A study on welding mode transition by electrical detection of laser-induced plasma at varying energy levels

摘要

The transition between heat conduction and deep penetration laser welding is investigated by the electrical detection of laser-induced plasma with an electrical passive probe. A further improved physical model based on plasma sheath effect is established to clarify the mechanism of plasma electrical signal. Different electrical signals are detected at varying levels of laser input energy and analyzed in the time and frequency domains. The amplitudes and the fluctuation frequency of the collected signals are demonstrated to be effective in reflecting the electron temperature and the plasma oscillation features respectively. These assessments are identical with the experimental results obtained by a high-speed camera. Combined with the signal characteristics and the weld profiles at different laser powers, the critical state and laser power density of mode transition are discussed and identified by an analytic calculation model.