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

Nasim Bakir,Andrey Gumenyuk,Michael Rethmeier,Antoni Artinov,Marcel Bachmann

doi:10.3390/met8060406

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.

Highlights

For several years, solid-state lasers have been widely applied in metal processing
It should of bethe noted that small cracks that can be observed in the weld crack and the heat-affected a micrograph weld cross-section presents a typical vertical solidification in the weld centerline
It should be noted that small cracks that can be observed in the weld and the heat-affected zone were not taken into in thisthat study

Summary

Introduction

The high-power of the laser sources and the excellent beam quality allow structures with wall thicknesses of more than 10 mm to be welded in one pass. When using the laser to weld steels with thickness above 10 mm, the risk of solidification cracking of materials increases due to carelessly coordinated process parameters and mechanical conditions. Apblett and Pellini [2] assumed that solidification cracking first occurs due to a critical strain. They believed that hot cracks occur at a temperature slightly above the solidus temperature when a film of liquid is still present between the dendrite structures. The hot cracks appear when the highly localized strains in the liquid films exceed their critical limit

Objectives

Discussion

Conclusion