Energy coupling characteristics of high-power fiber laser deep penetration welding under different penetration conditions

The physical essence of laser welding lies in the utilization of the photothermal effect of lasers. This paper systematically investigates the influence of laser power variations on weld morphology, molten pool characteristics, melting efficiency, and laser absorption rate by fixing the welding speed and plate thickness while adjusting the laser power to alter the plate's penetration state. It also analyses the photothermal energy conversion characteristics under different penetration states. The surface dimensions of the molten pool, the total absorption rate of the material, and the melting efficiency all first increase and then decrease with the increase in fiber laser power. As the fiber laser power increases, the weld seam successively exhibits the typical states of incomplete penetration, moderate penetration, and overpenetration. The cross section of the weld seam transitions from a “Y” shape in the incomplete penetration state to an “X” shape in the moderate penetration state, with further changes in the overpenetration state. Among these, the moderate penetration stage features the largest molten pool size, the most stable weld surface formation, and the highest melting efficiency and total absorption rate. In the incomplete penetration state, laser energy struggles to penetrate deeply into the material, resulting in low melting efficiency. In the overpenetrated state, the front wall of the keyhole tends to become vertical, and the rear portion of the laser spot directly penetrates the material, causing the absorption rate and melting efficiency to decrease.