Voxel-Scale Conversion Mapping Informs Intrinsic Resolution in Stereolithographic Additive Manufacturing

Abstract

In high-resolution stereolithography, printed parts deviate significantly from the projected photomask because of the reaction complexity on the voxel scale. To better understand the reaction process, we have developed a technique to measure local photopolymerization rates using a nanocylinder-tipped atomic force microscope cantilever. The drag force experienced during cantilever oscillations can be correlated to the viscosity and extent of reaction. Fluid dynamics simulations show micrometer-scale measurement localization, and the resonance-based measurement allows submillisecond temporal resolution. In a thiol−ene resin exposed to patterned light, oligomer diffusion length scales are significant compared to the size of printed structures. Consequently, part resolution is dictated by the competition between polymerization and diffusion. Because of the radical polymerization mechanism, increasing the light intensity at a constant dose decreases the local conversion, even though the diffusion length decreases. In the case of printed test structures with features matching the measured diffusion lengths, increased light intensity causes increased geometric aberration from the projected mask. Overall, the results indicate a need for enhanced control over polymerization and diffusion to obtain dimensionally accurate and mechanically homogeneous parts.

Dissociative Carbamate Exchange Anneals 3D Printed Acrylates

“…This effect has also been observed in polyurethane acrylates with a threefold increase in elastic modulus based on a fourfold increase in light intensity . Recent work on a VP-printed thiol–ene resin further explores the relationship between light intensity at a constant dose and local conversion using nanocylinder-tipped atomic force microscopy and rheo-Raman microscopy …”

“…30 Recent work on a VP-printed thiol−ene resin further explores the relationship between light intensity at a constant dose and local conversion using nanocylinder-tipped atomic force microscopy and rheo-Raman microscopy. 31 For the analysis of the VP-printed material under various print conditions without the confounding effect of layer interfaces, XY tensile bars were printed with loading parallel to the layer interfaces based on the ISO/ASTM 52921 standard. 32 To accurately explore the mechanical properties of VPprinted XY tensile bars from the resins IC-15 and IN-15, UV exposure times for each layer of 6 s (low) and 20 s (high) were used with an intensity of 14 mW/cm 2 at 405 nm, as measured by an ILT800-UVF radiometer.…”

A Data‐Driven Approach to Complex Voxel Predictions in Grayscale Digital Light Processing Additive Manufacturing Using U‐Nets and Generative Adversarial Networks

“…[6] Diffusion length scales can approach or exceed the pixel pitch depending on resin and exposure characteristics. [21,22] In addition to mass transfer, the reactions are generally exothermic, and thus the local generation of heat affects neighboring reaction rates. [4] To further complicate modeling, many of the underlying resin properties are inherently conversion dependent.…”

“…Numerous recent efforts have pushed the ability to include the above phenomena to predict VP printing. [4,6,[20][21][22] Because of the complexity of the reaction, often dozens of resin and light engine properties are needed to model a print, requiring significant experimental equipment and time. The multiphysics models provide immense insight into the cure reactions, but there is still a need for empirical models that provide accurate prediction without being subject to the dearth of material property information and the complexity of accurately accounting for all the underlying phenomena.…”

“…Characterizing voxel scale interactions requires microscopic tools to visualize and probe the part at sub-voxel scale (e.g., in this work, ≪ 80 μm) resolution. Tools such as atomic force microscopy provide a high-resolution characterization of voxel morphology and properties, [5,21,22,27] but they sacrifice field of view and thus throughput. X-ray computed tomography provides robust 3D characterization of fully printed parts and has seen broad adoption in metal additive manufacturing.…”