Z.D. Pritchard, M.P. de Beer, R.J. Whelan, T.F. Scott, M.A. Burns
University of Michigan,
Keywords: 3D printing, additive manufacturing, photopolymers, stereolithography, fluid mechanics, kinetics
Summary:Continuous stereolithographic 3D printing methods offer significantly improved production speeds over traditional, layer-wise stereolithography. In continuous stereolithography, cured resin is prevented from adhering to the resin bath by introducing a region near the window where polymerization cannot occur. Several approaches have been proposed in recent years, including CLIP, HARP, and two-color photoinitiation/photoinhibition. Here, we will present results of our efforts to model the various physical phenomena at work in continuous stereolithography. In our initial work, we describe a mathematical model for optical dose in continuous stereolithographic 3D printing. From this model, we develop a method for modifying the images projected into the polymer resin bath to achieve precise optical dose profiles, reducing curing-related print errors and enabling spatial tuning of crosslink density. We show how typical slicing methods—which are optimized for traditional stereolithography and highly-absorbing resins—are insufficient to realize the highest possible speeds in continuous stereolithography. We designed and printed parts susceptible to curing errors and show that our method significantly improves print fidelity at constant speed in both high- and low-absorbance height acrylate resins. For our test geometry, the magnitude of cure errors is reduced by 86 to 99 percent. Yet this correction approach is far from sufficient to ensure accurate parts and good material properties. We additionally will present mathematical and simulation-based models investigating competing initiation and inhibition reaction kinetics and fluid mechanics in the resin bath.