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Research Papers

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

[+] Author and Article Information
Chuang Wei

Edward P. Fitts Department of Industrial
and Systems Engineering,
North Carolina State University,
Raleigh, NC 27695

Jingyan Dong

Edward P. Fitts Department of Industrial
and Systems Engineering,
North Carolina State University,
Raleigh, NC 27695
e-mail: jdong@ncsu.edu

1Corresponding author.

Contributed by the Manufacturing Engineering Division of ASME for publication in the JOURNAL OF MANUFACTURING SCIENCE AND ENGINEERING. Manuscript received April 14, 2014; final manuscript received August 26, 2014; published online October 24, 2014. Assoc. Editor: Darrell Wallace.

J. Manuf. Sci. Eng 136(6), 061010 (Oct 24, 2014) (7 pages) Paper No: MANU-14-1179; doi: 10.1115/1.4028483 History: Received April 14, 2014; Revised August 26, 2014

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 μm 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 μm with the thickness in the range of 1–2 μm, 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.

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Figures

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Fig. 1

Schematic of the EHD-jet printing setup and experimental setup for EHD-jet printing

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Fig. 2

(a) Pulsating (microdripping) mode of EHD printing of wax. (b) Footprint of printed droplets from different voltages, from left 560 V to right 640 V.

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Fig. 3

Droplets dimension at different process conditions. (a) Morphology and cross section of a typical droplet (from tip III printed at 890 V). (b) Droplet volume, (c) footprint diameter, and (d) thickness for droplets printed by three different nozzles at respective working voltage range.

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Fig. 4

(a) Drop-on-demand printed letter patterns. (b) Micropillar structures by printing droplet directly on the top of the previous droplets.

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Fig. 5

(a) Schematic configuration for FEA study of the electrostatic force on the droplets. (b) Cross section plot of the nozzle, meniscus, and half ejected droplet. (c) Electrical field distribution around the nozzle tip during droplet ejection (the unit of the scale bar is V/μm).

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Fig. 6

FEA results (dots) and fitted relations from Eq. (1) (line) of electrostatic force for tip I. (a) Relationship between electrostatic forces and voltages. (b) Relationship between electrostatic forces and droplet diameter. (c) Relationship between electrostatic forces and nozzle diameter. (d) Verification of the force prediction from Eq. (1) (circle) using experimental obtained droplet diameter (square).

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Fig. 7

(a) Intersection points of the line for surface tension force and the curves for electrostatic force give the resulting droplets diameter at different voltages for tip I. (b) Comparison between droplets dimension from FEA (lines) and experimentally measured results (data points) for three different nozzles.

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Fig. 8

Effective voltage considering the dielectric substrate

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Fig. 9

Experimental results indicate a unified relationship between normalize droplet diameter and electrical bond number

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Fig. 10

(a) Schematic configuration for FEA study of electrostatic field strength and charge calculation. (b) Electrostatic field distribution along center axis for tip I at 560 V (bottom), 600 V (middle), and 640 V (top). The insertion shows the electrical field distribution around meniscus apex. (c) Charge of a single droplet for three tips at their own working range.

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Fig. 11

(a) Typical velocity profile for droplet in-flight for tip I at 560 V, 600 V, and 640 V. (b) Impact velocity for three nozzles at different voltages. (c) Reynolds number and (d) Weber number at impact for three nozzles, tip I, tip II, and tip III.

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