Redeployable, 4D printed wave spring actuators

Abstract

Wave springs are a novel type of axial compression spring that offer complete axial load transmission and a significant free height reduction when compared to coil springs. In this paper, it is shown that direct 4D printing using bilayers on a fused filament fabrication system can be used to create deployable, polymer wave springs that do not suffer from layering effects, as is common in other cyclically loaded additively manufactured parts. Bilayer actuators enable a flat print configuration and subsequent deployment by a thermal stimulus that then aligns the layers in the direction of the wave in the spring. Due to this, the springs exhibit exceptional performance under cyclic loading, reaching 104 cycles without failure. After plastic deformation caused by extended cyclic loading, the springs can be redeployed to recover their original mechanical properties using cold programming. These findings show the great potential of direct 4D printing in fused filament fabrication to create functional, 4D printed components with complex geometry and greatly increased lifespan compared to conventional 3D printed parts. The presented approach to compression spring fabrication further provides a standard component that enables the design of highly integrated, monolithically printed, and tunable mechanical systems.