Simulation of Powder Packing and Thermo-Fluid Dynamic of 316L Stainless Steel by Selective Laser Melting

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JMEPEG https://doi.org/10.1007/s11665-020-05230-w

Simulation of Powder Packing and Thermo-Fluid Dynamic of 316L Stainless Steel by Selective Laser Melting L. Liu, M. Huang, Y.H. Ma, M.L. Qin, and T.T. Liu Submitted: 25 March 2020 / Revised: 27 July 2020 / Accepted: 10 October 2020 A mesoscopic model was established to investigate thermo-ﬂuid dynamic behavior in selective laser melting of 316L stainless steel. A powder packing model, including particle size distribution based on the discrete element method, was developed to describe the relative density variation of the powder bed with different layer thicknesses. A ﬁnite element method model with Gaussian laser beam was established to predict the dynamic thermal behavior and ﬂow mechanism of the particles for a single-line scanning. The level-set method was used to trace the free surface of the molten metal with temperature-dependent surface tension. A function to describe the relative density of the powder bed with its thickness was obtained. An evaporation model considering the inﬂuence of mass, energy loss, and evaporation on the surface morphology of the molten pool was established. According to the temperature and velocity ﬁeld in the molten pool, a vortex formed by the Marangoni effect might decrease the depth and increase the width of the molten pool. The molten pool was not disconnected by Plateau–Rayleigh instability due to the small length/diameter ratio at low scanning speeds. The model assuming regularly arranged powder bed underestimates the maximum temperature as compared to the model considering a randomly packed powder bed because a higher relative density of the former facilitates heat conduction. The simulated results are consistent with experimental results, including porosity, material loss, and surface defects. Keywords

evaporation, particle size distribution, powder bed fusion, selective laser melting, 316L stainless steel

1. Introduction Selective laser melting (SLM) is one of the main categories of additive manufacturing in which a laser beam is used to melt the metal powder layer by layer to form high-density components. SLM is receiving increasing attention in ﬁelds such as aerospace, automotive, and medicine due to its potential to fabricate complex metallic components without mold (Ref 1). But the process can be susceptible to defects, such as surface porosity, poor surface, and balling, which could be minimized through numerical simulation (Ref 2, 3). In the simulation of SLM, the powder is generally treated as a homogeneous continuum body, and molten pool dynamics are neglected (Ref 1, 4). However, SLM involves complex physical processes, such as heat transfer, phase transformation, and molten metallic ﬂow, which inﬂuence the ﬁnal component quality and properties (Ref 5). When the molten pool dynamics were included in the simulation treating powder as a continuum, phenomena such as surface roughness (Ref 6) and porosity evolution (Ref 7) were simulated. In reality, the randomly packed powder bed adds the complexity of the process (Re

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