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.
| Identifer | oai:union.ndltd.org:GATECH/oai:smartech.gatech.edu:1853/31740 |
| Date | 17 November 2009 |
| Creators | Kambly, Kiran |
| Publisher | Georgia Institute of Technology |
| Source Sets | Georgia Tech Electronic Thesis and Dissertation Archive |
| Detected Language | English |
| Type | Thesis |
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