Title : Process parameters optimization and mechanical properties of additively manufactured ankle-foot orthoses based on polypropylene
Abstract:
Nowadays, additive manufacturing (AM) has revolutionized many industries, including medical devices. It allows for the design of individualized and complex structures tailored to specific patient needs, while reducing costs and production time. In particular, Fused Filament Fabrication (FFF) 3D printing offers promising opportunities for the customized manufacturing of ankle-foot orthoses based on polypropylene (PP). However, optimizing printing parameters remains a major challenge due to the specific properties of this polyolefin, particularly its low interlayer adhesion and volumetric shrinkage. This study aims to identify the optimal printing conditions to enhance the mechanical performance of PP-based ankle-foot orthoses. Firstly, a thorough thermo-mechanical characterization was conducted allowing the implementation of a (thermo-)elastic material model for the used PP filament. Thereafter, a Taguchi design of experiments was established to study the influence of several printing parameters (extrusion temperature, layer thickness, infill density, infill pattern and part orientation) on the mechanical properties of 3D printed specimens. Three-point bending tests were conducted to evaluate the strength and stiffness of the samples, while additional tensile tests were performed on the 3D printed orthoses according to ISO 22675 standard to validate the optimal configurations. Finally, the applicability of the finite element method (FEM) to simulate the FFF process-induced deflections, part distortion (warpage) and residual stresses in 3D printed orthoses was investigated using a numerical simulation tool (Digimat-AM®). The comparison between experimental results and numerical simulations enabled the proposal of an optimized set of parameters, ensuring improved quality and robustness of the printed orthoses. The findings of this study contribute to a better understanding of ankle-foot orthoses 3D printing with polypropylene, paving the way for more reliable and customized production targeted towards rehabilitation purposes.
