2023 Annual International Solid Freeform Fabrication Symposium (SFF Symp 2023): Materials: Polymers Material Extrusion
Program Organizers: Joseph Beaman, University of Texas at Austin
Tuesday 1:40 PM
August 15, 2023
Room: 417 AB
Location: Hilton Austin
Session Chair: Chad Duty, University of Tennessee
1:40 PM
Benchmarking the Tensile Properties of Polylactic Acid (PLA) Recycled through Fused Granule Fabrication Additive Manufacturing: Dawood AL Nabhani1; Ali Kassab1; Osama Habbal1; Pravansu Mohanty1; Georges Ayoub1; Christopher Pannier1; 1University of Michigan - Dearborn
To progress toward a circular economy of thermoplastic polymers using distributed recycling by additive manufacturing, the mechanical degradation of polymers through multiple recycling cycles must be quantified. This work presents a procedure and benchmark dataset of tensile property degradation for polylactic acid (PLA) feedstock in multiple recycling passes with the fused granule fabrication process. To establish recycling with minimal processing (shredding and sieving but not pelletizing from a filament), modifications were required to the granule feeding hopper of the GigabotX 2 XLT printer. Tensile test coupons are die cut from machined sheets from a vase-like 3D printed tube shape. Tensile properties are presented for 3D prints of the virgin material and one, two, three, and four passes of recycling by additive manufacturing.
2:00 PM
Determination and Compensation of the Shrinkage Behavior of Cylindrical Elements in the FDM Process: Thorsten Koers1; Balazs Magyar1; 1Paderborn University
Fused Deposition Modeling (FDM) is an additive manufacturing process to produce complex thermoplastic geometries layer by layer. The filament is melted in a nozzle, iteratively deposited and then cools down. Due to the solidification process, the deposited filament strands deviate from their intended position due to shrinkage, resulting in significant geometric deviations in the final part. In terms of dimensional accuracy, there is need for optimization, especially for local curved geometries in relation to the global part with higher nominal dimensions. The aim of this study is to investigate the size and shape deviations for cylindrical FDM elements and to compensate the expected deformations by using an in-house software with adaptive scaling factors in the x-y plane. Previous studies mainly focus on simple, non-curved objects, this study also considers the influence of curvature and global as well as local deviations on the final part.
2:20 PM
Development and Analysis of Direct-write Photopolymer, Multi-material Manufacturing Process: Kyle Holland1; Allison Murray1; 1Marquette University
There is a need to develop technology that allows for the benefits of isotropy afforded by stereolithography to a direct-write UV cure, multi-material application. This work addresses this open question through a multi-nozzle, direct-write manufacturing process with local UV curing. The effects of extrusion methodology, post-process cure time and temperature, and print orientation on the ultimate strength and elastic modulus are discussed. The resulting material has near isotropic mechanical properties, as compared to the highly anisotropic effects in some other extrusion-based printing methodologies. With an eye toward particulate reinforced resins, there is an exploration of composite loaded resins with variable solids loadings printed using this methodology. Through the dual-nozzle approach, variable loadings across a part are demonstrated, thereby opening the door for tailored internal meso-structures of printed resin-based polymers.
2:40 PM
Estimating Effective Stiffness of FFF Components based on Layer-by-Layer Raster Orientation obtained from Ultrasonic Waveform Analysis: Atik Amin1; David Jack1; Trevor Fleck1; 1Baylor University
The quality of the internal raster path of an AM product is an important factor that affects the performance of these components. To address this issue, this research proposes an automated approach using a novel ultrasonic testing method to extract the layer-by-layer raster orientation non-destructively of AM components. The proposed method uses the 2D Fast Fourier Transformation on gated ultrasonic waveforms to extract the raster path of each individual deposited layer. The results demonstrate that the approach can determine the raster orientation, with an error margin of 1°~2° for an 18 layer sample fabricated from nylon resin system, and for the PCTG and the PET-CF system the first 9-10 layers. The extracted layer information is then used to predict the effective stiffness of an ASTM D638 dog bone utilizing classical laminate theory and the results for each of the material systems are compared to physical testing of the fabricated specimen.
3:00 PM
Experimental Characterization of Enhanced Fused Filament Fabricated Tall Thin-walled Structures Using Polylactic Acid (PLA): Parimal Patel1; Rakin Ahmed1; Tanvir Shanto1; Ankur Jain1; Robert Taylor1; 1The University of Texas at Arlington
Printing tall thin-walled structures with good mechanical properties and geometric accuracy using Fused Filament Fabrication (FFF) technique has been challenging due to weak layer-to-layer bonding. In this work, a previously demonstrated concept of providing additional thermal energy during printing is utilized to print relatively taller and larger structures compared to standard tensile test specimens. A three-point bend test is carried out on a Polylactic Acid (PLA) structure representative of functional parts printed using this technique. In addition, geometrical deviation and surface roughness are evaluated using a Faro Arm scanner and a Mitutoyo SJ210 profilometer, respectively. Results demonstrate that providing additional in-situ thermal energy more than doubles the bending strength while maintaining or exceeding geometrical accuracy and surface finish, compared to a standard specimen. These results demonstrate the potential for printing effective thin-walled components using this technique in order to meet practical strength requirements in a variety of applications.
3:20 PM
Effects of Fiber Alignment on the Thermomechnical Properties of Large-format Printed Composite Polymer Structures: Tyler Corum1; Vipin Kumar2; Ahmed Hassen2; Chad Duty1; 1University of Tennessee; 2Oak Ridge National Laboratory
Large-format additive manufacturing (LFAM) was used in this study to create a fiber reinforced structure made from 20% by weight carbon fiber reinforced acrylonitrile butadiene styrene (CF-ABS). While adding fiber reinforcements does increase stiffness and reduce the coefficient of thermal expansion (CTE) of LFAM prints, the final structure exhibits highly anisotropic thermomechanical properties. Fibers are shear aligned by the print nozzle during the extrusion process and the resulting bead has highly aligned edges or skin areas and a randomly aligned center. Since fiber reinforcements provide more resistance to thermal expansion in the longitudinal direction than the transverse, the orientation of these fibers in the print influences the CTE experienced by the structure at elevated temperatures. This study used X-ray computed tomography (X-CT) and digital image correlation (DIC) to correlate the degree of fiber alignment to the thermal expansion of LFAM structures by serial sectioning printed beads.
3:40 PM
Fatigue Life Prediction of Functionally Graded TPU and PLA Components Produced by Material Extrusion: Suhas Alkunte1; Mithila Rajeshirke1; Ismail Fidan1; Orkhan Huseynov1; 1Tennessee Tech University
The objective of the present research is to examine the fatigue life estimation of functionally graded additive manufacturing (FGAM) components produced by the Material Extrusion (MEX). The current research studies demonstrate the potential of functionally graded materials (FGMs) in enhancing the mechanical properties of engineered structures. The raw materials employed for the experimentation of this study are a combination of Polylactic acid (PLA) and Thermoplastic Polyurethane (TPU). To predict fatigue life, several researchers have utilized various statistical approaches. In this investigation, an experimental study is conducted utilizing Tension-Tension (T-T) loading conditions and different stress levels (80, 60, 40, and 20% of Ultimate tensile strength), followed by the application of Basquin’s Model for fatigue life prediction. The results obtained indicate that the model may be utilized to predict fatigue response. Overall, the soft-hard material combinations with adaptable properties produced through FGAM have potential applications in dental and orthopedic fields.
4:00 PM
Fused Filament Fabrication of Polymer Blends with In Situ Layerwise Chemical Modifications: Donald Benza1; Camden Chatham1; Jonathon Baker1; 1Savannah River National Lab
Additive manufacturing (AM) promises voxel-level control over both shape and material properties; however, voxel-level control over material properties is difficult to achieve. The authors present one uniquely AM approach to material property control: layerwise chemical modification via introduction of reactive species during fused filament fabrication. Layerwise chemical modification can be accomplished by introducing a reactive gas species, such as ozone, in close contact with the molten polymer extrudate during part fabrication. Such reactions are considered “surface” reactions as they are diffusion limited. The AM benefit is that repeated modification of layer-interfaces compounds the “surface modification” across every layer. This is especially profound when printing polymer blends that natively exhibit unique behaviors at interfaces. Chemical modification at each layer interface provides an opportunity to alter blend morphology towards compatibilization during manufacturing and providing another handle for spatial control of material properties in AM parts.