A numerical investigation on the physical mechanisms of single track defects in selective laser melting

Tang, C. Y.; Tan, Jie; Wong, Chee How

doi:10.1016/j.ijheatmasstransfer.2018.06.073

Cited by 224 publications

(65 citation statements)

References 43 publications

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“…This tendency is well known and several authors [12][13][14] have already observed it on various materials (such as aluminum alloys, maraging steels, stainless steels) processed using various manufacturing parameters. The increase in porosity rate observed at high VED, and assumed to be due to the destabilization of the key-hole welding mode is in full agreement with a recent simulation work by Tang [35].…”

Section: Comparison Of the Optimized Measurement Methodssupporting

confidence: 90%

Optimization and comparison of porosity rate measurement methods of Selective Laser Melted metallic parts

Terris

Andreau

Peyre

et al. 2019

Additive Manufacturing

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The systematic occurrence of porosities inside selective laser melted (SLM) parts is a well-known phenomenon. In order to improve the density of SLM parts, it is important not only to assess the physical origin of the different types of porosities, but also to be able to measure as precisely as possible the porosity rate so that one may select the optimum manufacturing parameters. Considering 316 L steel parts built with different input energies, the current paper aims to (1) present the different types of porosities generated by SLM and their origins, (2) compare different methods for measuring parts density and (3) propose optimal procedures. After a preliminary optimization step, three methods were used for quantifying porosity rate: the Archimedes method, the helium pycnometry and micrographic observations. The Archimedes method shows that results depend on the nature and temperature of the fluid, but also on the sample volume and its surface roughness. During the micrographic observations, it has been shown that the results depend on the magnification used and the number of micrographs considered. A comparison of the three methods showed that the optimized Archimedes method and the helium pycnometry technique gave similar results, whereas optimized micrographic observations systematically underestimated the porosity rate. In a second step, samples were analyzed to illustrate the physical phenomena involved in the generation of porosities. It was confirmed that: (1) low Volume Energy Density (VED) causes non-spherical porosities due to insufficient fusion, (2) in intermediary VED the small amount of remaining blowhole porosities come from gas occlusion in the melt-pool and (3) in excessive VED, cavities are formed due to the keyhole welding mode.

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Section: Comparison Of the Optimized Measurement Methodssupporting

confidence: 90%

Optimization and comparison of porosity rate measurement methods of Selective Laser Melted metallic parts

Terris

Andreau

Peyre

et al. 2019

Additive Manufacturing

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“…(2) excessive melt temperature caused metal evaporation, and strong recoil pressure caused great disturbance to the stability of the molten pool [57].…”

Section: Multi-layer Deposition and Surface Remeltingmentioning

confidence: 99%

WITHDRAWN: On the in situ elimination of pores during laser powder bed fusion of a titanium alloy

Zhang

Liao

Liu

et al. 2021

Preprint

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The printing quality of the laser powder bed fusion (LPBF) components largely depends on the presence of various defects such as massive porosity. Thus, the efficient elimination of pores is an important factor to the production of a sound LPBF product. In this work, the efficacy of two in situ laser remelting approaches on the elimination of pores during LPBF of a titanium alloy Ti-6.5Al-3.5Mo-l.5Zr-0.3Si (TC11) were assessed using both experimental and computational methods. These two remelting methods are the surface remelting, and the layer-by-layer printing and remelting. A multi-track and multi-layer phenomenological model was established to compute the evolution of pores with the temperature and velocity fields. The results showed that surface remelting with a high laser power such as 180 W laser can effectively eliminate pores within three deposited layers. However, such a remelting cannot reach defects in deeper regions. Alternatively, the layer-by-layer remelting with a laser power of 180 W can effectively eliminate the pores formed in the previous layer in real time. The results obtained from this work can provide useful guidance for the in situ control of printing defects supported by the real time monitoring, feedback and operation systems of the intelligent LPBF equipment.

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“…The models are classified into three categories according to the modeling scale: micro-scale, meso-scale, and macro-scale. The micro-scale model was aimed at calculating the grain growth and solidification microstructure, and the meso-scale model was adaptive to predict the fluid flow of melting pool and evolution of individual powder particles [ 7 , 8 , 9 , 10 ]. The macro-scale model based on the finite element method (FEM) has been employed to resolve the product-scale process evolution, which is appropriately adopted to predict the shrinkage and warping in this work.…”

Section: Introductionmentioning

confidence: 99%

Numerical Model and Experimental Validation for Laser Sinterable Semi-Crystalline Polymer: Shrinkage and Warping

Yuan

Zhu

et al. 2020

Polymers

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Shrinkage and warping of additive manufacturing (AM) parts are two critical issues that adversely influence the dimensional accuracy especially in powder bed fusion processes such as selective laser sintering (SLS). Powder fusion, material solidification, and recrystallization are the key stages causing volumetric changes of polymeric materials during the abrupt heating–cooling process. In this work, the mechanisms of shrinkage and warping of semi-crystalline polyamide (PA) 12 in SLS are well investigated. Heat-transfer and thermo-mechanical models are established to predict the process-dependent shrinkage and warping. The influence of raw material- and laser-related parameters are considered in the heat-transfer and thermo-mechanical models. Such models are established considering the natural thermal gradient and dynamic recrystallization, which induce internal strain and volumetric change. Moreover, an experimental design via orthogonal approach is introduced to validate the feasibility and accuracy of the proposed models. Finally, the quantitative relationships of process parameters with product shrinkage and warping are established; the dimensional accuracy in part-scale can be well predicted and validated with printed parts in a real experiment.

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A numerical investigation on the physical mechanisms of single track defects in selective laser melting

Cited by 224 publications

References 43 publications

Optimization and comparison of porosity rate measurement methods of Selective Laser Melted metallic parts

Optimization and comparison of porosity rate measurement methods of Selective Laser Melted metallic parts

WITHDRAWN: On the in situ elimination of pores during laser powder bed fusion of a titanium alloy

Numerical Model and Experimental Validation for Laser Sinterable Semi-Crystalline Polymer: Shrinkage and Warping

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