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Numerical and Experimental Study of the Acoustic Signal Generated by Vapour Flow in Laser Welding
S-S. Ao, Z. Luo, C-F. Zhao, M-N. Feng and W-D. Liu

The acoustic signal is a good indicator for the weld quality detection in laser welding processing; however, the mechanism of the acoustic signal generation by the vapour flow is not clear. In this paper a two-dimensional (2-D) model is built to investigate the characteristics of acoustic signal generated by the vapour flow in laser welding. By the numerical simulation, the results indicate that the vapour flow velocity in the keyhole centre is higher than the vicinity of the keyhole with the highest velocity of the vapour flow inside the keyhole reaching 280 m/s. To verify the validity of the simulation, typical experiments are presented for laser welding steel plates with a Nd:YAG laser. A microphone is used to sample the acoustic signal and a digital high-speed camera is to observe the contour of the vapour flow. Experimental results are further proven to the extent that the simulation method is effective to analyse the mechanism of acoustic signal generation by the vapour flow.

Keywords: Nd:YAG laser, laser welding, acoustic signal, vapour flow, numerical model, computational fluid dynamics (CFD), steel, Ffowcs Williams and Hawkings (FW-H) equation, Navier-Stokes equation, velocity turbulence

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