A Convective Heat-Transfer Model for Partial and Full Penetration Keyhole Mode Laser Welding of a Structural Steel

Abstract

In the keyhole mode laser welding of many important engineering alloys such as structural steels, convective heat transport in the weld pool significantly affects temperature fields, cooling rates, and solidification characteristics of welds. Here we present a comprehensive model for understanding these important weld parameters by combining an efficient keyhole model with convective three-dimensional (3-D) heat-transfer calculations in the weld pool for both partial and full penetration laser welds. A modified turbulence model based on PrandtlÕs mixing length hypotheses is included to account for the enhanced heat and mass transfer due to turbulence in the weld pool by calculating spatially variable effective values of viscosity and thermal conductivity. The model has been applied to understand experimental results of both partial and full penetration welds of A131 structural steel for a wide range of welding speeds and input laser powers. The experimentally determined shapes of the partial and full penetration keyhole mode laser welds, the temperature profiles, and the solidification profiles are examined using computed results from the model. Convective heat transfer was the main mechanism of heat transfer in the weld pool and affected the weld pool geometry for A131 steel. Calculation of solidification parameters at the trailing edge of the weld pool showed nonplanar solidification with a tendency to become more dendritic with increase in laser power. Free surface calculation showed formation of a hump at the bottom surface of the full penetration weld. The weld microstructure becomes coarser as the heat input per unit length is increased, by either increasing laser power or decreasing welding velocity.

Fiber Laser Welding of Dissimilar 2205/304 Stainless Steel Plates

“…Few studies have been reported on the mechanisms that are responsible for the shape of weld bead profiles [54][55][56]. The effect of surface deformation and melt flow on weld bead formation was first investigated by Bradstreet [57] when correlated the bead profile of a convex-shaped profile to the surface tension, which controls edge wetting in the weld pool.…”

A level set approach for the simulation of the multipass hybrid laser/GMA welding process

“…It can be noted that the right hand side of this advection-diffusion equation is both time and space averaged. Equation (21) corresponds to the conservation equation energy for a specific added metal and energy rates. In the numerical resolution, Eq.…”

“…Lastly, buoyancy forces can no longer be neglected since it has been proved they have a great influence in horizontal GTA welding [17]. Because of the improvements in hybrid welding modelling and the research focus on keyhole phenomenon, these numerical methods have been carried over to laser/GMAW modelling [18,19,20,21,22]. As a result, the numerically obtained bead shapes better fit the experimental ones.…”

Theoretical investigations into heat transfer in laser-welded steel sheets

“…[10][11][12][13][14][15][16]. Mathematical and numerical models usually describe chosen phenomena, due to the computational complexity of the problem.…”

“…Mathematical and numerical models usually describe chosen phenomena, due to the computational complexity of the problem. Therefore, coupled thermal phenomena and phase transformations in solid state are usually ignored in numerical analysis of welding processes [5,8,9,15,16]. However, latent heat generated during phase transformations in heat treatment of steel influences temperature distribution and has a significant effect on numerically predicted microstructure composition [17,18].…”