Functional Assessment of Chemically Etched Compliant Mechanisms for Thickness Reduction

Abstract

Compliant mechanisms are currently often made from polymers because they are easy to manufacture and naturally compliant. However, polymers suffer from creep, viscoelasticity, and environmental degradation, which can be hurdles in mechanism design. Metal compliant mechanisms do not have these issues, but current manufacturing techniques like additive manufacturing (SLM) or water-jet cutting cannot reliably produce the thin features needed for low stiffness. This research presents a new approach: using chemical etching as a predictable and effective method to reduce thickness. To validate this approach, an empirical etching distance model is developed and applied to the first two of three case studies. First, a Continuously Variable Transmission (CVT) prototype was etched to reduce its flexure thickness. The process significantly improved the mechanism’s accuracy, raising the match rate to the theoretical model from 16% to 85%. Secondly, a bistable mechanism was tested. Etching allowed the mechanism to be scaled down while maintaining bistability and, importantly, reduced peak stresses enough to prevent plastic deformation during actuation. Finally, a cross-flexure mechanism was etched to compare the etching approach against lattice flexures. The etched samples have a greater reduction in actuation stiffness and a better relative stiffness compared to the lattice design. These results demonstrate that chemical etching effectively overcomes the minimum thickness limitations of standard manufacturing. A key insight is that the minimum achievable thickness is not limited by the production method, but by its thickness uniformity. By shifting the focus to uniformity and using etching for thinning, designers can use etching to exploit the benefits of metals for compliant mechanisms.