NachhaltigAngewandte Naturwissenschaften und WirtschaftsingenieurwesenIPH TeisnachBeitrag (Sammelband oder Tagungsband)
Christian J. Trum, M. Jung, Beate Schmidbauer, Sebastian Sitzberger, E. Willenborg, Rolf Rascher
Hybrid-process-chain for polishing optical glass lenses – HyoptO
Proceedings of SPIE Optical Engineering + Applications (24 August - 04 September, 20208; Optical Manufacturing and Testing XIII; online conference), San Diego, United States, vol. 11487
2020
DOI: 10.1117/12.2568400
Abstract anzeigen
A number of process steps that build on one another are required to manufacture optical components from glass. The polishing steps are the most time-consuming and therefore cost-intensive parts of the process chain. Low removal rates and the depth of the Sub Surface Damage (SSD) to be removed contribute to this. An alternative for the complete removal of the SSD-penetrated material using contactless polishing methods such as Ion Beam Figuring (IBF) is the healing of the SSD. Due to the induced energy during laser-polishing, the material is remelted at the defects and the SSD are closed. However, laser-polishing is also associated with disadvantages in terms of shape accuracy and surface quality. The project HyoptO is therefore devoted to the development of a hybrid-process-chain consisting of laser processing and conventional polishing. It is expected that the healing times of the SSD can significantly reduce the process times in the subsequent polishing steps. However, there are a few questions to be answered regarding the economic use of the hybrid-process-chain. These include:
NachhaltigAngewandte Naturwissenschaften und WirtschaftsingenieurwesenIPH TeisnachBeitrag (Sammelband oder Tagungsband)
M. Jung, Christian J. Trum, Beate Schmidbauer, E. Willenborg, Rolf Rascher
Non-ablative removal of sub surface damages in ground optical glass substrates by controlled melting of thin surface layers using CO2-laser radiation
Proceedings of SPIE 11478 (Seventh European Seminar on Precision Optics Manufacturing [8 July 2020; Teisnach]), Bellingham, WA, USA
2020
DOI: 10.1117/12.2564801
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The form generation of optical surfaces by grinding and mechanical polishing results in small sub surface damages in the form of micro cracks that conventionally have to be removed by further removal of the damaged surface layers. In order to reduce process time and material cost non-ablative methods for removal of micro cracks are desired. Utilising the low optical penetration depths of less than 10 μm for CO2-laser radiation in glass, the laser energy can be used to heat up and melt thin surface layers. Using a 1.5 kW CO2-laser, a quasi-line focus formed by a scanner unit and a constant feed speed, it is possible to close all micro cracks present in the rough grinded test surfaces (max. SSD-depth ~ 63 μm), while achieving a process time of less than 2 seconds for a Ø 30 mm N-BK7 lens, respectively 7.5 seconds for fused silica. With a Sa as low as 50 nm and low distortion from the original shape the surfaces can directly be conventionally polished, further reducing the process chain complexity.
NachhaltigAngewandte Naturwissenschaften und WirtschaftsingenieurwesenIPH TeisnachBeitrag (Sammelband oder Tagungsband)
Sebastian Sitzberger, Johannes Liebl, Christian J. Trum, Rolf Rascher
Concept of a two-part clamping system for lenses in optical metrology
Proceedings of SPIE 11478 (Seventh European Seminar on Precision Optics Manufacturing [8 July 2020; Teisnach]), Bellingham, WA, USA
2020
DOI: 10.1117/12.2566547
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The developed concept represents a universally applicable clamping system designed to fit in any measuring machine with
any measuring principle. The design ensures that, as long as the lens remains clamped, the measurement results are
reproducible. Form errors due to tension remain constant across all measuring and processing steps. The version presented
in this paper was developed especially for small lenses in the diameter range up to 40 mm. On the one hand, the design
allows for fast measurement of loose lenses. On the other hand, the device can also be used for measurement comparisons,
since lenses can also be mounted permanently. In the following, the concept and first results of measurement tests are
presented.
NachhaltigAngewandte Naturwissenschaften und WirtschaftsingenieurwesenIPH TeisnachBeitrag (Sammelband oder Tagungsband)
Christian J. Trum, Sebastian Sitzberger, Rolf Rascher
Improved performance of CMP processes through targeted adjustment of polishing slurry and polish pad
Proceedings of SPIE Optical Engineering + Applications (19-23 August, 2018; Optical Manufacturing and Testing XII; San Diego, CA, USA), San Diego, United States, vol. 10742
2018
ISBN: 978-1-5106-2055-1
DOI: 10.1117/12.2321031
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Chemical-mechanical polishing (CMP) of optical glasses is widespread and forms the basis for many high-precision polishing processes. The pads, slurries and glass materials used in polishing have many different properties. The effects of these properties on the process results are often unknown. The right choice and combination is therefore often a challenge.
By means of a plan processing of N-BK7 and SF56 samples by a plan-polishing process, the influence on the process results, material removal rate (MRR), micro roughness and cleanliness caused by slurry and polishing pad is shown. It turns out that the type of polish pad has the biggest impact on the results. The easy-to-process material N-BK7 shows only little influence by the type of slurry used. The more challenging SF56, however, shows significant effects, especially in the area of the resulting micro roughness and the appearance of surface damages like orange peel. Especially the use of Auerpol® PZ500 shows clear advantages here.
For a selection of three out of nine polishing pads, the effect of density variation of the slurry was also investigated. Lower particle concentrations lead to lower material removal rates. This applies to both materials. The more sensitive SF56 shows a reduction in micro roughness by the use of a less dense slurry.
The correct selection of the polishing pad has a positive effect on the material removal rate and/or the micro roughness in all tested materials. An adaptation of the type and concentration of the slurry is especially important for more sensitive materials and in combination with the right polishing pad.
In view of the development towards special materials and small lot sizes, the targeted and correct selection of polishing slurries and pads becomes more and more important. The information required for this purpose on the behavior of the pads and slurries available on the market must therefore first be determined in a targeted manner and clearly presented.
NachhaltigAngewandte Naturwissenschaften und WirtschaftsingenieurwesenIPH TeisnachBeitrag (Sammelband oder Tagungsband)
Sebastian Sitzberger, Christian J. Trum, Rolf Rascher, M. Zaeh
Workpiece self-weight in precision optics manufacturing: compensation of workpiece deformations by a fluid bearing
Proceedings of SPIE 10829 (Fifth European Seminar on Precision Optics Manufacturing [April 10-11, 2018; Teisnach])
2018
ISBN: 978-1-5106-2270-8
DOI: 10.1117/12.2318577
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The effects, the extent and the importance of workpiece deformations, particularly lenses, caused by the weight of the workpiece itself, were examined in a previous paper1 . The considered deformations are in the single-digit to two-digit nanometer range. The investigation was carried out by FEM calculations. The conclusion of the previous aper was that a full-surface support of a workpiece in the processing of one surface presumably produces the best results. Furthermore, it was found that if the second functional surface is not to be touched in the process, a full contact lens mounting on its circumference is advisable. An alternative method for fixing precision lenses is therefore desirable. This can be accomplished in two steps. As a first step, the lens must be gripped at its periphery so that none of the optically functional surfaces of the lens is compromised. However, the complete circumference has to be fixated gaplessly because a punctual fixation has the disadvantage of deforming the lens surface asymmetrically. As a second step, the freely hanging lens surface should be supported to minimize deformation. An approach had to be found that supports the surface like a solid bearing but at the same time does not touch it. Therefore, the usage of an incompressible fluid as a hydrostatic bearing for full-surface support is pursued. For this purpose, the bottom side of the lens has to be stored on water. The results of the FEM simulation showed that with a fluid bearing the resulting deformations can be drastically reduced in comparison to a freely hanging surface. Furthermore, under the right conditions, a resulting deformation comparable to a full surface solid support can be achieved. The content of this paper is a test series under laboratory conditions for a first validation of the theoretical results. Therefore, a prototype model to test a lens fixation with a fluid bearing was developed and manufactured. The resulting deformations were measured with an interferometer and the effects are discussed.
NachhaltigAngewandte Naturwissenschaften und WirtschaftsingenieurwesenBeitrag (Sammelband oder Tagungsband)
Christian J. Trum, Rolf Rascher
Improving efficiency of chemo-mechanical polishing processes by systematic selection and conditioning of the polishing suspension
Proceedings of SPIE 10009 (Third European Seminar on Precision Optics Manufacturing, 100090Y [April 12th 2016, Teisnach])
2016
DOI: 10.1117/12.2236000
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During design of optical systems or individual components, customers and designers already predetermine the way through production and the necessary resources. They define the tolerances that are required for their application like shape, micro-roughness and cleanliness, as well as the glass material that is necessary for the targeted optical effect. By the tolerances, they have also an influence on the manufacturer and his decisions on the production environment, measurement technology and the process chain that in his opinion is necessary to meet the specification. In most cases the type of polishing suspension and its parameters are also predetermined by the use of central polishing supply systems.
With this paper, the authors want to give a prospect of a currently running research with the aim of increasing the efficiency of chemo-mechanical polishing processes by a systematic selection and conditioning of the polishing suspension. They want to show that small amounts of well-conditioned and stabilized polishing suspension could be a tool to improve the efficiency in CMP processes under the influence of the global trend to products that are more individual and down to one piece flow production.
Main parts of this research are the identification of influences of polishing suspensions on the quality criteria of optical components and the creation of a method to find well-working suspension parameters in a deterministic and reproducible way. © (2016) COPYRIGHT Society of Photo-Optical Instrumentation Engineers (SPIE). Downloading of the abstract is permitted for personal use only.
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