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PublicationProzesskettenentwicklung für die Replikation und die Qualifizierung komplexer Mikrobauteile mit mikrooptischen Funktionsstrukturen(Fraunhofer Verlag, 2024)Mikrooptiken sind für industrielle Anwendungen im Bereich der Lasertechnik, des Quantencomputings sowie der biomedizinischen Technik von besonderem Interesse. Die Integration von Mikrolinsensystemen in komplexe Kunststoffbauteile ist aktuell jedoch noch eine große Herausforderung. Die Erfüllung der Anforderungen an die Maßhaltigkeit des Kunststoffbauteils und die funktionsgerechte Abformung der mikrooptischen Funktionsstrukturen kann aktuell nicht prozesssicher erfolgen. In dieser Arbeit wird zunächst eine Messempfehlung zur Qualifizierung von Mikrooptiken entwickelt. Deren Anwendung ermöglicht die Beurteilung der Fertigungsqualität sowie die Ableitung einer Funktionshypothese. Aus der experimentellen Analyse des Spritzgussprozesses zur Fertigung von Mikrooptiken werden anschließend Aussagen zur Wirkung relevanter Prozessstellgrößen auf die Replikationsqualität abgeleitet. Durch die Erweiterung der Analysen mit den Verfahren der röntgenbasierten particle-image-velocimetry (PIV) und der in-situ-Spannungsoptik wird schließlich ein Replikationsprozess definiert, der die prozesssichere Fertigung eines komplexen Kunststoffbauteils mit mikrooptischen Funktionsstrukturen ermöglicht.
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PublicationAutomated manufacturing of drug-coated balloons for coronary artery disease( 2023)Drug-coated balloons were established as an improvement for coronary angioplasty in recent years. However, due to the balloons' high manufacturing variance, coating them evenly is challenging. Therefore, production is still carried out at least partially manually. Within the framework of the presented research project, a four-axis machine kinematics has been developed, enabling even coating of balloon catheters of various sizes in a controlled climate. High-precision measurement using a confocal sensor allows for compensation for the manufacturing variance of the balloon catheter by means of surface mapping. The average coating thickness as well as its distribution can be determined similarly. Thus, in case of insufficient coating, local reapplication can be carried out. With the developed machine system, it is therefore possible to produce coating area densities in the range of 4 μg mm-2 < a < 20μg mm-2 with minimal inhomogeneities.
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PublicationComparison of binderless carbide with conventional carbide as a cutting material for milling( 2023)In order to be able to use the resources more sustainably and at the same time reduce the costs of machining, it is important to identify new types of cutting materials. Up to now, tools made of carbide have often been used in machining. Carbide has a high hardness H and, compared to other tool materials, enables long tool life T. This has a positive effect on process reliability. Conventional carbide usually consists of tungsten carbide WC and cobalt Co. The tungsten carbide WC represents the hard material itself. The cobalt Co is a binder and ensures that the hard materials are kept together. This combination makes the carbide less hard than the pure hard materials. The reduction of the hardness H of the material also results in a reduction in the tool life T of the milling tool. Various approaches are being pursued to increase the tool life T of the milling tool. One approach is the reduction of the binder in carbides. The reduction of the binder increases the hardness H of the material and thus the tool life T of the milling tool. Conventional carbide has a cobalt content of 6% < Co < 10%. The new cutting material, the binderless carbide, on the other hand, has a cobalt content of 0.40 % < Co < 3 %. The complete elimination of a binder is not possible from a manufacturing point of view at this time. To validate the milling tool made of binderless carbide, it is compared with milling tools made of conventional carbide. The two milling tools have identical geometries. This is to ensure that the influence of the cutting material on the machining result can be identified. For this reason, the identical experimental milling tests are carried out with the milling tool made of binderless carbide and the milling tool made of conventional carbide. The following parameters are recorded during the experimental tests: - Mean roughness depth Rz depending on the cutting path lc - Arithmetic average roughness Ra depending on the cutting path lc - Cutting edge rounding rß depending on the cutting path lc The experimental results show that the increased hardness H of the material has increased the tool life T of the milling tool. This makes it possible to use the available resources more sustainably and efficiently. In addition, the increase in tool life T results in an increase in the economic efficiency of milling.
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PublicationInjection mould measurement system for increasing manufacturing control and production quality( 2023)Tool and mould making is one of the most important sectors of industrial manufacturing. Currently, over a third of polymer products are manufactured by injection moulding or stamping. These processes are complex, as the melted or heated polymers are subject to thermomechanical changes. Since injection moulding and stamping are mostly used for mass production, process repeatability and quality of the final product are very important. Improper adjustments of process variables lead to various defects in the final product along with high amount of waste and rejects. The need for measurement and control of the process is mandatory. Frequently, the tool is not operated by the owner of the mold or the end user of the plastic components, respectively, but by an injection molding service provider within the supply chain. Consequently, it is impossible for the tool owner to trace the quality of parts regarding the parameters applied for processing. This is crucial information to connect parts outside the tolerances to the respective process characteristics. The increase of quality in the production is achievable through correlating the processing parameters applied with the produced components. Therefore, the aim of the research herein is to develop an autonomous sensor system for monitoring injection moulding and stamping processes. The system comprises an external component of the tool in order to record and document the parameters applied such as tool temperature, pressure, number of machined parts and geolocation among others. In conjunction with a connected laser marking system for injection moulding, the unique identification of the components and the unchangeable connection of the production parameters with an individual component is enabled. The direct technological added value is given by the fact that the customer is able to monitor the production at any time, any place, comparing the actual production with the agreed and specified conditions. Furthermore, this information enables the creation of new business models for the tool owner. Even though this work is at initial stages, the preliminary results detailed herein are rather encouraging.
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PublicationApplication of laser doppler vibrometry to characterize the laser drilling process( 2023)Laser drilling is being used more and more frequently in many industries, such as the aerospace, medical and electronics industries, to produce precision bores. A wide range of technically difficult-to-machine materials are applied. Laser drilling has already been intensively researched in order to investigate the basic mechanisms of the drilling process and the influences of various machining parameters on the quality of the holes. These findings have explicitly led to more successful machining processes of various technical components and industries. Despite all the advantages, there are some limitations of the laser drilling process and thereby a demand for innovative solutions to increase productivity. This paper presents a novel approach to the characterisation of the laser drilling process through the analysis of the acoustic signal characteristics. The objective is to apply a new generation of optical microphones to detect key aspects of the laser drilling process. This enables the development of new strategies to optimize the laser processing parameters, increasing repeatability and productivity for industrial applications.
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PublicationSkalierbare Herstellung von ATMPs( 2022)
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PublicationWolframschmelzcarbidbasierte MMC-Schichten für den industriellen Einsatz im Formenbau( 2022)Zur Steigerung der abrasiven Verschleißbeständigkeit können Oberflächen lokal mit Hartpartikeln verstärkt werden. Diese sogenannten Metal-Matrix-Composit(MMC)-Schichten können mittels Laserstrahldispergieren gefertigt und durch Mikrofräsen nachbearbeitet werden. Im hier vorgestellten Forschungsvorhaben wurde als Grundwerkstoff verwendete Aluminiumbronze (CuAl10Ni5Fe4) mit Wolframschmelzcarbid verstärkt. Der Hartpartikelgehalt kann dabei durch eine Steigerung des Pulvermassenstroms bis zur Packungsdichte des unverarbeiteten Pulvers erhöht werden. Über eine temperaturbasierte Leistungsregelung kann eine gleichbleibend homogene MMC-Schicht mit konstanter Dicke und Tiefe dispergiert werden. Durch das Mikrofräsen mit optimierten Parametern können qualitativ hochwertige MMC-Oberflächen für den industriellen Einsatz in Spritzgusswerkzeugen hergestellt werden. Dabei wurde vor allem der Zahnvorschub fz als kritischer Prozessparameter identifiziert.
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PublicationAutomated defect detection of CT projection image data using Monte Carlo simulation( 2022)During the last decade industrial computed tomography has become one of the most important metrological procedures for internal inspection, where it sees widespread application in additive manufacturing. Evaluating the CT volume data for defects is currently a lengthy process involving data acquisition, reconstruction, surface reconstruction, and nominal/actual comparison. The goal of the presented project is the development of a new pipeline for automated defect detection operating solely with projection data. Using this pipeline, the amount of necessary projections NP and therefore the measurement time of each object will be heavily reduced. Reference projection data of non-defect objects were generated using a multi-GPU Monte Carlo X-ray simulation. The innovative implementation of the Monte Carlo simulation on GPUs makes the photon number of 5x1011required for a proper simulation of an X-ray projection feasible for the first time. This generated reference data was then compared to real data and the differences evaluated. With this new processing pipeline, it is now possible to achieve a defect analysis with less than six projection images, which decreases the minimum measurement time tmby nearly two magnitudes.
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PublicationSurface optimization of dental implants with laser surface texturing and silver coating( 2022)The risk of bacterial inflammation at the interface between implant and tissue exists following the implantation of a dental prosthesis. Nearly half of implants are at risk of colonisation by pathogenic bacteria, which is associated with the occurrence of peri-implant mucositis. This disease can develop into peri-implantitis and thereby trigger a severe inflammatory process. The occurrence of peri-implantitis includes different phases. The initial attachment of microorganisms is only possible by pioneer bacteria, such as the gram-positive streptococci. Since the pathogenic cannot form a biofilm unless attached to a surface, the attachment of the pioneer bacteria is crucial for the onset of peri-implantitis. Due to the flexibility and contact free process, laser material processing is used for the surface structuring of several materials. In the biomedical field, laser-based surface texturing enables the production of implants with improved biological reaction surfaces to positively influence protein adsorption and cell adhesion. This paper presents laser texturing and silver coating to reduce initial biofilm formation on Ti6Al4V. The laser processing includes the manufacturing of LIPSS (Laser Induced Periodic Surface Structures), which enables the functionalisation of the surface. Furthermore, the surfaces are coated with silver to act as an inhibitor of biofilm formation. The implant material undergoes an in vitro culture of the microorganism Streptococcus salivarius in order to determine the biofilm formation applying both techniques. The analysis was realized by fluorescence microscopy with the application of 4', 6-diamidino-2-phenylindole (DAPI) on the adhered biofilm. Results show that the surface modification plays a major role in the inhibition of biofilm formation.
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PublicationImproved surface generation of multi-material objects in computed tomography using local histograms( 2021)During the last decade industrial computed tomography (iCT) has become one of the most important metrological procedures for internal inspection, where it sees wide-spread use in injection molding and additive manufacturing. Evaluating the CT volume data of multi-material objects represents a major technical challenge. Due to artifacts caused by beam hardening, an over-segmentation of strongly absorbing materials occurs, severely limiting the accuracy of dimensional measurements. The goal of the project presented is the development of an innovative artifact-reduced multi-material segmentation. This is applied to and tested on various complex reconstructed CT data sets. Global approaches show high signal-to-noise-ratio (SNR) but are not able to compensate for local deviations. For smaller volumes the data sets become more consistent, but the SNR decreases due to the reduced data volume. Thus, a more localized approach for the volume image data has the potential to provid e results of higher accuracy. With this newly presented algorithm it is now possible to perform segmentation of all materials, while eliminating over-segmentation errors as well as local noise artifacts almost completely for all tested datasets.
