Additive manufacturing of pyrophyllite parts

Robocasting is an additive manufacturing (3D Printing) technique which allows the layer-wise manufacturing of complex structures through means of a CNC-controlled extrusion device depositing slurries/pastes with a high volume % solids loading onto a build plate. The aim of the study was to determine whether pyrophyllite parts could be produced using robocasting technology with a relatively simple and inexpensive paste system with inexpensive preparation and printing apparatus. Various shaped objects were produced and has shown some promising results. The use of polyethyl-glycol as an organic binder, coupled with water as the dispersant allowed for the reliable printing of complex shapes provided that adequate drying was effected and the optimised printing parameters were used. Successful drying of the printed green bodies was performed and no cracking was observed. Debindering and sintering yielded predictable anisotropic shrinkage which could be accounted for during part design and printing using scaling factors. The average relative density of sintered parts was found to be around 95% which was deemed less than ideal but various strategies could still be employed in future to improve the sintered density. The presence of bubbles/air gaps, likely introduced during mixing/printing was found to be the limiting factor in the average flexural strength of the printed products. Nevertheless, a reasonably high Weibull modulus coupled with a respectable average flexural strength of 142 MPa was measured. The measured Vickers hardness was comparable to that obtained through conventional manufacturing techniques and the fracture toughness was similar to that reported by previous studies done on robocast ceramics.