Measurements of laser-induced plasma temperature field in deep penetration laser welding

Laser-induced plasma in deep penetration laser welding is located inside or outside the keyhole, namely, keyhole plasma or plasma plume, respectively. The emergence of laser-induced plasma in laser welding reveals important information of the welding technological process. Generally, electron temperature and electron density are two important characteristic parameters of plasma. In this paper, spectroscopic measurements of electron temperature and electron density of the keyhole plasma and plasma plume in deep penetration laser welding conditions were carried out. To receive spectra from several points separately and simultaneously, an Optical Multi-channel Analyser (OMA) was developed. On the assumption that the plasma was in local thermal equilibrium, the temperature was calculated with the spectral relative intensity method. The spectra collected were processed with Abel inversion method to obtain the temperature fields of keyhole plasma and plasma plume.

► We use an optical ulti-channel analyzer to capture spectrum of keyhole plasma.
► We use a modified inverse Abel transform to get radial distribution of plasma.
► We measure the electron temperature field of the keyhole plasma and plasma plume.
► Temperature fields of two kinds of plasma are almost cylindrically symmetrical.
► Temperatures at the centre of two kinds of plasma are higher than those around.