Sonication for the porosity gradation of foams meets replica templating: A hybrid manufacturing process for lightweight multifunctional structures

Advancements in the design of porous structures with high performance properties offer opportunities to many industries such as transport (towards diminished fuel emissions via mass reduction) or medical devices (achieving personalised orthopaedics by mimicking bone). However, the manufacturing of those parts lags behind because it is difficult to realise a complex porous structure design via conventional routes. Traditional manufacturing methods (e.g. casting) cannot produce complex porous distributions and new ones (e.g. 3D printing) have a limited palette of processable materials. We propose a hybrid manufacturing process in which a sacrificial cellular structure (i.e. a polymeric porous foam) is tailored using a sonication technology that increases density in zones where reinforcement is needed (e.g. stress loading) and decreases it where mass is not needed, achieving lightweight topologically-optimised structures. This template is then used in a replica process to create porous metal structures with an ad-hoc porosity distribution for a bespoke application. Their characterisation required the creation of a bespoke tool that could combine complex geometry, porosity distribution and properties at a given location simultaneously. The multifunctionality is achieved by coupling features thanks to the gradation within the structure which grants enhanced coexisting thermal, shock-absorbent, controlled-diffusing and/or vibration damping properties. These lightweight multifunctional structures are unmatched by those fabricated by conventional production methods.