Numerical study of solidifying molten metal droplet impingement on a cold solid surface

Abstract

Metallic droplet deposition is of interest in the industry because of the potential use in additive manufacturing. This work discusses the complex phenomena involved in droplet impingement, especially the effect of temperature dependant surface tension. The volume of fluid (VOF) method is used to solve the axis-symmetric Navier-Stokes equations, which are used to describe the droplet's behaviour. Different temperature dependencies for the surface tension are modelled, to see the effect on the interface and substrate melting. Furthermore, the effect of droplet size, initial temperature on droplet shape and substrate melting is studied. To judge the accuracy of the VOF model, a series of benchmarks are tried. The VOF model used in this work is as accurate or more accurate than previous works. The results show that droplets with a higher percentage of oxygen flatten, this is due to thermo-capillary forces. A higher temperature results in more spreading of the droplet, this is because higher temperatures result in higher surface tensions. These surface tensions keep the droplet together when it first makes contact with the substrate. This causes less air is trapped underneath the droplet, which causes the droplet to spread out more. The air also causes the droplet to cool down less fast, this results in a phenomenon where the hotter droplet is solidified faster than the colder one.