4D printing and collaborative design of highly flexible shape memory alloy structures: a case study for a metallic robot prototype

Abstract

Abstract This paper investigates the entire process of 4D printing of shape memory alloys (SMAs), characterized by pre-programming of the future responsive shape of a deformable structure during its 3D forming. Taking an inchworm-inspired crawling robot as an application case, we propose a system prototype composed of two deformable SMA structures, i.e. a curved sheet and a spring coil. From the behavioral synergism of these two antagonistically configured structures, the initial and responsive shapes of each binary structure were collaboratively designed. The feature shapes of different structures were then pairwise combined to generate the robot’s gait, which was realized through the alternating activations of the two components. We also investigated the processing strategy and methods of the presented structures with small feature sizes and unique configurations, based on the optimal 3D printing process of selective laser melting of nickel–titanium alloys. The experimental results verified the design expectations and demonstrated the performance stability of the SMA structures under multiple testing cycles. This research confirmed the possible use of hard materials to create customized smart structures with high levels of flexibility and deformation control, providing new ideas for further development of intelligent, flexible robots.