Laser powder-bed fusion additive manufacturing Physics of complex melt flow and formation mechanisms of pores, spatter, and denudation zones

Abstract

This study demonstrates the significant effect of the recoil pressure and Marangoni convection in laser powder bed fusion (L-PBF) of 316L stainless steel. A three-dimensional high fidelity powder-scale model reveals how the strong dynamical melt flow generates pore defects, material spattering (sparking), and denudation zones. The melt track is divided into three sections: a topological depression, a transition and a tail region, each being the location of specific physical effects. The inclusion of laser ray-tracing energy deposition in the powder-scale model improves over traditional volumetric energy deposition. It enables partial particle melting, which impacts pore defects in the denudation zone. Different pore formation mechanisms are observed at the edge of a scan track, at the melt pool bottom (during collapse of the pool depression), and at the end of the melt track (during laser power ramp down). Remedies to these undesirable pores are discussed. The results are validated against the experiments and the sensitivity to laser absorptivity is discussed.

Investigation of the anisotropic cyclic damage behavior of selective laser melted AISI 316L stainless steel

“…The instability of the melt pool is based on recoil pressure caused by Marangoni force. 10,11 To avoid these forces, the reduction of energy density is necessary, however, causing again an increase in porosity, as the powder is possibly incompletely fused. This so-called lack of fusion can also be produced by choosing insufficient distance of two adjacent scan lines as the powder particles are not able to fuse completely.…”

Multi-scale modeling of electron beam melting of functionally graded materials

“…The factor is selected based on the reshaping time scale, which is about one order of magnitude smaller than the thermal diffusion time scale [9]. Thus, the effective thermal diffusion in the molten regions caused by the reshaping flow is approximately to [10] times of the pure thermal diffusion. It should also be mentioned that neither evaporation nor the subsequent mass loss was considered in this study, since evaporation is not the concern of this study.…”

“…[15] and [16]. In order to compensate the missing convective heat transfer due to the molten material flow, the thermal conductivity at the temperature above the liquidus temperature was artificially enlarged by a factor of [10] in the following models. The factor is selected based on the reshaping time scale, which is about one order of magnitude smaller than the thermal diffusion time scale [9].…”

“…K€ orner et al [9] employed the Lattice Boltzmann Method (LBM) to study the successive consolidation process in powder layers. Khairallah et al [10] developed a meso-scopic model to investigate the formation mechanism of pores, spatter and denudation using the ALE3D multi-physics code. The model incorporated surface tension, Marangoni effect and recoil pressure.…”

A scalable parallel finite element framework for growing geometries. Application to metal additive manufacturing

“…[7][8][9][10][11] At the part scale, finite element (FE) modelling has proved to be useful to assess the influence of process parameters, 12 compute temperature distributions, 13,14 or evaluate distortions and residual stresses. [15][16][17] Recent contributions have introduced microstructure simulations of grain growth 18,19 and crystal plasticity, 20 melt-pool-scale models 3,21 and even multiscale and multiphysics solvers. [22][23][24][25][26] Furthermore, advanced frameworks (eg, grounded on multilevel hp-FE methods combined with implicit boundary methods 27 ) or applications to topology optimisation 28 have also been considered.…”