WP3 was in charge of all the manufacturing activities within AERIALIST. A broad spectrum of additive manufacturing (AM) technologies were utilized. The project has demonstrated that AM technology now allows the printing of structured acoustic absorbent materials at the appropriate microscopic scale and in useful sample volumes. This was a key objective of the project and a strong success; however a number of challenges remain before large scale industrialization of AM parts can be achieved. Within AERIALIST the following technologies were utilized extensively:
(i) stereolithography (SLA)
(ii) digital light processing / masked stereolithography (DLP/MSLA)
(iii) selective laser melting (SLM)
(iv) fused deposition modelling / fused filament fabrication (FDM/FFF)
The various technologies provide different capabilities in terms of materials, resolution and build volumes. Prior to AERIALIST it was unknown to what extent manufacturing tolerances or defects impact the targeted metabehaviour. This is now an active topic of research and AERIALIST has made valuable contributions to this field of research.
AERIALIST has conducted initial work on creating independent open-source slicing capabilities to overcome computational limits during the manufacturing process, which enable the production of greater volume of cellular metamaterials by directly replicating layers in the z dimension. This approach allows the production of arbitrarily large sample volumes provided a repeating layering structure can be identified and significantly reduce computer processing requirements, with a significant increase in the volume of metamaterial produced per hour.
Another significant advancement within AERIALIST was the demonstration that low cost AM techniques can also be used to produce these lattice structures with satisfactory quality.
AERIALIST actively engaged in the EU COST action DENORMS to collaborate with other researchers investigating AM for acoustic metamaterials. The AERIALIST team published a comprehensive investigation of the influence of AM processes on the performance of a benchmark porous material design coming from the DENORMS network. At the scale of the microstructure, it was seen that deviations in surface roughness and dimensional fidelity had comparable impact on the experimentally measured values of the absorption coefficient.
One of the main concerns encountered during AERIALIST was the lack of consistency in the additively manufactured specimens. This was found in the acoustic measurements but also in the mechanical and geometric properties of the parts.
The source of this repeatability issue was thoroughly investigated from an analytical point of view. Over the project several experimental campaigns were carried out to determine the level of variation between the samples on the mechanical properties and geometric properties. The aim of this research within AERIALIST was to reduce uncertainty in both the acoustic and mechanical properties of AM parts, which was achieved at a satisfactory level, examining also the effect of the print orientation.
Final activities within AERIALIST WP3 have looked at novel post processing approaches to address the surface roughness of AM parts. While traditional machining such as milling is possible for large parts with a basic geometry clearly novel approaches are required for complex topographies within a microstructure lattice, like electrochemical-machining (ECM) process.