scholarly journals Printability and Microstructure of Selective Laser Melting of WC/Co/Cr Powder

Materials ◽  
2019 ◽  
Vol 12 (15) ◽  
pp. 2397 ◽  
Author(s):  
Sabina Luisa Campanelli ◽  
Nicola Contuzzi ◽  
Paolo Posa ◽  
Andrea Angelastro
Keyword(s):  
Selective Laser Melting ◽  
Complex Geometry ◽  
Melting Process ◽  
Powder Layer ◽  
Laser Melting ◽  
Heterogeneous Distribution ◽  
High Melting Temperature ◽  
Hardness Tests ◽  
Small Cracks ◽  
Melting And Solidification

The selective laser melting process is a growing technology for the manufacture of parts with very complex geometry. However, not all materials are suitable for this process, involving rapid localized melting and solidification. Tungsten has difficulties due to the high melting temperature. This study focuses on the possibility of processing a WC/Co/Cr composite powder using selective laser melting. Samples were fabricated and characterized in terms of density, defects, microstructure and hardness. Tests were conducted with hatch spacing of 120 μm and process speed of 40 mm/s. A constant laser power of 100 W and a powder layer thickness of 30 μm were used. A relative density of 97.53%, and therefore a low porosity, was obtained at an energy density of 12.5 J/mm2. Microscopic examination revealed the presence of small cracks and a very heterogeneous distribution of the grain size.

Numerical Study of Porosity Formation With Implementation of Laser Multiple Reflection in Selective Laser Melting

2019 ◽  
Author(s):  
Bo Cheng ◽  
Charles Tuffile
Keyword(s):  
Selective Laser Melting ◽  
Laser Scanning ◽  
Numerical Study ◽  
Fluid Model ◽  
Melting Process ◽  
Scanning Speed ◽  
Powder Layer ◽  
Cfd Model ◽  
Laser Melting ◽  
Porosity Formation

Abstract In selective laser melting (SLM) process, the build part quality is determined by process parameters such as laser scanning speed and power. The presence of porosity, a major printing defect that significantly affects part performance, may arise in laser melting process due to insufficient or excess energy input. The improvement of build quality heavily depends on fundamental understanding of porosity formation in the SLM process. In this study, the discrete element method (DEM) has been utilized to simulate the creation of a newly deposited powder layer. A computational fluid dynamics (CFD) model was developed to simulate the melting and solidification process of Ti-6Al-4V powders in the SLM process. The thermo-fluid model includes effect of surface tension and recoil pressure as well as laser ray multi-reflection in keyhole. The predictability of the developed CFD model has been validated against literature experimental data. It is found that the collapse of an unstable deep keyhole was responsible for the formation of pores. In addition, higher laser scanning speeds tend to form unstable melt pools, e.g., melt pool break-up.

Microstructure Characterization of AlSi10Mg Fabricated by Selective Laser Melting Process

2018 ◽  
Vol 941 ◽  
pp. 1437-1442
Author(s):  
Takashi Maeshima ◽  
Keiichiro Oh-Ishi ◽  
Hiroaki Kadoura ◽  
Masashi Hara
Keyword(s):  
Selective Laser Melting ◽  
Molten Pool ◽  
Three Dimensional ◽  
Melting Process ◽  
Powder Layer ◽  
Base Temperature ◽  
Fish Scale ◽  
Laser Melting ◽  
Microstructure Observation ◽  
Three Dimensional Finite Element

Multi-scale microstructure observation and three dimensional finite element thermal analysis of AlSi10Mg alloy fabricated by selective laser melting (SLM) process were demonstrated in order to understand the microstructure formation process during SLM fabrication. The unique hierarchically microstructures were observed: (1) the “fish scale” microstructure corresponding to a part of molten pool consists of columnar and equiaxed grains and (2) these grains contain a substructure of α-Al surrounded by Si particles. It is revealed that a supersaturated Si concentration due to the predicted rapid cooling rate on the order of 106 oC/s. In addition, the base temperature during the fabrication increases gradually with some peak temperature of each laser path as the laser scan has proceeded on a powder layer. Although the thermal changes cause no melting of the AlSi10Mg except directly fused region by selective laser so called molten pool, those are capable of causing precipitation and/or clustering.

scholarly journals Investigation of Residual Stresses Induced during the Selective Laser Melting Process

2013 ◽  
Vol 554-557 ◽  
pp. 1828-1834 ◽  
Author(s):  
Laurent van Belle ◽  
Guillaume Vansteenkiste ◽  
Jean Claude Boyer
Keyword(s):  
Residual Stress ◽  
Residual Stresses ◽  
Selective Laser Melting ◽  
Complex Geometry ◽  
Melting Process ◽  
Hole Drilling ◽  
Internal Stresses ◽  
Laser Melting ◽  
Selective Laser Melting Process ◽  
Engineering Materials

The selective laser melting process (SLM), belonging to the family of additive manufacturing processes, can create complex geometry parts from a CAD file. Previously, only prototypes were created by SLM, but now this process is used to manufacture quickly and directly functional parts. For example, in the PEP (Pôle Européen de la Plasturgie), this process is used to fabricate tooling parts or injection molds with cooling channels that can’t be obtained by conventional routes. During the process, the laser beam generates violent heating and cooling cycles in the material inducing important thermal gradients in the consolidated part. The cyclic thermal expansions and contractions exceeding the maximum elastic strain of the material induce heterogeneous plastic strains and generate internal stresses the level of which can reaches the yield stress of the material and cracks may appear during the process. This paper deals with the measurement and analysis of residual stresses during the selective laser melting of a simple part in maraging steel. The objective of this study is the analysis of experimental results to validate the numerical model previously presented in [1]. Some authors have investigated the residual stresses produced in SLM parts using different experimental measurement methods such as the incremental hole drilling method in [2], the layer removal method see in [3] and [4] or the non-destructive method, by neutron diffraction in [5]. A new method is proposed to evaluate the residual stresses induced during the SLM process, a rosette is fixed on the bottom face of the support. The residual stresses in the created part are calculated from strain and temperature variations when the fused layer is consolidating during the cooling between two layers. Process parameters like the powder thickness or the time cooling between successive layers are studied in this paper. [1] L. Van Belle, G. Vansteenkiste, J.C. Boyer, Comparisons of numerical modeling of the selective laser melting, Key Engineering Materials Vols. 504-506 (2012) pp 1067-1072 [2] C. Casavola, S.L. Campanelli, C. Pappalettere, Experimental analysis of residual stresses in the selective laser melting process, Proceedings of the XIth International Congress and Exposition, June 2-5, 2008 Orlando, Florida USA [3] M. Shiomi, K. Osakada, K. Nakamura, T. Yamashita, F. Abe, Residual stress within metallic model made by selective laser melting process, CIRP Annals - Manufacturing Technology, Vol. 53, No. 1. (2004), pp. 195-198 [4] T. Furumoto, T. Ueda, M.S. Abdul Aziz, A. Hosokawa and R. Tanaka, Study on reduction of residual stress induced during rapid tooling process, influence of heating conditions on residual stress, Key Engineering Materials Vols. 447-448 (2010) pp 785-789 [5] M. Zaeh, G. Branner, Investigation on residual stresses and deformation in selective laser melting, Production Engineering, Volume 4, Number 1 (2010)

scholarly journals Numerical-Experimental Study of the Consolidation Phenomenon in the Selective Laser Melting Process with a Thermo-Fluidic Coupled Model

Materials ◽  
2018 ◽  
Vol 11 (8) ◽  
pp. 1414 ◽  
Author(s):  
Francisco Cordovilla ◽  
Ángel García-Beltrán ◽  
Miguel Garzón ◽  
Diego Muñoz ◽  
José Ocaña
Keyword(s):  
Selective Laser Melting ◽  
Coupled Model ◽  
Melting Process ◽  
Metallic Powder ◽  
Added Value ◽  
Limiting Factors ◽  
Powder Layer ◽  
Laser Melting ◽  
Selective Laser Melting Process ◽  
Eulerian Formulation

One of the main limiting factors for a widespread industrial use of the Selective Laser Melting Process it its lack of productivity, which restricts the use of this technology just for high added-value components. Typically, the thickness of the metallic powder that is used lies on the scale of micrometers. The use of a layer up to one millimeter would be necessarily associated to a dramatic increase of productivity. Nevertheless, when the layer thickness increases, the complexity of consolidation phenomena makes the process difficult to be governed. The present work proposes a 3D finite element thermo-coupled model to study the evolution from the metallic powder to the final consolidated material, analyzing specifically the movements and loads of the melt pool, and defining the behavior of some critical thermophysical properties as a function of temperature and the phase of the material. This model uses advanced numerical tools such as the Arbitrary Lagrangean–Eulerian formulation and the Automatic Remeshing technique. A series of experiments have been carried out, using a high thickness powder layer, allowing for a deeper understanding of the consolidation phenomena and providing a reference to compare the results of the numerical calculations.

A Powder Shrinkage Model for Describing Real Layer Thickness during Selective Laser Melting Process

2010 ◽  
Vol 97-101 ◽  
pp. 3820-3823 ◽  
Author(s):  
Dan Qing Zhang ◽  
Qi Zhou Cai ◽  
Jin Hui Liu ◽  
Rui Di Li
Keyword(s):  
Layer Thickness ◽  
Metal Powder ◽  
Selective Laser Melting ◽  
Melting Process ◽  
Powder Layer ◽  
Laser Melting ◽  
Selective Laser Melting Process ◽  
Mathematical Explanations ◽  
Total Shrinkage ◽  
Initial Layers

Shrinkage tends to generate when loose metal powder melted in each processing layer along the direction of layer growing during selective laser melting process, resulting in an increased real layer thickness. The shrinkage model for layer shrinkage in SLM process is established. The variation of real layer thickness and the relevant mathematical explanations are discussed in this paper. The results show that the total shrinkage of metal powder layer sharply increases in the initial layers, and then reaches to a plateau value with the increased processing layers. This value is defined by the ratio of sliced layer thickness (h) to relative density (k) during selective laser melting process.

scholarly journals Simulation of Stress Field during the Selective Laser Melting Process of the Nickel-Based Superalloy, GH4169

Materials ◽  
2018 ◽  
Vol 11 (9) ◽  
pp. 1525 ◽  
Author(s):  
Zhanyong Zhao ◽  
Liang Li ◽  
Le Tan ◽  
Peikang Bai ◽  
Jing Li ◽  
...  
Keyword(s):  
Tensile Stress ◽  
Compressive Stress ◽  
Selective Laser Melting ◽  
Thermal Strain ◽  
Melting Process ◽  
Laser Melting ◽  
Nickel Based Superalloy ◽  
Melt Pool ◽  
Scanning Line ◽  
Melting And Solidification

In this paper, GH4169 alloy’s distributions of temperature and stress during the selective laser melting (SLM) process were studied. The SLM process is a dynamic process of rapid melting and solidification, and we found there were larger temperature gradients near the turning of scan direction and at the overlap of the scanning line, which produced thermal strain and stress concentration and gave rise to warping deformations. The stresses increased as the distance became further away from the melt pool. There was tensile stress in the most-forming zones, but compressive stress occurred near the melt pool area. When the parts were cooled to room temperature after the SLM process, tensile stress was concentrated around the parts’ boundaries. Residual stress along the z direction caused the warping deformations, and although there was tensile stress in the parts’ surfaces, but there was compressive stress near the substrate.

scholarly journals Modelling of Selective Laser Melting Process of Quartz Glass at Elevated Temperatures

2021 ◽  
Vol 248 ◽  
pp. 01001
Author(s):  
M.A. Gridnev ◽  
R.S. Khmyrov ◽  
A.V. Gusarov
Keyword(s):  
Selective Laser Melting ◽  
Quartz Glass ◽  
Elevated Temperatures ◽  
Melting Process ◽  
Coupled Processes ◽  
Powder Layer ◽  
Layer By Layer ◽  
Laser Melting ◽  
Material Quality ◽  
Powder Consolidation

Selective laser melting (SLM) to date is the method of additive manufacturing allowing fabricating products from powder layer-by-layer according to a 3D model. However, when applying this method to fragile materials, parts crack while fabricating due to high temperatures. Quartz glass is a promising material for fabricating products by SLM without cracks due to a low thermal expansion. However, quality of fabricated material differs from the fused cast ones. This article aims to test the method of SLM with preheating to improve the material quality. Experiments on single track formation in SLM are analysed by modelling the coupled processes of heat transfer and powder consolidation in the laser-interaction zone. The mathematical model is validated by the experiments. It is shown that the preheating can improve the material quality and increase the process productivity but overheating may result in undesirable crystallization.

scholarly journals Improving surface quality in selective laser melting based tool making

2021 ◽  
Author(s):  
Filippo Simoni ◽  
Andrea Huxol ◽  
Franz-Josef Villmer
Keyword(s):  
Surface Roughness ◽  
Additive Manufacturing ◽  
Surface Quality ◽  
Selective Laser Melting ◽  
Melting Process ◽  
Laser Remelting ◽  
Laser Melting ◽  
Great Cost ◽  
Starting Point ◽  
Processing Techniques

AbstractIn the last years, Additive Manufacturing, thanks to its capability of continuous improvements in performance and cost-efficiency, was able to partly replace and redefine well-established manufacturing processes. This research is based on the idea to achieve great cost and operational benefits especially in the field of tool making for injection molding by combining traditional and additive manufacturing in one process chain. Special attention is given to the surface quality in terms of surface roughness and its optimization directly in the Selective Laser Melting process. This article presents the possibility for a remelting process of the SLM parts as a way to optimize the surfaces of the produced parts. The influence of laser remelting on the surface roughness of the parts is analyzed while varying machine parameters like laser power and scan settings. Laser remelting with optimized parameter settings considerably improves the surface quality of SLM parts and is a great starting point for further post-processing techniques, which require a low initial value of surface roughness.

scholarly journals Fabrication of Mesh Patterns Using a Selective Laser-Melting Process

2019 ◽  
Vol 9 (9) ◽  
pp. 1922 ◽  
Author(s):  
Tae Woo Hwang ◽  
Young Yun Woo ◽  
Sang Wook Han ◽  
Young Hoon Moon
Keyword(s):  
Selective Laser Melting ◽  
Laser Scanning ◽  
Dimensional Accuracy ◽  
Base Plate ◽  
Steel Powder ◽  
Melting Process ◽  
304 Stainless Steel ◽  
Process Conditions ◽  
Laser Melting ◽  
Metal Mesh

The selective laser-melting (SLM) process can be applied to the additive building of complex metal parts using melting metal powder with laser scanning. A metal mesh is a common type of metal screen consisting of parallel rows and intersecting columns. It is widely used in the agricultural, industrial, transportation, and machine protection sectors. This study investigated the fabrication of parts containing a mesh pattern from the SLM of AISI 304 stainless steel powder. The formation of a mesh pattern has a strong potential to increase the functionality and cost-effectiveness of the SLM process. To fabricate a single-layered thin mesh pattern, laser layering has been conducted on a copper base plate. The high thermal conductivity of copper allows heat to pass through it quickly, and prevents the adhesion of a thin laser-melted layer. The effects of the process conditions such as the laser scan speed and scanning path on the size and dimensional accuracy of the fabricated mesh patterns were characterized. As the analysis results indicate, a part with a mesh pattern was successfully obtained, and the application of the proposed method was shown to be feasible with a high degree of reliability.

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