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PublicationProzessoptimierung beim Glaswafer-Trennschleifen( 2023)Fast-Axis-Kollimatoren (FAC) sind essenzielle optische Elemente für Diodenlasersysteme. Beim aktuellen Prozess des Trennschleifens mit nachgelagerter Reinigung von FAC-Optiken aus gepressten antireflexionsbeschichteten Glaswafern entstehen vermehrt Beschädigungen, die eine Verwendung der Optiken limitiert. Die Verwendung von Schneidfolie zur Substratfixierung beim Trennschleifen der FAC-Optiken ermöglicht ein defektfreies Schneiden und Lösen ohne Reinigung von der Folie und gleichzeitig können Kosten und Fertigungszeit eingespart werden.
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PublicationSurface Grinding of Borosilicate Crown Glass Optics via a Robotic Approach Based on Superposed Trajectories( 2023)The production of large-sized optical components with complex shapes requires several phases, including surface finishing. Currently, mainly skilled workers can correctly perform this operation, divided into the successive steps of grinding and polishing, leading to long production times, poor reproducibility of results, and exposure to human error. For this reason, the industry is trying to move towards automation involving, for example, high-precision machine tools and machining centers. However, these solutions require high investment costs and long setup times. Using robotic cells helps to reduce these expenses, manufacture larger components, and increase the flexibility in the production chain. In this research, we present an unconventional approach to the robot-assisted grinding of optical samples made of borosilicate crown glass. The samples were guided by a six-degree-of-freedom industrial robot on a rotating grinding disc while imposing to them different trajectories with complex geometry. We avoided regular grinding patterns, which are easily recognizable by human eyes and affect the quality assessment, by superposing multiple relative movements between the machined surface and the abrasive grains. The ground surfaces of the samples were characterized based on average roughness values, profile error data, and surface topography images. Finally, we selected the best robotic grinding procedure matching the trajectory and strategy with optimal surface quality, processing time, and productivity. The suggested methodology not only shortens the manufacturing sequence by eliminating manual methods but also provides components with optical properties within the required specifications for subsequent polishing steps.
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PublicationInvestigation of Surface Integrity Induced by Ultra-Precision Grinding and Scratching of Glassy Carbon( 2023)Glassy carbon provides material characteristics that make it a promising candidate for use as a mould material in precision glass moulding. However, to effectively utilize glassy carbon, a thorough investigation into the machining of high-precision optical surfaces is necessary, which has not been thoroughly investigated. This research analyses the process of material removal and its resulting surface integrity through the use of nano-scratching and ultra-precision grinding. The nano-scratching process begins with ductile plastic deformation, then progresses with funnel-shaped breakouts in the contact zone, and finally concludes with brittle conchoidal breakouts when the cutting depth is increased. The influence of process factors and tool-related parameters resulting from grinding has discernible impacts on the ultimate surface roughness and topography. Enhancing the cutting speed during cross-axis kinematic grinding results in improved surface roughness. Increasing the size of diamond grains and feed rates leads to an increase in surface roughness. An achievable surface roughness of Ra < 5 nm together with ductile-regime grinding behaviour meet optical standards, which makes ultra-precision grinding a suitable process for optical surface generation.
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PublicationVariationskraftgeregeltes 5-Achs-Schleifen( 2023)Eine variierende Anpresskrafteinstellung im Werkzeugeingriff des Schleifstiftes entlang stark gekrümmter Werkzeugkonturen ermöglicht eine konstante Schleifprofiltiefe. Dies verhindert unerwünschte Bauteilformabweichungen und erlaubt eine automatisierte Nachbearbeitung komplex geformter Konturen in einer Aufspannung. So wird ein durch einen Werkzeugwechsel unterbrochener Schnitt vermieden. Insbesondere Übergänge von ebenen auf stark gekrümmte, konvexe Flächen und kleine Radien in Kantenbereichen lassen sich mit diesem Verfahren automatisiert nachbearbeiten.
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PublicationMold protective coatings for precision glass molding( 2022-10-04)Precision Glass Molding (PGM) is a replicative technology to manufacture glass lenses with complex geometries such as aspheres, freeform-optics or lens arrays. During the PGM process, a glass preform is heated until the viscous state and afterwards pressed into the desired shape using two high-precise molds. This process enables the direct and efficient manufacture of high shape accuracy and surface quality optics without any mechanic post-processing step. The efficiency of the PGM process depends primarily on the lifetime of the high-precision molds made of cemented tungsten carbide. During each molding cycle, the molds have to withstand severe thermo-chemical and thermo-mechanical loads. Using protective coatings, the lifetime of the molds can be increased. In this study, the performances of a diamond-like carbon (DLC) and a precious metal alloy coating, namely PtIr, were evaluated in an industrial glass molding machine. The degradation mechanisms of the coatings were analyzed using surface characterization such as scanning electron microscopy (SEM) and energy-dispersive X-ray spectroscopy (EDX). At this, phenomena such as glass adhesion and coating disintegration were observed.
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PublicationAn Analytical Model for Robot-Based Grinding of Axisymmetric Mold Inserts Using a Rotary Unit( 2022)The grinding of mold inserts used for injection molding aims to improve the surface roughness according to precise quality standards. The insert surface must also have a surface topography that facilitates the release of the plastic material at the end of the injection process. In particular, fine machining lines must be parallel to the extraction direction from the mold to avoid the sticking of plastic material and subsequent surface damages compromising the functionality of the finished product. However, this step in the production chain is most often conducted manually. This paper presents an analytical model to grind a truncated cone-shaped mold insert for the mass production of plastic cups. The automated solution consists of a flexible robotic system equipped with a rotating external axis to improve the accessibility of the tool to the surface to be machined. The tool path programming requires the development of an analytical model considering the simultaneous mot ion of the insert and the robot joints. The effectiveness of the developed model is evaluated in terms of final surface quality, grinding lines direction, and total process time. The automated strategy developed can be easily implemented with machine tools and applied to inserts with different axisymmetric geometries.
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PublicationBio-inspired manufacturing of molded optics and optical systems( 2022)Manufacturing technology is driven by ever increasing demands of costs, quality and lead time. For many existing industries, digitization is key to obtain these goals in the future. In terms of optics production, it is rather a research topic. Meanwhile, the so called »Biological Transformation« is said to be the subsequent industrial revolution. This paper will explain this development and translate it to the optics production. Two examples of biologically transformed production scenarios will be presented. The presentation concludes with an assessment, whether »Biological Transformation« can deliver a substantial innovation push to optics manufacturing and glass molding in particular.
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PublicationPrecision Glass Molding of infrared optics with anti-reflective microstructures( 2020)
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PublicationVibration-Assisted Face Grinding of Mould Steel( 2020)This work investigates vibration-supported, force-controlled fine machining with elastic bonded mounted points for automated fine processing of mould steel samples. The aim is to compare conventional robot- or machine-tool-based face grinding with a vibration-supported grinding process. The influence of vibration support on the surface topography is investigated primarily to minimize kinematically caused grinding traces. First, the state of the art for the production of tool moulds and vibration-supported fine machining is explained. On this basis, the potentials for the reduction of grinding marks through vibration support for an increase in the degree of automation are derived and the experimental procedure is introduced. Subsequently, robot-based grinding tests with vibration support are carried out and compared with conventional grinding tests. After the tests carried out, the results are evaluated using tactile and optical measuring methods.
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PublicationNumerical and experimental determinations of contact heat transfer coefficients in nonisothermal glass molding( 2020)
