Additive Manufacturing Benchmarks 2022 (AM-Bench 2022): Polymer AM I
Program Organizers: Brandon Lane, National Institute of Standards and Technology; Lyle Levine, National Institute of Standards and Technology
Tuesday 1:30 PM
August 16, 2022
Room: Old Georgetown Room
Location: Hyatt Regency Bethesda
Session Chair: Kalman Migler, National Institute of Standards and Technology
1:30 PM Invited
In-situ Observation of the Extrusion Processes of Acrylonitrile Butadiene Styrene and Polylactic Acid for Material Extrusion Additive Manufacturing: Cheng Luo1; 1University of Texas at Arlington
In material extrusion additive manufacturing, solid polymer filaments are fed into extruders to generate extrudates needed to build 3D plastic parts. There is a finite gap between the inner surface of an extruder and the edge of a filament, which facilitates the insertion of the filament inside the extruder. It is still not clear how this gap is filled during the extrusion. On the other hand, it is important to know this information, for example, to model the distributions of temperature and pressure during the extrusion. In this work, the gap-filling processes of Acrylonitrile Butadiene Styrene (ABS) and Polylactic Acid (PLA) filaments were directly observed through a heated glass tube, with the aid of particles previously added in the filaments. For both materials, the gap filling inside an extruder was found to be affected by curved profile of the filament, conical geometry of the nozzle and temperature of the extruder.
2:00 PM
Investigating the Strength of Individual Welds of Polycarbonate Made with Fused Filament Fabrication: Ojaswi Agarwal1; Zheliang Wang; Lichen Fang1; Sung Kang1; Jonathan Seppala2; Thao Nguyen3; Kevin Hemker1; 1Johns Hopkins University; 2National Institute of Standards and Technology; 3Johns Hopkins Univesrity
In Fused Filament Fabrication (FFF), the reduced and anisotropic properties are attributed to the welding between layers. Welds have been reported to be substantially weaker than the bulk material [1-3] and serve as stress concentrators where failure localizes [4]. We develop three complementary tests to probe the strength of individual inter-road polymer welds. The three tests, combined with an in-situ characterization of the weld thermal history and imaging of the weld geometry, result in a holistic understanding of the polymer's behavior at the weld. The tests are the trouser tear test, a mixed-mode peel test, and a razorblade induced fracture test, all probing a single weld. We find the measured strength does depend on the local thermal history, but there is a strong influence from the size of the grooves. The grooves introduce a stress concentration that influences fracture behavior and can change the observed strength, independent of thermal history.
2:20 PM
Meshfree Models for Viscoelastic Filament Extrusion and Solidification: Eric Palermo1; Thomas O'Connor1; 1Carnegie Mellon University
We demonstrate RHEO – a new opensource meshfree framework for modeling multiphase viscoelastic hydrodynamics – by simulating a filament extrusion printing process. RHEO combines reproducing-kernel smooth particle hydrodynamics (RK-SPH) for viscoelastic fluids with a bonded-particle method (BPM) for elastic solids. This hybrid setup allows RHEO to model the flow of cooling polymer filaments, their temperature induced solidification, and subsequent remelting on later heating. We demonstrate this by showing results for the cooling and solidification of a molten filament deposited onto a cool substrate and predict how filament cross-sections vary with polymer viscoelasticity, thermal properties, and extrusion rate. We also demonstrate RHEO’s ability to capture the effects of remelting on filament cross sections by modeling the deposition of a second filament row on top of the first. While idealized, these demonstrations highlight RHEO’s ability to model a variety of multiphase free-surface flows relevant to both polymer and metal additive manufacturing.
2:40 PM
Morphology Evolution of Droplets in a Polymer Based Extensional Flow
: David Bigio1; Harsha Bharadwaj; 1University of Maryland
Fused Deposition Modelling (FDM) is a widely used Additive Manufacturing (AM) method. This presentation examines the incorporation of liquid additives into the nozzle region of an FDM system to understand their behavior in the polymer melt flow. The computational work provides background for a method wherein liquid additives are injected into the melted polymer through a single nozzle. A converging nozzle providing near constant extension rate along the centerline is modelled. The deformation of droplets inside a polymer undergoing purely extensional flow is studied for a range of exit (V) to platen (U) velocities and viscosity ratios ().The behavior of droplets for =1 is drastically different from that of lower 's, whichis attributed to the balance of shear stresses. Finally, the morphology of the deposited plastic strands is predicted. There is very different drop deformation history as the velocity ratio (V/U) transitions from V/U<1 to V/U>1.
3:00 PM Break