Printability regimes of pure metals using contactless magnetohydrodynamic drop-on-demand actuation

Viktor Sukhotskiy,Kareem Tawil,Erik Einarsson

doi:10.1063/5.0050354

Abstract

We demonstrate a computational study used to evaluate drop-on-demand printability of liquid metals via a contactless magnetohydrodynamic (MHD) pumping method. We show that the ejection regimes of pure liquid metal droplets can be categorized using two dimensionless quantities: We and a new dimensionless quantity S=Ha2Ca. By plotting We vs S, a linear relationship emerges which relates the velocity through the ejection orifice to the applied magnetic flux density. Additionally, satellite-free droplet generation is shown to be bounded by the ranges 1000≲S≲2000 and 10≲We≲20. These ranges, coupled with the linear We vs S relationship, allow one to predict the critical magnetic flux necessary to eject a satellite-free liquid metal droplet for any liquid metal with a very low viscosity to surface tension ratio (Oh&lt;0.005). We discuss the physics underlying the MHD ejection process and relate the pump action to the dimensionless quantities. We use an MHD finite element model to parametrically sweep through applied magnetic fields and explore two-phase ejection of Al, Cu, Fe, Li, Sn, Ti, Zn, and Zr droplets from a 200 μm orifice. The model is validated using experimental high speed video ejection of Zn and Al, and the reported relationship between We and S can be used to connect the input flux density to the resulting ejection regime.

Highlights

Drop-on-demand (DOD) printing is a well-established method for two-dimensional (2D) image reproduction, and for a variety of tissues, media, and devices that require deposition and patterning of functional materials ranging from metals to living cells.1–7 The physics of droplet formation from a circular orifice has been studied as early as Lord Kelvin’s siphon recorder,8 and the subsequent body of literature on droplet jetting of Newtonian fluids and related dimensionless quantities is still growing today.9–12 Most studies of DOD droplet formation have focused on aqueous fluids such as inks because the rheology is well understood and they are easy to obtain and handle
Using computational modeling and an experimental MHDDOD system, we explored the printability of pure liquid metals
The DOD ejection regimes of these low Oh fluids can be categorized using the We number, provided that the characteristic velocity of the fluid is defined as the velocity of the fluid column in the orifice prior to ejection

Summary

Introduction

Drop-on-demand (DOD) printing is a well-established method for two-dimensional (2D) image reproduction, and for a variety of tissues, media, and devices that require deposition and patterning of functional materials ranging from metals to living cells. The physics of droplet formation from a circular orifice has been studied as early as Lord Kelvin’s siphon recorder, and the subsequent body of literature on droplet jetting of Newtonian fluids and related dimensionless quantities is still growing today. Most studies of DOD droplet formation have focused on aqueous fluids such as inks because the rheology is well understood and they are easy to obtain and handle. Drop-on-demand (DOD) printing is a well-established method for two-dimensional (2D) image reproduction, and for a variety of tissues, media, and devices that require deposition and patterning of functional materials ranging from metals to living cells.. Most studies of DOD droplet formation have focused on aqueous fluids such as inks because the rheology is well understood and they are easy to obtain and handle. Dropwise deposition of non-aqueous fluids, such as liquid metals, is attracting increasing attention because of potential applications from metal additive manufacturing, conductive trace printing, advanced electronic devices, and even radiation.. Most studies in this area have focused on printing of metals with low melting points such as gallium, tin, and indium. DOD printing of high melting point metals remains a challenge due to difficulties with handling the fluids and mitigating oxide formation, in the context of droplet breakup mechanics.. Some techniques have shown promise in ejecting silver and copper, but not much work has been done to describe their droplet ejection dynamics. DOD printing of high melting point metals remains a challenge due to difficulties with handling the fluids and mitigating oxide formation, in the context of droplet breakup mechanics. An excellent review of liquid metal printing is presented by Ansell.

Methods

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Discussion

Conclusion