Additive manufacturing is an increasingly important counterpart to subtractive and constant volume manufacturing methods, however metal powder bed fusion methods often suffer from poor surface quality dominated by adhered unfused powder at the near-surface. Finishing steps are often required before part use in many applications, for example in aerospace components or biomedical implants, where 'better than cast' surfaces are sought. Here, we introduce electrochemical jet machining as a single-step process to i) selectively finish additively manufactured parts created by powder bed fusion, and ii) to subsequently micro-pattern these with the intention of increasing part functionality. Roughness of Ti-6Al-4V parts is shown to be reduced from an average Sq of 18.6 mm (as-built), to 2.4 mm upon rapid finishing, and the mechanisms of material removal are explored. Furthermore, repeating micro-dot patterns have been added to demonstrate the potential of the technique to allow tolerance superposition of additively manufactured parts. (c) 2021 Elsevier B.V. All rights reserved.

The thermal conductivity of AlSi10Mg made by laser powder bed fusion (LPBF), and its modification via heat treatment, has received little attention despite possible applications for heat exchangers and thermo-mechanical components. Here, we show that heat treatment can increase the thermal conductivity of LPBF AlSi10Mg to that of cast material. Our results indicate that post-manufacture annealing eliminates the thermal conductivity anisotropy present in the as-built condition, and enhances the conductivity by close to 30 % in the transverse direction (perpendicular to the LPBF build orientation). A solution heat treatment increases the thermal conductivity further still (36 % compared to the as-built condition), while a T6-like treatment provides the greatest increase (44 % compared to the as-built condition). These improvements are related to the evolution of the AlSi10Mg microstructure, especially the breakdown of the Si cellular structure. Additionally, the thermal conductivities of gyroid lattice structures were examined in the as-built and annealed conditions. Contrary to solid specimens, the lattice structures exhibited almost isotropic thermal conductivity in the as-built condition. Their thermal conductivities were increased by the annealing treatment in proportion to their volume fraction. Our findings contribute to the development of a general design-for-additive-manufacturing (DfAM) framework which will make the best possible use of AM materials and lattice structures for heat transfer components.

Lattice structures can add value to high-performance components manufactured by laser powder bed fusion due to their high specific strength and stiffness. A further use of lattice structures is in thermo-mechanical applications, where the high surface area of the lattice may aid heat transfer. However, little characterisation of lattices under thermal loading is currently available in the literature. In this study, a custom-built test rig was used to characterise the thermal conduction for three triply periodic minimal surface lattice types, namely: gyroid, diamond and Schwarz primitives, with unit cell size and volume fraction being varied.Results show that thermal conductivity is primarily a function of the material properties and volume fraction of the sample. However, some effects of the geometry, such as surface area to volume ratio, can be used to explain slight differences in the measured conductivity. The Schwarz primitive unit cell consistently gave the highest conductivity, with diamond and gyroid unit cells being marginally lower. Larger cell sizes typically gave higher conductivity than smaller cells, which can be attributed to greater intra-cell convective heat transfer and better interface coupling with the testing apparatus.The experimental results are used to derive equations that allow samples with a specified thermal conductivity to be designed, thus demonstrating how a component may be manufactured with a custom thermal profile by varying the volume fraction of the lattice.