MECHANISMS OF CARBON-DIOXIDE LASER STEREOLITHOGRAPHY IN EPOXY-BASED MATERIALS

We present in this article the use of infrared laser radiation to achi eve localized curing in thermosensitive epoxy resin compounds. In ster eolithography, the objective is to cure a localized region in a materi al by precisely confining the laser energy to the area that is to be c ured. Industry already uses ultraviolet laser radiation at 352 nm to f abricate three-dimensional structures. Via infrared laser curing, we d emonstrate the viability of a completely thermal localized curing proc ess. In our experiment, we have focused the beam from a carbon dioxide (CO2) laser onto a sample composed of epoxy resin, diethylene triamin e, and silica powder. Such resins typically cure, or solidify, when he ated to moderately high temperatures, and our results show that we can confine the heating of the material, and, therefore, its curing in al l three dimensions. We present a physical and a chemical model to desc ribe the process and measure the curing rate as a function of temperat ure. In order to model the flow of heat in our sample as a result of i nfrared laser irradiation, we solved the time-dependent heat equation in cylindrical coordinates using the Crank-Nicholson finite-difference method. The results allow us to predict the curing behavior of the sa mple as a function of laser irradiation conditions, and we find good a greement with our preliminary experimental observations. (C) 1996 John Wiley & Sons, Inc.