Hot-Formed PEEK Metamaterials: A Novel Fabrication Approach for Multi-Stable Mechanical Structures

Abstract

Multi-stable mechanical metamaterials, composed of bistable unit cells, exhibit multiple equilibrium states and maintain either configuration without continuous external actuation. Despite unique functionality, their integration into high-precision motion systems remains constrained by the limitations of conventional 3D fabrication techniques. This thesis utilises the MECOMOS (Mechanical Metamaterials for Compact Motion Systems) manufacturing platform to develop a novel multi-stable mechanical metamaterial. The proposed methodology employs a hot-forming technique to form 100 um and 200 um PEEK substrates into functional, millimeter scale bi-stable unit cells which are subsequently assembled to form a 3D homogeneous metastructure. The findings of this study are categorised into three primary stages: fabrication process optimisation, the unit cell design architecture and the functional performance of the assembled metastructure. Evaluation of the fabrication process was conducted through analysis of the dimensional stability of the SLA printed moulds and the hot forming parameters, revealing the necessity of a sufficient forming duration. Initial investigations into the unit cell geometry utilised a single cosine beam configuration, identifying the fundamental requirements for bistability: the geometric profile of the beam and the effective stiffness of the surrounding boundaries. Subsequent development of the three-dimensional (3D) unit cell, characterised via Finite Element Analysis (FEA) and quasi-static experiments, demonstrated a high sensitivity to geometric variations via the force-displacement response with peak forces remaining below 1N. Concurrently, the structural limits of the fabrication process established a minimum achievable beam feature size of 500 um. By arranging these 3D unit cells into a honeycomb lattice, the multi-stable functionality of the metamaterial was validated through deterministic row displacement and the tilt compliance of the multi-cell layers. Collectively, these results demonstrate the viability of replication-based fabrication for achieving tunable, millimeter scale multi-stable metamaterials suitable for precision motion components.