Curing characteristics of acrylic photopolymer used in stereolithography process

Rapid prototypes formed using stereolithography (SL) method have to undergo post-curing to increase their strength and rigidity. This study attempts to reduce, if not eliminate, post-cure distortion by characterising curing behaviours. Curing (both heat and UV initiated) characteristics of an acrylic-based photopolymer under actual fabrication conditions were studied using Raman spectroscopy as well as differential scanning calorimetry (DSC) and differential scanning photo-calorimetry (DSP). Specimens of single photopolymer lines were created using a SL machine. Raman spectroscopy was used to quantify the curing percentage at different areas on the cross-section of these lines. Curing percentages before and after post-curing were also obtained from the experiments. Difference in percentage of post-curing gave an indication of the distortions faced. It was found that uncured and partially cured resins trapped within the photopolymer resulted in inhomogeneity of curing in the specimens causing shrinkage and distortion.