Local Layer Splitting: An Additive Manufacturing Method to Define the Mechanical Properties of Soft Pneumatic Actuators During Fabrication

Abstract

Additive manufacturing of silicone is increasingly being explored to complement the traditional molding fabrication technique for Soft Pneumatic Actuators (SPAs). However, the mechanical behavior of SPAs is defined by their 3D form, which leads to prioritizing the SPAs mechanical properties over their aspect. In this paper, we propose a novel SPA fabrication method where the mechanical properties of a silicone part are defined during the fabrication phase rather than the 3D modeling phase, leading to the object's mechanical properties being independent of the object's aspect. This novel SPA fabrication method, named Local Layer Splitting (LLS), consists of local modifications of the printing layer height to integrate stiffness variation, thus generating controlled mechanical deformation when pressured. We discovered that silicone printing layer height impacts the final stiffness of the material, and it could be used to program bending deformation to actuators during printing. We first characterize the effect of the layer height parameters on 3D-printed silicone stiffness with tensile tests. Then, we present a custom slicer we developed to generate G-codes with local layer height variations depending on the x and y positions. We then characterize the bending and force achievable by SPAs made with the LLS process and find that they match those of state-of-the-art SPAs. Finally, we present and discuss how the LLS method impacts the SPAs design by shifting the bending behavior integration from the SPAs 3D conception to their fabrication phase.