Fraunhofer-Institut für Produktionsanlagen und Konstruktionstechnik IPK

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  • Publication
    Wolframschmelzcarbidbasierte MMC-Schichten für den industriellen Einsatz im Formenbau
    ( 2022)
    Langebeck, Anika
    ;
    Jahnke, Christian
    ;
    Wünderlich, Tim
    ;
    Hein, Christoph
    ;
    Bohlen, Annika
    ;
    Uhlmann, Eckart
    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.
  • Publication
    Improved surface generation of multi-material objects in computed tomography using local histograms
    ( 2021)
    Uhlmann, Eckart
    ;
    Hein, Christoph
    ;
    Kayser, Nicolas
    ;
    Dürre, Gregor
    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.
  • Publication
    Photocatalytic effect of TiO2-coated surfaces on the pathogenic microorganisms E.coli and S.aureus
    ( 2021)
    Uhlmann, Eckart
    ;
    Hein, Christoph
    ;
    Brehmer, Annika
    The use of titanium dioxide as a strong photocatalytic substance can have a large effect in combating the spread of pathogens through heavily contaminated surfaces. For this purpose, various materials, such as metal, glass, and polymer were coated with rutile- and anatase-rich titanium dioxide by sol-gel method. The contact angle and photocatalytic activity of the coated surface were measured under UV irradiation. The anatase-rich titanium dioxide showed higher photocatalytic activity, which further increased with the coating thickness. The process temperature had an effect on the photocatalytic activity due to the temperature-dependent conversion of anatase to rutile crystal conformation. The coated surfaces had strongly reduced contact angles compared to the uncoated material. In particular, the anatase-rich surfaces resulted in superhydrophilic properties. Photocatalytically induced antibacterial activity against pathogenic microorganisms in liquid environments was d emonstrated, especially for gram-negative Escherichia coli bacteria.
  • Publication
    Steuerung von Laser-induzierten periodischen Oberflächenstrukturen
    ( 2021)
    Uhlmann, Eckart
    ;
    Souza Schweitzer, Luiz Guilherme De
    ;
    Schneider, Peter
    ;
    Michel, Andre
    ;
    Hein, Christoph
    Laser-induzierte periodische Oberflächenstrukturen (LIPSS) weisen ein hohes Potenzial für Anwendungen in den Bereichen der Oberflächenfunktionalisierung auf. Die Steuerung der Richtung dieser Nanostrukturen kann nur durch Änderung der Laserpolarisation erfolgen. Auf dem Markt gibt es kein System zur automatischen Änderung der LIPSS-Orientierung. Für den industriellen Einsatz ist dies vom Vorteil, um Inhomogenität im Strukturverlauf zu vermeiden. In diesem Beitrag wird eine Systemlösung vorgestellt, indem die Steuerung der Richtung von Nanotexturen ermöglicht wird.
  • Publication
    Micro-milling of a sprue structure in tungsten carbide-based metal matrix composite
    ( 2021)
    Uhlmann, Eckart
    ;
    Polte, Julian
    ;
    Polte, Mitchel
    ;
    Hein, Christoph
    ;
    Hocke, Toni
    ;
    Jahnke, Christian
    Many industries rely on plastic components manufactured by micro-injection moulding. There is a high potential to further increase the cost-effectiveness by machining the moulds needed for this process from non-ferrous metals and reinforcing the parts of the mould, which experience high loads during the micro-injection moulding. Inserting tungsten carbide particles locally into the surface of these non-ferrous metals is one possibility of reinforcement. The resulting metal-matrix-composites (MMC) exhibit the needed wear resistance, while the ground material can be machined very effectively through micro-milling. In contrast, the Micro-milling of these MMC-materials is challenging and so far not state of the art. Thus, this investigation is concerned with the development and qualification of micro-milling parameters for tungsten carbide-based MMC-materials. Binderless polycrystalline diamond as innovative cutting material was applied for this purpose. The goal of the mil ling parameter development was to optimize the surface roughness and the form accuracy for machining an aluminium bronze workpiece reinforced with tungsten carbide particles through laser injection. Based on an analysis of a wide range of process parameters, an optimised milling strategy was applied to machine a sprue structure from the described MMC-material. Different parameter sets are evaluated by analysing the form accuracy and measuring the surface roughness of machined structures. A surface roughness of Ra = 80 nm and form accuracy of a = 3 µm could be achieved with optimized micro-milling parameters and qualified the developed parameters for industrial applications.
  • Publication
    Tool wear and surface roughness in micro-milling of aluminium and high-alloyed aluminium materials using cutting tools made of binderless carbide
    ( 2021)
    Uhlmann, Eckart
    ;
    Polte, Mitchel
    ;
    Wiesner, H.M.
    ;
    Polte, Julian
    ;
    Hein, Christoph
    Micro-milling can be applied for manufacturing in a wide range of materials and complex geometries. This process is especially important for the aerospace industry. High-alloyed aluminium is a common material for aerospace applications with complex micro- and macro-geometry due to its high wear resistance. The costs-effectiveness of producing these parts can be increased by using tools with improved wear behaviour and higher life times. However, wear-resistant tools are often associated with higher tool costs, which reduces the cost-effectivness of the whole production. An innovative solution is offered by the use of a cutting tool made of binderless tungsten carbide. The micro-milling of conventional and high-alloy aluminium with a new cutting material based on a binderless tungsten carbide is analysed in this investigation. The absence of a binding phase leads to an increased hardness and improves the wear behaviour of these tools. Therefore, tools with a tool diamete r of D = 10 mm were manufactured and there machinability was successfully proven. The feasibility of these innovative tools is demonstrated in a series of experiments. The experimental investigations were carried out on the five-axis high precision machine tool PFM 4024-5D PRIMACON GMBH, Peißenberg, Germany, with a workpiece made of TiAl 48-2-2. A surface roughness of Ra = 0.202 µm was detected after a path length due to primary motion lc = 70 m without any noticeable wear marks on the cutting tool. These results show the economic potential for milling tools based on binderless carbide for achieving high precision surfaces while reaching high lifetimes.
  • Publication
    Tool wear prevention in ultra-precision polymer machining
    ( 2020)
    Uhlmann, Eckart
    ;
    Fang, F.
    ;
    Polte, Julian
    ;
    Hein, Christoph
    ;
    Lai, M.
    ;
    Dörr, Martin
    ;
    Jahnke, Christian
    Polymers become more relevant in the field of optical components as their optical properties, like refractive index n and wavelength dependent dispersion n = f(λ), can be adjusted easily by additives. Due to their low density Ï polymeric optics are lightweight compared to glasses. The demand for ultra-precision machined polymer lenses is increasing. Small series and individualised components can only be produced economically by using ultra-precision machining. Within theses studies the influence of different measures to reduce diamond tool wear occurring during ultra-precision diamond face turning of polycarbonate (PC) and polysulfone (PSU) will be investigated. Continuous and interrupted face turning experiments are conducted to analyse the effects from separation of the diamond tool and workpiece. Results show increasing tool wear in interrupted cutting. Changes of the environmental conditions in the cutting process show an influence of increasing humidity H on diam ond tool wear. This contribution gives a qualitative and quantitative overview on the influencing factors on diamond tool wear in ultra-precision turning of polymers and gives an outlook on strategies to avoid its occurrence.
  • Publication
    Increased efficiency and accuracy in ultra-precision machining through adapted CAM software
    ( 2020)
    Uhlmann, Eckart
    ;
    Polte, Julian
    ;
    Hein, Christoph
    ;
    Kuche, Yves
    ;
    Dörr, Martin
    CAM software is widely used through the last 40 years for a broad field of applications. The networkability of machine tools and the digitally integrated production as an existing trend for the next years and exponentially increasing computing power enable direct data transfer between CAD/CAM software and machine tool. Increments ar < 5 nm are common in ultra-precision CNC codes and are not supported by most traditional CAM software. Therefore, ultra-precision machining often remains a manufacturing process with high manual effort in the machine setting and the generation of CNC codes. In order to increase the degree of automation in ultra-precision machining, machine manufacturers are developing their own, customised CAM software. The studies presented in this paper investigate the influence of different process preparation on relevant parameters during ultra-precision face turning of an n surface with monocrystalline diamond tools. Machine-specific CAM software is com pared with manual CNC code creation from a point cloud. The influence on the workpiece characteristics dimensional accuracy GF and average roughness depth Ra is investigated. The influence of the chosen strategy for the generation of the CNC code on the machining time tm is examined to compare the economics of the strategies. In order to keep the comparison significant, the cutting parameters cutting depth ap and feed f are kept constant in all strategies. Decreasing machining time tm increases efficiency in comparison to manual CNC code creation.
  • Publication
    Micro formed holographic security features in steel
    ( 2018)
    Uhlmann, Eckart
    ;
    Schulze, Stephanie
    ;
    Polte, Julian
    ;
    Hein, Christoph
    ;
    Matthiesen, Johannes
    ;
    Böge, Manfred
    Counterfeiting, with a global trade volume of approximately 450 billion euro a year compromises business results of companies in all industrial segments. At worst, product plagiarism causes severe damages to the individual brand reputation due to product defects or liability issues. Therefore, product integration of inseparable and unique security features is essential for a preserving market share in all manufacturing branches. This paper presents a novel approach regarding a replication technology for the manufacturing of holographic security features. Using a microstructured aluminium substrate with holographic properties as a base material, a forming die is manufactured by a combination of physical vapour deposition (PVD) and galvanic coating processes. Furthermore, a process adapted hardness progression between individual layers was created. By the use of this die, the forming of a holographic microstructure into high strength aluminium alloy (3.3547) and spring steel (1.1248) could be demonstrated within a preliminary study.
  • Publication
    Manufacturing and replication of sub-10 mm micro-bowls for biomedical sensor systems
    ( 2018)
    Uhlmann, Eckart
    ;
    Hein, Christoph
    ;
    Polte, Mitchel
    ;
    Polte, Julian
    ;
    Dähne, L.
    The technical implementation of a novel biosensor for the highly parallelized screening of biochemical binding reactions depends on the manufacturing of an array of micro-bowls with a diameter dB 10 µm with an aspect ratio ar 1. Since the operating principle of the biosensor is based on the stimulation of stationary optical waves in micro-spheres, micro-bowls for the immobilisation of these spheres in a microfluidic environment are necessary. Due to this operating principle, the micro-bowls need to separate the spheres from the fluid flow and ensure the careful adherence of single spheres, coincidently. Moreover, the pathway for the optical accessibility of the micro spheres should be unrestricted. This work presents a process chain for the manufacturing of microfluidic chips with an array of n 1,000 micro-spheres by ultra-precision milling of mold inserts, the replication by precision injection molding as well as experimental trial results. With regard to manufacturing of the mold inserts, the uniform and burr free ultraprecision milling of large aspect ratio micro posts was investigated within a parametric study. Furthermore, the replication of the micro-bowls was examined by taking the consistent replication of the entire bowl array, the adverse formation of fillets, and the replication of surfaces with optical functions into special account. By the analysis of the microfluidic and optical properties of the replicated structures, the correlation between mold manufacturing, replication, and operating conditions can be performed.