Bead parameterization of desktop and room-scale material extrusion additive manufacturing: How print speed and thermal properties affect heat transfer

Material extrusion (MatEx) additive manufacturing ranges in size from the desktop scale fused filament fabrication (FFF) to the room scale big area additive manufacturing (BAAM). The principles of how FFF and BAAM operate are similar - polymer feedstocks are heated until molten and then extruded to form three-dimensional parts through layer-by-layer additive manufacturing. However, the scales of FFF and BAAM differ substantially, which leads to critical differences in thermal behavior for these thermally-driven processes. This study compares heat transfer in FFF and BAAM using finite element thermal modeling. Parameterization is performed across material properties, layer number, and print speed at the desktop and room scale for MatEx. BAAM stays hotter than FFF for a longer period of time, which facilitates interlayer diffusion and weld formation, but can also lead to slumping or sagging. Changes in thermal diffusivity affect FFF more than BAAM, with FFF exhibiting a local maximum in weld time at the thermal diffusivity of ABS. In all cases, weld time is longer than relaxation time, indicating that polymer reorientation and interdiffusion is possible. For BAAM, the temperature and thermal history of the center of an extruded bead differs greatly from the surface of the bead, which has important implications for process monitoring, property prediction, and part performance.