Volumetric additive manufacturing of glass

Additive manufacturing (AM) technologies are non-conventional manufacturing techniques that employ 3D CAD models to create three-dimensional parts of precise geometric shapes. Such technologies allow for greater design freedom in the fabrication of complex structures with respect to conventional techniques, such as formative and subtractive ones, which would require higher tool usage and/or material waste. Glass, on the other hand, is a well-known material for its thermal, chemical, and mechanical stability, as well as for its optical properties, which makes it widely used in different sectors, such as everyday products (i.e., kitchenware and smartphones), as well as in the chemical and pharmaceutical industry (i.e., vials, micro-fluidics), and for electronics and optical devices. Nonetheless, the fabrication of glass components has been limited for many years to traditional blowing, lamination, and molding, thus allowing for the fabrication of quite simplified shapes. The combination of glass properties with the high degree of design freedom offered by AM techniques has the potential to advance further and enlarge the applicability range of glass. Among the various additive manufacturing techniques, volumetric AM has proven promising since it allows the object to be created directly within the volume of the chosen material, overcoming the use of supports as in the case of layer-by-layer technologies. This thesis project focused on the fabrication and characterization of glass components obtained through additive manufacturing; specifically, a technique based on the use of a photopolymer and a photoinitiator which, after excitation, induces the crosslinking of the polymer matrix in which silica nanoparticles are dispersed, forming a network of the desired geometry. The experimental work focused on the formulation of eight different silica-based ink compositions which were compared in terms of absorbance, refractive index, viscosity, and printability range, thus identifying the one allowing for the fabrication of transparent glass components with an adequate resolution. Specifically, the work was structured in different phases, such as (i) preparation and characterization of the optical and rheological properties of the inks; (ii) optimization of the printing parameters; (iii) thermal treatment of the printed samples to remove the organic part, to obtain dense and transparent glass components through sintering; (iv) physical and optical characterization of the sintered parts. The optimization of the polymer matrix, as well as its interaction with silica particles, was found to be the most critical aspect to tackle to obtain an ink possessing suitable rheology and transparency. The obtained results confirmed the possibility of creating glass parts with adequate transparency, resolution, and density comparable to traditional silica glass.