All-at-once vs. layer-by-layer
“Layer-based printing methods are limited in their speed by the hydrodynamic stresses that develop in the fluid—the light-sensitive precursor resin material—as the component being printed is drawn through a tray or bath of that material,” says Hayden Taylor, associate professor of mechanical engineering at UC-Berkeley. This process can take hours or even days depending on the size of the part being produced.
“In CAL, the object being printed does not move relative to the precursor resin during exposure, so the printing rate is limited only by the delivery of light dose and the ensuing polymerization reaction. This key difference means that a wider range of materials can be processed by CAL, including extremely high-viscosity or even solid, gelled precursors and those with a high loading of solid particles. Ultimately, we aim to bring CAL to a point where it can compete with injection molding for some applications.”
In addition to speed challenges, Taylor and his research partner, LLNL materials engineer Maxim Shusteff, say mechanical challenges also exist. Parts built layer-by-layer often result in a poor surface finish, which requires significant post-production surface treatment, and they could contain inherent stresses or flaws by nature of the layering process. Furthermore, conventional DLP-printed parts are built from the same material throughout, providing no easy way to combine different materials or insert a component within the structure.
The CAL approach seeks to address those problems by curing the material to form the entire part simultaneously, producing a smoother surface finish. The technique also enables the insertion of a different material—a metallic component, for example—within the vat of resin around which the printed part forms.