Investigating effects of printing parameters on flexural strength-to-modulus ratio of 3D printed compliant mechanisms

Purpose Fused filament fabrication 3D printers often struggle to achieve precise behavior in actuating mechanisms such as compliant mechanisms. As defined by the pseudo-rigid body model (PRBM), a high mechanical strength and a low modulus (or a high strength-to-modulus ratio) contribute to an effective compliant mechanism. When using fused filament fabrication (FFF) with polymers, these mechanical properties depend on a variety of factors, including process parameters. The purpose of this study is to experimentally demonstrate the effect of FFF process parameters on compliant mechanism performance. Design/methodology/approach This paper investigates the impact of printing parameters on strength and modulus of FFF-manufactured mechanisms by systematically varying slicing parameters and subjecting specimens to three-point bending tests. Findings The results from these studies indicate that select process parameters have significant impact on the strength-to-modulus ratio. Increasing wall thickness consistently increased the strength-to-modulus ratio and resulted in the largest measured ratio across all parameters. Ironing all layers and selecting a honeycomb or rectilinear infill pattern were also shown to have a statistically significant improvement to the strength-to-modulus ratio. Increasing wall thickness and ironing resulted in an increase in both strength and modulus but an overall increase in the strength-to-modulus ratio, demonstrating that FFF parameters affect compliant mechanism behavior in ways not predicted by traditional rigid-part intuition. The infill density and infill angle parameters showed little impact on strength-to-modulus ratio. Originality/value While the mechanical properties of FFF-manufactured parts have been studied extensively to optimize rigid applications, no generalized, quantitative link has connected printing parameters to compliant mechanism performance. This work establishes such a framework by mapping experimentally measured flexural strength-to-modulus ratios to achievable deflection through the PRBM. Designers can combine standardized beam tests with the PRBM to predict how slicer settings shift the usable range of motion of a flexure, independent of its geometry.