Fast, low-energy additive manufacturing of isotropic parts via reactive extrusion

Abstract

Abstract Despite the well-documented advantages of additive manufacturing (AM) compared to conventional manufacturing processes, most AM technologies are subject to some significant limitations, including slow processing times, substantial energy needs, and anisotropic part properties, which become even more important as part size increases. To address these limitations, a reactive extrusion AM (REAM) process is introduced, in which successive layers of a thermoset resin are deposited and cured rapidly in situ with no external energy input aside from that required to pump and position the resin. Mechanical properties of tensile specimens fabricated in multiple orientations indicate that the tensile modulus and ultimate strength are isotropic, but elongation at break and toughness depend on orientation. The isotropic properties are attributed to chemical crosslinking of polymer chains that occurs between layers of printed parts. Moreover, the tensile modulus and strength are influenced by the local thermal environment in the build, which varies within the build envelope because of the exothermic nature of the polymerization reaction and affects the degree of curing within the specimen. The degree of curing was measured via differential scanning calorimetry (DSC) and was commensurate with the tensile strength of the tested coupons. When coupled with a large nozzle and high material flow rates, the REAM system can create nearly isotropic structural parts substantially more quickly than other AM systems, while using appreciably less energy at the point of manufacture.