Analysis of powder flow dynamics using high-speed imaging in DED-LB processes

Abstract Laser Beam Directed Energy Deposition (DED-LB) is a versatile manufacturing technique enabling the coating and repair of components using advanced alloys, which can also fabricate functional parts from scratch. As a result, it can increase the cost-effectiveness of industries it by extending the life cycle of high-value parts. However, the DED-LB process involves complex physical phenomena whose result is determined by a large number of parameters, with powder flow being one of the most critical. The spatial distribution of particles at the nozzle exit can affect the position of the focal plane of the powder flow, the mass concentration, and the particle injection velocity into the melt pool. As a result, both the process efficiency and the quality of the deposited material are closely related to the powder flow. This study introduces a quantitative approach for analysing powder distribution below a DED-LB nozzle by employing a high-speed camera and digital image processing (DIP). The proposed method allows the determination of both the characteristics of the distribution and the trajectories of individual powder particles, which are used to obtain their average velocity profiles and their mean velocity when entering the melt pool. The method has been applied to different carrier and shielding gas combinations in order to assess their impact on the powder distribution. DIP results are benchmarked against CFD simulation, highlighting the strengths of each technique. Finally, single clads have been deposited employing the aforementioned gas combinations, enabling the evaluation of their influence on process efficiency and clad quality.