P. Li
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1
Gradient-index (GRIN) optical elements allow compact designs and better control of optical aberrations. While conventional fabrication methods can produce these components reliably, they limit the shapes and refractive index profiles that can be achieved. Additive manufacturing offers an alternative approach, en- abling complex three-dimensional geometries and spatially tailored optical properties. Digital light process- ing (DLP), in particular, provides high spatial resolution and grayscale exposure control, but UV exposure alone produces only small changes in refractive index. This thesis explores a dual-cure resin strategy to print GRIN optics. Hardware modifications to a commercial DLP printer allowed controlled grayscale exposure, enabling the fabrication of linear and radial GRIN demonstrators. These results show that combining a dual-cure resin system with controlled exposure can introduce spatial refractive index variation in a single printed compo- nent. A custom dual-cure resin was created by blending UV-curable photopolymers with a thermally activated epoxy. During DLP printing, UV light defines the geometry and initial polymer network, while subsequent heating activates the epoxy. Measurements on printed prism samples show that uniform UV curing changes the refractive index only slightly, with values around n = 1.52–1.53 for Formlabs Clear V4 and n = 1.53 for Elegoo ABS-like Transparent. Adding epoxy and applying thermal post-curing increases the refractive index, with shifts of ∆n ≈ 0.01–0.04 for Formlabs-based blends and ∆n ≈ 0.01–0.03 for Elegoo-based blends, depending on epoxy content. In summary, this work demonstrates a practical material-based approach for tuning refractive index in DLP- printed optics. Incorporating a thermally activated epoxy allows larger refractive index changes than UV curing alone, providing a foundation for future research on 3D-printed GRIN lenses.
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Gradient-index (GRIN) optical elements allow compact designs and better control of optical aberrations. While conventional fabrication methods can produce these components reliably, they limit the shapes and refractive index profiles that can be achieved. Additive manufacturing offers an alternative approach, en- abling complex three-dimensional geometries and spatially tailored optical properties. Digital light process- ing (DLP), in particular, provides high spatial resolution and grayscale exposure control, but UV exposure alone produces only small changes in refractive index. This thesis explores a dual-cure resin strategy to print GRIN optics. Hardware modifications to a commercial DLP printer allowed controlled grayscale exposure, enabling the fabrication of linear and radial GRIN demonstrators. These results show that combining a dual-cure resin system with controlled exposure can introduce spatial refractive index variation in a single printed compo- nent. A custom dual-cure resin was created by blending UV-curable photopolymers with a thermally activated epoxy. During DLP printing, UV light defines the geometry and initial polymer network, while subsequent heating activates the epoxy. Measurements on printed prism samples show that uniform UV curing changes the refractive index only slightly, with values around n = 1.52–1.53 for Formlabs Clear V4 and n = 1.53 for Elegoo ABS-like Transparent. Adding epoxy and applying thermal post-curing increases the refractive index, with shifts of ∆n ≈ 0.01–0.04 for Formlabs-based blends and ∆n ≈ 0.01–0.03 for Elegoo-based blends, depending on epoxy content. In summary, this work demonstrates a practical material-based approach for tuning refractive index in DLP- printed optics. Incorporating a thermally activated epoxy allows larger refractive index changes than UV curing alone, providing a foundation for future research on 3D-printed GRIN lenses.
This thesis presents the design, implementation, and evaluation of a hybrid additive manufacturing platform that combines spray based thin film deposition with digital light processing (DLP) UV curing. The system was developed as a low cost platform, with a total hardware budget below €1000, while integrating a custom mechanical assembly, pneumatic delivery, and an optically aligned projection unit in a coordinated layer by layer workflow. The hardware platform achieves a mechanical XY resolution of 100 μm with a measured XY misalignment of approximately 60 μm and supports controlled airbrush needle actuation with a 5.2 mm travel range at 0.1 mm resolution. The reconfigured DLP subsystem provides an effective pixel size of approximately 15μm and an irradiance of roughly 54 mW/cm2, enabling localized curing of deposited films. Printing performance was characterized through single line, single material, and multi-material benchmarks. The minimum stable line width produced by the spray deposition process was 0.5 mm, and dimensional tests showed a shrinkage of approximately 2% for features larger than 1-2 mm. Surface quality remained consistent with an average roughness of Ra = 1.01 μm. Multi-material trials demonstrated the feasibility of switching between materials, though interface sharpness remained constrained with measured interface widths greater than 0.5 mm. Together, these results establish a functional hybrid printing method capable of producing thin film structures with controlled geometry, while revealing key limitations related to overspray, alignment drift, material cross contamination, and optical resolution.
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This thesis presents the design, implementation, and evaluation of a hybrid additive manufacturing platform that combines spray based thin film deposition with digital light processing (DLP) UV curing. The system was developed as a low cost platform, with a total hardware budget below €1000, while integrating a custom mechanical assembly, pneumatic delivery, and an optically aligned projection unit in a coordinated layer by layer workflow. The hardware platform achieves a mechanical XY resolution of 100 μm with a measured XY misalignment of approximately 60 μm and supports controlled airbrush needle actuation with a 5.2 mm travel range at 0.1 mm resolution. The reconfigured DLP subsystem provides an effective pixel size of approximately 15μm and an irradiance of roughly 54 mW/cm2, enabling localized curing of deposited films. Printing performance was characterized through single line, single material, and multi-material benchmarks. The minimum stable line width produced by the spray deposition process was 0.5 mm, and dimensional tests showed a shrinkage of approximately 2% for features larger than 1-2 mm. Surface quality remained consistent with an average roughness of Ra = 1.01 μm. Multi-material trials demonstrated the feasibility of switching between materials, though interface sharpness remained constrained with measured interface widths greater than 0.5 mm. Together, these results establish a functional hybrid printing method capable of producing thin film structures with controlled geometry, while revealing key limitations related to overspray, alignment drift, material cross contamination, and optical resolution.