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Abstract:
This work demonstrates how a well-known malfunction that frequently occurs in material extrusion technologies, known as filament stringing or oozing, can be used to increase the acoustic performance of 3D printed sound absorbing materials. The purpose is first achieved with conventional slicer software by deliberately setting some printing parameters 'wrong' to provoke filament stringing. Acoustic materials based on the same original design of narrow slits are 3D printed with retraction enabled or disabled, or using a higher than required printing temperature. The uncontrolled filament stringing that occurs in this way creates fibres in the slits, which ultimately affects the sound absorption measured for these materials. This cannot be ignored in modelling if accurate sound absorption predictions are to be obtained. However, inspired by the uncontrolled stringing, we developed a new concept to print parts with deliberate parametrically adjustable micro-fibre substructures. These are achieved by directly designing innovative toolpaths with recently developed design software (FullControl GCODE Designer), which has never been used previously for sound absorption purposes. The method permits low-cost 3D printers to produce tailored complex acoustic materials with enhanced viscous dissipation effects and improved sound absorption properties. This behaviour is correctly captured by the proposed, experimentally verified, mathematical model of such acoustic composites. The examples presented in the article are also used to discuss some aspects of the reproducibility of acoustic materials 3D printed by extrusion.

Keywords:
Prototyping acoustic composites, Exploiting 3D printing imperfections, Fully controlled G-code, Filament stringing, Fibrous fillers, Sound absorption