Abstract: Aiming at the engineering requirements of high efficient root pass one-sided welding with backformation for medium-thick plate UF₆ vessels, a power modulated-galvanometer scanning laser assisted-pulsed TIG deep penetration welding method was proposed, and a welding test platform was established to carry out several sets of laser-assisted pulsed TIG welding process tests, which investigated the dynamic evolution of the arc-melting pool and the characteristic law of the temperature field distribution at the back of the weld pool, and revealed the physical mechanism of increasing the depth of melting of scanning galvanometer laser power modulation-pulsed TIG welding. The physical mechanism of power modulated-pulsed TIG melting depth increase was revealed. The results show that this process can stably realize the single-sided welding and double-sided forming of Y type 6 mm root face butt joint; when the laser power is reduced from 1 800 W to 720 W and then increased to 1 080 W, the back average temperature of the weld pool at the peak period ranges from 1 700 ℃ to 1 850 ℃ , and the average temperature of the base period changes from 1 550 ℃ to 1 600 ℃ , and the thermal effect of laser beam on the weld pool is weakness; the theoretical calculation of the metal vapor recoil pressure is 0.017 N, indicating a significant role in heat transfer; the high-energy beam laser instantaneously vaporizes the liquid melt at the bottom of the micro-region of the weld pool, resulting in a liquid metal film and forming a keyhole. As the energy density increases, the more arc energy is transferred to the bottom of weld pool, melting the more metal and achieving a deeper penetration.

Key words: pulsed TIG welding, laser shock, molten hole, temperature field, one-sided welding with backformation