Process Modeling of Single-Photon Laser Scanning Vat-Photopolymerization Operating Under Intermittent Exposure Conditions

Process modeling is an important tool in additive manufacturing (AM) because it elucidates the relationship between processing parameters and material properties. Ultraviolet laser scanning vat-photopolymerization (VPP-UVL) is a common additive manufacturing technique, with a strong physical modeling based on the Jacobs work curve framework. The work curve model was developed for continuous UV exposure (CE) systems and does not adequately describe the total exposure profile arising from the overlap of discrete exposures present in intermittent exposure (IE) setups, such as multiphoton polymerization and pulsed laser SLA. As a result, no model is available and process optimization is heavily reliant on trial-and-error approach. To address this issue, a model describing a single-photon polymerization VPP-UVL-IE process was developed. The VPP-UVL-IE model presented here has the same logarithmic dependence as the Jacobs work curve model, but with the addition of a multiplying factor carrying information on the spatial distribution of energy, that is, the overlap of individual exposures. The model is adaptable for non-gaussian beam profiles and can be solved for bidimensional analysis representing layer fabrication. To test the model, a custom-built VPP-UVL-IE additive manufacturing system was used, and structures were printed and characterized using SEM and stylus profilometry. The model`s reliability was investigated under constant overlap and exposure conditions. The model is very robust under constant overlap conditions, with good agreement between experimental data and simulation. For constant exposure, there is good qualitative agreement, but discrepancies occur due to insufficient modeling of the spatial distribution of energy. The 3D printing of complex structures is demonstrated, and the model indicates that VPP-UVL-IE can offer faster printing compared to VPP-UVL-CE.