Powder particle–wall collision-based design of the discrete axial nozzle-exit shape in direct laser deposition

date: 14.07.2022

category: Sporočila za javnost

 

Researchers of the Faculty of Mechanical Engineering, University of Ljubljana in collaboration with researchers from the Japanese company DMG MORI, have published results of numerical and experimental study of the influence of the powder particle wall collisions in the design of the exit geometry of an axial nozzle used for powder delivery in laser direct deposition.  Asist. dr. Andrej Jeromen, research assistent Ana Vidergar, dr. Makoto Fujishima, prof. dr. Gideon N. Levy, and prof. dr. Edvard Govekar have published the article “Powder particle–wall collision-based design of the discrete axial nozzle-exit shape in direct laser deposition“ in the Journal of materials processing technology (IF: 6.162).

To improve the efficiency of the direct laser deposition (DLD) of metal powders, a concentrated powder-stream distribution is required, which can be affected by the shape of the powder-delivery nozzle.  In this study, a simplified, powder particle–wall collision-based 3D numerical model of the powder flow in the

^{Fig. 1. a) Parameters of the conical nozzle’s exit and characteristic examples of the particle center-of-mass trajectories. Particle–wall collisions at a divergent exit-cone angle of the nozzle (β>0) in the case of smooth (b) and rough (c) inner surfaces of the nozzle.}

nozzle was used to simulate the influences of the nozzle-exit shape on the concentration of the powder stream distribution, characterized by its diameter d₉₀.  The nozzle-exit shape was parametrized by the exit-cone angle β, length L, and inner-surface roughness (Fig. 1). Based on the simulation results (Fig. 2)

^{Fig. 2. Simulated results of powder-stream diameter, d₉₀ , vs cone length, L: a) at a surface-roughness-angle standard deviation of σ_γ = 0 for different nozzle-exit cone angles, β, and b), c) and d) at nozzle-exit cone angles of β= 0°, 3.5°, and 7.2°, respectively, for different standard deviations of the surface-roughness angle, σ_γ.}

the nozzle exit shapes of three exit-cone angles (0°, 3.5° and 7.2°), various lengths and surface-roughness values were designed.  For the two larger particle sizes of 82 µm and 132 µm considered, the wall-collision-dominated regime and the influence of the nozzle-exit shape were experimentally confirmed. In particular, a significant decrease in the powder-stream diameter when increasing the divergent nozzle-exit cone angle or decreasing its surface roughness and the nonlinear influence of the cone length were shown (Fig. 3).

^{Fig. 3. Examples of acquired summed images}

Using single-layer, powder-deposition experiments (Fig. 4) it was demonstrated that by modifying the design of the nozzle-exit shape, the powder-catchment efficiency was increased by 13% due to the increased nozzle-exit cone angle and by 19% due to the reduced surface roughness.

^{Fig. 4. Example cross-section images of the deposited layer}

 

 

Link to the article: https://doi.org/10.1016/j.jmatprotec.2022.117704

 

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