Study of the Factors on Controlling Cured Layer Thickness in DLP 3D Printing

Digital Light Processing (DLP) 3D printing is an additive manufacturing technique that uses a digital light projector to cure photopolymer resin layer-by-layer to create high-precision solid structures. In addition to the planar resolution, the control of curing depth has a critical impact on the success of precise printing and the geometric features of the printed product. This issue is aggravated in the case of projection micro-stereolithography (PμSL), which uses an objective lens to enhance the planar resolution of the projected pattern. In this study, we investigated possible measures to control the cured layer thickness from both material and optical perspectives. As-received commercial resin was used to obtain the raw cured layer thickness, and then Sudan I or carbon black was added separately to study their effects. Eventually, the grayscale of the exposed pattern was adjusted to reduce light intensity and achieve a thinner layer thickness. Combining the above measures reduced the single-layer cured thickness from the raw 250 μm to 5.8 μm, approaching the usual minimum layer dimension setting of 5 μm. By exploring the variables affecting cured layer thickness, the findings in this study are expected to improve DLP 3D printing technology in producing high-resolution structures, especially in the z-direction.