front keyhole wall in deep penetration laser welding. The results revealed that the velocity of molten layer increased when the laser power density increased. The molten layer could be torn off to form droplets owing to the high evaporating pressure induced by the high power density laser. The heating efficiency of laser induced vapour plume was lower than that of the molten metal. In reflection experiments, only when the incident angle was 88°, the absorption of reflected laser was greater than that of the first incident laser. The concaved surface of molten layer had a great effect to the reflected laser. During multiple reflections, the considerable absorption of laser energy mainly happened in the first two times. The calculated data were closer to the actual conditions when the influence of polarisation variation was avoided.
This research was supported in part by the National Natural Science Foundations of China (grant no. 51175165) and the Key National Science and Technology Project (grant no. 2013ZX04001131) and the State Scholarship Fund of the China Scholarship Council (CSC). Many thanks are given to Mr M. Mizutani, Mr D. You and Mr Q. Pan for their help in using the equipments during experiments.