# Monitoring Approach to Evaluate the Performances of a New Deposition Nozzle Solution for DED Systems

^{1}

^{2}

^{3}

^{*}

## Abstract

**:**

## 1. Introduction

- an off-axis configuration, in which a single powder flow laterally passes through the laser beam;
- a continuous coaxial configuration, in which a conical powder flow surrounds and interacts with the laser beam;
- a discontinuous coaxial configuration, with several powder flows from different injection nozzles (i.e., multiple nozzle deposition) distributed around the laser beam (up to eight in a robotized laser-based direct metal deposition system recently developed [7]).

## 2. Materials and Methods

_{50}: 70 ± 5 μm, as mentioned by the powder supplier).

- in the first one, only one nozzle is active without the presence of the substrate (see Figure 3a);
- in the second one, two nozzles are active without the presence of the substrate (see Figure 3b);
- in the third one, two nozzles and a flat substrate placed at 15 mm from the centre of the nozzle outlet are present. In this case, a flat substrate is included in order to analyse the effectiveness of the provided nozzle solution in limiting the spread of the powder particles at the first layer deposition (see Figure 3c).

_{k}is the corresponding total intensity of the powder flow for each evaluated plane. For each experimental video, the intensity thresholds chosen for the binary-mask filter are those satisfying Equation (1) (see Figure 6).

## 3. CFD Modeling and Theoretical Assumptions

^{®}FLUENT (v15.0) and based on the Navier-Stokes equations. To describe a turbulent flow, the time-averaging governing equations are:

- conservation of mass:$$\frac{\partial}{\partial x}\left(\rho {u}_{i}\right)=0$$
^{3}), u_{i}is the gas velocity, and x_{i}is the gas position. - Conservation of momentum:$$\frac{\partial}{\partial x}\left(\rho {u}_{i}{u}_{j}\right)=-\frac{\partial p}{\partial {x}_{i}}+\frac{\partial \left(\left[\left(\mu +{\mu}_{t}\right)\left(\frac{\partial {u}_{i}}{\partial {x}_{j}}+\frac{\partial {u}_{j}}{\partial {x}_{i}}\right)\right]\right)}{\partial {x}_{j}}+\rho {g}_{i}$$
^{−5}kg/m s), and μ_{t}is the turbulent viscosity.

_{1ε}= 1.44, C

_{2ε}= 1.92, k = 1.0, and ε = 1.3 are empirical constants; Pr

_{t}is the turbulent Prandtl number; G

_{k}is the generation of turbulence kinetic energy due to the mean velocity gradients; and G

_{b}is the generator of turbulence kinetic energy due to buoyancy.

^{®}FLUENT, which integrates the differential equation of a particle’s force balance in a Lagrange coordinate system. The balance of the forces is given by:

_{p}is the particle velocity, u is the fluid phase velocity, ρ is the fluid density, ρ

_{p}is the density of the particles, g is the gravitational acceleration, and F

_{i}is an additional acceleration (force/unit particle mass) term. The F

_{D}coefficient is the drag force per powder mass unit and it can be calculated as:

_{D}, μ is the molecular viscosity of the fluid, d

_{p}is the particle diameter, Re is the relative Reynolds number, and C

_{D}is the drag coefficient, defined as:

_{1}, a

_{2}, and a

_{3}are empirical constants. The second term on the right of Equation (8) consists of the gravity and buoyancy forces per unit particle mass. Therefore, the particle velocity can be acquired as:

- only the forces of drag, inertia, and gravity are included in the analysis;
- collisions among particles are not considered;
- the grain size distribution is considered uniform with an average diameter of 70 μm, since it corresponds to the mass median diameter of the powder particle distribution;
- the gas-powder flow is assumed to be a steady state flow;
- the powder particles are assumed to be spherical in shape;
- the substrate “traps” the powder particles reaching the surface.

## 4. Results

^{−0.4}kg/s, the spread of the powder flow at 15 mm from the nozzle outlet decreases to about −14.6% on average.

^{−0.5}to 1.08e

^{−0.4}kg/s, the spread of the powder flow increases (see Table 2). This is mainly due to the increase in the carrier inertia that limits the effect of the shielding gas. Moreover, the influence of the shielding gas is not linear, as happens in the process condition with only one active nozzle. In this case, the experimental analysis shows a significant reduction in the powder particles diffusions for medium values of the shielding gas, followed by a critical enlargement at the highest values. For medium values of the shielding gas, in fact, the average 95% of the powder flow width at 15 mm decreases down to −11.8%, whereas for higher mass flow rates the width only decreases down to −5.6%. The reason for this behaviour can be related to the location at which the two powder flows meet each other. Indeed, upon increasing the shielding mass flow rate from 3.9e

^{−0.4}kg/s to 5.84e

^{−0.4}kg/s, the zone where the two powder flows meet each other ends up being lower compared to the previous cases, moving away from the nozzle outlet. This phenomenon affects the measurements since for high values of the shielding mass flow, the deposition plane is no longer located at 15 mm from the nozzle outlet.

^{−0.4}kg/s and 5.84e

^{−0.4}kg/s, respectively. In particular, when no shielding is applied, the top edges of the area with the maximum powder concentration are indented, indicating a strong rebound of the powder particles on the metal surface of the substrate. On the contrary, Figure 8b,c show a red area with more defined edges and then a limited rebound of the powder particles. The zone with the higher particle concentration seems to be qualitatively smaller for higher values of the shielding mass flow rate (see Figure 8c). Nevertheless, to have a feedback and a quantitative analysis of the influence of the shielding, carrier, and powder mass flow on the deposition efficiency of the process under this process conditions, further experimental tests are required.

## 5. Discussion

- the experimental analysis is based on 2D images (as those reported in Figure 4);
- the employment of a “binary-mask” filter requires the application of an intensity threshold to highlight the shape of the powder flow;
- the particle mass concentration is provided by the numerical software with no filtering.

- the critical issue in the choice of the filtering value to apply to the CFD outputs;
- the inadequacy of the employed CFD model and assumptions.

^{®}FLUENT, which allows for the modeling of multiple separate, yet interacting phases, where Eulerian treatment is used for each phase, in contrast to the Eulerian-Lagrangian treatment that is used only for the discrete phase model. The application of this numerical model together with a more accurate estimation of the distribution of the powder grain size (i.e., Rosin-Rammler particle size distribution) could improve the experimental fitting of the powder behaviour at the expense of more computational time and memory.

## 6. Conclusions

- the solution of a shielding gas external to the carrier gas significantly affects the powder distribution and powder flow geometry, decreasing the powder spread in correspondence to the deposition plane;
- the external shielding gas contains the spread of the powder particles in opposition to the gravity force and carrier gas inertia that tend to enlarge the powder flow;
- in the case of one active nozzle, increasing the shielding mass flow rate up to 2.92e
^{−0.4}kg/s leads an average reduction of −14.6% of the powder flow width in correspondence to the deposition plane; - in the case of two active nozzles with the presence of the substrate, the shielding gas qualitatively seems to reduce the powder rebound, reducing the extension of the zone of higher particle concentration;
- the employed CFD model does not fit the experimental results. A new and more complex theoretical model has to be implemented to simulate the process (i.e., Eulerian multiphase model) providing a more reliable distribution of the powder grain size (i.e., Rosin-Rammler particle size distribution);
- the results of the experimental campaign highlight that the analysed deposition nozzle can be a good solution for the improvement of the catchment efficiency of a DED system, reducing the powder spread in correspondence to the deposition plane.

## Acknowledgments

## Author Contributions

## Conflicts of Interest

## References

- Dunsky, C. Process monitoring in laser additive manufacturing. Ind. Laser Solut. Manuf.
**2014**, 29, 14–20. [Google Scholar] - Sames, W.J.; List, F.A.; Pannala, S.; Dehoff, R.R.; Babu, S.S. The metallurgy and processing science of metal additive manufacturing. Int. Mater. Rev.
**2016**, 61, 315–360. [Google Scholar] [CrossRef] - Herzog, D.; Seyda, V.; Wycisk, E.; Emmelmann, C. Additive manufacturing of metals. Acta Mater.
**2016**, 117, 371–392. [Google Scholar] [CrossRef] - Scott, J.; Gupta, N.; Weber, C.; Newsome, S.; Wohlers, T.; Caffrey, T. Additive Manufacturing: Status and Opportunities; Science and Technology Policy Institute: Washington, DC, USA, 2012; pp. 1–29. [Google Scholar]
- Toyserkani, E.; Khajepour, A.; Corbin, S.F. Laser Cladding; CRC Press: Boca Raton, FL, USA, 2004. [Google Scholar]
- Zekovic, S.; Dwivedi, R.; Kovacevic, R. Numerical simulation and experimental investigation of gas-powder flow from radially symmetrical nozzles in laser-based direct metal deposition. Int. J. Mach. Tools Manuf.
**2007**, 47, 112–123. [Google Scholar] [CrossRef] - Ding, Y.; Dwivedi, R.; Kovacevic, R. Process planning for 8-axis robotized laser-based direct metal deposition system: A case on building revolved part. Robot. Comput. Integr. Manuf.
**2017**, 44, 67–76. [Google Scholar] [CrossRef] - Fessler, J.R.; Merz, R.; Nickel, A.H.; Prinz, F.B. Laser deposition of metals for shape deposition manufacturing. In Solid Freeform Fabrication Symposium; Bourell, D., Beaman, J., Marcus, H., Crawford, R., Barlow, J., Eds.; University of Texas at Austin: Austin, TX, USA, 2017. [Google Scholar]
- Thompson, S.T.; Bian, L.; Shamsaei, N.; Yadollahi, A. An overview of Direct Laser Deposition for additive manufacturing; Part I: Transport phenomena, modelling and diagnostics. Add. Manuf.
**2015**, 8, 36–62. [Google Scholar] [CrossRef] - Balu, P.; Leggett, P.; Kovacevic, R. Parametric study on a coaxial multi-material powder flow in laser-based powder deposition process. J. Mater. Process. Technol.
**2012**, 212, 1598–1610. [Google Scholar] [CrossRef] - Zhu, G.; Li, D.; Zhang, A.; Tang, Y. Numerical simulation of metallic powder flow in a coaxial nozzle in laser direct metal deposition. Opt. Laser Technol.
**2011**, 43, 106–113. [Google Scholar] [CrossRef] - Smurov, J.; Doubenskaia, M.; Zaitsev, A. Comprehensive analysis of laser cladding by means of optical diagnostics and numerical simulation. Surf. Coat. Technol.
**2013**, 220, 112–121. [Google Scholar] [CrossRef] - Kovaleva, I.; Kovalev, O.; Zaitsev, A.; Smurov, I. Numerical simulation and comparison of powder jet profiles for different types of coaxial nozzles in direct material deposition. Phys. Procedia
**2013**, 41, 810–872. [Google Scholar] [CrossRef] - Costa, L.; Vilar, R. Laser powder deposition. Rapid Prototyp. J.
**2009**, 15, 264–279. [Google Scholar] [CrossRef] - Song, L.; Bagavath-Singh, V.; Dutta, B.; Mazumder, J. Control of melt pool temperature and deposition height during direct metal deposition process. Int. J. Adv. Manuf. Technol.
**2012**, 58, 247–256. [Google Scholar] [CrossRef] - Tabernero, I.; Lamikiz, A.; Ukar, E.; Lopez de Lacalle, L.N.; Angulo, C.; Urbikain, G. Numerical simulation and experimental validation of powder flux distribution in coaxial laser cladding. J. Mater. Process. Technol.
**2010**, 210, 2125–2134. [Google Scholar] [CrossRef] - Wen, S.Y.; Shin, Y.C.; Murthy, J.Y.; Sojka, P.E. Modeling of coaxial powder flow for the laser direct deposition process. Int. J. Heat Mass Transf.
**2009**, 52, 5867–5877. [Google Scholar] [CrossRef] - ImageJ v1.51k. Available online: https://imagej.nih.gov/ij/ (accessed on 26 May 2017).

**Figure 3.**(

**a**) One active nozzle; (

**b**) two active nozzles; (

**c**) two active nozzles with a substrate at 15 mm.

**Figure 4.**

**(a**) Acquired image; (

**b**) acquired image after subtracting the background; (

**c**) evaluation planes on the image filtered by “binary-mask”.

**Figure 5.**Binary-mask filter: resulting powder flow for different intensity thresholds (carrier = 4.51e

^{−0.5}kg/s; shielding = 2.92e

^{−0.4}kg/s; powder feed rate = 0.14 g/s): (

**a**) intensity threshold of 206; (

**b**) intensity threshold of 198.

**Figure 8.**Two active nozzles with a substrate at 15 mm. Carrier mass flow = 1.08e

^{−0.4}kg/s, powder feed rate = 0.2 g/s: (

**a**) shielding = 0 kg/s; (

**b**) shielding = 3.9e

^{−0.4}kg/s; (

**c**) shielding = 5.84e

^{−0.4}kg/s.

**Figure 9.**(

**a**) Particle mass concentration along the nozzle axis; (

**b**) particle mass concentration at the deposition plane and the 10 evaluation lines.

**Figure 10.**Carrier mass flow rate = 4.51e

^{−0.5}kg/s and powder feed rate = 0.1 g/s: (

**a**) shielding mass flow = 0 kg/s; (

**b**) shielding mass flow = 1.95e

^{−0.4}kg/s; (

**c**) shielding mass flow = 2.92e

^{−0.4}kg/s.

Process Parameters for One Nozzle | Low level | Medium level | High level |
---|---|---|---|

carrier mass flow rate (kg/s) | 4.51e^{−0.5} | 5.41e^{−0.5} | |

shielding flow rate (kg/s) | 0 | 1.95e^{−0.4} | 2.92e^{−0.4} |

powder feed rate (g/s) | 0.1 | 0.14 |

One Active Nozzle | Powder Feed Rate = 0.1 g/s | Powder Feed Rate = 0.14 g/s | ||||||
---|---|---|---|---|---|---|---|---|

Carrier = 4.51e^{−0.5} kg/s | Carrier = 5.41e^{−0.5} kg/s | Carrier = 4.51e^{−0.5} kg/s | Carrier = 5.41e^{−0.5} kg/s | |||||

95 % Width (mm) | Variation (%) | 95 % Width (mm) | Variation (%) | 95 % Width (mm) | Variation (%) | 95 % Width (mm) | Variation (%) | |

Shielding = 0 kg/s | 4.93 | - | 4.98 | - | 4.77 | - | 4.97 | - |

Shielding = 1.95e^{−0.4} kg/s | 4.33 | −12 | 4.57 | −8.3 | 4.41 | −7.6 | 4.33 | −12.8 |

Shielding = 2.92e^{−0.4} kg/s | 4.29 | −13 | 4.35 | −12.7 | 4.22 | −11.5 | 3.91 | −21.3 |

Two Active Nozzles | Powder Feed Rate = 0.2 g/s | Powder Feed Rate = 0.28 g/s | ||||||

Carrier = 9.02e^{−0.5} kg/s | Carrier = 1.08e^{−0.4} kg/s | Carrier = 9.02e^{−0.5} kg/s | Carrier = 1.08e^{−0.4} kg/s | |||||

95 % Width (mm) | Variation (%) | 95 % Width (mm) | Variation (%) | 95 % Width (mm) | Variation (%) | 95 % Width (mm) | Variation (%) | |

Shielding = 0 kg/s | 5.73 | - | 6.34 | - | 5.27 | - | 5.56 | - |

Shielding = 3.9e^{−0.4} kg/s | 5.11 | −10.9 | 5.22 | −17.8 | 4.40 | −16.5 | 5.68 | −2.3 |

Shielding = 5.84e^{−0.4} kg/s | 5.29 | −7.8 | 5.58 | −12.1 | 5.32 | −1.1 | 5.64 | −1.5 |

One Active Nozzle | Powder Feed Rate = 0.1 g/s | ||
---|---|---|---|

Carrier = 4.51e^{−0.5} kg/s | |||

Shielding = 0 kg/s | Shielding = 1.95e^{−0.4} kg/s | Shielding = 2.92e^{−0.4} kg/s | |

Experimental 95% of the total width [mm] | 4.93 | 4.33 | 4.29 |

Numerical 95% of the total width [mm] | 5.9 | 5.5 | 7.5 |

Two Active Nozzles | Powder Feed Rate = 0.2 g/s | ||

Carrier = 9.02e^{−0.5} kg/s | |||

Shielding = 0 kg/s | Shielding = 3.90e^{−0.4} kg/s | Shielding = 5.84e^{−0.4} kg/s | |

Experimental 95% of the total width [mm] | 5.73 | 5.11 | 5.29 |

Numerical 95% of the total width [mm] | 4.6 | 9.4 | 4.2 |

© 2017 by the authors. Licensee MDPI, Basel, Switzerland. This article is an open access article distributed under the terms and conditions of the Creative Commons Attribution (CC BY) license (http://creativecommons.org/licenses/by/4.0/).

## Share and Cite

**MDPI and ACS Style**

Mazzucato, F.; Tusacciu, S.; Lai, M.; Biamino, S.; Lombardi, M.; Valente, A.
Monitoring Approach to Evaluate the Performances of a New Deposition Nozzle Solution for DED Systems. *Technologies* **2017**, *5*, 29.
https://doi.org/10.3390/technologies5020029

**AMA Style**

Mazzucato F, Tusacciu S, Lai M, Biamino S, Lombardi M, Valente A.
Monitoring Approach to Evaluate the Performances of a New Deposition Nozzle Solution for DED Systems. *Technologies*. 2017; 5(2):29.
https://doi.org/10.3390/technologies5020029

**Chicago/Turabian Style**

Mazzucato, Federico, Simona Tusacciu, Manuel Lai, Sara Biamino, Mariangela Lombardi, and Anna Valente.
2017. "Monitoring Approach to Evaluate the Performances of a New Deposition Nozzle Solution for DED Systems" *Technologies* 5, no. 2: 29.
https://doi.org/10.3390/technologies5020029