Abstract

In metallic additive manufacturing using direct energy deposition, particles and melt pool undergo complex interactions, including particle impact, penetration, and melting. The spatio-temporal evolution of these processes dictates the final material properties and workpiece quality. However, due to the opaqueness of metallic melt pools, in-situ visualization is nearly impossible. To model this system, we use high-speed imaging to investigate the heat transfer and melting dynamics of spherical ice particles (D ≈ 2 mm) impacting heated water baths of varying temperatures (23 – 70°C) with velocities ranging from 0.8 to 2.1 m/s. To visualize the outflow of molten ice, representative of mixing and material homogeneity, the particles were colored with food dye. We show that after impact, molten liquid forms an annular plume travelling downwards in the bath, until hitting the bottom of the enclosure and expanding radially. Due to positive buoyancy forces, unmolten ice particles rise to the top of the water bath, where they fully melt. As temperatures increase, we observe random particle movement, indicating the presence of convective currents. Through video analysis, we examine the relationships between bath temperature, impact velocity, and heat transfer. As expected, increasing the bath temperature decreases the total melt time of the ice particle. Interestingly, the impact velocity has only a minor effect on the melting time. Using non-dimensional analysis, we derive an expression for the correlation between Nusselt and Jakob numbers. Outcomes from this work can be used to match characteristic time scales during additive manufacturing to tailor material properties.

Document Type

Final Report

Author's School

McKelvey School of Engineering

Author's Department

Mechanical Engineering and Materials Science

Class Name

Mechanical Engineering and Material Sciences Independent Study

Date of Submission

5-6-2020

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