Process-structure-property effects of ultraviolet curing in multi-material jetting additive manufacturing

Abstract

Material jetting (MJT) is an additive manufacturing process that involves selective jetting of a liquid material that is subsequently solidified, often via ultraviolet (UV) irradiation. The process presents designers with the opportunity to tune material properties on a voxel-by-voxel basis to fabricate high-resolution, multi-material parts. However, MJT is mainly constrained to prototyping and modeling applications, due to a limited selection of functional materials and challenges in attaining repeatable and reproducible part quality. Specifically, MJT’s indiscriminate UV dosing poses the risk of providing inconsistent dosing to parts, which could cause unintended variations in mechanical properties that are dependent on part design and build layout. To enable relating MJT processing conditions to final part properties, an MJT process model is presented that predicts accumulated exposure in parts of different materials, surface finishings, and build layouts by accounting for inputs relating to surface exposure, part design, and build plate configuration. Fundamentally guided by the Beer-Lambert law, the model leverages physical measurements of an MJT system, including UV spectral intensity distribution and toolpathing, to quantify cumulative exposure in batch-printed parts. Experimental characterization of parts printed in different configurations enabled correlation of parts’ total received exposure to their mechanical properties (tensile, three-point bend, Shore hardness, and dynamic mechanical analysis). It is observed that, especially in build layouts featuring multiple parts with dissimilar heights, the indiscriminate application of UV irradiation in MJT can lead to overexposure of parts, which results in changes in mechanical properties, including increased modulus and hardness. The effects of overexposure are largely dependent on material, toolpathing, and build layout. Connecting accumulated exposure to mechanical performance enables improved strategies for part design, build plate configuration, and process modification to better ensure consistency of UV dosage and reliable mechanical performance for batch-printed end-use parts.