Realizing arbitrary 3D microarchitectures with curved and near-sharp segments via toolpath strategies in aerosol jet printing

Aerosol Jet (AJ) printing is a jetting-based additive manufacturing (AM) technique that uses droplets in an aerosol form to deposit nanoparticles or polymer inks at a length scale of about 10 micrometers. The desired structural geometries via AJ printing can be obtained at a high efficiency and accuracy by engineered toolpaths and fill strategies. Recently, AJ printing is used to create three-dimensional (3D) freestanding microarchitectures such as microlattices, spirals, walls, and micropillars without any auxiliary support during printing. In this work, we demonstrate that for curved segments, the difference in the printed material volume on the convex side vs concave side leads to the accumulation of material while building freestanding 3D microarchitectures. This effect is most severe for sharp corners, which leads to build-defects such as protrusions and voids. We carry out a systematic study of the material accumulation on curved segments of AJ printed 3D microarchitectures. For 3D microwall segments with sharp curved portions, a positive (or negative) material accumulation causing large overgrowths (or voids) as a function of the angle between the tangents on the two sides of the microwalls and the radii of curvature are studied. For sharp bends (<15°) in the microwalls, adding a radius of curvature may not be sufficient to avoid overgrowths and voids, and the lines can be considered as individual segments. For microwall bends with >45° angle between the segments, smaller radii of curvature can be tolerated. We conclude that a fillet radius equal to the line width for 30° angles is necessary to avoid accumulation and therefore the protrusion defects. A simple model based on mass-conservation is also developed which shows the importance of considering ink self-leveling during printing. This information is then used for toolpath strategies to avoid defects on sharp curved microwall segments for complex 3D architectures such as protruding star shape and Scotty Dog, the Carnegie Mellon University mascot. This research will enable the defect-free fabrication of highly complex 3D microarchitectures via jetting-based AM techniques such as AJ printing.