The development of temperature fields and powder flow during laser direct metal deposition wall growth

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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Experimental and Numerical Analysis of the Powder Flow in a Multi-Channel Coaxial Nozzle of a Direct Metal Deposition System

Journal of Manufacturing Science and Engineering ◽

10.1115/1.4049640 ◽

2021 ◽

Vol 143 (7) ◽

Author(s):

Piyush Pant ◽

Dipankar Chatterjee ◽

Sudip Kumar Samanta ◽

Aditya Kumar Lohar

Keyword(s):

Gas Flow ◽

Flow Characteristics ◽

Turbulence Models ◽

Deposition Process ◽

Metal Deposition ◽

Direct Metal Deposition ◽

Powder Flow ◽

Coaxial Nozzle ◽

Proposed Model ◽

Blown Powder

Abstract The work explores the powder transport process, using numerical simulation to address the dynamics of the powder flow in an in-house built multi-channel coaxial nozzle of a direct metal deposition (DMD) system. The fluid turbulence is handled by the standard k–ɛ and k–ω turbulence models, and the results are compared in order to predict their suitability. An image-based technique using CMOS camera is adopted to determine the powder flow characteristics. The model is validated with the in-house experimental results and verified available results in the literature. The findings of this work confirms the application of the k–ω model for powder gas flow investigations in blown powder additive manufacturing (AM) processes due to its better predictive capability. The proposed model will assist in simulating the direct metal deposition process.

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THREE-DIMENSIONAL STAGNATION-POINT FLOW OVER A PERMEABLE STRETCHING/SHRINKING SHEET WITH A SECOND ORDER SLIP FLOW

Advances in Mathematics: Scientific Journal ◽

10.37418/amsj.10.9.16 ◽

2021 ◽

Vol 10 (9) ◽

pp. 3273-3282

Author(s):

M.E.H. Hafidzuddin ◽

R. Nazar ◽

N.M. Arifin ◽

I. Pop

Keyword(s):

Differential Equations ◽

Stagnation Point ◽

Flow Model ◽

Nonlinear Partial Differential Equations ◽

Slip Flow ◽

Three Dimensional ◽

Flow Characteristics ◽

Second Order ◽

Stagnation Point Flow ◽

Shrinking Sheet

The problem of steady laminar three-dimensional stagnation-point flow on a permeable stretching/shrinking sheet with second order slip flow model is studied numerically. Similarity transformation has been used to reduce the governing system of nonlinear partial differential equations into the system of ordinary (similarity) differential equations. The transformed equations are then solved numerically using the \texttt{bvp4c} function in MATLAB. Multiple solutions are found for a certain range of the governing parameters. The effects of the governing parameters on the skin friction coefficients and the velocity profiles are presented and discussed. It is found that the second order slip flow model is necessary to predict the flow characteristics accurately.

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Simulations of Flow and Temperature Fields in a Two Heater PCR Device

Volume 4 ◽

10.1115/ht-fed2004-56401 ◽

2004 ◽

Author(s):

Tom Mautner

Keyword(s):

Thermal Diffusion ◽

Wall Temperature ◽

Lattice Boltzmann ◽

Three Dimensional ◽

Temperature Fields ◽

Thermal Coupling ◽

Uniform Temperature ◽

Temperature Distributions ◽

Flow Through ◽

Heater Design

One module in a bioagent detector currently under development involves a new two-heater, flow-through polymerase chain reaction (PCR) module which is being designed to save space and power and to reduce the amplification time. As in all PCR devices, thermal cycling requires three temperatures and residence times. These are 90–95°C for DNA denaturation, 50–65°C for hybridization and 72–77°C for replication with a time ratio of 4:9:4. The current design uses two heaters with heat conduction in the substrate providing the hybridization temperature. Typically, the flow and temperature fields in microfluidic devices have three-dimensional complexity, thus numerical simulations were performed to provide design guidelines in the development of the two-heater PCR device. The lattice Boltzmann (LB) method was used to perform low Reynolds number (typically Re = 0.10) simulations for two and three dimensional channel geometries having various wall temperature distributions. The momentum and thermal lattice Boltzmann equations were coupled via a body force term in the momentum equation. Initial computations using two- and three-heater configurations in two dimensions demonstrated excellent comparisons with published data provided that both the top and bottom walls were heated. If only one wall was heated, large vertical thermal gradients occurred resulting in non-uniform temperature fields. However, when the same conditions were applied to three dimensional channels, lower temperatures were observed in the center of the channel regardless of the wall temperatures or channel aspect ratio. Parametric studies were performed to evaluate the effects of thermal coupling, thermal diffusion coefficients, entrance temperatures, wall temperature configurations and channel geometry. If was found that moderate variation of the thermal diffusion coefficient produced only minor differences in the temperature field, and large changes in the thermal coupling magnitude demonstrated transition from natural to forced convection flows. The simulations also indicate that the largest effect on flow and temperature uniformity arises from the applied wall temperature distribution (various thickness channel walls). It was found, in 2D, that if the channel wall starts from ambient temperature, the applied heating, on the outer surfaces only, may not result in the desired wall or fluid temperatures. However, once the channel walls are heated to a uniform temperature, excellent temperature distributions are obtained for both thick and thin channel walls. These results indicate that the two-heater design has potential in providing a new flow-through PCR device. However, careful attention must be paid to the wall heater design to provide the required sample temperatures.

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

Journal of Manufacturing Science and Engineering ◽

10.1115/1.2162588 ◽

2005 ◽

Vol 128 (2) ◽

pp. 541-553 ◽

Cited By ~ 39

Author(s):

Heng Pan ◽

Todd Sparks ◽

Yogesh D. Thakar ◽

Frank Liou

Keyword(s):

Gas Flow ◽

Particle Concentration ◽

Metal Deposition ◽

Direct Metal Deposition ◽

Powder Flow ◽

Shielding Gas ◽

Two Phase ◽

Coaxial Nozzle ◽

Gravity Driven ◽

Nozzle Geometries

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.

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Surface Finish Issues after Direct Metal Deposition

Materials Science Forum ◽

10.4028/www.scientific.net/msf.706-709.228 ◽

2012 ◽

Vol 706-709 ◽

pp. 228-233 ◽

Cited By ~ 3

Author(s):

P. Peyre ◽

M. Gharbi ◽

C. Gorny ◽

M. Carin ◽

S. Morville ◽

...

Keyword(s):

Surface Finish ◽

Experimental Tests ◽

Metal Deposition ◽

Direct Metal Deposition ◽

Physical Mechanisms ◽

Melt Pool ◽

3D Profilometry ◽

Surface Finishes ◽

3D Shapes

Derived from laser cladding, the Direct Metal Deposition (DMD) laser process, is based upon a laser beam – projected powder interaction, and allows manufacturing complex 3D shapes much faster than conventional processes. However, the surface finish remains critical, and DMD parts usually necessitate post-machining steps. In this context, the focus of our work was: (1) to understand the physical mechanisms responsible for deleterious surface finishes, (2) to propose different experimental solutions for improving surface finish. Our experimental approach is based upon: (1) adequate modifications of the DMD conditions (gas shielding, laser conditions, coaxial or off-axis nozzles), (2) a characterization of laser-powder-melt-pool interactions using fast camera analysis, (3) a precise check of surface aspects using 3D profilometry, SEM, (4) preliminary thermo-convective simulations to understand melt-pool hydrodynamics. Most of the experimental tests were carried out on a Ti6Al4V titanium alloy, widely investigated already. Results confirm that surface degradation depends on two aspects: the sticking of non-melted or partially melted particles on the free surfaces, and the formation of menisci with more or less pronounced curvature radii. Among other aspects, a reduction of layer thickness and an increase of melt-pool volumes to favor re-melting processes are shown to have a beneficial effect on roughness parameters.

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An analytical model of the melt pool and single track in coaxial laser direct metal deposition (LDMD) additive manufacturing

Journal of Micromechanics and Molecular Physics ◽

10.1142/s2424913017500138 ◽

2017 ◽

Vol 02 (04) ◽

pp. 1750013 ◽

Cited By ~ 4

Author(s):

Jian Liu ◽

Erica Stevens ◽

Qingchen Yang ◽

Markus Chmielus ◽

Albert C. To

Keyword(s):

Analytical Model ◽

Interaction Model ◽

Source Model ◽

Metal Deposition ◽

Direct Metal Deposition ◽

Single Track ◽

Gaussian Laser Beam ◽

Track Geometry ◽

Geometry Model ◽

Melt Pool

An analytical model was developed for the melt pool and single scan track geometry as a function of process parameters. For computational efficiency, the developed model has simple mathematical forms with essential physics taken into account, without the need for complicated numerical simulation. In this research, a non-diverging Gaussian laser beam and coaxial diverging Gaussian powder stream combination is used to represent the coaxial laser direct metal deposition (LDMD) process. Analytical laser-powder interaction model is used to obtain the distribution of attenuated laser intensity and temperature of heated powders at the substrate. On the substrate, the melt pool is calculated by integrating Rosenthal's point heat source model. An iterative procedure is used to ensure the mass–energy balances and to calculate the melt pool and catchment efficiency. By assuming that the assimilated powder will reshape due to surface tension before solidification, a simple clad geometry model is established. The proposed model is used to simulate the geometry of single track depositions of Ti6Al4V, which shows a good agreement between model prediction and experimental results. This work demonstrates that the developed model has the potential to be used to narrow the parameter space for process optimization.

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