Design and testing of multi-material flexure hinges for Fused Filament Fabrication

Flexure hinges are non-assemble flexible joints that allow the relative rotation of two adjacent rigid parts through bending. Traditionally thermoplastic material hinges are made through injection moulding. 3D printing technologies such as Fused Filament Fabrication (FFF) introduced new possibilities regarding hinges development due to design freedom and the availability of multiple materials. However, the current state of the art focuses mainly on single materials hinges with non-symmetrical design for one-way folding. For this reason, this paper aimed to identify and test multiple design solutions for two-way folding hinges made of compatible and low-compatible thermoplastic materials using design thinking methods. The design process considered the materials' bond formation, resulting in overlapping designs for compatible materials and interlocking designs for the others. The considered materials were acrylonitrile butadiene styrene (ABS) and polylactic acid (PLA) with thermoplastic co-polyesters (TPC) for the hinge. The resulting designs of multi-material two-way folding hinges were tested using a tensile test to evaluate the performance of the interlocking mechanism. The results show that macroscopic interlocking provides the best results.