Charles-André Gandin

Finite Element Multi-scale Modeling of Chemical Segregation in Steel Solidification Taking into Account the Transport of Equiaxed Grains

The transport of solid crystals in the liquid pool during solidification of large ingots is known to have a significant effect on their final grain structure and macrosegregation. Numerical modeling of the associated physics is challenging since complex and strong interactions between heat and mass transfer at the microscopic and macroscopic scales must be taken into account. The paper presents a finite element multi-scale solidification model coupling nucleation, growth, and solute diffusion at the microscopic scale, represented by a single unique grain, while also including transport of the liquid and solid phases at the macroscopic scale of the ingots. The numerical resolution is based on a splitting method which sequentially describes the evolution and interaction of quantities into a transport and a growth stage. This splitting method reduces the non-linear complexity of the set of equations and is, for the first time, implemented using the finite element method. This is possible due to the introduction of an artificial diffusion in all conservation equations solved by the finite element method. Simulations with and without grain transport are compared to demonstrate the impact of solid phase transport on the solidification process as well as the formation of macrosegregation in a binary alloy (Sn-5xa0wtxa0pct Pb). The model is also applied to the solidification of the binary alloy Fe-0.36xa0wtxa0pct C in a domain representative of a 3.3-ton steel ingot.

Finite Element Modeling of Ceramic Deposition by LBM (SLM) Additive Manufacturing

The Marangoni effect caused by surface tension gradient is modeled. The resulting convection flow in the melt pool is demonstrated with different values of the Marangoni coefficient. Its influence on the temperature distribution, the shape of melt pool and thus the shape of solidified track is presented. The role of Marangoni convection on the stability of melt pool and the surface quality of the final track are also discussed.

Macroscopic Finite Element Thermal Modelling of Selective Laser Melting for IN718 Real Part Geometries

A 3D finite element model is developed to study heat exchange during the selective laser melting (SLM) process. The level set functions are used to track the interface between the constructed workpiece and non-melted powder, and interface between the gas domain and the successive powder bed layers In order to reach the simulation in macroscopic scale of real part geometries in a reasonable simulation time, the energy input and the formation of the additive deposit are simplified by considering them at the scale of an entire layer or fraction of each layer. The layer fractions are identified directly from a description (e.g. using G-code) of the global laser scan plan of the part construction. Each fraction is heated during a time interval corresponding to the exposure time to the laser beam, and then cooled down during a time interval equal to the scan time of the laser beam over the considered layer fraction. The global heat transfer through the part under additive construction and the powder material non-exposed to the laser beam is simulated. To reduce the computational cost, mesh-adaptation is adopted during the construction process. The proposed model is able to predict the temperature distribution and evolution in the constructed workpiece and non-melted powder during the SLM process at the macroscale, for parts made of complex geometry. Application is shown for a nickel based material (IN718), but the numerical model can be easily extended to other materials by using their data sets.