Local redesign for additive manufacturability of compliant mechanisms using topology optimization

Abstract

Compliant mechanisms are crucial components in current and future high-precision applications. Topology optimization and additive manufacturing offer freedom to design complex compliant mechanisms that were impossible to realize using conventional manufacturing. Design for additive manufacturing constraints, such as the maximum overhang angle and minimum feature size, tend to drastically decrease the performance of topology optimized compliant mechanisms. It is observed that, among others, design for additive manufacturing constraints are only dominant in the flexure regions. Flexures are most sensitive to manufacturing errors, experience the highest stress levels and removal of support material carries the highest risk of failure. It is crucial to impose these constraints on the flexure regions, while in others part of the compliant mechanism design, these constraints can be relaxed. We propose to first design the global compliant mechanism layout in the full domain without imposing any design for additive manufacturing constraints. Subsequently we redesign selected refined local redesign domains with design for additive manufacturing constraints, whilst simultaneously considering the mechanism performance. The method is applied to a single-input-multi-output compliant mechanism case study, limiting the maximum overhang angle, introducing manufacturing robustness and limiting the maximum stress levels of a selected refined redesign domain. The high resolution local redesigns are detailed and accurate, without a large additional computational effort or decrease in mechanism performance. Thereto, the method proves widely applicable, computationally efficient and effective in its purpose.