Additive Manufacturing of Optically Transparent Glass

We present a fully functional material extrusion printer for optically transparent glass. The printer is composed of scalable modular elements able to operate at the high temperatures required to process glass from a molten state to an annealed product. We demonstrate a process enabling the construction of 3D parts as described by computer-aided design models. Processing parameters such as temperature, which control glass viscosity, and flow rate, layer height, and feed rate can thus be adjusted to tailor printing to the desired component, its shape, and its properties. We explored, defined, and hard-coded geometric constraints and coiling patterns as well as the integration of various colors into the current controllable process, contributing to a new design and manufacturing space. We report on performed characterization of the printed materials executed to determine their morphological, mechanical, and optical properties. Printed parts demonstrated strong adhesion between layers and satisfying optical clarity. This molten glass 3D printer demonstrates the production of parts that are highly repeatable, enable light transmission, and resemble the visual and mechanical performance of glass constructs that are conventionally obtained. Utilizing the optical nature of glass, complex caustic patterns were created by projecting light through the printed objects. The 3D-printed glass objects described here can thus be extended to implementations across scales and functional domains including product and architectural design. This research lies at the intersection of design, engineering, science, and art, representing a highly interdisciplinary approach. Introduction and Background Additive manufacturing (AM) has undergone significant developments since its conception, as documented by Charles Hull in his patent of 1984 for the construction of parts using a photo-crosslinkable polymer. Numerous processes have since been introduced, as summarized by the American Society for Testing and Materials, which defines seven categories according to which the wide range of processes can be classified. Each of the various approaches relies on different physical characteristics and phenomena and is often associated with specific materials. Throughout the history of manufacturing, the design process has often been guided by the constraints of the fabrication method. Current freeform fabrication capabilities enable a more flexible design space: fewer design constraints provide entirely new opportunities for the construction and assembly of objects at different length scales. Specifically, additional complexity in product scale is now possible without negatively affecting its production rate, cost, or quality. Furthermore, AM allows for simple, rapid, and economic design iteration, capitalizing on the efficacy of nonlinear design and optimization. Extruded material built in three dimensions has proved its commercial value with the development of an entire consumerlevel industry based on the principles of fused deposition modeling (FDM). However, FDM printers, in their current embodiment, are unable to handle high-melting-point materials, and require feeding the material in filament form, thereby presenting significant limitations in size and scale. Two 3D printing methods are typically used for materials that require high temperature processing, such as metals and Media Lab, Department of Mechanical Engineering, and Department of Material Science and Engineering Glass Lab, Massachusetts Institute of Technology, Cambridge, Massachusetts. Department of Industrial Engineering, University of Padova, Padova, Italy. Wyss Institute for Biologically Inspired Engineering, Harvard University, Cambridge, Massachusetts. Department of Materials Science and Engineering, The Pennsylvania State University, University Park, Pennsylvania. *These three authors have contributed equally to this work. 3D PRINTING AND ADDITIVE MANUFACTURING Volume 2, Number 3, 2015 a Mary Ann Liebert, Inc. DOI: 10.1089/3dp.2015. 0021