Analytical and numerical modelling of the direct metal deposition laser process

Abstract

The direct metal deposition (DMD) laser process is a novel technique, well adapted for aeronautical applications, that allows the building of complex 3D geometries through the interaction between a powder nozzle system and a continuous laser beam. A three-step analytical and numerical approach was carried out to predict the shapes of manufactured structures and thermal loadings induced by the DMD process. First, powder temperature was calculated using a recent analytical model, then the geometry of walls was predicted by a combined numerical + analytical modelling using a discretization of the physical interaction domain, and finally, a finite element calculation was carried out on COMSOL 3.3 Multiphysics software to describe thermal behaviour during DMD of a titanium alloy.Our thermal model takes into account the moving interface during metal deposition with a specific function κ (t, x, y, z) allowing the conductivity front to move simultaneously with the moving laser source (with an appropriate spatial energy distribution), thus representing rather precisely the DMD process. This allowed us to provide an adequate representation of temperatures near the melt-pool, and to reproduce with a good accuracy thermal cycles and melt-pool dimensions during the construction of up to 25-layer walls. This was confirmed by comparisons with experimental thermocouple data T = f(t), and fast camera melt-pool recording.

Simplified numerical model for the laser metal deposition additive manufacturing process

“…Such an absorption coefficient is in the same order of magnitude (around 0.3) but a little higher than what has been previously found in anterior work. 16 When compared with experimental data, it was confirmed that numerical results (Table II, Fig. 8), provided a correct estimation of layer heights and melt-pool dimensions (MP), despite a slight overestimation (þ10%) of MP height and length by the numerical model as shown in the histograms of Fig.…”

“…11,12 Last, recent modeling like those by Mirzade 13 have considered undercooling during crystallization as a possible modification of melt zone contours whereas Suarez et al In our recent work, different FE models were proposed, starting from rather simple solid simulations considering layer growth through the x-displacement of a thermal conductivity front (Heaviside step function) 16 on predefined layers. The main drawback of this model was the heat source positioning (on the top of planar additive layers) which was not fully representative of the real laser absorption on an inclined shape.…”

“…16 It also can be noticed that laser power P 0 has a limited influence on layer height, but mostly tends to reduce A h , due to a reduction of efficient mass feeding for increased layer widths- Table I). A fast camera (Photron SA3, C-Mos sensor), operating between 2000 and 4000 Hz, was installed near the laser head to provide a real time lateral analysis (Fig.…”

Microstructures and Grain Refinement of Additive-Manufactured Ti-xW Alloys

“…This periodicity, as well as the truncated cellular structures shown in Figure 3((a), (a-3)), indicates that a Mullins and Sekerka instability [33,34] is operating with a characteristic wavelength of *Laser absorption based on experimental results from other authors. [43] ~7 lm. Of note, the Mullins and Sekerka can be established by small perturbations in the solid-liquid interface, or in the thermal fields that arise from very localized turbulence at the solid/liquid interface.…”

Flow characteristics of metallic powder grains for additive manufacturing

“…Thus, the powder interacts strongly with the the fluid dynamics of the shielding gas, that effects crucially the trajectory of single powder particles and hence, its location of deposition. Numerical approaches developed by He et al [2], Peyre et al [3], Wen et al [4] and Qi et al [5] describe the fusion process, however, neglect the transport of powder between nozzles and substrate. Therefore, the objective of the current contribution is to describe numerically the complex process of powder deposition on a substrate.…”