THERMAL DEFORMATION OF A PHOTO-CURED POLYMER FOR THE ANALYSIS OF STEREOLITHOGRAPHY

Abstract

Thermal deformation and residual stresses generated in the stereolithography product must be understood in order to employ the three-dimensional stereolithography for high-precision model building. The purpose of this study is to understand how residual stresses are generated in the three-dimensional stereolithography by solving the governing equations for heat transfer and nonlinear polymerization reaction kinetics simultaneously with finite-difference/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 generation, and the heat-transfer rate in the two-dimensional domain at any time. As the result of numerical prediction, the distribution of temperature, thermal stress, rate of polymerization, percent conversion, photo-initiator concentration, and laser-light intensity was obtained in the defined domain. In stereolithography, the rate of polymerization and temperature increase rapidly at the initial stage and become stable as time elapses. The photo-initiator concentration decreases as time passes, but it is not influenced significantly by the rapid increase in the rate of polymerization or in temperature. Changes in temperature, heat-transfer rates, and thermal stresses are substantial in the region directly exposed to the laser.