Thermal deformation of a photo-cured polymer for the analysis of stereolithography

Thermal deformation and residual stresses generated in the stereolithograph y product must be understood in order to employ the three-dimensional stere olithography for high-precision model building. The purpose of this study i s to understand how residual stresses are generated in the three-dimensiona l stereolithography by solving the governing equations for heat transfer an d nonlinear polymerization reaction kinetics simultaneously with finite-dif ference/finite-element numerical methods. Two cases were considered for the basic understanding of stereolithography. One is when the laser beam stays at one point and the other is when the laser scans along one line. In both cases it is possible to determine the rate of polymerization, heat generat ion, and the heat-transfer rate in the two-dimensional domain at any time. As the result of numerical prediction, the distribution of temperature, the rmal stress, rate of polymerization, percent conversion, photo-initiator co ncentration, and laser-light intensity was obtained in the defined domain. In stereolithography, the rate of polymerization and temperature increase r apidly at the initial stage and become stable as time elapses. The photo-in itiator concentration decreases as time passes, but it is not influenced si gnificantly by the rapid increase in the rate of polymerization or in tempe rature. Changes in temperature, hear-transfer rates, and thermal stresses a re substantial in the region directly exposed to the laser.