This paper will present the recent development achievements of a German SME supply chain to manufacture super light-weighted HB-Cesic® mirrors for IR to visible applications. We will present recent design developments for achieving extreme light-weighted mirror substrates with extremely high stiffness and performance and in the second part the newly established German supply chain for the manufacturing of such extreme light-weighted mirror substrates.
This paper will present the recent development achievements of a German SME supply chain to manufacture super lightweighted
HB-Cesic® mirrors for IR to visible applications. We will present recent design developments for achieving
extreme light-weighted mirror substrates with extremely high stiffness and performance and in the second part the newly
established German supply chain for the manufacturing of such extreme light-weighted mirror substrates.
Conventional or chemo-mechanical polishing represents the polishing technology most often applied for manufacturing precision glass optics. It is applied on various machine types and for all kinds of geometries. But it still represents the manufacturing step with the lowest process stability.
This work deals with the analysis and descriptive modeling of contact conditions occurring in the process area. The polishing process is assumed as a hydrodynamic system. The model aims for a qualitative description of the formation of a fluid film between pad and surface. The models enable the theoretical discussion of the effects of major process parameters on the fluid film thickness. Secondly, the theoretical considerations are validated by experiments on a tribometer. With this test bench the effects of the polishing parameters as well pad properties on the contact conditions are investigated. Additional experiments are conducted on a polishing machine for validation the results. It is found, that the hydrodynamic theory describes the formation of fluid film in polishing. Under typical polishing conditions, the friction regime is in the range of mixed friction. That means pad asperities and polishing grains are not completely separated from the surface by a fluid film. The transition into erosive wear and pure liquid friction was not reached. But an analysis of the surface quality in dependence on the relative speed showed, that the quality starts decreasing after a minimum, far before reaching the transition point. Based on the derived qualitative description, the effects of process parameters and pad properties on the fluid film can be discussed.
Different grades of silicon carbide (SiC) became an established material for structures as well as optical mirrors in space-borne
applications. But the manufacturing still causes high efforts and restrains an extension of application in further
fields. The research project MirrorFab aims for a qualification of an optimized process chain for manufacturing mirrors
made of Cesic®. Cesic® consists of a matrix of SiC reinforced with chopped carbon fibers. There is a space qualified
Cesic® manufacturing process and an established network for the supply chain. The project addresses the required gain in
efficiency and flexibility in the manufacturing capabilities. The consortium covers the major parts of the process chain. It
aims for increasing the performance of each manufacturing technology. Additionally, the consideration of the complete
process chain enables a holistic optimization approach. This paper deals particularly with the process optimization of the
grinding step after infiltration. The benefit of the use of an ultra precision grinding machine for mirrors in the range of
200 mm is evaluated. This paper presents the results of a systematical study on the influence of the grit size, the type of
bond as well the major machining parameters on the surface roughness and the grinding forces, when machining the
material Cesic®. A major finding is, that the use of ultra fine grinding wheels does not result in a superior surface quality
compared to the use of a D46 grinding wheel with resinoid bond.
This work deals with the chemo-mechanical sub-aperture polishing of glass lenses using spiral tool path and pressure-inflated
membrane tools. Current trends in manufacturing precision optics in Europe go to smaller lot sizes and an
increasing ratio of custom specific lens design. This requires deterministic processes as well as methods for an analytical
process set-up without empirical try-outs. Chemo-mechanical polishing is typically applied for pre-polishing step, which
aims for smoothing the surface with moderate shape correction. But due to kinematic effects the spiral-polishing process
often shows changes in the radius of curvature, which are right now corrected by empirical try-outs and iterative
corrections. This paper suggests an analytical tool for the compensation of these effects and contributes doing so to an
efficient pre-polishing of aspheres. A mathematical model calculates the local distribution of material removal. It is
based on Preston's equation and takes into account the influence of the major input parameters, such as feed rate, spindle
revolutions and spot size. The given results show a significant reduction in shape deviation applying this methods
compared to a polishing process without any compensation.
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