Additive manufacturing (AM), widely known as 3D printing, is a direct digital manufacturing process, where a component can be produced layer by layer from 3D digital data with no or minimal use of machining, molding, or casting. AM has developed rapidly in the last 10 years and has demonstrated significant potential in cost reduction of performance-critical components. This can be realized through improved design freedom, reduced material waste, and reduced post processing steps. Modeling AM processes not only provides important insight in competing physical phenomena that lead to final material properties and product quality but also provides the means to exploit the design space towards functional products and materials. The length-and timescales required to model AM processes and to predict the final workpiece characteristics are very challenging. Models must span length scales resolving powder particle diameters, the build chamber dimensions, and several hundreds or thousands of meters of heat source trajectories. Depending on the scan speed, the heat source interaction time with feedstock can be as short as a few microseconds, whereas the build time can span several hours or days depending on the size of the workpiece and the AM process used. Models also have to deal with multiple physical aspects such as heat transfer and phase changes as well as the evolution of the material properties and residual stresses throughout the build time. The modeling task is therefore a multi-scale, multi-physics endeavor calling for a complex interaction of multiple algorithms. This paper discusses models required to span the scope of AM processes with a particular focus towards predicting as-built material characteristics and residual stresses of the final build. Verification and validation examples are presented, the over-spanning goal is to provide an overview of currently available modeling tools and how they can contribute to maturing additive manufacturing.

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A new 3D finite element model, developed in a level set approach, is proposed to model hybrid gas metal arc / laser welding in multipass conditions. This heat and mass transfer model couples the resolution of the heat conservation equation, the momentum and mass conservation equations and the weld bead development. The arc welding total power is divided in two parts: one corresponding to the energy transferred to the fusion zone by droplets of melted filler material, the rest being transferred to the workpiece by the surrounding plasma. The droplets energy input is modelled as a volumetric heat source. Regarding the heat surface fluxes associated with plasma and laser heating, the "Continuum Surface Force" approach is used to model them as volumetric heat sources concentrated in the immediate neighbourhood of the metal-gas interface. A resolution scheme, consisting in ignoring high velocity fluid flow in the fusion zone, through the use of an augmented liquid viscosity, is proposed and discussed. Accordingly, the liquid thermal conductivity is enhanced to result in a realistic heat transfer to the workpiece. The formation of the weld bead is obtained through the introduction of a source term in the mass conservation equation, and the application of the normal component of surface tension forces, proportional to the mean curvature of the metal-gas interface. This approach is proposed to reduce computation time. The resolution scheme is applied to the simulation of hybrid welding of 18MND5 (ASME SA 533) steel grade. Results are compared to experimental measurements and observations operated in conditions close to industrial ones. The influence of the enhancement applied to the liquid conductivity coefficient is shown and discussed. A strong sensitivity evolution is demonstrated when varying it from the physical value to the value proposed in the welding literature. As proposed, the simplified resolution scheme leads to a good estimation of the weld bead surface development. Nevertheless, there are still noticeable differences with the whole set of experimental results that are discussed and can be explained by model limitations and insufficient knowledge of material and interfacial properties.

Abstract. The hybrid arc/laser welding process has been developed in order to overcome the difficulties encountered for joining high thickness steel sheets. This innovative process gathers two heat sources: an arc source developed by a MIG torch and a prelocated laser source. This coupling improves the efficiency of the process, the weld bead quality and the final deformations. The Level-Set approach for the modelling of this process enables the prediction of the weld bead development and the temperature field evolution. The simulation of the multi-passes welding of a 18MnNiMo5 steel grade is detailed and the results are compared to the experimental observations. Résumé. Le procédé de soudage hybride Arc/Laser est une solution aux assemblages difficiles de tôles de fortesépaisseurs. Ce procédé innovant associe deux sources de chaleur : un arcélectrique produit par une torche MIG et une source laser placée en amont. Ce couplage améliore le rendement du procédé, la qualité du cordon et les déformations finales. La modélisation de ce procédé par une approche Level Set permet une prédiction du développement du cordon et du champ de température associé. La simulation du soudage multi-passes d'une nuance d'acier 18MnNiMo5 est présentée ici et les résultats sont comparés aux observations expérimentales.