Solid freeform fabrication of aqueous alumina-poly(vinyl alcohol) gelcasting suspensions

Solid freeform fabrication of aqueous alumina-poly(vinyl alcohol) (Al₂O₃-PVA) gel-casting suspensions was conducted using a computer-controlled extrusion apparatus fitted with a two-nozzle delivery system. The impact of casting parameters on the shear rate profiles experienced during deposition was evaluated via conventional flow analysis and computer simulations. In addition, the influence of these parameters on line resolution/uniformity, printability, and as-cast component properties was studied using laser profilometry, optical microscopy, and scanning electron microscopy. Continuous printability was achieved for tip diameters ranging from 0.254 to 1.370 mm for all mixing rates and suspension compositions studied. Printed lines were uniform with good edge definition, and line dimensions were independent of mixing rate for these process conditions. The Al₂O₃ volume fraction (φ_Al(2)O(3)) in the as-deposited layers depended on casting conditions and cross-linking agent concentration, where (φ_Al(2)O(3)) increased with decreased tip diameter and increased cross-linking agent concentration. The free-formed Al₂O₃ components exhibited uniform particle packing, with minimal macrodefects (e.g., slumping or staircasing) and no discernable microdefects (e.g., bubbles or cracking).