Material loss analysis in glass additive manufacturing by laser glass deposition

The properties of glass (e.g., transparency, chemical and thermal inertness) are advantageous for optical, microfluidic, and chemical applications. Additive manufacturing allows the creation of complex geometries and novel functionalities. In contrast to metals and polymers, there are limited options for digitally creating transparent glass geometries. Glass becomes viscous when heated above its transition temperature. This allows a bubble-free forming but requires precise thermal management. Previously explored studies established the deposition of multiple types of glasses using fiber and rod feedstocks. A significant challenge is the speed of the process. Phonon modes in all of these glasses directly absorb CO2-laser radiation (λ = 10.6 μm) with an optical penetration depth of <10 μm [J. Bliedtner, H. Müller, and A. Barz, Lasermaterialbearbeitung: Grundlagen–Verfahren–Anwendungen–Beispiele (Carl Hanser Verlag GmbH Co KG, Munich, Germany, 2013), ISBN:3446429298]. The thermal energy must diffuse through the glass with low thermal conductivity to the interface with the workpiece. Faster deposition rates result in the temperature of the process zone exceeding the evaporation temperature for the material and cause material loss. This study quantifies the material loss due to evaporation for the first time and investigates the use of a CO laser (Coherent J-3-5) for the laser glass deposition process. Lower absorption in silica at the 5.5 μm wavelength of this laser permits much deeper optical penetration into the glass. The effects of surface versus volumetric heating resulting from the choice of laser are experimentally investigated by the deposition of glass fibers with different deposition rates with demonstrations of lower vaporization rates under faster deposition conditions.