The Investigation of Gravity-Driven Metal Powder Flow in Coaxial Nozzle for Laser-Aided Direct Metal Deposition Process

[+] Author and Article Information
Heng Pan, Todd Sparks, Yogesh D. Thakar, Frank Liou

Department of Mechanical and Aerospace Engineering, University of Missouri—Rolla, 1870 Miner Circle, Rolla, MO, 65401

J. Manuf. Sci. Eng 128(2), 541-553 (Sep 18, 2005) (13 pages) doi:10.1115/1.2162588 History: Received September 21, 2004; Revised September 18, 2005

The quality and efficiency of laser-aided direct metal deposition largely depends on the powder stream structure below the nozzle. Numerical modeling of the powder concentration distribution is complex due to the complex phenomena involved in the two-phase turbulence flow. In this paper, the gravity-driven powder flow is studied along with powder properties, nozzle geometries, and shielding gas settings. A 3-D numerical model is introduced to quantitatively predict the powder stream concentration variation in order to facilitate coaxial nozzle design optimizations. Effects of outer shielding gas directions, inner/outer shielding gas flow rate, powder passage directions, and opening width on the structure of the powder stream are systematically studied. An experimental setup is designed to quantitatively measure the particle concentration directly for this process. The numerical simulation results are compared with the experimental data using prototyped coaxial nozzles. The results are found to match and then validate the simulation. This study shows that the particle concentration mode is influenced significantly by nozzle geometries and gas settings.

Copyright © 2006 by American Society of Mechanical Engineers
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Figure 1

Schematic of (a) the conventional coaxial nozzle and (b) the coaxial nozzle in the laser deposition process

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Figure 2

Schematic of the coaxial nozzle used in the direct deposition process

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Figure 3

Snapshot of the simulation

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Figure 4

Microscopic image of H13 tool steel powder particles (a) and size distribution function (b)

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Figure 5

(a) Illustration of 2-D nonspherical particle-wall collision model. (b) Nonspherical particle can be represented by a “satellited” particle that consists of two identical spheres with radius r.

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Figure 6

The surface finishing of powder passage. (a) Microscopic roughness profile of unpolished surface; (b) polished surface and roughness angle distribution on polished surface (c).

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Figure 7

The variations of powder passage configurations

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Figure 8

Schematic computational domain

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Figure 9

Schematic experimental setup to capture instantaneous particle concentration distribution. The laser sheet depth is approximately 1mm.

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Figure 10

The configurations of coaxial nozzle outlet for testing. (a) Outer gas inclined at 30deg; (b) outer gas inclined at 60deg.

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Figure 11

Comparison of computed and measured velocity and turbulence along radial direction at 15mm away from a coaxial nozzle

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Figure 12

Comparison of computed and measured particle concentration distribution. (a) Stream structure. (b) Concentration variation along central axis.

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Figure 13

Powder stream structures formed by different nozzle configurations

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Figure 14

Concentration variation along axial and radial directions in different nozzles

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Figure 15

Measured and calculated particle concentration variation along central axis: (a) case 2; (b) case 5; (c) case 3; (d) case 6; (e) case 4; and (f) case 7

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Figure 16

Flow streamline and turbulence kinetic energy distribution below the coaxial nozzles with different outer gas directions operated at 6m∕s outer gas and 2.5m∕s inner gas. Streamline (a) 90 deg; (c) 60 deg; (e) 30 deg and turbulence (b) 90 deg; (d) 60 deg; (f) 30 deg.

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Figure 17

Plots of axial velocity variation along the axis in 60deg nozzle setting (as specified in Fig. 1) under different outer gas flow rates

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Figure 18

Variations of particle concentration along axis in (a) Nozzle I and (b) Nozzle IV

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Figure 19

Definition of velocities and angles before and after collision

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Figure 20

Schematic of experimental setup to measure restitution and friction coefficients

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Figure 21

Typical image of particle trajectories (a) and the determination of velocities and angle of collision (b)

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Figure 22

The correlation charts between (e, μ) and (U2∕U1, α2∕α1) with impact angle at 30deg

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Figure 23

Measured dependence of the restitution and friction coefficients of H13 tool steel powder particles (100μm) on the impact angle for ABS plastic wall




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