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Author: Grafiati
Published: 10 December 2022
Last updated: 28 January 2023

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1

Shuja, S. Z., and B. S. Yilbas. "Laser produced melt pool: Influence of laser intensity parameter on flow field in melt pool." Optics & Laser Technology 43, no. 4 (June 2011): 767–75. http://dx.doi.org/10.1016/j.optlastec.2010.12.003.

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2

Xu, Yixuan, Dongyun Zhang, Junyuan Deng, Xuping Wu, Lingshan Li, Yinkai Xie, Reinhart Poprawe, Johannes Henrich Schleifenbaum, and Stephan Ziegler. "Numerical Simulation in the Melt Pool Evolution of Laser Powder Bed Fusion Process for Ti6Al4V." Materials 15, no. 21 (October 28, 2022): 7585. http://dx.doi.org/10.3390/ma15217585.

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In order to track the free interface of the melt pool and understand the evolution of the melt pool, the flow of fluid, and the interface behavior of gas and liquid, a physical model is developed by using the VOF method in this paper. Its characteristics are a combined heat source model, including a parabolic rotation and a cylindrical distribution, and a powder bed stochastic distributed model with powder particle size. The unit interface between the metallic and gas phase in the laser–powder interaction zone can only be loaded by the heat source. Only the first and second laser scanning tracks are simulated to reduce the calculation time. The simulation results show that process parameters such as laser power and scanning speed have significant effects on the fluid flow and surface morphology in the melt pool, which are in good agreement with the experimental results. Compared with the first track, the second track has larger melt pool geometry, higher melt temperature, and faster fluid flow. The melt flows intensely at the initial position due to the high flow rate in the limited melt space. Because there is enough space for the metal flow, the second track can obtain smooth surface morphology more easily compared to the first track. The melt pool temperature at the laser beam center fluctuates during the laser scanning process. This depends on the effects of the interaction between heat conduction or heat accumulation or the interaction between heat accumulation and violent fluid flow. The temperature distribution and fluid flow in the melt pool benefit the analysis and understanding of the evolution mechanism of the melt pool geometry and surface topography and further allow regulation of the L-PBF process of Ti6Al4V.
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3

Peng, Jin, Liqun Li, Shangyang Lin, Furong Zhang, Qinglong Pan, and Seiji Katayama. "High-Speed X-Ray Transmission and Numerical Study of Melt Flows inside the Molten Pool during Laser Welding of Aluminum Alloy." Mathematical Problems in Engineering 2016 (2016): 1–13. http://dx.doi.org/10.1155/2016/1409872.

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By using the X-ray transmission imaging system, melt flows inside a molten pool were studied during laser welding of aluminum alloy at different welding speeds. Then, the correlation between temperature gradients along the direction of weld penetration and melt flows in the rear part of a molten pool was analyzed by using a three-dimensional numerical method. And the presented model was verified by experimental results. The corresponding investigation was carried out to further study the correlation between temperature gradient and melt flow behavior of the molten pool in the plate heated by preheating temperature. The results indicated that, in the rear part of the molten pool, the maximum flow velocity was located at the bottom of the molten pool. The melt metal in the rear molten pool caused by different welding speeds had significantly different flow trends. As the welding speed increased, the absorbed intensity on the keyhole front wall also increased as well as the recoil pressure that could maintain the keyhole opened. Consequently, the increase of the welding speed was more beneficial to improving the stability of the molten pool.
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4

Sun, Shou Jin, and Milan Brandt. "Investigation of Hastelloy C Laser Clad Melt Pool Size and its Effect on Clad Formation." Key Engineering Materials 384 (June 2008): 213–27. http://dx.doi.org/10.4028/www.scientific.net/kem.384.213.

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The melt pool size of a single-track clad in the laser cladding of Hastelloy C, a Nickel based alloy, on mild steel substrate has been investigated. The effect of laser processing parameters, such as laser power density, scan rate and powder mass flow rate on the melt pool size has been examined. It was found that the melt pool size is strictly controlled by the melt pool temperature which increases with laser power but decreases with increasing scan rate and powder mass flow rate. The melt pool size is critical for the clad formation in terms of clad height and dilution with the substrate. The clad height increases linearly with the ratio of melt pool size to powder stream diameter while the dilution is an exponential function of the ratio of melt pool size to laser spot size.
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5

Ur Rehman, Asif, Fatih Pitir, and Metin Uymaz Salamci. "Laser Powder Bed Fusion (LPBF) of In718 and the Impact of Pre-Heating at 500 and 1000 °C: Operando Study." Materials 14, no. 21 (November 5, 2021): 6683. http://dx.doi.org/10.3390/ma14216683.

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The morphology of a melt pool has a critical role in laser powder bed fusion (LPBF). Nevertheless, directly characterizing the melt pool during LPBF is incredibly hard. Here, we present the melt pool flow of the entire melt pool in 3D using mesoscopic simulation models. The physical processes occurring within the melt pool are pinpointed. The flow patterns throughout the same are exposed and measured. Moreover, the impact of pre-heating at 500 and 1000 °C has been described. The study findings offer insights into LPBF. The findings presented here are critical for comprehending the LPBF and directing the establishment of improved metrics for process parameters optimization.
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6

Das, Saurabh, and Satya Prakash Kar. "Role of Marangoni Convection in a Repetitive Laser Melting Process." Materials Science Forum 978 (February 2020): 34–39. http://dx.doi.org/10.4028/www.scientific.net/msf.978.34.

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To effectively interpret the fluid flow dynamics in the molten metal pool, a numerical model was established. The moving repetitive Gaussian laser pulse is irradiated in the work piece. The consideration of laser scanning speed makes the transport phenomena complex. The continuity and momentum equations are solved to get the flow velocity of the molten metal in the melt pool. The energy equation is solved to know the temperature field in the work piece. The algebraic equations obtained after discretization of the governing equations by Finite Volume Method (FVM) are then solved by the Tri Diagonal Matrix Method. Enthalpy-porosity technique is used to capture the position of the melt front which determines the shape of the melt pool. Marangoni convection is considered to know its effect on the shape of the melt pool. The surface tension coefficient is taken as both positive and negative value while calculating the Marangoni force. The two possible cases will cause the Marangoni force to distort the flow dynamics in the melt pool . It's dominance over the buoyancy force in controlling the melt pool shape is focused in the present study. Further, the present model will present an insight to the consequences of laser scanning velocity over the melt pool dimensions and shape.
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7

Shuja, S. Z., and B. S. Yilbas. "Laser Heating and Flow Field Developed in the Melt Pool." Numerical Heat Transfer, Part A: Applications 59, no. 12 (June 15, 2011): 970–87. http://dx.doi.org/10.1080/10407782.2011.582418.

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8

Ebrahimi, Amin, Aravind Babu, Chris R. Kleijn, Marcel J. M. Hermans, and Ian M. Richardson. "The Effect of Groove Shape on Molten Metal Flow Behaviour in Gas Metal Arc Welding." Materials 14, no. 23 (December 4, 2021): 7444. http://dx.doi.org/10.3390/ma14237444.

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One of the challenges for development, qualification and optimisation of arc welding processes lies in characterising the complex melt-pool behaviour which exhibits highly non-linear responses to variations of process parameters. The present work presents a computational model to describe the melt-pool behaviour in root-pass gas metal arc welding (GMAW). Three-dimensional numerical simulations have been performed using an enhanced physics-based computational model to unravel the effect of groove shape on complex unsteady heat and fluid flow in GMAW. The influence of surface deformations on the magnitude and distribution of the heat input and the forces applied to the molten material were taken into account. Utilising this model, the complex thermal and fluid flow fields in melt pools were visualised and described for different groove shapes. Additionally, experiments were performed to validate the numerical predictions and the robustness of the present computational model is demonstrated. The model can be used to explore the physical effects of governing fluid flow and melt-pool stability during gas metal arc root welding.
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9

Shen, Hongyao, Jinwen Yan, and Xiaomiao Niu. "Thermo-Fluid-Dynamic Modeling of the Melt Pool during Selective Laser Melting for AZ91D Magnesium Alloy." Materials 13, no. 18 (September 18, 2020): 4157. http://dx.doi.org/10.3390/ma13184157.

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A three dimensional finite element model (FEM) was established to simulate the temperature distribution, flow activity, and deformation of the melt pool of selective laser melting (SLM) AZ91D magnesium alloy powder. The latent heat in phase transition, Marangoni effect, and the movement of laser beam power with a Gaussian energy distribution were taken into account. The influence of the applied linear laser power on temperature distribution, flow field, and the melt-pool dimensions and shape, as well as resultant densification activity, was investigated and is discussed in this paper. Large temperature gradients and high cooling rates were observed during the process. A violent flow occurred in the melt pool, and the divergent flow makes the melt pool wider and longer but shallower. With the increase of laser power, the melt pool’s size increases, but the shape becomes longer and narrower. The width of the melt pool in single-scan experiment is acquired, which is in good agreement with the results predicted by the simulation (with error of 1.49%). This FE model provides an intuitive understanding of the complex physical phenomena that occur during SLM process of AZ91D magnesium alloy. It can help to select the optimal parameters to improve the quality of final parts and reduce the cost of experimental research.
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10

LI, YOU-RONG, DONG-MING MO, LAN PENG, and SHUANG-YING WU. "NUMERICAL INVESTIGATION OF SILICON MELT FLOW IN A SHALLOW ANNULAR POOL UNDER AN AXIAL MAGNETIC FIELD." International Journal of Modern Physics B 21, no. 18n19 (July 30, 2007): 3486–88. http://dx.doi.org/10.1142/s0217979207044792.

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In order to understand the effect of the magnetic field on surface patterns on semi-conducting silicon melt in industrial Czochralski furnaces, we conducted a series of unsteady three-dimensional numerical simulations of silicon melt flow in a shallow annular pool under the axial magnetic field for the magnetic field strength from 0 to 0.1T. The pool is heated from the outer cylindrical wall and cooled at the inner wall. Bottom and top surfaces are adiabatic. When the magnetic field is weak, the simulation can predict various three-dimensional oscillatory flows depending on the radial temperature difference. With the much larger magnetic field, three-dimensional flow becomes axisymmetric steady flow. Details of flow and temperature disturbances are discussed and the critical magnetic field strengths for the onset of axisymmetric steady flow are determined.
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11

Ur Rehman, Asif, Muhammad Arif Mahmood, Fatih Pitir, Metin Uymaz Salamci, Andrei C. Popescu, and Ion N. Mihailescu. "Mesoscopic Computational Fluid Dynamics Modelling for the Laser-Melting Deposition of AISI 304 Stainless Steel Single Tracks with Experimental Correlation: A Novel Study." Metals 11, no. 10 (September 30, 2021): 1569. http://dx.doi.org/10.3390/met11101569.

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For laser-melting deposition (LMD), a computational fluid dynamics (CFD) model was developed using the volume of fluid and discrete element modeling techniques. A method was developed to track the flow behavior, flow pattern, and driving forces of liquid flow. The developed model was compared with experimental results in the case of AISI 304 stainless steel single-track depositions on AISI 304 stainless steel substrate. A close correlation was found between experiments and modeling, with a deviation of 1–3%. It was found that the LMD involves the simultaneous addition of powder particles that absorb a significant amount of laser energy to transform their phase from solid to liquid, resulting in conduction-mode melt flow. The bubbles within the melt pool float at a specific velocity and escape from the melt pool throughout the deposition process. The pores are generated if the solid front hits the bubble before escaping the melt pool. Based on the simulations, it was discovered that the deposited layer’s counters took the longest time to solidify compared to the overall deposition. The bubbles strived to leave through the contours in an excess quantity, but became stuck during solidification, resulting in a large degree of porosity near the contours. The stream traces showed that the melt flow adopted a clockwise vortex in front of the laser beam and an anti-clockwise vortex behind the laser beam. The difference in the surface tension between the two ends of the melt pool induces “thermocapillary or Benard–Marangoni convection” force, which is insignificant compared to the selective laser melting process. After layer deposition, the melt region, mushy zone, and solidified region were identified. When the laser beam irradiates the substrate and powder particles are added simultaneously, the melt adopts a backwards flow due to the recoil pressure and thermocapillary or Benard–Marangoni convection effect, resulting in a negative mass flow rate. This study provides an in-depth understanding of melt pool dynamics and flow pattern in the case of LMD additive manufacturing technique.
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12

Yang Guang, 杨. 光., 赵恩迪 Zhao Endi, 钦兰云 Qin Lanyun, 李长富 Li Changfu, and 王. 维. Wang Wei. "Effect of electromagnetic stirring on melt flow velocity of laser melt pool and solidification structure." Infrared and Laser Engineering 46, no. 9 (2017): 906006. http://dx.doi.org/10.3788/irla201746.0906006.

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13

Han, Lijun, Frank W. Liou, and Srinivas Musti. "Thermal Behavior and Geometry Model of Melt Pool in Laser Material Process." Journal of Heat Transfer 127, no. 9 (April 25, 2005): 1005–14. http://dx.doi.org/10.1115/1.2005275.

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Melt pool geometry and thermal behavior control are essential in obtaining consistent building performances, such as geometrical accuracy, microstructure, and residual stress. In this paper, a three dimensional model is developed to predict the thermal behavior and geometry of the melt pool in the laser material interaction process. The evolution of the melt pool and effects of the process parameters are investigated through the simulations with stationary and moving laser beam cases. The roles of the convection and surface deformation on the heat dissipation and melt pool geometry are revealed by dimensionless analysis. The melt pool shape and fluid flow are considerably affected by interfacial forces such as thermocapillary force, surface tension, and recoil vapor pressure. Quantitative comparison of interfacial forces indicates that recoil vapor pressure is dominant under the melt pool center while thermocapillary force and surface tension are more important at the periphery of the melt pool. For verification purposes, the complementary metal oxide semiconductor camera has been utilized to acquire the melt pool image online and the melt pool geometries are measured by cross sectioning the samples obtained at various process conditions. Comparison of the experimental data and model prediction shows a good agreement.
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14

Li, Y. R., L. Peng, S. Y. Wu, N. Imaishi, and D. L. Zeng. "Thermocapillary-buoyancy flow of silicon melt in a shallow annular pool." Crystal Research and Technology 39, no. 12 (December 2004): 1055–62. http://dx.doi.org/10.1002/crat.200410290.

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15

ZHANG, Quan-zhuang, Lan PENG, and Na MAO. "ICOPE-15-C164 Three-dimensional flow in a thin Czochralski pool of silicon melt with bidirectional temperature gradients." Proceedings of the International Conference on Power Engineering (ICOPE) 2015.12 (2015): _ICOPE—15——_ICOPE—15—. http://dx.doi.org/10.1299/jsmeicope.2015.12._icope-15-_217.

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16

Tian, Yang, Dacian Tomus, Aijun Huang, and Xinhua Wu. "Melt pool morphology and surface roughness relationship for direct metal laser solidification of Hastelloy X." Rapid Prototyping Journal 26, no. 8 (June 23, 2020): 1389–99. http://dx.doi.org/10.1108/rpj-08-2019-0215.

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Purpose Limited research has attempted to reveal the different modes of the melt pool formation in additive manufacturing. This paper aims to study the mechanisms of surface roughness formation, especially on the aspect of melt pool formation which determine the surface profile and consequently significantly influence the surface roughness. Design/methodology/approach In this study, the conditions under which different modes of melt pool formation (conduction mode and keyhole mode) occur for the case of as-fabricated Hastelloy X using direct metal laser solidification (DMLS) are derived and validated experimentally. Top surfaces of uni-directionally built samples under various processing conditions are cut, grinded, polished and etched to reveal their individual melt pool morphologies. Similarly, up-skin (slope angle < 90°) and down-skin (slope angle > 90°) melt pool morphologies are also investigated to compare the differences. Surface tension gradients and resultant Marangoni flow, which dominate the melt flow in the melt pool, is also calculated to help better evaluate the melt pool shape forming. Findings Two types of melt pool formation modes are dominating in DMLS: conduction mode and keyhole mode. Melt pool formed by conduction mode generally has an aspect ratio of 1:2 (depth vs width) and is in elliptical shape. Appropriate selection of scanning laser power and speed are required to maintain a low characteristic length and width ratio to prevent ballings. Melt pool formed by keyhole mode has an aspect ratio of 1:1 or less. High-energy contour promotes formation of key-hole-shaped melt pool which fills the gaps between layers and smoothens the up-skin surface roughness. Low-energy contour scan is necessary for down-skin surface to form small melt pool profiles and achieve low Ra. Originality/value This paper provides valuable insight into the origins of surface quality problem of DMLS, which is a very critical issue for upgrading the process for manufacturing real components. This paper helps promote the understanding of the attributes and capabilities of this rapidly evolving three-dimensional printing technology and allow appropriate control of processing parameters for successful fabrication of components with sound surface quality.
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17

Pinkerton, A. J., and L. Li. "The development of temperature fields and powder flow during laser direct metal deposition wall growth." Proceedings of the Institution of Mechanical Engineers, Part C: Journal of Mechanical Engineering Science 218, no. 5 (May 1, 2004): 531–41. http://dx.doi.org/10.1243/095440604323052319.

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The additive manufacturing technique of laser direct metal deposition (DMD) has had an impact in rapid prototyping, tooling and small-volume manufacturing applications. Components are built from metallic materials that are deposited by the continuous injection of powder into a moving melt pool, created by a defocused laser beam. The size of the melt pool, the temperature distributions around it and the powder flux are critical in determining process characteristics such as deposition rate. In this paper, the effects that changes in the distance between the laser deposition head and the melt pool have on these factors as a part is built using a coaxial powder feeding system are considered via a two-part analytical model. A heat flow model considers three-dimensional temperature distributions due to a moving Gaussian heat source in a finite volume and a simple mass-flow model considers changes in powder concentration with distance from the deposition head. The model demonstrates the effect of adjusting the melt pool standoff in different ways on melt pool and powder flow characteristics as a DMD structure is built, and hence allows the effect on build rate to be predicted. Its validity is verified by comparison with a series of 316L stainless steel walls, built using different standoff adjustment methods. The model is found to be able to explain the dimensional characteristics found.
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18

Wagner, Jonas, Peter Berger, Philipp He, Florian Fetzer, Rudolf Weber, and Thomas Graf. "Reduced finite-volume model for the fast numerical calculation of the fluid flow in the melt pool in laser beam welding." IOP Conference Series: Materials Science and Engineering 1135, no. 1 (November 1, 2021): 012010. http://dx.doi.org/10.1088/1757-899x/1135/1/012010.

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Abstract In this paper we propose a reduced two-dimensional finite-volume model for the fast calculation of the melt flow. This model was used to determine the influence of the welding speed, viscosity in the melt and vapour flow inside of the keyhole on the fluid flow field, the temperature distribution, and the resulting weld-pool geometry for laser beam welding of aluminium. The reduced computational time resulting from this approach allows the fast qualitative investigation of different aspects of the melt flow over a wide range of parameters. It was found that the effect of viscosity within the melt is more pronounced for lower welding speeds whereas the effect of friction at the keyhole walls is more pronounced for higher welding speeds. The weld-pool geometry mainly depends on the welding speed.
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19

Li, Zhiyong, Gang Yu, Xiuli He, Shaoxia Li, and Zhuang Shu. "Surface Tension-Driven Flow and Its Correlation with Mass Transfer during L-DED of Co-Based Powders." Metals 12, no. 5 (May 14, 2022): 842. http://dx.doi.org/10.3390/met12050842.

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Laser direct energy deposition (L-DED) is one of the most promising additive manufacturing methods, which has been paid more and more attention in recent years. An improved heat and mass transfer model was developed here to analyze thermal behavior, driving force, surface tension-driven flow and its correlation with dilution during L-DED of Co-based powders to a 38MnVS substrate. Thermal behavior was firstly studied for its fundamental influence on fluid flow and mass transfer. Next, the roles of capillary force and thermal capillary force were characterized using both the dimensional analysis and simulation methods, and the mechanism of surface tension-driven flow was also qualitatively investigated. Finally, flow characteristics inside the melt pool were studied in detail and their correlation with the dilution phenomenon was analyzed based on the multi-component mass transfer model. The temperature gradient was found to be much larger at the front of the melt pool, and it took about 200 ms for the melt pool to reach a quasi-steady condition. Moreover, sharp changes in the curvature of the solid/liquid boundary were observed. Surface tension was demonstrated as the main driver for fluid flow and resulted in centrally outward Marangoni flow. Capillary force contributes to the reduction of the curvature of the free surface, and thermal capillary force (Marangoni force) dominated the Marangoni convection. Alloy elements from the powders, such as Co and Ni, were added to the front part of the melt pool and mainly diluted at the upper side of the rear region near the symmetric plane of the melt pool. Fundamental results in this work provide a valuable understanding of the surface tension-driven flow and its correlation with concentration dilution during the additive manufacturing process.
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20

Li, You-Rong, Lan Xiao, Shuang-Ying Wu, and Nobuyuki Imaishi. "Effect of pool rotation on flow pattern transition of silicon melt thermocapillary flow in a slowly rotating shallow annular pool." International Journal of Heat and Mass Transfer 51, no. 7-8 (April 2008): 1810–17. http://dx.doi.org/10.1016/j.ijheatmasstransfer.2007.06.029.

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21

Weston, Brian, Robert Nourgaliev, Jean-Pierre Delplanque, and Andrew T. Barker. "Preconditioning a Newton-Krylov solver for all-speed melt pool flow physics." Journal of Computational Physics 397 (November 2019): 108847. http://dx.doi.org/10.1016/j.jcp.2019.07.045.

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22

Li, You-Rong, Nobuyuki Imaishi, Takeshi Azami, and Taketoshi Hibiya. "Three-dimensional oscillatory flow in a thin annular pool of silicon melt." Journal of Crystal Growth 260, no. 1-2 (January 2004): 28–42. http://dx.doi.org/10.1016/j.jcrysgro.2003.08.017.

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23

Mahmood, Muhammad Arif, Asif Ur Rehman, Fatih Pitir, Metin Uymaz Salamci, and Ion N. Mihailescu. "Laser Melting Deposition Additive Manufacturing of Ti6Al4V Biomedical Alloy: Mesoscopic In-Situ Flow Field Mapping via Computational Fluid Dynamics and Analytical Modelling with Empirical Testing." Materials 14, no. 24 (December 15, 2021): 7749. http://dx.doi.org/10.3390/ma14247749.

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Laser melting deposition (LMD) has recently gained attention from the industrial sectors due to producing near-net-shape parts and repairing worn-out components. However, LMD remained unexplored concerning the melt pool dynamics and fluid flow analysis. In this study, computational fluid dynamics (CFD) and analytical models have been developed. The concepts of the volume of fluid and discrete element modeling were used for computational fluid dynamics (CFD) simulations. Furthermore, a simplified mathematical model was devised for single-layer deposition with a laser beam attenuation ratio inherent to the LMD process. Both models were validated with the experimental results of Ti6Al4V alloy single track depositions on Ti6Al4V substrate. A close correlation has been found between experiments and modelling with a few deviations. In addition, a mechanism for tracking the melt flow and involved forces was devised. It was simulated that the LMD involves conduction-mode melt flow only due to the coaxial addition of powder particles. In front of the laser beam, the melt pool showed a clockwise vortex, while at the back of the laser spot location, it adopted an anti-clockwise vortex. During printing, a few partially melted particles tried to enter into the molten pool, causing splashing within the melt material. The melting regime, mushy area (solid + liquid mixture) and solidified region were determined after layer deposition. This research gives an in-depth insight into the melt flow dynamics in the context of LMD printing.
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24

Aggoune, Samia, Farida Hamadi, Karim Kheloufi, Toufik Tamsaout, El-Hachemi Amara, Kada Boughrara, and Cherifa Abid. "The Marangoni Convection Effect on Melt Pool Formation during Selective Laser Melting Process." Defect and Diffusion Forum 412 (November 12, 2021): 107–14. http://dx.doi.org/10.4028/www.scientific.net/ddf.412.107.

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In order to predict the effect of the Marangoni convection and the morphology of melted stainless steel powder, during the selective laser melting (SLM) process, a transient three-dimensional numerical model is developed at the mesoscale. The evolution of the temperature and velocity fields’ is then studied. The initial powder bed distribution is obtained by the discrete element method (DEM) calculation, and the temperature distribution and the molten pool shape deformation are calculated and analyzed by the Ansys-Fluent commercial code. The molten pool shape is obtained by considering the influence of Marangoni convection on the internal flow behavior. The recoil force was not considered in our calculation. As main results, a slight deviation between the position of the maximum temperature of the molten pool and the center of the laser spot is observed. The direction of the heat diffusion is more likely to be horizontal and the flow centrifugal, which causes the melt track to be wide. Finally, the Marangoni convection is the main driver of the flow.
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25

Kaplan, Alexander F. H., Stephanie M. Robertson, Joerg Volpp, and Jan Frostevarg. "Melt pool forming a buttonhole in tailored blank welding with multiple laser spots." IOP Conference Series: Materials Science and Engineering 1135, no. 1 (November 1, 2021): 012022. http://dx.doi.org/10.1088/1757-899x/1135/1/012022.

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Abstract Laser beam welding of tailored blank butt joints of different sheet thickness generates asymmetric melt pool conditions. By employing two, three or four tailored laser beams, additional options for shaping the melt pool conditions can be offered. As observed by high speed imaging, in most multi-spot cases a large stable buttonhole was generated, by the trailing laser beams asymmetrically towards the thinner sheet. Correspondingly, the ablation pressure from the multiple boiling fronts has generated a fast melt jet, particularly along the thicker sheet. In many cases the boiling front kept open to the keyhole rear. The buttonhole differs from the Catenoid-like shape reported earlier. The walls are steeper and the horizontal shape can be asymmetric. The melt pool can switch between different stable modes. Inclined arrangement of three beams enabled even two separate, parallel boiling fronts and melt jets, combining behind the opening. Despite the large buttonhole, sound welds were achieved. Solely for four equal laser beams, arranged as a square, a melt pool without buttonhole was generated. Provided the driving forces from the ablation pressure along with the melt flow are sufficiently explored and understood, new opportunities to optimize the welding process are available.
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26

Chang, Qing Ming, Chang Jun Chen, Xia Chen, and Si Qian Bao. "Numerical Study on Laser Cladding Process of Magnesium Alloys." Advanced Materials Research 214 (February 2011): 224–29. http://dx.doi.org/10.4028/www.scientific.net/amr.214.224.

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In this paper, a three-dimensional simulation model for laser-cladding processes of magnesium alloys is proposed. The applied loading is a moving heat source that depends on process parameters such as power density, laser beam diameter and scanning speed. The effects of process parameters on the melt pool are quantitatively discussed by numerical analysis. In these parameters, Marangoni force is the most important in affecting the molten metal flow and the contour of the melt pool. Both the length and depth of the melt pool vary sharply with temperature dependence of surface tension when the absolute value of this temperature dependence is at lower value.
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27

Choi, J., L. Han, and Y. Hua. "Modeling and Experiments of Laser Cladding With Droplet Injection." Journal of Heat Transfer 127, no. 9 (March 22, 2005): 978–86. http://dx.doi.org/10.1115/1.2005273.

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Laser aided Directed Material Deposition (DMD) is an additive manufacturing process based on laser cladding. A full understanding of laser cladding is essential in order to achieve a steady state and robust DMD process. A two dimensional mathematical model of laser cladding with droplet injection was developed to understand the influence of fluid flow on the mixing, dilution depth, and deposition dimension, while incorporating melting, solidification, and evaporation phenomena. The fluid flow in the melt pool that is driven by thermal capillary convection and an energy balance at the liquid–vapor and the solid–liquid interface was investigated and the impact of the droplets on the melt pool shape and ripple was also studied. Dynamic motion, development of melt pool and the formation of cladding layer were simulated. The simulated results for average surface roughness were compared with the experimental data and showed a comparable trend.
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28

Alam, M. M., and A. F. H. Kaplan. "Analysis of the Rapid Central Melt Pool Flow in Hybrid Laser-Arc Welding." Physics Procedia 39 (2012): 853–62. http://dx.doi.org/10.1016/j.phpro.2012.10.110.

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29

Li, Linmin, Baokuan Li, Lichao Liu, and Yuichi Motoyama. "Numerical Modeling of Fluid Flow, Heat Transfer and Arc–Melt Interaction in Tungsten Inert Gas Welding." High Temperature Materials and Processes 36, no. 4 (April 1, 2017): 427–39. http://dx.doi.org/10.1515/htmp-2016-0120.

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AbstractThe present work develops a multi-region dynamic coupling model for fluid flow, heat transfer and arc–melt interaction in tungsten inert gas (TIG) welding using the dynamic mesh technique. The arc–weld pool unified model is developed on basis of magnetohydrodynamic (MHD) equations and the interface is tracked using the dynamic mesh method. The numerical model for arc is firstly validated by comparing the calculated temperature profiles and essential results with the former experimental data. For weld pool convection solution, the drag, Marangoni, buoyancy and electromagnetic forces are separately validated, and then taken into account. Moreover, the model considering interface deformation is adopted in a stationary TIG welding process with SUS304 stainless steel and the effect of interface deformation is investigated. The depression of weld pool center and the lifting of pool periphery are both predicted. The results show that the weld pool shape calculated with considering the interface deformation is more accurate.
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30

Ur Rehman, Asif, Fatih Pitir, and Metin Uymaz Salamci. "Full-Field Mapping and Flow Quantification of Melt Pool Dynamics in Laser Powder Bed Fusion of SS316L." Materials 14, no. 21 (October 21, 2021): 6264. http://dx.doi.org/10.3390/ma14216264.

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Laser powder bed fusion (LPBF) has a wide range of uses in high-tech industries, including the aerospace and biomedical fields. For LPBF, the flow of molten metal is crucial; until now, however, the flow in the melt pool has not been described thoroughly in 3D. Here, we provide full-field mapping and flow measurement of melt pool dynamics in laser powder bed fusion, through a high-fidelity numerical model using the finite volume method. The influence of Marangoni flow, evaporation, as well as recoil pressure have been included in the model. Single-track experiments were conducted for validation. The temperature profiles at different power and speed parameters were simulated, and results were compared with experimental temperature recordings. The flow dynamics in a single track were exposed. The numerical and experimental findings revealed that even in the same melting track, the melt pool’s height and width can vary due to the strong Marangoni force. The model showed that the variation in density and volume for the same melting track was one of the critical reasons for defects. The acquired findings shed important light on laser additive manufacturing processes and pave the way for the development of robust, computational models with a high degree of reliability.
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31

Johan Sebastian Grass Nuñez, Johan Sebastian Grass Nuñez, Daniel Andres Rojas Perilla, German Alberto Barragan de los Rios, and Reginaldo Teixeira Coelho. "Numerical and Experimental Analysis of Gas Flow in a Coaxial Nozzle Applied to Directed Energy Deposition (DED)." International Journal of Engineering Materials and Manufacture 6, no. 3 (July 15, 2021): 102–13. http://dx.doi.org/10.26776/ijemm.06.03.2021.01.

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create a melt pool on the substrate. A nozzle is used to carry metal powder within a gas flow until the melt pool, concentrating the flow at the same point. Coaxial nozzles usually have also a shield gas flow to prevent oxidation and an internal flow to protect the optical system. A right flow configuration must be selected to avoid high turbulence at the nozzle exit, leading to an efficient, inexpensive, and high-quality process. Due to the complexity of the process, CFD – Computer Fluid Dynamics are becoming necessary to understand the behaviour of those gas flows in DED processes. CFD can offer results close to reality and may allow an optimization of the whole nozzle designs, besides selecting the best gas flows for each application. The present work develops a CFD simulation of the gas flow behaviour in a coaxial nozzle with three internal annular channels (internal, carrier and shield). An initial set of gas flow was selected, based on previous experience of the manufacturer, and then improved. It searches for the low gas consumption, to form a focal point coinciding with the laser focus and a low velocity, which favours the deposition quality. To check the accuracy of the proposed CFD model, experimental measurements of gas velocity were performed and compared with simulated results.
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32

Al-Aloosi, Raghad Ahmed, Zainab Abdul-Kareem Farhan, and Ahmad H. Sabry. "Remote laser welding simulation for aluminium alloy manufacturing using computational fluid dynamics model." Indonesian Journal of Electrical Engineering and Computer Science 27, no. 3 (September 1, 2022): 1533. http://dx.doi.org/10.11591/ijeecs.v27.i3.pp1533-1541.

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The process of remote laser welding is simulated in this study to identify the keyhole-induced porosity generation mechanisms and keyhole. Three processes are simulated and discussed: laser power levels, laser-beam shaping configurations, and laser keyhole process. The simulation finding reveals that pore development is caused by strong melt flow behind the keyhole. As verification, the equivalent experimental test is also carried out. According to the findings, a welding speed with a high level helps to keep the keyholes released and prevents the flow of strong melt; a big advanced leaning-angle also provides inactive molten pool flow, making it difficult for bubbles to float to the backside of the molten pool. The conclusions of this study offer crucial insight into the method of porosity of aluminum (Al) alloys laser welding, as well as advice on how to avoid keyhole-induced porosity. It is also obtained that a smaller laser beam with constant power raises the velocity, welding pool depth, and liquid metal temperature.
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33

Singh, Sapam Ningthemba, Sohini Chowdhury, Yadaiah Nirsanametla, Anil Kumar Deepati, Chander Prakash, Sunpreet Singh, Linda Yongling Wu, Hongyu Y. Zheng, and Catalin Pruncu. "A Comparative Analysis of Laser Additive Manufacturing of High Layer Thickness Pure Ti and Inconel 718 Alloy Materials Using Finite Element Method." Materials 14, no. 4 (February 12, 2021): 876. http://dx.doi.org/10.3390/ma14040876.

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Investigation of the selective laser melting (SLM) process, using finite element method, to understand the influences of laser power and scanning speed on the heat flow and melt-pool dimensions is a challenging task. Most of the existing studies are focused on the study of thin layer thickness and comparative study of same materials under different manufacturing conditions. The present work is focused on comparative analysis of thermal cycles and complex melt-pool behavior of a high layer thickness multi-layer laser additive manufacturing (LAM) of pure Titanium (Ti) and Inconel 718. A transient 3D finite-element model is developed to perform a quantitative comparative study on two materials to examine the temperature distribution and disparities in melt-pool behaviours under similar processing conditions. It is observed that the layers are properly melted and sintered for the considered process parameters. The temperature and melt-pool increases as laser power move in the same layer and when new layers are added. The same is observed when the laser power increases, and opposite is observed for increasing scanning speed while keeping other parameters constant. It is also found that Inconel 718 alloy has a higher maximum temperature than Ti material for the same process parameter and hence higher melt-pool dimensions.
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34

Schleier, Max, Cemal Esen, and Ralf Hellmann. "High speed melt flow monitoring and development of an image processing algorithm for laser fusion cutting." Journal of Laser Applications 34, no. 4 (November 2022): 042026. http://dx.doi.org/10.2351/7.0000785.

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This contribution presents high-speed camera monitoring of melt pool dynamics for steel during laser fusion cutting and compares the images with recordings in aluminum. The experiments are performed by a 4 kW multimode fiber laser with an emission wavelength of 1070 nm. To visualize the thermal radiation from the process zone during the cutting process, the kerf is captured at sample rates of up to 170 000 frames per second without external illumination with a spectral response between 400 and 700 nm, allowing measurements of the melt flow dynamics from geometric image features. The dependencies of the melt flow dynamics on laser processing parameters, such as feed rate, gas pressure, and laser power, can be evaluated. The monitoring system is placed both off-axis and mounted to a conventional cutting head, with the monitoring path aligned to the processing laser for a coaxial and lateral view of the cut kerf. The measured signal characteristics of the images captured from the melt pool are examined in the visible spectral range of the emitted thermal radiation from the process zone. Moreover, a specifically developed image processing algorithm is developed that process and analyze the captured images and extract geometric information for a measurement of the melt flow.
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35

Pan, Z., V. K. Nadimpalli, T. L. Christiansen, S. A. Andersen, M. B. Kjer, O. V. Mishin, and Y. Zhang. "Influence of shielding gas flow on the uniformity of additively manufactured martensitic stainless steel." IOP Conference Series: Materials Science and Engineering 1249, no. 1 (July 1, 2022): 012026. http://dx.doi.org/10.1088/1757-899x/1249/1/012026.

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Abstract Shielding gas flow is essential to the additive manufacturing (AM) process, and the effects of argon shielding gas flow variation on the macroscopic homogeneity of additive manufactured stainless steel parts have been studied using an open-architecture AM system. Such a variation manifests itself layer-by-layer within one part and part-by-part across the build plate. Within one build, a combination of balling behavior, conduction melting and keyhole melting is observed across the build plate using the same laser parameters. Quantitative characterization of the melt pool shapes show that the melt pool width and the penetration depth exhibit the largest variations. Possible relations between the gas flow condition and macroscopic structure variations are discussed and guidelines for improved design of a gas flow system as well as future research directions are suggested for achieving macroscopically uniform metal AM.
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36

Schmidt, Leander, Klaus Schricker, Jean Pierre Bergmann, and Christina Junger. "Effect of Local Gas Flow in Full Penetration Laser Beam Welding with High Welding Speeds." Applied Sciences 10, no. 5 (March 9, 2020): 1867. http://dx.doi.org/10.3390/app10051867.

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Spatter formation is a major issue in deep penetration welding with solid-state lasers at high welding speeds above 8 m/min. In order to limit spatter formation, the use of local gas flows represents a technically feasible solution. By using the gas flow, the pressure balance inside the keyhole, and therefore the keyhole stability, is affected. Existing investigations demonstrate a reduction in spatter and pore formation for partial penetration welding up to a welding speed of 5 m/min. However, the effect of the gas flow is not yet clarified for full penetration welding at welding speeds above 8 m/min. By using a precisely adjustable shielding gas supply, the effect of a local gas flow of argon was characterized by welding stainless steel AISI304 (1.4301/X5CrNi18-10). The influence of the gas flow on the melt pool dynamics and spatter formation was recorded by means of high-speed videography and subsequently analyzed by image processing. Schlieren videography was used to visualize the forming flow flied. By the use of the gas, a change in melt pool dynamics and gas flow conditions was observed, correlating to a reduction in loss of mass up to 70%. Based on the investigations, a model of the acting effect mechanism was given.
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37

Kazmer, David, Clemens Grosskopf, and Varun Venoor. "Vortical Fountain Flows in Plasticating Screws." Polymers 10, no. 8 (July 26, 2018): 823. http://dx.doi.org/10.3390/polym10080823.

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Variances in polymers processed by single-screw extrusion are investigated. While vortical flows are well known in the fluids community and fountain flows are well known to be caused by the frozen layers in injection molding, our empirical evidence and process modeling suggests the presence of vortical fountain flows in the melt channels of plasticating screws adjacent to a slower-moving solids bed. The empirical evidence includes screw freezing experiments with cross-sections of processed high-impact polystyrene (HIPS) blended with varying colorants. Non-isothermal, non-Newtonian process simulations indicate that the underlying causality is increased flow conductance in the melt pool caused by higher temperatures and shear rates in the recirculating melt pool. The results indicate the development of persistent, coiled sheet morphologies in both general purpose and barrier screw designs. The behavior differs significantly from prior melting and plastication models with the net effect of broader residence time distributions. The process models guide potential strategies for the remediation of the processing variances as well as potential opportunities to achieve improved dispersion as well as complex micro and nanostructures in polymer processing.
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38

Demuth, Cornelius, and Andrés Fabián Lasagni. "An Incompressible Smoothed Particle Hydrodynamics (ISPH) Model of Direct Laser Interference Patterning." Computation 8, no. 1 (January 30, 2020): 9. http://dx.doi.org/10.3390/computation8010009.

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Functional surfaces characterised by periodic microstructures are sought in numerous technological applications. Direct laser interference patterning (DLIP) is a technique that allows the fabrication of microscopic periodic features on different materials, e.g., metals. The mechanisms effective during nanosecond pulsed DLIP of metal surfaces are not yet fully understood. In the present investigation, the heat transfer and fluid flow occurring in the metal substrate during the DLIP process are simulated using a smoothed particle hydrodynamics (SPH) methodology. The melt pool convection, driven by surface tension gradients constituting shear stresses according to the Marangoni boundary condition, is solved by an incompressible SPH (ISPH) method. The DLIP simulations reveal a distinct behaviour of the considered substrate materials stainless steel and high-purity aluminium. In particular, the aluminium substrate exhibits a considerably deeper melt pool and remarkable velocity magnitudes of the thermocapillary flow during the patterning process. On the other hand, convection is less pronounced in the processing of stainless steel, whereas the surface temperature is consistently higher. Marangoni convection is therefore a conceivable effective mechanism in the structuring of aluminium at moderate fluences. The different character of the melt pool flow during DLIP of stainless steel and aluminium is confirmed by experimental observations.
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39

Mo, Dong Ming. "Stability Analysis of Thermocapillary Convection of B2O3/Sapphire Melt in an Annular Pool." Materials Science Forum 1036 (June 29, 2021): 175–84. http://dx.doi.org/10.4028/www.scientific.net/msf.1036.175.

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Aiming at the thermocapillary convection stability of sapphire crystal grown by liquid-encapsulated Czochralski method, by non-linear numerical simulation, obtained the flow function and temperature distribution of R-Z cross section, as well as the velocity and temperature distribution at liquid-liquid interface and monitoring point of B2O3/sapphire melt in annular two liquid system, covered with solid upper wall and in microgravity. By means of linear stability analysis, obtained the neutral stability curve and critical stability parameters of the system, and revealed the temperature fluctuation of the liquid-liquid interface. The calculated results of B2O3/sapphire melt were compared with 5cSt silicone oil/HT-70. The results show that under the same geometrical conditions, the flow of B2O3/sapphire melt system is more unstable than 5cSt silicone oil/HT-70, there are two unstable flow patterns, radial three-dimensional steady flow cell and hydrothermal waves near the hot wall. The larger the ratio of Pr number of upper and lower fluid layers is, the better the effect of restraining the flow of lower fluid layers is.
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40

Li, Erlei, Zongyan Zhou, Lin Wang, Ruiping Zou, and Aibing Yu. "Modelling of keyhole dynamics and melt pool flow in laser powder bed fusion process." Powder Technology 400 (March 2022): 117262. http://dx.doi.org/10.1016/j.powtec.2022.117262.

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41

Üstündağ, Ömer, Nasim Bakir, Andrey Gumenyuk, and Michael Rethmeier. "Influence of an external applied AC magnetic field on the melt pool dynamics at high-power laser beam welding." IOP Conference Series: Materials Science and Engineering 1135, no. 1 (November 1, 2021): 012017. http://dx.doi.org/10.1088/1757-899x/1135/1/012017.

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Abstract The study deals with the determination of the influence of an externally applied oscillating magnetic field on the melt pool dynamics in high power laser beam and hybrid laser arc welding processes. An AC magnet was positioned under the workpiece which is generating an upward directed electromagnetic force to counteract the formation of the droplets. To visualise the melt flow characteristics, several experiments were carried out using a special technique with mild steel from S355J2 with a plate thickness of up to 20 mm and a quartz glass in butt configuration. The profile of the keyhole and the melt flow were recorded with a highspeed camera from the glass side. Additionally, the influence of the magnetic field orientation to the welding direction on the filler material dilution on laser hybrid welding was studied with variating oscillation frequency. The element distribution over the whole seam thickness was measured with X-ray fluorescence (XRF). The oscillation frequency demonstrated a great influence on the melt pool dynamics and the mixing of the elements of the filler wire. The highspeed recordings showed, under the influence of the magnetic field, that the melt is affected under strong vortex at the weld root, which also avoids the formation of droplets.
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42

Turichin, Gleb A., Ekaterina A. Valdaytseva, Stanislav L. Stankevich, and Ilya N. Udin. "Computer Simulation of Hydrodynamic and Thermal Processes in DLD Technology." Materials 14, no. 15 (July 25, 2021): 4141. http://dx.doi.org/10.3390/ma14154141.

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This article deals with the theoretical issues of the formation of a melt pool during the process of direct laser deposition. The shape and size of the pool depends on many parameters, such as the speed and power of the process, the optical and physical properties of the material, and the powder consumption. On the other hand, the influence of the physical processes occurring in the material on one another is significant: for instance, the heating of the powder and the substrate by laser radiation, or the formation of the free surface of the melt, taking into account the Marangoni effect. This paper proposes a model for determining the size of the melt bath, developed in a one-dimensional approximation of the boundary layer flow. The dimensions and profile of the surface and bottom of the melt pool are obtained by solving the problem of convective heat transfer. The influence of the residual temperature from the previous track, as well as the heat from the heated powder of the gas–powder jet, taking into account its spatial distribution, is considered. The simulation of the size and shape of the melt pool, as well as its free surface profile for different alloys, is performed with 316 L steel, Inconel 718 nickel alloy, and VT6 titanium alloy
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43

Peng, Jin, Jigao Liu, Xiaohong Yang, Jianya Ge, Peng Han, Xingxing Wang, Shuai Li, and Zhibin Yang. "Numerical Simulation of Droplet Filling Mode on Molten Pool and Keyhole during Double-Sided Laser Beam Welding of T-Joints." Crystals 12, no. 9 (September 6, 2022): 1268. http://dx.doi.org/10.3390/cryst12091268.

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The effects of droplets filling the molten pools during the double-sided laser beam welding (DSLBW) of T-joints was established. The dynamic behavior of the keyhole and the molten pool under different droplet filling modes were analyzed. The results indicated that compared with the contact transition, the stability of metal flow on the keyhole wall was reduced by free transition and slight contact transition. At the later stage of the droplet entering the molten pool via free transition, slight contact transition, and contact transition, the maximum flow velocity of the keyhole wall was 5.33 m/s, 4.57 m/s, and 2.99 m/s, respectively. When the filling mode was free transition or slight contact transition, the keyhole collapsed at the later stage of the droplet entering the molten pool. However, when the filling mode was contact transition, the middle-upper part of the interconnected keyholes became thinner at the later stage of the droplet entering the molten pool. At the later stage of the droplet entering the molten pool via free transition, the flow vortex at the bottom of the keyhole disappeared and the melt at the bottom of the keyhole flowed to the rear of the molten pool, however, the vortex remained during slight contact transition and contact transition.
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44

Zhang, Quan-Zhuang, Lan Peng, Fei Wang, and Jia Liu. "Effect of pool rotation on three-dimensional flow in a shallow annular pool of silicon melt with bidirectional temperature gradients." Fluid Dynamics Research 48, no. 4 (May 25, 2016): 045501. http://dx.doi.org/10.1088/0169-5983/48/4/045501.

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45

Shi, Lin, Laihege Jiang, and Ming Gao. "Numerical research on melt pool dynamics of oscillating laser-arc hybrid welding." International Journal of Heat and Mass Transfer 185 (April 2022): 122421. http://dx.doi.org/10.1016/j.ijheatmasstransfer.2021.122421.

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46

Han, L., and F. W. Liou. "Numerical investigation of the influence of laser beam mode on melt pool." International Journal of Heat and Mass Transfer 47, no. 19-20 (September 2004): 4385–402. http://dx.doi.org/10.1016/j.ijheatmasstransfer.2004.04.036.

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47

Zhang, Chen, Xinwei Li, and Ming Gao. "Effects of circular oscillating beam on heat transfer and melt flow of laser melting pool." Journal of Materials Research and Technology 9, no. 4 (July 2020): 9271–82. http://dx.doi.org/10.1016/j.jmrt.2020.06.030.

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48

Kao, A., T. Gan, C. Tonry, I. Krastins, and K. Pericleous. "Thermoelectric magnetohydrodynamic control of melt pool dynamics and microstructure evolution in additive manufacturing." Philosophical Transactions of the Royal Society A: Mathematical, Physical and Engineering Sciences 378, no. 2171 (April 13, 2020): 20190249. http://dx.doi.org/10.1098/rsta.2019.0249.

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Large thermal gradients in the melt pool from rapid heating followed by rapid cooling in metal additive manufacturing generate large thermoelectric currents. Applying an external magnetic field to the process introduces fluid flow through thermoelectric magnetohydrodynamics. Convective transport of heat and mass can then modify the melt pool dynamics and alter microstructural evolution. As a novel technique, this shows great promise in controlling the process to improve quality and mitigate defect formation. However, there is very little knowledge within the scientific community on the fundamental principles of this physical phenomenon to support practical implementation. To address this multi-physics problem that couples the key phenomena of melting/solidification, electromagnetism, hydrodynamics, heat and mass transport, the lattice Boltzmann method for fluid dynamics was combined with a purpose-built code addressing solidification modelling and electromagnetics. The theoretical study presented here investigates the hydrodynamic mechanisms introduced by the magnetic field. The resulting steady-state solutions of modified melt pool shapes and thermal fields are then used to predict the microstructure evolution using a cellular automata-based grain growth model. The results clearly demonstrate that the hydrodynamic mechanisms and, therefore, microstructure characteristics are strongly dependent on magnetic field orientation. This article is part of the theme issue ‘Patterns in soft and biological matters'.
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49

Zeng, Quanren, Yankang Tian, Zhenhai Xu, and Yi Qin. "Simulation of thermal behaviours and powder flow for direct laser metal deposition process." MATEC Web of Conferences 190 (2018): 02001. http://dx.doi.org/10.1051/matecconf/201819002001.

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Laser engineering net-shaping (LENS), based on directed energy deposition (DED), is one of the popular AM technologies for producing fully dense complex metal structural components directly from laser metal deposition without using dies or tooling and hence greatly reduces the lead-time and production cost. However, many factors, such as powder-related and laser-related manufacturing parameters, will affect the final quality of components produced by LENS process, especially the powder flow distribution and thermal history at the substrate. The powder concentration normally determines the density and strength of deposited components; while the thermal behaviours of melt pool mainly determines the cooling rate, residual stress and consequent cracks in deposited components. Trial and errors method is obviously too expensive to afford for diverse applications of different metal materials and various manufacturing input parameters. Numerical simulation of the LENS process will be an effective means to identify reasonable manufacturing parameter sets for producing high quality crack-free components. In this paper, the laser metal powder deposition process of LENS is reported. The gas-powder flow distribution below the deposition nozzle is obtained via CFD simulation. The thermal behaviours of substrate and as-deposited layer/track during the LENS process are investigated by using FEM analysis. Temperature field distributions caused by the moving laser beam and the resultant melt pool on the substrate, are simulated and compared. The research offers a more accurate and practical thermal behaviour model for LENS process, which could be applied to further investigation of the interactions between laser, melt pool and powder particles; it will be particularly useful for manufacturing key components which has more demanding requirement on the components’ functional performance.
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50

Hong, Wang, Ling Yun Wang, and Ri Sheng Li. "Porosity Formation after the Irradiation Termination of Laser." Advanced Materials Research 800 (September 2013): 201–4. http://dx.doi.org/10.4028/www.scientific.net/amr.800.201.

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Porosity is formed because of the keyhole collapse. The porosity formation is associated with the melt pool dynamics, the keyhole collapse and solidification processes. The objective of the paper is t to investigate porosity formation mechanisms and fluid flow in the melt pool using the volume of fluid method. The results indicate that the formation of porosity in continuous wave keyhole mode laser welding is associated to keyhole collapse, backfilling of liquid metal close the gas exit of the laser welding keyhole, surface tension of the gas/liquid interface play an important role in the backfilling downward to the keyhole right after laser beams left.Keywords: porosity; keyhole; collapse; welding; model
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