Impact of strand deposition and infill strategies on the properties of monolithic copper via material extrusion additive manufacturing

The present research presents a comprehensive study on the process optimisation and characterisation of fully dense and pure Cu parts manufactured by Material Extrusion Additive Manufacturing (MEX). This technology is an emerging approach to additively manufacture high-performance metal components due to its multi-step nature that allows to shape and subsequently sinter complex design parts. A commercially available filament with 60 vol% (93 wt%) copper particles and polymeric binders was used and characterised in this study. Two approaches were combined for the first time to maximise the final density of the copper parts; a statistical approach (using ANOVA) and an optimisation approach based on the strand cross-section. Based on the former, the flow rate multiplier during printing has a significant effect on the density of the as-printed parts. The latter aimed at studying the effect of the ratio between extrusion width, layer height, and nozzle diameter on the deposited strand morphology. An extrusion width equal to and a layer height lower than the nozzle diameter contribute to precise strand dimensions, leading to improved control of the final green density. After solvent and thermal debinding followed by pressureless and supportless sintering in pure H-2 at 1050 degrees C, the copper parts resulted in a relative density > 95 % and an electrical conductivity of similar to 93 %IACS as an indication of the purity of the starting material and the quality of the whole process chain. Tensile testing of as-sintered dog-bone samples, built with 0 degrees, 90 degrees and +/- 45 degrees infill patterns and a single wall contour, revealed the best results for the +/- 45 degrees strategy with an ultimate tensile strength of 164 MPa and an elongation at fracture of 24 %. Finally, a copper coil for electromagnetic applications was manufactured, for the first time, via filament-based MEX and tested. It reported an electrical conductivity competitive to that reported in the literature (similar to 70 %IACS). This result was discussed in relation to a simple monolithic Cu geometry to provide insight into the complexity and concomitant scientific relevance of applying MEX to functional components.