Enhancing Fused Filament Fabrication Capabilities with Co-extruded Thermoplastic Filaments

The recent advances of fused filament fabrication (FFF) introduced materials that go beyond ABS and PLA, i.e., highly-filled composites, or engineered polymer such as PEEK. Despite such advancement, issues such as composite embrittlement, warping due to uncontrolled crystallinity and residual stress, and buckling of soft filaments have prevented further expansion of material library for FFF. Our recent works on co-extruded dual-material filaments integrate materials with distinct glass transition temperature (Tg) and hardness into a single filament structure which offers multifaceted benefits. Primarily, these filaments pave the way for the fabrication of materials that have traditionally presented challenges in FFF due to their inherent characteristics. Examples in the present study will include polyolefin FFF printing and soft TPE filaments that are susceptible to buckling under the pressures of the extrusion process. By integrating a robust core with these materials, the structural integrity of the filament is preserved, facilitating the FFF process without compromising on material properties.Moreover, leveraging the differential Tg properties, annealing can be executed at an intermediate temperature; this sits between the high Tg of the core and the low Tg of the shell. This method effectively heals the shell-shell interfaces, enhancing the durability and longevity of the printed object. Simultaneously, the core, exhibiting a higher Tg, provides a scaffolding that maintains the original printed geometry, preventing warping and deformation commonly associated with annealing processes. Engineering applications that are unique to AM process are presented.