Laser Metal Deposition (LMD) is an innovative technology adopted in Additive Manufacturing (AM) processes and its use is becoming more and more popular in various application fields, such as part manufacturing, repair, and prototype fabrication. This technique is capable of creating several layers of solidified material, by the simultaneous delivery of metal powders and the laser beam, and offers an effective way to produce complicated geometries thanks to its high flexibility. However, complex physical phenomena occur during the additive process, which have a great impact on the success of the process, and many of these have yet to be fully understood. With the aim of shedding light on these aspects, a detailed numerical study, focused on LMD technology, will be conducted using three-dimensional models based on Com- putational Fluid Dynamics (CFD). The particle flow problem regarding the coupling between the fluid phase (i.e., the carrier gas) and the solid phase (i.e., a metallic material powder) is first investigated using OpenFOAM, an open source software widely used in the CFD community. In particular, two different numerical approaches are investigated: the first approach is based on an Eulerian method to describe the carrier gas flow combined with a Lagrangian method to describe the particle flow (LE method), and the second approach is based on a pure Eulerian method to model both the carrier gas and the particle flow (EE method). Simulations results show the main features of the two approaches considered in terms of reliability in reproducing the key geometrical and physical features of the LMD process, together with a comparison with experimental evidences. On the other hand, the thermal problem, that describes the interaction between particles flow and the laser beam, play a crucial role and cannot be neglected. For this purpose, the time-dependent Navier-Stokes equations for incompressible flows are coupled with the energy equation in order to represent the temperature field, whereas the Lagrangian description of the particle dynamic is enriched accounting the thermal evolution, and the consequent phase changing of the metallic powder due to the particle-laser interaction. This model is developed in a C++ in-house code using the open source Finite Element library deal.II and it is validated through consolidated results available in the literature. Furthermore, different schemes able to solve the Navier-Stokes equations, coupled with the heat transfer equation, are implemented and compared, so as to prove both accuracy and efficiency. Then, with the aim of investigating the LMD process in detail, and in particular the thermal behaviour of the powder exiting from the nozzle, a sensitivity analysis is performed in terms of the parameters most meaningful from a technological viewpoint, i.e., the nozzle inclination, the carrier gas and powder flow rate, and the laser power. The results of such an analysis show that it is possible to predict both the configuration and the energy distribution that character- izes the flow of the powder leaving the nozzle until it reaches the substrate. In particular, the influence of both laser power and nozzle geometry to phase change conditions of powder flux are analyzed in order to improve the set up of the printing process, which can lead to increased productivity and less material waste.

Computational Fluid Dynamics simulations of Laser Metal Deposition process exploring open source software

MURER, MAURO
2021-07-08T00:00:00+02:00

Abstract

Laser Metal Deposition (LMD) is an innovative technology adopted in Additive Manufacturing (AM) processes and its use is becoming more and more popular in various application fields, such as part manufacturing, repair, and prototype fabrication. This technique is capable of creating several layers of solidified material, by the simultaneous delivery of metal powders and the laser beam, and offers an effective way to produce complicated geometries thanks to its high flexibility. However, complex physical phenomena occur during the additive process, which have a great impact on the success of the process, and many of these have yet to be fully understood. With the aim of shedding light on these aspects, a detailed numerical study, focused on LMD technology, will be conducted using three-dimensional models based on Com- putational Fluid Dynamics (CFD). The particle flow problem regarding the coupling between the fluid phase (i.e., the carrier gas) and the solid phase (i.e., a metallic material powder) is first investigated using OpenFOAM, an open source software widely used in the CFD community. In particular, two different numerical approaches are investigated: the first approach is based on an Eulerian method to describe the carrier gas flow combined with a Lagrangian method to describe the particle flow (LE method), and the second approach is based on a pure Eulerian method to model both the carrier gas and the particle flow (EE method). Simulations results show the main features of the two approaches considered in terms of reliability in reproducing the key geometrical and physical features of the LMD process, together with a comparison with experimental evidences. On the other hand, the thermal problem, that describes the interaction between particles flow and the laser beam, play a crucial role and cannot be neglected. For this purpose, the time-dependent Navier-Stokes equations for incompressible flows are coupled with the energy equation in order to represent the temperature field, whereas the Lagrangian description of the particle dynamic is enriched accounting the thermal evolution, and the consequent phase changing of the metallic powder due to the particle-laser interaction. This model is developed in a C++ in-house code using the open source Finite Element library deal.II and it is validated through consolidated results available in the literature. Furthermore, different schemes able to solve the Navier-Stokes equations, coupled with the heat transfer equation, are implemented and compared, so as to prove both accuracy and efficiency. Then, with the aim of investigating the LMD process in detail, and in particular the thermal behaviour of the powder exiting from the nozzle, a sensitivity analysis is performed in terms of the parameters most meaningful from a technological viewpoint, i.e., the nozzle inclination, the carrier gas and powder flow rate, and the laser power. The results of such an analysis show that it is possible to predict both the configuration and the energy distribution that character- izes the flow of the powder leaving the nozzle until it reaches the substrate. In particular, the influence of both laser power and nozzle geometry to phase change conditions of powder flux are analyzed in order to improve the set up of the printing process, which can lead to increased productivity and less material waste.
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Descrizione: Computational Fluid Dynamics simulations of Laser Metal Deposition process exploring open source software
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Utilizza questo identificativo per citare o creare un link a questo documento: http://hdl.handle.net/11571/1447833
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