Welding Phenomena and Reflected Beam Monitoring during YAG Laser Lap Welding of Zn-Coated Steels(Physics, Processes, Instruments & Measurements)

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A study was performed with the objectives of understanding lap welding phenomena of Zn-coated steels with a Nd: YAG laser as well as obtaining a fundamental knowledge of monitoring signals for the formation of sound or bad weld beads. The behavior of the molten pool and a reflected beam was simultaneously observed through a high-speed video and the monitoring of reflected beam intensity. The effect of sheet gap on porosity formation and bead appearance was confirmed, and characteristic monitoring signals were obtained according to these gaps at high welding speeds. In the case of no gap, spatter was frequently generated, and the reflected beam fluctuated intensely at low frequencies. On the other hand, in welding sheets with a wide gap, lap welds were not produced and the high frequency signals of a reflected beam were detected. Moreover, sound welds were produced in the sheets with a proper gap, and a moderate reflected beam was monitored. From these results, it was concluded that the reflected beam was dependent upon the sheet gap, and its signals and analytical results were beneficial for the judgment of sound welds, underfilled welds due to spattering and incomplete lap welds due to a wide gap.
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