Material physics and metrology of material extrusion additive manufacturing

Material extrusion additive manufacturing covers a small set of processes and a broad set of materials. The two most common versions are fused filament fabrication (FFF), and direct ink write (DIW). Fused filament fabrication, and at large scale, big area additive manufacturing (BAAM), use thermoplastics or thermoplastic composites processed through liquefication followed by solidification to generate 3-dimensional structures. The technique can produce a wide range of components, from medical implants to wind-mill turbine-blade molds. Further, highly-loaded thermoplastics composites can create green bodies, which are post-processed into metallics or ceramics. Unlike fused filament fabrication, direct ink write utilizes a rich set of material physics (yield stress, thixotropy, support-bath, precipitation, and chemical reactions) to produce 3-dimensional structures. Direct ink write has the advantage of finer resolution and more expansive material space, allowing bioprinting, production of tissues scaffolds, and electronic components.
In material extrusion, flow fields and thermal gradients greatly influence the final material structure, especially at the interface between layers. Over the last decade, a significant effort has gone into measuring and predicting process-structure-property relationships in material extrusion. In this talk, I will discuss the state of the art process, structure, and property characterizations, including determination of the melt-front in the “hot-end” using in-situ neutron imaging, in-situ residual stress measurements using thermography and high-speed birefringence, chain orientation from birefringence and polarized Raman spectroscopy, and flow-induced crystallization using autonomous experimentation with micro-focused wide-angle x-ray scattering. Additionally, I will discuss where modeling and theory fill in experimental gaps and the current measurement and material challenges.