Large Area Maskless Photopolymerization (LAMP) is a direct digital manufacturing technology being developed at Georgia Tech to produce ceramic molds for investment casting of turbine airfoils. In LAMP, UV light incident on a spatial light modulator is projected in the form of a structured black and white bitmap image onto a platform supporting slurry comprising a ceramic particle loaded photocurable resin. Curing of the resin is completed rapidly with exposures lasting 20~160ms. Three-dimensional parts are built layer-by-layer by sequentially applying and selectively curing resin layers of 25-100 micron thickness. In LAMP, diacrylate-based ceramic particle-loaded resins with photoinitiators sensitive in the range of spectral characteristics of the UV source form the basis for an ultra-fast photopolymerization reaction. At the start of the reaction, the monomer molecules are separated by van der Waals distance (~10⁴Å). As the reaction proceeds, these monomer molecules form a closely packed network thereby reducing their separation to covalent bond lengths (~ 1 Å). This results in bulk contraction in the cured resin, which accumulates as the part is fabricated layer-by-layer. The degree of shrinkage is a direct measure of the number of covalent bonds formed. Thus, shrinkage in LAMP is characterized by estimating the number of covalent bonds formed during the photopolymerization reaction. Polymerization shrinkage and accompanying stresses developed during photopolymerization of ceramic particle-loaded resins in LAMP can cause deviations from the desired geometry. The extent of deviations depends on the photoinitiator concentration, the filler loading, the degree of monomer conversion, and the operating parameters such as energy dose. An understanding of shrinkage and stresses built up in a part can assist in developing source geometry compensation algorithms and exposure strategies to alleviate these effects. In this thesis, an attempt has been made to understand the curing kinetics of the reaction and its relation to the polymerization shrinkage. Realtime Fourier Transform Infrared Spectroscopy (RTFTIR) is used to determine the conversion of monomers into polymer networks by analyzing the changes in the chemical bonds of the participating species of molecules. The conversion data can further be used to estimate the curing kinetics of the reaction and the relative volumetric shrinkage strain due to polymerization.

Orientador: Prof. Dr. Marcos Roberto da Rocha Gesualdi / Dissertação (mestrado) - Universidade Federal do ABC, Programa de Pós-Graduação em Engenharia Elétrica, 2017. / Estudos da aplicação de moduladores espaciais de luz do tipo LCoS (Liquid Cristal on Silicon) e técnicas holográficas em substituição às máscaras no processo de fotolitografia são apresentados. Hologramas Gerados por Computador (HGC) a partir de duas imagens com dimensões conhecidas, simulando uma máscara de campo claro e uma máscara de campo escuro, foram aplicados a um modulador espacial de luz LCoS conectado a um arranjo óptico capaz de reduzir as imagens reconstruídas, permitindo o levantamento dos parâmetros de maior relevância no processo de fotolitografia para fabricação de estruturas micrométricas e, a partir da sua caracterização, identificar os limites impostos pelo modulador espacial de luz LCoS nesse processo. Registro das imagens, com diferentes dimensões, adquiridas à partir da reconstrução dos HGC provenientes das máscaras de campo claro e campo escuro, foram realizados através de uma câmera CCD e filmes de alta resolução. Os resultados permitiram a visualização e medição de estruturas com até 13 Pm e representam uma base de estudo na busca de alternativas para substituição das máscaras em processos de fotolitografia / Application studies of the Spatial Light Modulators LCoS type (Liquid Crystal on Silicon) and holographic techniques to replace the masks in the photolithography process are presented. Computer-generated Holograms (HGC) from two images with known dimensions, simulating a clear field mask and a dark field mask, were applied to a Spatial Light Modulators LCoS connected to an optical arrangement capable of reducing the reconstructed images, allowing the survey of the parameters of greater relevance in the process of photolithography to fabricate micrometric structures and from its characterization to identify the limits imposed by the Spatial Light Modulators LCoS in this process. Recording of the images, with different dimensions, acquired from the reconstruction of the HGC from clear field and dark field masks, were performed through a CCD camera and high resolution films. The results allowed the visualization and measurement of structures up to 13 ìm and represent a base of study in the search of alternatives for replacing the masks in photolithography processes.

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