Numerical Simulation on the Origin of Solidification Cracking in Laser Welded Thick-Walled Structures

Abstract

Abstract:One of the main factors affecting the use of lasers in the industry for welding thick structures is the process accompanying solidification cracks. These cracks mostly occurring along the welding direction in the welding center, and strongly affect the safety of the welded components. In the present study, to obtain a better understanding of the relation between the weld pool geometry, the stress distribution and the solidification cracking, a three-dimensional computational fluid dynamic (CFD) model was combined with a thermo-mechanical model. The CFD model was employed to analyze the flow of the molten metal in the weld pool during the laser beam welding process. The weld pool geometry estimated from the CFD model was used as a heat source in the thermal model to calculate the temperature field and the stress development and distributions. The CFD results showed a bulging region in the middle depth of the weld and two narrowing areas separating the bulging region from the top and bottom surface. The thermo-mechanical simulations showed a concentration of tension stresses, transversally and vertically, directly after the solidification during cooling in the region of the solidification cracking.

Improvement of Filler Wire Dilution Using External Oscillating Magnetic Field at Full Penetration Hybrid Laser-Arc Welding of Thick Materials

“…A homogeneous filler material distribution becomes important, especially at the single-layer HLAW of thicker materials and during the welding of modern thermomechanical rolled high-strength steels or cryogenic steels. One of the main reasons for the inhomogeneous mixing of the filler wire is explained by Marangoni convection, which mainly influences the flow behavior near the surfaces, which was discussed in detail in [18,19]. For that reason, a mixture of the filler wire did not take place.…”

“…The peak values in the velocity magnitude are located on the free surfaces. T ct was shown numerically for LBW in [18,19]. Figure 2 shows the Ni concentration of a HLAW mm thick steel plate.…”

Assessment of thermal cycles by combining thermo-fluid dynamics and heat conduction in keyhole mode welding processes

“…From the simulation results, a strong interaction between the movement of the laser source and the thermo-capillary driven vortexes is obtained leading to a teardrop shape at the upper and bottom surface of the workpiece. Additionally, it shows that a bulging in the weld pool, near the middle of the plate thickness occurs caused by the backflows on the upper and lower side due to the thermo-capillary driven flows [47]. The effect of natural convection is very small as compared to the thermo-capillary convection.…”

Methodology to Reduce Distortion Using a Hybrid Thermal Welding Process

“…However, it is not possible to simulate all of the physics involved in the welding process in a realistic way, as detailed in the study by Lindgren [ 10 ]. At present, the FEM simulations for welding often use a Lagrangian mesh [ 1 , 2 , 3 , 4 , 5 , 6 , 7 , 8 , 11 ]. In this work, the heat source was modeled with the Goldak [ 12 ] approximation (Equation (1)) for the weld heat input, and the propane torch source was modeled by 3D conical approximation.…”

“…A reduction of the distortion can be achieved through different strategies based on treatments applied either previous to, throughout, or after the weld process. These techniques can be mechanical [ 2 ], thermal [ 3 ], electromagnetic [ 4 ] or use other welding processes [ 5 , 6 ], and can be based on minimizing net stress in the assembly or inducing additional stresses after the welding process, such as in straightening.…”