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Research Papers

Numerical Modeling of Heat Distribution in the Electron Beam Melting® of Ti-6Al-4V

[+] Author and Article Information
Mahdi Jamshidinia

e-mail: mjamshidinia@mail.smu.edu

Fanrong Kong

ASME Membership: 000100003082
e-mail: kongfr2241@gmail.com

Radovan Kovacevic

e-mail: kovacevi@lyle.smu.edu
Research Center for Advanced Manufacturing (RCAM),
Lyle School of Engineering,
Southern Methodist University,
3101 Dyer Street,
Dallas, TX 75205

1Corresponding author.

Manuscript received May 1, 2013; final manuscript received September 25, 2013; published online November 7, 2013. Assoc. Editor: Yung Shin.

J. Manuf. Sci. Eng 135(6), 061010 (Nov 07, 2013) (14 pages) Paper No: MANU-13-1207; doi: 10.1115/1.4025746 History: Received May 01, 2013; Revised September 25, 2013

Electron beam melting® (EBM) is one of the fastest growing additive manufacturing processes capable of building parts with complex geometries, made predominantly of Ti-alloys. Providing an understanding of the effects of process parameters on the heat distribution in a specimen built by EBM®, could be the preliminary step toward the microstructural and consequently mechanical properties control. Numerical modeling is a useful tool for the optimization of processing parameters, because it decreases the level of required experimentation and significantly saves on time and cost. So far, a few numerical models are developed to investigate the effects of EBM® process parameters on the heat distribution and molten pool geometry. All of the numerical models have ignored the material convection inside the molten pool that affects the real presentation of the temperature distribution and the geometry of molten pool. In this study, a moving electron beam heat source and temperature dependent properties of Ti-6Al-4V were used in order to provide a 3D thermal-fluid flow model of EBM®. The influence of process parameters including electron beam scanning speed, electron beam current, and the powder bed density were studied. Also, the effects of flow convection in temperature distribution and molten pool geometry were investigated by comparing a pure-thermal with the developed thermal-fluid flow model. According to the results, the negative temperature coefficient of surface tension in Ti-6Al-4V was responsible for the formation of an outward flow in the molten pool. Also, results showed that ignoring the material convection inside the molten pool resulted in the formation of a molten pool with narrower width and shorter length, while it had a deeper penetration and higher maximum temperature in the molten pool. Increasing the powder bed density was accompanied with an increase in the thermal conductivity of the powder bed that resulted in a reduction in the molten pool width on the powder bed top surface. Experimental measurements of molten pool width and depth are performed to validate the numerical model.

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Figures

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Fig. 1

Schematic of the components of EBM setup

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Fig. 2

The flowchart of experimental procedure used for EBM of Ti-6Al-4V

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Fig. 3

The geometry of the domain; (a) the domain overview, (b) horizontal view of the domain cross-section, and (c) longitudinal view of the domain cross-section

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Fig. 4

Two solid powder particles sintering zone

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Fig. 5

Estimation of normalized contact conductivity of a powder bed with density equal 56% [34,35]

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Fig. 6

Numerical procedure flowchart used for EBM of Ti-6Al-4V [22]

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Fig. 7

The independency of numerical analysis results to mesh density [22]

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Fig. 8

The effect of time step size on molten pool width

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Fig. 9

Electron beam melted Ti-6Al-4V trace, (a) The 3D image of the electron beam trace provided by profilometer and (b) The image of the electron beam trace provided by optical microscope [22]

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Fig. 10

The numerical model validation by comparing the numerical and experimental results of (a) molten pool width for different electron beam currents, (b) molten pool width for different electron beam scanning speeds, (c) molten pool depth for different electron beam scanning speeds, (d) schematic of molten pool depth, and (e) schematic of molten pool width

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Fig. 11

Comparison of the numerically simulated temperature distribution and molten pool width in EBM® with respect to the experimental results

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Fig. 12

The effect of electron beam scanning speed on the molten pool half width with 14 mA as an electron beam current, (a) scanning speed = 100 mm/s, (b) scanning speed = 300 mm/s, and (c) scanning speed = 500 mm/s

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Fig. 13

The effects of electron beam current (a); and electron beam scanning speed (b) on numerically estimated molten pool length

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Fig. 14

The effect of fluid convection on temperature distribution and molten pool geometry in a model with 100 mm/s electron beam scanning speed and 14 mA electron beam current, (a) temperature distribution on the powder bed top surface, (b) molten pool geometry at Y = 6 mm along the electron beam scanning direction, and (c) molten pool geometry on the powder bed top surface, (1) pure-thermal model, (2) thermal-fluid flow model

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Fig. 15

The comparison of molten pool geometry and fluid convection patterns in the model at 100 mm/s electron beam scanning speed and 14 mA electron beam current, (a) view along the electron beam moving direction at Y = 6 mm, (b) view normal to electron beam moving direction at symmetry wall, and (c) top view

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Fig. 16

The numerical 3D representation of the temperature distribution and fluid flow at 100 mm/s electron beam scanning speed and 14 mA electron beam current

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Fig. 17

The effect of powder bed density on molten pool dimension

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