Characterization of Pure Photopolymers and Suspensions for Digital Light Processing (DLP)

Several additive manufacturing (AM) technologies are nowadays available for layer-by-layer fabrication of complex parts, allowing reduction of costs and waste compared to conventional manufacturing technologies. Among all AM technologies, digital light processing (DLP), an advanced version of stereolithography (SLA), is emerging for manufacturing 3D objects using liquid photopolymers and suspensions (e.g. including ceramic and metal particles) as feedstock. In case of supsensions, the printed object can be thermally treated for debinding and sintering, producing ceramic and metal objects. DLP takes the advantage of a digital light projector, which selectively polymerizes the feedstock, printing each layer with a single exposure, thus eliminating the scanning time required in SLA. The technology can be adopted for several applications in the field of biomedical, automobile, aerospace, and electronics due to the technological advancement in projection-based manufacturing technology and the development of innovative materials in form of elastomers, shape memory polymers, and suspensions (ceramics, metals, composites, and nanocomposites). For successful manufacturing, feedstocks need to be thoroughly characterized for optimal printing. Therefore, this work presents a systematic study to characterize both pure photopolymers and suspensions, discussing two radiation-independent characteristic parameters of photopolymers, the critical energy (Ec) and the penetration depth (Dp). This also includes some of the basic theoretical aspects of light-matter interaction that can guide the manufacturing process development and optimization. Based on such findings, we present a “printing window”, identifying the boundaries for minimum and maximum radiation exposure for optimized polymerization and thus providing guidelines for the optimal printing conditions of each individual feedstock.