Numerical simulation of weld pool geometry in laser beam welding

Abstract

A linear correlation between the depth and the length of the weld pool is found in laser beam welding experiments with varied laser beam power and constant welding speed. On the other hand, the weld pool length changes only slightly with increased welding speed and constant laser beam power. The existing analytical and numerical models fail to explain these dependences. The observed effects are essentially conditioned by the fluid flow in the weld pool caused by the thermocapillary effect, by the friction forces of the metal vapour passing through the capillary and by the convexity of weld pool and fusion zone caused by thermal expansion of the weld pool and the joined workpieces. In order to predict the weld pool length more accurately the model developed by Sudnik et al in 1996 is enlarged by the heat transport produced by the recirculating flow in radial sections of the weld pool. Verification of the model for 16MnCr5 steel with sheet thicknesses of 2 and 6 mm shows that it is suitable for predicting the weld pool geometry and for analysing the thermodynamics of the process. In order to gain a better understanding of the structure of heat transport in the weld pool, the different modes of transport are compared in respect of their contribution to the depth-to-length ratio of the weld pool. A calculation of the weld pool length for welding speeds of 1-8 m min −1 with a laser beam power of 2.5 kW shows that the relative contributions of the transport modes are as follows. Approximately 50-90% of the weld pool length (increasing with welding speed) results from conductive and translatory heat transport (with the fusion zone convexity contributing approximately 20-30%). The remaining 50-10% of the weld pool length (decreasing with welding speed) result from convective heat transport. The model predicts the shoulder in the weld pool trough. It also explains the change in the weld pool length by the effect of the gap width, by the transition from through welding to penetration welding and by improvements in beam quality.

Benefits And Prospects Of Laser Welding Application In Vacuum

“…In the work [12] the authors has described the application of this technique for electron beam welding. In the works [13,14] you can find theoretical fundamentals of numerical modeling of stationary pro-melting provided by a laser beam, and in the work [15] the fundamental part of studies is greatly emphasized. The found analytical solutions and the use of numerical simulations (for simplified statements) contributed to the development of the applied LaserCad software product designed for the use in production in order to forecast laser beam welding results.…”

Modeling of laser welding of steel and titanium plates with a composite insert

“…The rapid transfer of heat in it due to natural convection of the melt can be modeled by an increased coefficient of the thermal conductivity in the region occupied by the pool. Here, we do not take into account the influence of the convective movement of the melt in the pool on its shape, in contrast to how it was done in [14,19].…”

“…Various models of heat transfer from the laser beam to the metal during the welding were proposed [13,14,19]. In most of them, at first, the keyhole in the liquid metal is calculated under assumptions made in a particular model.…”

“…Surface tension and excess pressure largely prevent the low vapor recoil forces from distorting the cross-sectional shape "averaged over time". After many researchers [15,19] the keyhole cross-section is considered to be a circle.…”

“…It creates a motivation for the usage of numerical simulation in addition to experiments [2][3][4][5][6]. Mathematical modeling may significantly complement the experiment which is often much more expensive than computer simulations [13][14][15][16][17][18][19].…”