The role of crystallization and annealing on the thermal conductivity of material extrusion additively manufactured parts

Abstract

Despite the significant research being conducted on the mechanical reliability of additively manufactured parts, comparatively little focus has been paid to the property of thermal conductivity. Additively manufactured thermally conductive parts have the potential to benefit thermal management technologies that are currently a bottleneck of many classes of advanced electronic devices. Creating parts with high thermal conductivities remains a major challenge for the most prevalent form of material extrusion additive manufacturing, fused filament fabrication, which creates parts by extruding multiple layers of molten polymeric extrudate using an automated gantry system. The low thermal conductivity of these parts stems from several types of interfaces and voids inherent to the fused filament fabrication additive process, which create significant internal resistance to the flow of heat through a part. To increase thermal conductivity, many researchers and companies have added thermally conductive particles into the polymeric filaments. Still the achievable properties are largely constrained by the printing defects inherent to the printing process, especially when compared to injection molded parts. In this work, we investigate the role of thermal post-processing to both anneal the printed part and to tune the crystallization state of the polymer. We find that careful thermal post-processing of parts made with commercial filaments can improve thermal conductivity values to 2.5 times the as-printed property values. Further, we detail several correlations between processing conditions and thermal conductivity outcomes that will improve the implementation of fused filament fabrication for addressing thermal management challenges in industry.