Development and Modeling of Melt Electrohydrodynamic-Jet Printing of Phase-Change Inks for High-Resolution Additive Manufacturing

This paper presents the development and modeling a high-resolution electrohydrodynamic-jet ((EHD-jet) printing process using phase-change ink ((i.e., wax), which is capable of producing sub-10 mu m footprints ((sub-10 fL in volume) for super-resolution additive manufacturing. In this study, we successfully apply EHD-jet printing for phase-change ink ((wax), which is widely used as modeling and supporting material for additive manufacturing, to achieve micron-scale features. The resolution for single droplet on substrate is around 5 mu m with the thickness in the range of 1-2 mu m, which provides great potential in both high-resolution 3D printing and 2D drop-on-demand microfabrication. The droplet formation in EHD printing is modeled by finite element analysis ((FEA). Two important forces in EHD printing, electrostatic force and surface tension force, are modeled separately by FEA. The droplet size is obtained by balancing the electrostatic force and surface tension of the pending droplets around meniscus apex. Furthermore, to predict the droplet dimension at different process conditions, a dimensionless scaling law is identified to describe the relationship between dimensionless droplet diameter and modified nondimensional electrical bond number. Finally, the droplets in-flight velocity and impact characteristics ((e. g., Reynolds number and Weber number) are modeled using the results from FEA analysis.