Powder Binder Interactions in 3D inkjet printing

Abstract

Three dimensional printing is an additive manufacturing technique that is the next step in the development of additive manufacturing technology. It is a tool less process which can be used to fabricate parts having complex geometries in a single step process with minimal material wastage. It involves the deposition of metal powder in successive layers followed by the selective local deposition of ink which functions as a binder using a print head. On completion of the printing process the part is cured, cleaned of loose powder and placed in an oven for debinding followed by sintering in a sintering oven. The parts so produced may then be processed as desired by techniques such as polishing to achieve the desired surface finish. In order to maintain high quality product each processing stage needs to be evaluated as a source of error. One of the most important variables in this process is the interaction between the metal powder and the ink during printing. The speed, accuracy, surface finish and yield are dependent on the quality of the powder ink interactions. The focus of this thesis is the study of powder ink interactions by controlling the characteristics of both the powder and the ink and consequently improving the quality of their interactions. This involves testing both existing metal powder ink combinations and new combinations through controlled tailoring of their properties. The combinations are assessed based on the goals of ease of processing, handling, sintering and product quality. The variables modified include particle size distribution of the powder, powder bed temperature, ink viscosity, surface tension and powder bed packing. The differences between the powder ink interactions in the case of both virgin and recycled powder are also assessed to establish better process control and improve quality.