Glass filters are often used in the field of medical technology and chemical analysis to separate particles of a defined size out of liquids. Depending on the application, different pore width from 1.6 μm to 500 μm are necessary. Glass materials are particularly suitable, because a high purity, the chemical resistance and a high thermal resistance of the filter are necessary. Traditionally, these glass filters are produced by conventional sintering. In the new investigations, selective laser sintering is investigated as an alternative method. The conventional sintering process allows defined pore sizes to be adjusted by varying the sintering time. The high purity of the glass filters can be achieved by a binder-free production. The material properties of the glass material, such as the chemical resistance or thermal stability is maintained by the sintering process. Typically, fused silica or borosilicate glasses are used as basis materials. High-temperature selective laser sintering (HT-SLS) is an additive manufacturing process for the production of silicate and porous components. This manufacturing technology allows complex and unconventional geometrics to be realized efficiently and flexibly. For this purpose, the volume model to be produced is first separated into the desired layer geometry and number of layers. In the subsequent specific process cycle, the glass powder is distributed by a squeegee on a building platform in a defined manner. A solid material layer is created by means of scanning CO2 laser radiation. After lowering the building platform and transporting the powder again, the component can be generated layer by layer. For the production of the glass filters by HT-SLS, initial investigations are carried out with synthetic and natural fused silica glass powders with particle diameters in the range of 19... 78 μm in spheroidized and vitrified form. A laser sintering furnace has been specially designed for the HT-SLS, which achieves process temperatures up to T = 1000 °C as well as low contamination of the glass powder. In addition, material-specific scan and parameter concepts are developed. A high component quality can be achieved by combining a hull-and-core scan strategy with a 180° scan field rotation each sintered layer. Also a bidirectional beam guide and a material-specific parameter concept is needed. The absorption of CO2 laser radiation and the heat-conduction of the powder are supported by the process-dependent plasma and the preheating of the building platform. The generated porous components are investigated with regard to the density and the bending strength. Component densities of ρ = 65 % and bending strengths of σ = 13.6 MPa are achieved. Basically, HT-SLS is an alternative method to the classical sintering process of glass powder to produce glass filters. In particular, an increase in efficiency with regard to the producible component geometry of the porous components can be achieved. This new technology offers a high degree of innovation, while at the same time requiring a high level of research.
The production of complex glass components with 2.5D or 3D-structures involves great effort and the need for advanced CNC-technology. Especially the final surface treatment, for generation of transparent surfaces, represents a timeconsuming and costly process. The ultrasonic-assisted grinding procedure is used to generate arbitrary shaped components and freeform-surfaces. The special kinematic principle, containing a high-frequency tool oscillation, enables efficient manufacturing processes. Surfaces produced in this way allow for application of novel smoothing methods, providing considerable advantages compared to classic polishing. It is shown, that manufacturing of transparent glass surfaces with low roughness down to Rq = 10 nm is possible, using an ultra-fine grinding process. By adding a CO2-laser polishing process, roughness can be reduced even further with a very short polishing time.
The efficient production of complex glass components is often not possible with classical manufacturing methods. In order to obtain glazed three-dimensional quartz glass moldings, the alternative method of selective laser beam sintering is investigated.
Using synthetic and natural silica powders enables an additive production by high-temperature selective laser sintering (HT-SLS). Particle-diameters in the range of 19...78 μm and spheroidal and vitrified particle-shapes allow to manufacture green bodies. For this purpose, an experimental set up as well as material-specific scan and parameter concepts are developed. Component densities of ρR = 65 % and surface roughness of Ra = 32.21 μm are achieved. Subsequently a glassy, opaque molded body is produced by temperature pressure sintering. The component density increases to ρR = 96 % with a shrinkage of 16%. In order to use the glazed molded body as glass fiber preform, polishing of the shell surface is necessary. Surface roughness of Ra = 10.4 nm can be realized by laser beam polishing.
Basically, HT-SLS is an alternative method to the classical isostatic pressing of glass powder. In particular, an increase in efficiency with regard to the producible component geometry of the green bodies can be achieved.
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