Session: 16-03-04: Foundational Framework II

Paper Number: 173611

Enhancing Fused Filament Fabrication Capabilities With Co-Extruded Thermoplastic Filaments 

Although material extrusion additive manufacturing has advanced significantly in machinery and feedstocks,  fundamental issues of weak bonding between the layers and lack of structural integrity of some materials have hindered further expansion of its material library. Here we present ur recent work on fabrication and evaluation of core/shell filaments by integrating materials with distinct glass transition temperatures (T_g) and varying degrees of hardness. These filaments facilitate the production of materials that have traditionally posed challenges in fused filament fabrication/fused deposition modeling (FFF or FDM), such as buckling, poor printability, or weak “z-direction” mechanical property.

By leveraging the differing T_g, the printed parts are annealed at an intermediate temperature between the high T_g of the core and the low T_g. This technique effectively heals the interlayer of the print roads, thereby improving the durability and longevity of the printed object. Additionally, the core's higher T_g provides a supportive scaffolding that preserves the original geometry of the print, preventing the warping and deformation often seen with annealing. These materials range from PC+ABS engineering polymers to two different PEIs with distinct T_g. The mechanical properties in z-direction approaches that of the bulk injection molded properties after annealing. Using these materials, engineered parts suitable for additive manufacturing are demonstrated.

Secondly, we utilize ABS+TPE core-shell composites to tackle barriers of elastomeric material prints due to filament buckling and print stringing; we also expand on how variations in core-shell volume fractions influence mechanical tunability. We investigated the effects of raster orientation and core-shell ratio on controlled mechanical anisotropy in 3D-printed structures. Our findings indicate that a 0° raster orientation results in stiffer parts, whereas a 90° orientation yields more flexible structures, dictated by the inter-layer interfaces and raster contact area. At a 0° orientation, stress distribution is observed across the bulk material, while a 90° orientation confines stress within individual rasters, influencing the failure behavior. By adjusting ABS content and raster orientation, we achieve a broad range of tensile modulus (2242.58 MPa to 55.68 MPa) and strength (35.91 MPa to 6.90 MPa), and flexural modulus (2609.15 MPa to 48.75 MPa) and strength (75.16 MPa to 17.67 MPa). Furthermore, both symmetric and asymmetric layup structures demonstrate how raster orientation impacts bending performance, resulting in distinctly anisotropic behaviors under load. The localized orientation of rasters drives selective bending within the same layer. Through analytical and numerical modeling, we conduct homogenization of microstructural unit cells and simulate composite laminate behavior, finding good agreement with experimental results within the linear elastic range. Finite element modeling predicts asymmetric bending behavior due to local nonlinearity in the TPE material. Our findings offer valuable insights for designing soft materials in additive manufacturing, presenting pathways to optimize mechanical performance for soft robotics through precise control of raster orientation and core-shell composition.

Presenting Author: Jay H. Park University of Massachusetts Lowell

Presenting Author Biography: Biography: Jay Park is an Associate Professor in the Department of Plastics Engineering at UMass Lowell (2018- ). His expertise is in fiber processing, rheology, polymer nanocomposites, and multi-scale material manufacturing. Park received a B.S. in Chemical Engineering from the Johns Hopkins University (2004) then his Ph. D. in Chemical and Biomolecular Engineering from Cornell University (2013). He subsequently held postdoctoral appointments at MIT (2014-2017) and U.S. Army Research Lab (2017-2018), where he has gained expertise in high-performance fiber and plastics at both fundamental and application levels. In particular, he has expertise in harnessing processing-structure-property relationships of various fiber spinning methods, such as electrospinning, melt spinning, wet-spinning, and fused filament fabrication. His current research areas are i) functional nonwovens, ii) smart fibers and textiles, and iii) multi-material additive manufacturing. He has demonstrated well-balanced teaching and research, as recognized by the Department Teaching Excellence Award and KICHE President Young Investigator Award in 2023.

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