Mastering the density of 3D printed thermoplastic elastomer foam structures with controlled temperature

This paper presents an innovative approach towards controlling the material properties of 3D-printed thermoplastic elastomer foam specimens by adjusting the material extrusion process parameters. A foamable filament made of a thermoplastic elastomer and thermally expanded microspheres (TEMs), which is suitable for producing foamed parts, is used to study the effects of the material extrusion printing parameters. In particular, the material density is analyzed with respect to the nozzle temperature and diameter. It is observed that samples printed from 200 ∘ C to 250 ∘ C exhibit a density reduction with temperature due to the expansion of TEMs compounded within the foamable filament. This density reduction increases with increasing the TEM content, as well as by raising the nozzle temperature. The uniaxial expansion of the sample is plotted, by measuring the increase in thickness of a 3D-printed spiral cylinder against nozzle temperature, and a linear relationship is found between the coefficient of thermal expansion and the TEM amount. Further, a Gompertz function is used to predict the change in density of foamable filaments in correlation with the printing temperature. Finally, when the density of the samples decreases, the specific modulus of the samples increases with nozzle temperature. This implies that by modifying the printing conditions, such foamable filaments may be applied to adjust the stiffness to weight ratio of a component.