Additive Manufacturing Benchmarks 2022 (AM-Bench 2022): Polymer AM II
Program Organizers: Brandon Lane, National Institute of Standards and Technology; Lyle Levine, National Institute of Standards and Technology
Tuesday 3:30 PM
August 16, 2022
Room: Old Georgetown Room
Location: Hyatt Regency Bethesda
Session Chair: David Kazmer, University of Massachusetts - Lowell
3:30 PM Invited
A Rheological Approach for Measuring Cure Depth of Filled and Unfilled Photopolymers at Additive Manufacturing Relevant Length Scales: Daniel Rau1; John Reynolds1; Jackson Bryant1; Michael Bortner1; Christopher Williams1; 1Virginia Tech
We introduce a novel experimental method that uses a UV photorheometer to enable accurate and repeatable measurements of photocured films thinner than 50 μm to create working curve equations. This technique enables measurement of a wide range of photopolymers at additive manufacturing (AM) process-relevant cure depths with process-relevant irradiance and wavelengths and has applications in advanced material development for both AM and traditional UV processing technologies. A rheometer equipped with a photocuring attachment delivers ultraviolet (UV) irradiation to a photoresin and cures a thin film. The thickness of the resultant film is measured by lowering the rheometer’s upper plate and monitoring the axial force on the plate. Our technique correlates encoder measured distance with axial force to measure cure depth under different UV curing conditions. This method could be used as an industry standard for measuring cure depths and creating system-independent working curves.
4:00 PM
The Effect of Nozzle Size and Print Speed on the Fiber Orientation and Porosity During Large-scale Additive-compression Manufacturing: Pritesh Yeole1; Joshua Crabtree2; David Nuttall; Uday Vaidya1; Merlin Theodore2; Vlastimil Kunc; Vipin Kumar2; 1University of Tennessee; 2Oak Ridge National Laboratory
Additive Manufacturing (AM) of polymer composites has proven to be a fantastic tool for prototyping. However, replacing the traditional manufacturing process with AM is still far-sighted. The main hurdle is the low mechanical properties of 3D printed parts due to high porosity. However, AM has a unique capability to align the fibers in the deposition direction. By controlling the deposition direction, preferred fiber alignment can be achieved, which affects the mechanical properties of the printed part. Oak Ridge National Laboratory (ORNL) has developed a new manufacturing process, where the AM printed preform is followed by a traditional compression molding (CM) process. This work studied various parameters such as extrusion rate (V) and nozzle sizes (D) to understand the fiber alignment and porosity and their effect on the mechanical properties prepared via the AM-CM process. High mechanical properties with increased V/D ratios are observed.
4:20 PM
Process-induced Crystallization in Thermoplastic Material Extrusion: Jonathan Seppala1; 1National Institute of Standards and Technology
In thermoplastic material extrusion, anisotropic properties are attributed to rapid cooling and subsequent limited diffusion time across the interface. However, the thermal history and flow-field have an additional effect on semi-crystalline polymers, resulting in changes to the crystal structure due to non-quiescent or flow-induced crystallization. These effects are most dramatic at the interface and can produce varying and asymmetric crystal morphologies in the extrudate. To quantify these effects, we use a combination of in-situ thermography and polarized light imaging to characterize cooling rate and residual stress during printing and ex-situ polarized imaging and micro-beam wide-angle x-ray scattering to characterize the non-equilibrium state of the polymer and final crystalline morphology. These measurements show that high extrusion speeds and low extrusion temperatures leave the polymer in a stretched and aligned state, which changes the nucleation density and crystal morphology at the interface between layers.