Generation of optical and acoustic emissions in laser weld plumes

Abstract

The goal of this work is the formulation of an analytical model of optical and acoustic emission generation by laser welds. A simplified model of the visible portion of the laser weld plume is used as a basis for the prediction of optical and acoustic signals. The optical emission is calculated from the strongest helium and iron lines in the visible spectrum. The sound pressure is calculated as a function of vapor flow rate by considering the displacement of ambient air by vapor emanating from the keyhole. The model reveals that generation of visible light increases roughly in proportion to the flow rate of vapor from the plume. However, the acoustic signal is predicted to vary as the time derivative of the flow rate. Experimental measurements of visible light are found to be of the same magnitude as predicted by the model and the fluctuation of the optical and acoustic signals are found to be consistent with the hypothesis that they are both fundamentally due to vapor flow rate variations.