The calculation of keyhole depth based on the primary absorption of front keyhole wall in laser deep-penetration welding

The establishment of an accurate prediction model of keyhole depth during laser welding is of great significance for predicting the weld depth or pre-selecting suitable welding process parameters. In this paper, based on the primary absorption of the incident laser by the front keyhole wall, the tilt angle of the keyhole wall was calculated point by point according to the equilibrium relationship between the laser energy absorbed by the material and the energy required for evaporation at any position of the front keyhole wall. A prediction model for the keyhole depth in laser deep penetration welding has been established by taking into account the laser optical parameters, the focusing system parameters, the welding process parameters, and the material properties. The transformation law of the front keyhole wall profile, the Fresnel absorption coefficient, and the keyhole depth with laser power, welding speed, focusing focal length, and other parameters was calculated in the model, which is basically in line with the consensus. At the same time, the keyhole depth results of calculations and measurements under some parameter conditions were compared. It can be found that the prediction model of keyhole depth during laser deep penetration welding can be used to approximate the calculation of weld depth, and the feasibility of the model was preliminarily verified. Moreover, combined with previous experimental results, the conclusion that the primary absorption of front keyhole wall is the key factor determining the keyhole depth can be re-verified by using mathematical calculations. It also shows that the complex energy coupling law in keyhole has a noticeable difference in the influence of different physical phenomena during laser deep penetration welding.