Statistical analysis of plasma thermodynamic behavior based on laser deep penetration welding of TC4 titanium alloy

The laser-induced plasma is an important characteristic that affects the welding process and weld quality. The plasma plume erupting velocity and temperature are the two critical parameters of plasma thermodynamic behavior. In this paper, a kind of passive dual-probe device was proposed to measure the erupting velocity of the plasma plume, and the feasibility of the method was demonstrated. The temperature distribution of the plasma plume was also investigated. The experimental results showed that for the reason of the state of the keyhole was different, the MPV at the beginning of the laser pulse period increased from 14 m/s to 26 m/s with the peak power increased from 1980 W to 2520 and from 4 m/s to 25 m/s with the peak power increased from 1200 W to 1500 in the pulse laser welding process, while the MPV decreased from 20 m/s to 11 m/s with the laser power increase from 1200 W to 1500 W in the continuous laser welding process. The MPT decreased with the increase of height in pulse laser welding process; but in the continuous laser welding process, the plasma plume was heated by absorbing the laser energy and a hot core occurred in the plasma plume, the MPT first increased and then decreased with the increase of probe height.