Design and Classification of Compliant Geometries in Orthotics Using Extrusion Additive Manufacturing

Abstract

This paper focuses on characterisation of localised compliance in material extrusion additive manufacturing (MEAM) for use in single wall 3D-printed orthotics. Specifically designed 3D-printed specimens were developed as representative sections of an orthotic edge to include localised compliance created by custom tool paths. Toolpath designs were created with intricate control over the nozzle position and printing conditions, including the explicit design of start and end points for each layer to avoid defects being introduced by the process. A new testing method, using cantilever testing principles, was used to evaluate the specimens' bending stiffness. Specimens with sinusoidal waveforms of varying wavelengths and fixed amplitude at three different extrusion thicknesses were tested along with straight specimens (i.e. wavelength approaching infinity). To allow direct comparison between specimens of different thicknesses, the bending stiffness results for all specimens were normalised to the reference specimen for each thickness. Increasing the frequency of the sine waves (reducing the wavelength) led to a reduced normalised stiffness for all extrusion thicknesses.