Ink Jet Deposition of Ceramic Suspensions: Modeling and Experiments of Droplet Formation
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ABSTRACT We have successfully printed green ceramic objects from slurries of A12 0 3 dispersed in paraffin wax using a commercial ink-jet printer developed for pattern making (Sanders Prototype MM6PRO). Concentrated suspensions are generally more viscous than the fluids normally passed through ink jet heads. This may alter the response of the printing system to its process parameters, e.g. driving voltage and frequency. We have explored the influence of fluid properties on the ink jet behaviour using Computational Fluid Dynamics (CFD) modelling and a parallel experimental study to determine the optimum printing conditions for particulate suspensions. INTRODUCTION Ink jet printing is an attractive option for direct write technologies and for the micromanufacture of parts. Drop-on-demand printers provide a relatively inexpensive means of accurately delivering small volumes of material to precise locations enabling the reproduction of predetermined patterns stored in computer files. By overprinting, three dimensional objects can be constructed. Multi-material or composite structures can be readily fabricated if more than one ink jet droplet formation device is used. If the building droplets are sufficiently small, graded or functionally gradient structures can also be deposited. We have recently demonstrated that ink jet printing, using a piezoelectric drop-on-demand printer, can be used to successfully deposit ceramic suspensions with a very high volume loading of ceramic particles [1, 2]. This paper reports on our current progress on printing concentrated ceramic suspensions. In it we present the results of a simple computational fluid mechanics model of the ink jet printer, assuming Newtonian flow. This can be used to successfully predict the jetting parameters of a number of fluids and thus allow the identification of the optimum printing parameters. EXPERIMENTAL Suspension preparation Alumina suspensions were prepared by dispersing a fine, sub-micron powder (u-A120 3 RA45E, Alcan Chemicals Ltd., U.K.) in paraffin wax (Mobilwax 135", Mobil Special Products, U.K.) containing variable additions of sterylamine (1-Octadecylamine, Lancaster Synthesis, U.K.) and a proprietary dispersant (Hypermer LP I, ICI Surfactants, U.K.). All formulations were mixed by conventional ball milling at 100...C for periods of 10 hours. By controlling the ratio between surfactants molecular weight, and terminal group functionality (i.e., acidic or basic), suspension shear viscosities as low as 40 mPa.s were obtained for apparent particulate volume fractions of 0.4 (steady shear viscosity was measured in a concentric cylinder Brookfield Viscometer at I 00s1 and 100.. .C). Detailed preparation procedures and findings have been reported previously [1]. 65 Mat. Res. Soc. Symp. Proc. Vol. 624 © 2000 Materials Research Society
In situ monitoring of drop formation In this study, phase change drop on demand print heads were used (Sanders Design Inc., Wilton, NH). These are tubular piezoelectric transducers surrounded with a temperature controlle
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