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SPECIAL ISSUE ON NANOMANUFACTURING

# Micromachined Ultrasonic Print-Head for Deposition of High-Viscosity Materials

[+] Author and Article Information
J. Mark Meacham1

OpenCell Technologies, 500 Bishop Street Northwest, Suite E3, Atlanta, GA 30318j.mark.meacham@opencelltech.com

Amanda O’Rourke, Yong Yang, Andrei G. Fedorov, F. Levent Degertekin, David W. Rosen

George W. Woodruff School of Mechanical Engineering, Georgia Institute of Technology, 813 Ferst Drive Northwest, Atlanta, GA 30332

1

Corresponding author.

J. Manuf. Sci. Eng 132(3), 030905 (May 19, 2010) (11 pages) doi:10.1115/1.4001551 History: Received April 20, 2009; Revised April 06, 2010; Published May 19, 2010; Online May 19, 2010

## Abstract

The recent application of inkjet printing to fabrication of three-dimensional, multilayer and multimaterial parts has tested the limits of conventional printing-based additive manufacturing techniques. The novel method presented here, termed as additive manufacturing via microarray deposition (AMMD), expands the allowable range of physical properties of printed fluids to include important, high-viscosity production materials (e.g., polyurethane resins). AMMD relies on a piezoelectrically driven ultrasonic print-head that generates continuous streams of droplets from $45 μm$ orifices while operating in the 0.5–3.0 MHz frequency range. The device is composed of a bulk ceramic piezoelectric transducer for ultrasound generation, a reservoir for the material to be printed, and a silicon micromachined array of liquid horn structures, which make up the ejection nozzles. Unique to this new printing technique are the high frequency of operation, use of fluid cavity resonances to assist ejection, and acoustic wave focusing to generate the pressure gradient required to form and eject droplets. We present the initial characterization of a micromachined print-head for deposition of fluids that cannot be used with conventional printing-based rapid prototyping techniques. Glycerol-water mixtures with a range of properties (surface tensions of $∼58–73 mN/m$ and viscosities of $0.7–380 mN s/m2$) were used as representative printing fluids for most investigations. Sustained ejection was observed in all cases. In addition, successful ejection of a urethane-based photopolymer resin (surface tension of $∼25–30 mN/m$ and viscosity of $900–3000 mN s/m2$) was achieved in short duration bursts. Peaks in the ejection quality were found to correspond to predicted device resonances. Based on these results, we have demonstrated the printing of fluids that fall well outside of the accepted range for the previously introduced printing indicator. The micromachined ultrasonic print-head achieves sustained printing of fluids up to $380 mN s/m2$, far above the typical printable range.

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## Figures

Figure 1

Schematic of the AMMD printer (not to scale): (a) two-fluid multiplexed printer assembly including ejector microarray with two orifice sizes and (b) cross section of the print-head assembly

Figure 2

SEM images of Si microarrays used in the ejection experiments. Top, side, and bottom views illustrate the geometry of the 45 μm square orifices. Scale bars are provided.

Figure 3

Experimental setup: (a) schematic of the test fixture highlighting the main components and (b) detail view providing the nominal dimensions of the microarray assembly. Jettability: the still photographs define the reference scale for a performance criterion to evaluate the ejection capability. For all reference images, the ejection fluid is water. Scale bars are 10 cm.

Figure 4

Representative drop-weight-volume images: (a) water droplet prior to detachment, (b) glycerol droplet, and (c) droplet of polyurethane photopolymer resin. Scale bars are 5 mm.

Figure 5

Speed of sound c a function of temperature T for a photopolymer resin with urethane oligomers that was provided by the Albany International Research Corporation (Mansfield, MA). Measurements were taken using a pulser-receiver (Panametrics 5072PR, Olympus NDT, Waltham, MA) that was driven at 7.5 MHz.

Figure 6

Viscosity μ for a photopolymer resin with urethane oligomers that was provided by the Albany International Research Corporation (Mansfield, MA): (a) viscosity as a function of the shear rate γ and (b) temperature T in °C. Measurements were taken using a cone-plate rheometer (Physica MCR300, Anton-Paar GmbH, Graz, Germany).

Figure 7

Jettability Jab as a function of the operating frequency f for glycerol-water mixtures with increasing weight-percent glycerol. For all cases, the device was operated at less than 100% duty cycle with a burst frequency fd.c. of 500 Hz and a pulse count n of 200.

Figure 8

Jettability Jab as a function of pulse count n for glycerol-water mixtures with increasing weight-percent glycerol. For all cases, the operating frequency f was 950 kHz, and the burst frequency fd.c. was 500 Hz.

Figure 9

Operation using photopolymer resin with urethane oligomers that was provided by the Albany International Research Corporation (Mansfield, MA): (a) picture of the ejector microarray after cleaning the front face with methanol, (b) the microarray immediately after turning on the device (a short burst of ejection was observed lasting approximately 0.5 s), and (c) the microarray after a period (∼10–15 s) of weeping. Note that in (c) the liquid is very active.

Figure 10

Printing indicator for successfully ejected fluids. Open symbols (circles for glycerol-water mixtures and diamonds for photopolymer resin) indicate that the operating temperature was above 60°C. All other operating conditions were below 45°C. Glycerol-water mixtures fall in a surface tension envelope between ∼58 mN/m and 67 mN/m, while the surface tension of the photopolymer resin is only known to lie below 30 mN/m.

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