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.
Additive manufacturing has gained interest in the industry due to its flexibility in design and the possibility to integrate functionalities. Thereby, glass has a high potential to be developed also in this field due to its thermal stability, chemical resistance, and optical transmission. Laser glass deposition is a method for fabricating glass components on a glass substrate. The energy input and the resulting temperature are crucial factors in this process, which can influence the material properties and the resulting geometry. Also, depending on the temperature in the substrate, difficulties such as high residual stresses or thermal shock can occur. The temperature on the glass substrate and in the melt zone can be changed either directly by the laser power or laser spot size, or indirectly by other process variables such as travel speed or path planning strategy. In this study, the energy input and the resulting temperature in the melt zone are numerically investigated under selected process parameters. Based on this, a regression function was created so that the generated temperature can be calculated by corresponding laser power, laser spot diameter, and axis velocity. Moreover, different tool path strategies for the production of horizontally multilayered surfaces were thermally investigated. The results showed a more uniform temperature profile with zigzag movement than the spiral tool path. The influence of the turning point angle in path planning on the temperature change was also investigated. It was observed that the 90° corner in contrast to the smaller angle has no significant influence on the temperature change.
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