Droplet formation and settlement of phase-change ink in high resolution electrohydrodynamic (EHD) 3D printing

Abstract

This paper presents a modeling framework to model the droplet formation and settlement on substrate of phase-change ink in high resolution electrohydrodynamic (EHD) printing process, which can successfully produce sub 10-μm droplet footprints and 3D microstructure. We have used Finite Element Analysis (FEA) to develop the model for droplet formation and droplet settlement. Two important competitive forces in EHD printing, electrostatic force and surface tension force are modeled by FEA. The droplet size is obtained by balancing the electrostatic force and surface tension of the pending droplets at the tip of the meniscus under different printing conditions. With the results from FEA analysis about the charge on a droplet and electrostatic field distribution, the droplets in-flight velocity and impact velocity on the substrate are derived numerically. With the derived impact velocity, the droplet spreading and settlement on the substrate is also modeled by FEA. The results from FEA models are compared with the experimental measured droplet dimensions at different process conditions to validate the developed model, which demonstrate very good agreement between the experimental results and model prediction. We have successfully applied EHD printing process for phase-change wax material, which is widely used in 3D printing or additive manufacturing for supporting and model material, to achieve high resolution sub 10-μm 3D structures.