Layerless fabrication with continuous liquid interface production

Abstract

Despite the increasing popularity of 3D printing, also known as additive manufacturing (AM), the technique has not developed beyond the realm of rapid prototyping. This confinement of the field can be attributed to the inherent flaws of layer-by-layer printing and, in particular, anisotropic mechanical properties that depend on print direction, visible by the staircasing surface finish effect. Continuous liquid interface production (CLIP) is an alternative approach to AM that capitalizes on the fundamental principle of oxygen-inhibited photopolymerization to generate a continual liquid interface of uncured resin between the growing part and the exposure window. This interface eliminates the necessity of an iterative layer-by-layer process, allowing for continuous production. Herein we report the advantages of continuous production, specifically the fabrication of layerless parts. These advantages enable the fabrication of large overhangs without the use of supports, reduction of the staircasing effect without compromising fabrication time, and isotropic mechanical properties. Combined, these advantages result in multiple indicators of layerless and monolithic fabrication using CLIP technology.stereolithogaphy | continuous liquid interface production | 3D printing | additive manufacturing | isotropic properties Additive manufacturing (AM), or 3D printing, is a growing field that employs the selective layering of material to build a part, which has distinct advantages compared with subtractive manufacturing (1). The benefits of additive over subtractive manufacturing are numerous and include unlimited design space, freedom of complex geometries, and reduction of waste by-products (2). Significant advancements were made to AM in the 1980s with the development of the stereolithography (SL) apparatus, a platform that uses the exposure of a rastering UV laser to selectively solidify a resin through a photopolymerization process in a top-down manner (3). The method has since been modified to solidify in a bottom-up process through the use of a digital light projection (DLP) chip that eliminates the rastering laser. The process of bottomup SL begins with a computer-aided design (CAD) file that is then converted into a series of 2D renderings using a method called "slicing" (Fig. 1A). The original object is then reconstructed in a layer-by-layer manner by reproducing these 2D renderings, one slice at a time. This process is done iteratively whereby a photoactive resin is selectively exposed to UV light through a transparent substrate, allowing for selective photopolymerization corresponding to a specific slice shape (4). Once the slice has been exposed, a series of mechanical steps of separation, recoating, and repositioning follow (Fig. 1B) to allow for subsequent exposure.The polymeric materials used in the SL process are known to have intrinsic properties that are a function of the chemical structure, molecular weight, and topology (3). Printed part properties differ from intrinsic polymeric properties because they a...

Additive manufacturing of periodic ceramic substrates for automotive catalyst supports

“…They were cut after curing and some of them are also evident in Figure (bottom right). The “staircase effect” is also evident at the low magnification of the optical microscope. Overall the structures were close to their nominal dimensions (as evidenced by the CT reconstruction).…”

Novel materials

“…Research over the last decade has established a broad range of materials and methods for printing 3D objects. The article by Janusziewicz et al (6) reports progress on one of the most powerful and newest of these techniques. Here, specialized photosensitive polymers enable a process in which continuous exposure of a liquid precursor material to programmed patterns of light yields-in a continuous manner-3D objects in complex geometries, without the rough, layered morphologies that characterize parts formed using traditional methods.…”

Mitigation and control of the overcuring effect in mask projection micro-stereolithography

“…This presents a new approach to solving this problem while building on previous research which focused mainly on improvements in hardware [8,9] and resin chemistry [6,7]. Future work will include the creation of an STL file modification program.…”

“…Most recently Tumbleston et al [9] made improvements to SL DLP hardware by introducing an oxygen permeable build platform which inhibits polymerization and enables 'layerless' fabrication at faster build speeds. A second more widely researched approach involves altering the SL resin material with a chemical light absorber [6][7][8]. In this work we develop a third approach in mitigating for the overcuring effect by simulating the process and predicting the level of overcuring likely to occur.…”

“…This effect is most prevalent in channels or features oriented horizontally (in a parallel plane to that of the build platform). Currently there are two main approaches in controlling the cure depth; 1. the chemical approach, which involves doping the resin material with a chemical light absorber [6][7][8]; and 2. by improving the system's hardware and optical elements to improve the homogeneity of the light dosage and control the cure depth [9]. Here we investigate a third approach through modification of the 3D CAD file prior to printing to mitigate for UV light leakage from successive build layers.…”