2023 Annual International Solid Freeform Fabrication Symposium (SFF Symp 2023): Process Develoepment: Photopolymerization and Other Processes
Program Organizers: Joseph Beaman, University of Texas at Austin

Wednesday 8:00 AM
August 16, 2023
Room: 400/402
Location: Hilton Austin

Session Chair: Michael Cullinan, University of Texas at Austin

8:00 AM
Probing Temperature and Degree-of-conversion States via Tomographic Fluorescence Imaging: Sui Man Luk¹; Chi Chung Li¹; Joseph Toombs¹; Martin de Beer²; Hayden Taylor¹; ¹University of California, Berkeley; ²Lawrence Livermore National Laboratory
    Tomographic volumetric additive manufacturing rapidly solidifies freeform objects via photopolymerization, which raises both local temperature and degree-of-conversion (DOC). In-situ monitoring of temperature and DOC during the printing process is crucial for metrology and process control. In this study, we propose a tomographic fluorescence imaging technique to detect the spatiotemporal evolution of temperature and DOC during volumetric printing. Our solution employs a fluorescent dye that is sensitive to both variations in temperature and DOC. DOC is considered as a function of, and is expressed in, the absorbed optical dose of the resin. By tomographically measuring changes in the dye’s fluorescence intensity and feeding such changes to a temperature–dose–intensity calibration, the local dose and temperature during the print can be confined to a set of possible states. At exemplar locations where a priori information is known for one quantity, the other quantity can be resolved. This work illustrates the potential of and lays foundations for the development of two-wavelength spatiotemporal measurement systems that uniquely resolve both temperature and DOC.

8:20 AM
Process Modeling for Fluid-Interface Supported Resin Printing: Siva Appana¹; Stacy Ross¹; Christian Sims¹; Amit Jariwala¹; ¹Georgia Institute of Technology
    The article discusses a new technique for conducting top-down Stereolithography (SLA) 3D printing, which reduces or eliminates the need for solid support. The technique involves printing from a thin resin layer above a static immiscible supporting fluid that prevents deflection from buoyant and gravitational forces on thin overhangs from anchored parts due to minute density differences between the supporting fluid and cured resin. The complex curing and shrinkage dynamics are a primary knowledge gap. Experimental validations reveal that curing the first overhang layer with minimal distortion and curl poses a significant challenge. The article details the latest design and implementation of the FISP prototype to enable reliable curing and presents a Multiphysics model simulated on COMSOL to characterize and model the curing process, including the effects of chemical shrinkage on the overall deformation in the part and the decay of light intensity through a volumetric intensity light model.

8:40 AM
In-situ Interferometric Monitoring of Dual-wavelength Vat Photopolymerization: Yue Zhang¹; Haolin Zhang¹; Xiayun Zhao¹; ¹University of Pittsburgh
    Dual-wavelength digital light processing based vat photopolymerization process (VPP), referred to as VPP_2λ, is an emerging multi-material 3D printing technology, which uses two concurrent optical masks to selectively cure different components in a single vat. The VPP_2λ process will facilitate the design and fabrication of various applications including flexible electronics and small robotics. In this work, we develop a non-destructive in-situ interferometric monitoring (ICM) method to monitor the unique wavelength-selective multi-material photopolymerization process dynamics during the VPP_2λ. The ICM-acquired interferogram data is processed by using machine learning to accurately identify good pixels that could reflect the characteristic curing stages. The good pixels are further analyzed using a multi-beam interference based sensor model to estimate each voxel’s average refractive index. A correlation model is developed to use the refractive index values to predict the profile of degree of curing (DoC) for revealing the spatially varying kinetics in VPP_2λ.

9:00 AM
Design and Integration of a Multi-modal Machine Safety Architecture for a Novel AM-CM System: Paritosh Mhatre¹; Vipin Kumar¹; David Nuttall¹; ¹Oak Ridge National Laboratory
    Large format Additive manufacturing (AM) technology has enabled the re-imagining of fabrication processes for complex geometries, bypassing the expensive and long-lead tooling requirements. Additionally, combining AM processes with traditional manufacturing processes has been identified to leverage the best aspects of the individual processes. Oak Ridge National Laboratory is developing one such novel process for polymer composites, combining Additive Manufacturing with Compression Molding (AM-CM), to combine the advantage of high fiber alignment possible in AM-printed parts with low porosity resulting from the improved bead-to-bead interface achieved with traditional CM. The resulting system is intended to be used in tandem mode as well as segregated mode to utilize individual processes as necessary. A custom multi-modal safety integration was therefore developed to achieve this operation of AM-CM, providing a control on operating mode and involved hazards, further reducing the cycle time by minimizing time required to control the safety state of the system.

9:20 AM
A Solid Free Form Fabrication Equipment to Manufacture Axisymmetric Parts with Improved Surface Quality: Rajeev Dwivedi¹; Indira Dwivedi²; Arihant Panwar³; Bharat Dwivedi⁴; ¹STEM and Robotics Academy; ²Eastlake High School; ³Frisco ISD; ⁴Lake Washington School District
    Competetive and Hobby grade Rocket makers quite often build custom nozzles. Solid freeform fabrication is most natural choice for Manufacturing of the Nozzles. Differnt geometries can be quickly manufactured and tested. However staircase effect and limited accuracy of 2-1/2 based deposition prevents the design intent from fabrication. Additionally using differnt blends of ceramic and sustaining the geometry during curing becomes challenging. This research presents a unique 3D printing system that dispenses ceramic to enable manufacturing of axi-symmetric parts as continuous bead. Relative motion of the material dispenser and rotational substrate as well as unique path planning enables a continually sculpted surface to reduce the staircase effects.

9:40 AM
Wire + Arc Additive Manufacturing of Cryogenic Liquid Hydrogen Storage Tank Demonstrator: Muhammad Shamir¹; Evren Yasa¹; James Whincup¹; James Hughes¹; ¹University of Sheffield
    Transportation is responsible for the largest single source of carbon emissions in the UK, making the drive to achieve net zero emissions a key goal to reduce emissions from transportation, including civil aviation. One potential solution is the use of hydrogen as a fuel source. However, this approach presents challenges such as additional storage affecting aerodynamic stability and requires specialized tank geometries. Wire Arc Additive Manufacturing (WAAM) provides design freedom to manufacture complex non-uniform shapes. To achieve cryogenic aerospace applications, aluminium 6xxx/ 2xxx alloys are preferred for aircraft LH2 storage. Nevertheless, welding aluminium can be problematic due to its high thermal/electrical conductivity and affinity to humidity leading to deposition defects. Therefore, this study aims to investigate the feasibility of depositing 2219 series by optimizing process parameters and testing mechanical properties in as-built and heat treated conditions. Moreover, it demonstrates the potential of WAAM for producing tanks suitable for LH2 storage.