DescriptionThis thesis developed a suspension for the additive manufacturing of silicon nitride by stereolithography. The suspension went through several iterations before it was finalized and used for printing. These iterations included optimizing the mixing method, the dispersion level, choosing a dispersant, and settling on a dispersant amount. Once all these iterations were completed, the formulation was optimized and its print characteristics were analyzed.Once the Si3N4 SLA suspension formulation had been established, the relationship between energy dose, cure depth, and lateral dimensional growth needed to be examined. This investigation was done on single-layer prints to understand the relationship between energy dose and depth of cure and energy dose and lateral dimensional growth. The result of this study showed that the lateral dimensional growth and cure depth increased as the energy dose increased. Too high of an energy dose caused overgrowth and poor resolution, and too low of an energy dose influenced the light penetration depth. Based on these observations, it was possible to determine a “printability zone” for multi-layer printing that identified energy doses for minimal growth without foregoing a high cure depth. Two energy doses, 63 mJ/cm2 (low) and 127 mJ/cm2 (medium) were picked from that zone. The final energy dose, 254 mJ/cm2 (high) was chosen from outside the zone to fully investigate the relationships mentioned above.
A total of 5 samples were printed at each energy dose, each with dimensions 5mm x 5mm x 3mm, and a layer thickness of 10 μm. The lateral dimensional growth was measured for each dose and compared with the previously established trends. It was found that in multi-layer printing, the lateral dimensional growth increased as the energy dose was increased, however, the growth was larger than the predictions based on single-layer printing projected. As an example, the projected growth at 127 mJ/cm2 was between 5-6%, but the measured growth for the print was 12%. To further the study of this relationship, the samples were put under a scanning electron microscope to see how much growth there was. The images showed that as the energy dose increased, the layers became more delaminated at the edges of the cubes. By drawing a line where the projected image should end, the lateral dimensional growth at each energy dose can be clearly seen. These findings confirm that when printing a dark powder suspension, it is important to take the scattering of the suspension into consideration before and while printing. Otherwise, the printed sample will stray from the near-net shape. This study concludes that the best print quality using silicon nitride suspension stereolithography will result from using the lowest possible energy dose that does not develop delamination.