In silico quantification of 3D thermal gradients and voids during fused filament fabrication deposition to enhance mechanical and dimensional stability

Fused filament fabrication (FFF) is one of the most widely used additive manufacturing techniques for polymeric materials. However, the mechanical and dimensional quality of the final printed parts are still deviating from the maximal performance, due to the presence of voids, and incomplete inter- and intralayer bond formation implying suboptimal molecular chain entanglement. The current work puts forward a three-dimensional Ansys Polyflow & REG; computational study in which temperature gradients and void formation are analysed for the deposition of up to eight strands, accounting compared to the state of the art for (i) bond formation at the strand interfaces by material deformation; (ii) non-Newtonian viscosity variations; (iii) measured temperature dependent material properties, including conductivity, specific heat capacity and viscosity; and (iv) convection. Selecting acrylonitrile butadiene styrene (ABS) as polymeric material, it is demonstrated that a dynamic heat transfer is obtained with contributions from the heated bed to layers printed above, and from just printed warmer layers to colder layers printed before in both the vertical and transversal direction. These extra heat transfers renew the interlayer contact between two strands, as the temperature at the weld line can be pushed several times above the glass transition temperature. A tuning of this renewable welding is possible based on a variation of the bed and nozzle temperature; the latter more relevant upon increasing the number of layers printed. It is further highlighted that the void shape and size is different close and away from the bed (2.5-8% void percentage variation). Moreover, a novel computational method is put forward to quantify the surface roughness based on edge analysis (80-120 & mu;m variation)