Volumetric Additive Manufacturing System Optics

Volumetric additive manufacturing is a novel 3D printing method to form parts in a single exposure, in contrast to traditional stereolithography 3D printing which builds parts layer-by-layer. Photopolymerizable resin is exposed with grayscale images from different angles over 360 degrees to deliver a 3D distribution of light energy which cures the resin to form the desired part. The exposure images are calculated using computed tomography (CT), the same principles which are used to convert X-ray images obtained during a computerized axial tomography (CAT) scan to reconstruct a 3D volume of the patient. A digital micromirror device is used to project the sequence of calculated exposure images into a cylindrical vial of resin as it is rotated thus exposing over 360 degrees. The polymerization kinetics of the resin, the alignment of the resin vial to the projected images, and the uniformity of the illumination field are all tightly coupled together and must all be understood and controlled to generate quality parts. Projecting a good image is challenging as the vial and resin are essentially a strong cylindrical lens located at the image plane, and the desired build space is not a plane but a volume. We perform an analysis of the cylindrical lensing on the image quality (and thus the print quality) and investigate methods to correct for the lensing. We demonstrate different methods to improve print quality and discuss the benefits and limitations of each technique.