Researchers at the National Institute of Standards and Technology in Boulder, Colorado, discovered a technique to measure nano-vibrations that affect high-resolution stereolithography printing. The technique measures vibrations during the printing process to detect and correct deviations from the computer design.
The research is an important step in high-resolution stereolithography. Recent developments in the more general field of stereolithography work on much larger objects, where fine detail is not necessarily required. While high-temperature and high-tech materials are being adapted to stereolithography printing, less attention is being paid to the processes with which these materials may be shaped.
Stereolithographic printing may come to rely on these corrections for greater accuracy because the technique is premised on printed points’ relationship with other printed points. Tobin E. Brown, Veruska Malavé, Callie I. Higgins, Anthony P. Kotula, Benjamin W. Caplins, Edward J. Garboczi and Jason P. Killgore published their discovery in Applied Polymer Materials.
The technique tracks the printed material as it is being transformed by the photochemical process. A nanocylinder-tipped atomic force microscope measures the light reflecting off of the printing object, thus creating an accurate measurement of the photopolymerization in real time. The measurement operates on voxels, coordinates that are represented with reference to surrounding voxels in order to render a dynamic image. In an additive manufacturing context, these measurements could allow a printer to correct for errors.
The technique is not yet ready, however, for this real-time task. The researchers instead used the technique to confirm that stereolithography is not yet suitable for mass-produced high-resolution parts. They measured a resin’s reaction to various calibrations of the laser responsible for photopolymerization. Light intensity was the primary variable. As exposure to light and the intensity of the light were changed, the researchers discovered that part resolution is dictated by the competition between polymerization and diffusion. The amount of light that touched the resin and the length of exposure time altered the resin’s chemical properties and its characteristics. The researchers concluded that
Overall, the results indicate a need for enhanced control over polymerization and diffusion to obtain dimensionally accurate and mechanically homogeneous parts.