Browsing by Subject "photopolymerization"

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An Improved Vat Photopolymerization Cure Model Demonstrates Photobleaching Effects
(University of Texas at Austin, 2018) Emami, Mohammad Mahdi; Rosen, David W.
An improved high-fidelity simulation model for a grayscale projection micro-stereolithography process has been developed. The modeling purpose is to accurately predict cured part shapes and dimensions, given a radiation intensity distribution. The model employs COMSOL to solve a series of chemical reaction differential equations that model the evolution of chemical species (photoinitiator, monomer, and polymer) concentrations. Additionally, the model incorporates the effects of oxygen inhibition and species diffusion. This research offers two primary contributions to the cure model: the consideration of volumetric intensity to model variations in photoinitiator absorbance as a function of depth into the resin and a change to the rate model for photoinitiator to free radical conversion. The effects of these changes demonstrate observed photobleaching effects. Simulated cured part profiles are compared to experiments and demonstrate good agreement. Additionally, initial results are presented on the usage of the simulation model in a new process planning method.
Process Modeling and In-Situ Monitoring of Photopolymerization for Exposure Controlled Projection Lithography (ECPL)
(University of Texas at Austin, 2017) Wang, J.; Zhao, C.; Zhang, Y.; Jariwala, A.; Rosen, D.
Exposure controlled projection lithography (ECPL) is an additive manufacturing process in which photopolymer resin is used to fabricate three-dimensional features. During this process, UV curing radiation, controlled by a dynamic mask, is projected through a transparent substrate onto the resin. COMSOL software has been used to model the photopolymerization reaction kinetics, predicting the cured part geometry based on certain process parameters. Additionally, an Interferometric Curing Monitoring (ICM) system has been implemented to acquire real-time information about the optical properties of the cured part. Potential sources of error with the real-time monitoring system were investigated. Additionally, refractive index and degree of conversion changes were modeled throughout the reaction. Measured and simulated results were compared to understand the ICM signal with the reaction kinetics. These comparisons were used to validate the simulation model and identify system level errors that must be reconciled to improve the accuracy and precision of the ECPL process.
Real-Time Selective Monitoring of Exposure Controlled Projection Lithography
(University of Texas at Austin, 2013) Jones, Harrison H.; Kwatra, Abhishek; Jariwala, Amit S.; Rosen, David W.
Exposure Controlled Projection Lithography (ECPL) is a stereolithographic process in which incident radiation, patterned by a dynamic mask, passes through a transparent substrate to cure photopolymer which grows progressively from the substrate surface. We present here a novel method of capturing useful information about the curing process from a simple, inexpensive, real-time monitoring system based on interferometry. This approach can be used to provide feedback control to the ECPL process, thus making the process more robust and increasing system accuracy. The results obtained from this monitoring system provide a means to better visualize and understand the various phenomena occurring during the photopolymerization of transparent photopolymers. In order to lessen the measurement error, caused by internal diffraction within the substrate, the interferometry system has been designed such that the laser light used can be selectively targeted. This selective monitoring approach is experimentally validated to measure the height and profile of the cured part in real-time.
Robot-aided selective embedding of a spatially steered fiber in polymer composite parts made using vat photopolymerization
(University of Texas at Austin, 2023) Khatua, Vivek; Gurumoorthy, B.; Ananthasuresh, G.K.
Fiber-Reinforced Polymer Composite (FRPC) parts are predominantly laminates, shells, or surfaces wound with 2+D fiber patterns even after the emergence of additive manufacturing. Making FRPC parts with embedded continuous fibers in 3D is not reported previously even though topology optimization demonstrates that such designs are optimal. Earlier attempts in 3D fiber reinforcement include making parts with channels into which fibers are inserted or coextruding fiber with resin. In this work, A Vat-Photopolymerization Machine, and a process for concurrent embedding of spatially steered continuous fibers inside the matrix is developed. A single continuous fiber was embedded spatially using a robot to gradually steer the fiber as the part is built layer upon layer. An example of a fiber embedded along a helix in a cylindrical matrix is included in this work. Furthermore, a hinge effect was demonstrated when a fiber was embedded at a place that has substantial bending about the axis of the fiber.