The effect of sintering hold-time on heat transfer relevant properties of 3D-printed copper and bronze samples produced by bound powder extrusion

Bound Powder Extrusion (BPE) is in principle an excellent opportunity for the heat transfer industry as high thermal conductivity metals can be manufactured with relative ease and at low cost. The process uses a filament made from a mixture of metal powder and polymeric binder to print parts on a low-cost consumer-grade printer, whereafter debinding and sintering remove the binder. However, the properties of the printed parts are still relatively unknown. In this study, copper and bronze parts were manufactured using BPE, with the parts being thermally debound and sintered to produce pure metal components. These parts were then characterised across several properties. For copper samples, it was found to lose about 8% of its mass during manufacturing and shrank by 12–30% as sintering hold time was increased. Similarly, bronze lost about 10% of its mass and shrank by 20–40%. Porosity and thermal conductivity were found to be functions of sintering time, varying by 25–45% and 40–70 W/mK, respectively, for copper and 27–45% and 2–9 W/m for bronze, which represents between 6 and 20% of the respective solid metals’ thermal conductivity. Pore formation was caused by delamination from gas build-up or voids left by the binding material removal. Specific heat capacity of copper and bronze was found to be like solid parts, with carbon impurities thought to be the cause of any differences seen. Surface roughness and hardness were found to be non-homogeneous across the samples. The roughness of the samples was significantly higher than that of samples produced by traditional subtractive manufacturing processes, while hardness’s were 30–50% of the respective solid samples, pointing to lower strength of the parts.