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 $S=H{a}^{2}Ca$ . 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 $1000\lesssim S\lesssim 2000$ and $10\mathit{\text{≲We≲}}20$ . 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 ($Oh<0.005$ ). 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.

The fabrication of printed electronic devices via molten metal droplet jetting has enormous potential in flexible electronic device applications due to the extremely high electrical conductivity and excellent substrate adhesion of printed features. However, large pinholes (which could be detrimental to the feature performance) have been experimentally observed when molten metal droplets of aluminum 4043 alloy are deposited and solidified on a polyimide (PI) substrate. In this study, we have shown that subjecting the polymer substrate to elevated temperature during droplet deposition considerably reduces the number and size of pinholes. The formation mechanism behind the large pinholes is interpreted as the release of the adsorbed/absorbed moisture from the polymer substrate into the solidifying droplet due to the rapid rise in temperature of the substrate upon droplet impact. Through numerical modelling, we have shown that the temperature of the polyimide substrate underneath the deposited droplet exceeds the boiling point of water while the metal droplet is still in liquid state, showing the possibility of water vapor escaping from the substrate and causing pinholes in the solidifying metal.

A wax-based contact printing method to create microfluidic devices is demonstrated. This printing technology demonstrates a new pathway to rapid, cost-effective device prototyping, eliminating the use of expensive micromachining equipment and chemicals. Derived from the traditional Ukrainian Easter egg painting technique called “pysanky” a series of microfluidic devices were created. Pysanky is the use of a heated wax stylus, known as a “kistka”, to create micro-sized, intricate designs on the surface of an egg. The proposed technique involves the modification of an x-y-z actuation translation system with a wax extruder tip in junction with Polydimethysiloxane (PDMS) device fabrication techniques. Initial system optimization was performed considering design parameters such as extruder tip size, contact angle, write speed, substrate temperature, and wax temperature. Channels created ranged from 160 to 900 μm wide and 10 to 150 μm high based upon system operating parameters set by the user. To prove the capabilities of this technology, a series of microfluidic mixers were created via the wax technique as well as through traditional photolithography: a spiral mixer, a rainbow mixer, and a linear serial dilutor. A thermo-fluidic computational fluid dynamic (CFD) model was generated as a means of enabling rational tuning, critical to the optimization of systems in both normal and extreme conditions. A comparison between the computational and experimental models yielded a wax height of 57.98 μm and 57.30 μm, respectively, and cross-sectional areas of 11,568 μm² and 12,951 μm², respectively, resulting in an error of 1.18% between the heights and 10.76% between the cross-sectional areas. The device’s performance was then compared using both qualitative and quantitative measures, considering factors such as device performance, channel uniformity, repeatability, and resolution.

Like most additive manufacturing methods, droplet-based molten metal jetting (MMJ) techniques face a fundamental trade-off between printing resolution and speed, which naturally imposes limits on the fabrication of parts. Herein, we present some of these limits and propose a novel method and nozzle design to circumvent them: multi-resolution metal additive manufacturing via magnetohydrodynamic (MHD) droplet-on-demand MMJ. Multi-resolution printing enables high resolution and high deposition by selectively ejecting molten metal droplets of varying size from a single-reservoir nozzle equipped with two orifices. When ejecting droplets from the smaller orifice, fine resolution features can be printed at the expense of deposition rate. Conversely, larger orifices allow coarser features to be printed quickly. The complexity of activating only a single orifice is overcome by carefully tailoring MHD pulses to comply with the characteristic fluid dynamics of each individual orifice. The concept is established using 3D fluid dynamics simulations of a nozzle equipped with two orifices (200 and 500 μm diameter) and validated experimentally with an identical nozzle configuration using an aluminum alloy as the ejection liquid.

Wetting behavior of molten metals on solid substrates is a critical phenomenon influencing numerous industrial applications, including welding, anti-corrosion coatings, and metal additive manufacturing (AM). In particular, molten metal jetting (MMJ), an emerging AM technology, requires that the molten metal remain pinned at the nozzle exit. Thus, each new metal requires a specific nozzle material to ensure consistent droplet ejection and deposition, making it important to rapidly identify the appropriate wetting combinations. However, traditional measurements of wetting angles require expensive equipment and only allow one combination of materials to be investigated at a time which can be time consuming. This work introduces a rapid screening method based on sessile droplet experiments to evaluate wetting profiles across multiple metal–substrate combinations simultaneously. This study investigates the wetting interactions of molten Al alloy (Al4008), Cu, and Sn on various ceramic and metal substrates to identify optimal material combinations for MMJ nozzle designs. Results demonstrate that Al4008 achieves wetting on ceramic substrates such as AlN, TiO₂, and SiC, with varying mechanisms including chemical reactions and weak surface interactions. Additionally, theoretical predictions regarding miscibility gaps and melting point differences were verified for Cu and Sn on refractory metals like Mo and W. Findings from this study contribute to the establishment of a materials compatibility library, enabling the selection of wetting/non-wetting combinations for stable MMJ operation. This resource not only advances MMJ technologies but also provides valuable insights for broader applications such as welding, coating, and printed electronics.