SUMMARY

Large Area Maskless Photopolymerization (LAMP) is a promising technique for fabricating integrally cored ceramic molds to produce airfoils through investment casting. LAMP builds airfoil molds layer-by-layer through photopolymerization of ceramic-loaded photocurable monomers. Each layer of the mold is generated by projecting black and white bitmaps of UV radiation on the monomer system through a scanning spatial light modulator. To date, LAMP has successfully produced molds for uncored airfoil castings. However, challenges remain to successfully produce integrally cored molds, which are: (a) mitigation of internal stresses that arise during layer-by-layer build-up due to volumetric shrinkage and; (b) fabrication of unsupported structures in the mold geometry. This thesis aims to address these challenges through the implementation of "grayscale" levels in the bitmaps. The intensity of the UV light incident on the monomer system can be reduced by selectively turning off pixels within the nominally “white” or “on” regions of the projected bitmaps, effectively producing a grayscale exposure. In an effort to reduce internal stresses, the grayscale can be tuned to create regions of uncured resin within the mold geometry to reduce the connectivity between photopolymerized regions and thus the net effect of volumetric shrinkage. Grayscaling can also be used as an artificial support structure through partial polymerization to create a gel state around the unsupported segments of the mold, which could be dissolved away after completion of mold fabrication. In order to implement grayscale exposure, cure depth experiments and FTIR measurements were conducted to develop empirical relationships to exposure time. From these findings, a theoretical model was developed to predict the cure depth resulting from grayscale exposure. Based on these results, grayscales are selected to test the efficacy of mitigating internal stresses and fabricating unsupported geometrical features.