Wenda Tan

Investigation of keyhole plume and molten pool based on a three-dimensional dynamic model with sharp interface formulation

Laser keyhole welding is a complicated multi-phases, multi-physics process, especially when assisting gases are involved. A three-dimensional transient model is developed to investigate the dynamics of keyhole, together with the vapour plume and molten pool, in a self-consistent manner. The model features the utilization of sharp interface method for accurate consideration of the complex surface phenomena on the keyhole wall and a comprehensive hydrodynamic calculation for both the vapour plume and molten pool. The model is validated against experiments and the simulation results are discussed. It is found that the interplay of the multiple reflections and the plume attenuation due to particle absorption/scattering is crucial for the laser absorption intensity and hence the temperature on the keyhole wall, and the keyhole wall temperature distribution has profound influences on the fluid flow and temperature/species distributions in both the molten pool and keyhole plume.

Analysis of multi-phase interaction and its effects on keyhole dynamics with a multi-physics numerical model

A numerical model is developed to investigate the three-dimensional transient dynamics of the keyhole in continuous welding processes with/without assisting gas. The model features the utilization of the sharp interface method for accurate consideration of the complex boundary conditions on the keyhole wall and a comprehensive hydrodynamic calculation for both the gaseous and liquid phases. The model gives good prediction of the weld geometry, and more importantly, provides detailed information regarding the multi-phase interaction and its effects on keyhole dynamics. It is shown that different welding parameters can cause different coupling effects between the vapour plume and molten pool and hence produce keyholes of different shapes. The addition of assisting gas flow not only modifies the interaction between the vapour plume and molten pool, but also reduces the laser attenuation by the plume. These two-folded effects can significantly change the keyhole shape. The dependence of laser absorptivity on incidence angle is found to be a major source of keyhole fluctuation. If the welding heat input is high and the keyhole is deep, vertical and slim, the fluctuation may cause keyhole collapse and hence porosity in the final weldment.

Numerical Modeling of Transport Phenomena and Dendritic Growth in Laser Spot Conduction Welding of 304 Stainless Steel

A multiscale model is developed to investigate the heat/mass transport and dendrite growth in laser spot conduction welding. A macroscale transient model of heat transport and fluid flow is built to study the evolution of temperature and velocity field of the molten pool. The molten pool shape is calculated and matches well with the experimental result. On the microscale level, the dendritic growth of 304 stainless steel is simulated by a novel model that has coupled the cellular automata (CA) and phase field (PF) methods. The epitaxial growth is accurately identified by defining both the grain density and dendrite arm density at the fusion line. By applying the macroscale thermal history onto the microscale calculation domain, the microstructure evolution of the entire molten pool is simulated. The predicted microstructure achieves a good quantitative agreement with the experimental results.

Laser keyhole welding of stainless steel thin plate stack for applications in fuel cell manufacturing

Abstract An investigation based on both experimental and numerical approaches is presented in this paper on laser keyhole welding processes to join stacks consisting of multiple stainless steel plates. The welding parameters are shown to be decisive factors for weld penetration depth and welding productivity. The cooling rate varies with welding parameters and the location of solidification sites, and it directly determines the primary dendrite arm spacing for the columnar dendrites inside the weld zone. The joint fails in coach peel tests when the loading pressure is 93.4 MPa, and the fracture surface shows a mixed brittle and ductile mode. The corrosion resistance of the weld to the polymer electrolyte membrane fuel cell working environment is comparable to that of the substrate.

Numerical Modeling of Transport Phenomena and Dendritic Growth in Laser Conduction Welding of 304 Stainless Steel

A multi-scale model is developed to investigate the heat/mass transport and dendrite growth in laser spot conduction welding. A macro-scale transient model of heat transport and fluid flow is built to study the evolution of temperature and velocity field of the molten pool. The molten pool geometry and other solidification parameters are calculated, and the predicted pool geometry matches well with experimental result. On the micro-scale level, the dendritic growth of 304 stainless steel is simulated by a novel model that has coupled the Cellular Automata (CA) and Phase Field (PF) methods. The epitaxial growth is accurately identified by defining both the grain density and dendrite arm density at the fusion line. By applying the macro-scale thermal history onto the micro-scale calculation domain, the microstructure evolution of the entire molten pool is simulated. The predicted microstructure achieves a good quantitative agreement with the experimental results.Copyright