Session: 20-17-01: Rising Stars of Mechanical Engineering

Paper Number: 172714

Vibration-Assisted High-Resolution Electrohydrodynamic (Ehd) Jet Printing 

Electrohydrodynamic (EHD) jet printing has become a promising and cost-effective technique for producing high-resolution and scalable features. In EHD printing, printing materials are subjected to a high electric field to form a Taylor-cone structure. When the electrostatic force exceeds the ink surface tension and viscous force, a fine jet or droplet that is smaller than the nozzle size will be ejected. While EHD printing can create fine features, it becomes more susceptible to nozzle clogging when employing smaller nozzles. The issue poses a critical challenge in EHD printing due to solvent evaporation, ink drying near or within the nozzle tip, and high material concentrations, which prevent utilizing EHD printing with novel materials for nanoscale fabrication. Moreover, pressure or other external forces are required to assist the ink flow for printing of highly viscous materials, which increases the complexity of process control and the required energy.

In this work, we developed a novel ultrasonic vibration-assisted EHD printing system and associated process to effectively mitigate the nozzle clogging for the printing of high-viscosity and high-evaporation-rate inks. First, an ultrasonic vibration-assisted EHD printhead was designed and fabricated by integrating a piezoelectric-based ultrasonic transducer and a traditional EHD printhead. The vibration unit was able to transmit a longitudinal vibration forward to the printing nozzle and the ink. The designed vibration printhead can provide various vibration frequencies and amplitudes to adapt to different printing materials. A high-evaporation-rate and high-viscosity material (4%wt PEO solution) was selected to conduct the tests. A series of experiments was conducted to assess the effectiveness of the printhead and characterize the printhead design and process parameters (i.e., vibration frequency, vibration amplitude, and printing voltage). The results demonstrated that superimposing ultrasonic vibration on the EHD printing nozzle can effectively enhance current EHD printing capabilities, such as reducing required pressure, eliminating nozzle clogging, and providing stable and continuous printing for high viscosity and high solvent evaporation rate material. In addition, an FEA study was performed to study the impact of the vibration on the ink flow inside the nozzle. The FEA simulation results clearly showed that without adding vibration to the printing nozzle, ink circulation did not occur between the inner nozzle wall and the ink. In contrast, ultrasonic vibration induced internal ink circulation along the inner nozzle wall, which is the main reason that vibration can effectively eliminate the nozzle clogging. With the optimal parameters, a filament with a diameter of around 1μm can be continuously printed from a 51μm nozzle, and we successfully applied this developed ultrasonic-assisted EHD process to print high-resolution 2D patterns, which demonstrated the potential of using this technology for fabricating transparent devices.

Presenting Author: Yiwei Han University of Mississippi

Presenting Author Biography: Yiwei Han received his Bachelor’s degree in Manufacturing Engineering from North Dakota State University in 2013, and the Ph.D. degree in Industrial and System Engineering from North Carolina State University in 2018. He joined the Department of Manufacturing and Industrial Engineering at the University of Texas Rio Grande Valley in 2018. In 2019, he joined the Department of Mechanical Engineering at the University of Mississippi, and his research interests include additive manufacturing, process modeling, and printing of flexible and stretchable electronics.

Authors:

Yiwei Han University of Mississippi
Yi Wang University of Missouri