Printability and mechanical behavior as a function of base material, structure, and a wide range of porosities for polymer lattice structures fabricated by vat-based 3D printing

Abstract

Lattice structures offer desirable functionality for engineering design such as having a high strength-to-weight ratio and efficient heat exchange. Lattice parameters can be adjusted to achieve specific benchmarks such as porosity, surface area, weight, or mechanical performance. One of the biggest challenges of creating components with lattice structures is that they are difficult to fabricate with conventional methods due to their complex, highly periodic shape. Additive manufacturing (AM) techniques such as stereolithography (SLA) vat photopolymerization (VPP) have emerged as manufacturing methods for successfully creating these structures. However, a seamless characterization and subsequent understanding of the relationship between base material properties and lattice geometry across a wide range of porosity has not been fully investigated. In this study, SLA VPP was used to print structures from two distinctly different lattices, specifically the TPMS (triply periodic minimal surface) gyroid and strut-based diamond lattices, five unique photopolymer materials with varying stiffness and strength, and twenty-six levels of porosity ranging from 34% to 84%. The broad porosity sweep provides a more continuous understanding of the impact of porosity on mechanical behavior. Analysis of mechanical and volumetric properties yielded several discoveries, including substantial effects of photopolymer resin viscosity and porous volume fraction on volumetric accuracy, printability, and defects. Based on the experimental data we propose a model for predicting mechanical properties as a function of porosity that outperformed the traditional Gibson-Ashby model. The discoveries and methods included in this work provide a foundation for future analysis of mechanical and volumetric properties of 3D printed lattices across an expansive range of structural porosities and materials.