Direct Ink Jet Printing of Alumina Components
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Direct Ink Jet Printing of Alumina Components C. Ainsley, N. Reis, and B. Derby Manchester Materials Science Centre, UMIST, Grosvenor St, Manchester M1 7HS, U.K. ABSTRACT Alumina slurries containing up to 40% by volume ceramic particles suspended in alkane waxes have been developed with viscosity sufficiently low to allow direct ink-jet printing. Components fabricated by printing have been dewaxed, sintered and shrinkage and density measured. Small differences in shrinkage have been measured parallel and perpendicular to the droplet motion but these are within experimental scatter. The manufacturing process appears to generate bands of slightly larger grain size material at the interface between deposited layers. INTRODUCTION The use of ink jet printing for the manufacture of three-dimensional objects has been developed as a cost-effective freeform fabrication technology. Sachs and co-workers originally developed a process of selectively printing binders onto powder beds [1]. This approach has proved very successful but is limited to printing objects composed of a single material. Evans and co-workers developed a method of directly printing ceramic slurries using ink-jet devices [2-4], an approach that is in principle more versatile and could be used to fabricate objects made of more than one material. However, their work used printers originally developed for conventional graphics printing and thus only low viscosity suspensions could be printed. This limited the volume loading of the suspensions to about 10% in aqueous or alcohol based carrier vehicles. The key fluid parameters that control the printability of a fluid can be described in terms of dimensionless fluid quantities, particularly the Reynolds and Weber numbers, Re = vaρ/η, We = v(aρ/γ)1/2; where v, a, ρ, η and γ are velocity, a characteristic length, density, viscosity and surface tension respectively [5,6]. To a simple approximation, however, ink viscosity is the key parameter in the ink jet process, since the pressures involved are small (< 1 MPa) compared to other ceramic forming methods. As a consequence, the maximum suspension viscosity which can be ink jet printed is considerably lower than that used with many other ceramic forming methods. This raises a fundamental problem for ceramic processing because the high solid loadings desirable for post-processing operations (in order to reduce shrinkage and related defects) can dramatically increase the suspension viscosity. This effect is particularly marked as volume fractions exceed 50%. The dichotomy of exploiting direct ink jet printing for ceramic fabrication lies in reducing fluid viscosity to manageable limits for printing while keeping a sufficiently high volume fraction of ceramic powder in suspension for practical processing. Recent work at Manchester [8-10] has developed the direct ink-jet printing process using alumina powder suspended in alkane (paraffin) waxes, and ink-jet printers originally developed for rapid prototyping applications. This has produced printable ceramic slurries contai
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