Measurement of anisotropic thermal conductivity and inter-layer thermal contact resistance in polymer fused deposition modeling (FDM)

Additive manufacturing, or 3D printing, is an exciting manufacturing technique based on layer-by-layer build-up as opposed to the subtractive approach in most traditional machining processes. Specifically, in polymer-based additive manufacturing processes, filaments of a polymer are dispensed from a rastering extruder to define each layer. Due to the directional nature of this process, it is of interest to determine whether thermal transport properties of the built part are direction dependent. Such an understanding is critical for accurate design of components that serve a thermal function. This paper reports measurement of thermal conductivity of additively manufactured polymer samples in the filament rastering direction and in the build direction. Samples are designed and built in order to force heat flow only in one direction during thermal property measurement. Experimental data indicate significant anisotropy in thermal conductivity, with the value in the build direction being much lower than in the raster direction. Both thermal conductivities are found to depend strongly on the air gap between adjacent filaments. A theoretical thermal conduction model is found to be in good agreement with experimental data. These measurements are also used to determine the inter-layer thermal contact resistance, which is found to be a non-monotonic function of the air gap. Cross section images of samples confirm the strong effect of the gap on the microstructure, and hence on thermal properties. Results from this paper provide a key insight into the anisotropic nature of thermal conduction in additively manufactured components, and establish the presence of significant inter-layer thermal contact resistance. These results may be helpful in the fundamental understanding of heat transfer in 3D-printed components, as well as in accurate design and fabrication of heat transfer components through 3D printing.