Fraunhofer-Institut für Produktionsanlagen und Konstruktionstechnik IPK
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PublicationImproved surface generation of multi-material objects in computed tomography using local histograms( 2021)
;Uhlmann, E. ;Hein, C. ;Kayser, N.Duerre, G.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.
PublicationPhotocatalytic effect of TiO2-coated surfaces on the pathogenic microorganisms E.coli and S.aureus( 2021)
;Uhlmann, E. ;Hein, C.Brehmer, A.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.
PublicationMicro-milling of a sprue structure in tungsten carbide-based metal matrix composite( 2021)
;Uhlmann, E. ;Polte, J. ;Polte, M. ;Hein, C. ;Hocke, T.Jahnke, C.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 Âµm could be achieved with optimized micro-milling parameters and qualified the developed parameters for industrial applications.
PublicationTool wear and surface roughness in micro-milling of aluminium and high-alloyed aluminium materials using cutting tools made of binderless carbide( 2021)
;Uhlmann, E. ;Polte, M. ;Hein, C. ;Polte, J.Wiesner, H.M.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, PeiÃenberg, Germany, with a workpiece made of TiAl 48-2-2. A surface roughness of Ra = 0.202 Âµm 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.
PublicationDevelopment of a mechanical, biocide-free method of disinfection for cathodic dip coating processes( 2021)
;Uhlmann, E. ;Hilt, M. ;Hein, C. ;Cudazzo, M. ;Huth-Herms, K. ;Jahnke, C.Quast, M.Technical fluids are often contaminated by bacteria as Burkholderia cepacia (B. cepacia), which is found in different industrial issues and affects manufacturing process chains by the formation of planktonic cell-aggregates and biofilms within the working fluids. B. cepacia is one of nine species of the Burkholderia cepacia complex (Bcc), a group of gram-negative, motile, non-spore-forming, and rod-shaped bacteria. Because of the opportunistic pathogenicity to plants, animals, humans, and the multi-drug and biocide resistance, B. cepacia is difficult to treat. This study aims to provide an application to reduce the germ numbers ng in an eco-friendly and continuous process without the use of biocides. The approach to disinfect technical fluids is to apply high shear forces in a rotor-stator assembly to the fluid. A prototype of the rotor-stator assembly with a variably adjustable shear gap gs and rotor speed srot was constructed. First experiments with a frequency frot 1 0 Hz â¤ frot â¤ 40 Hz a shear gap gs = 83 Âµm and gs = 166 Âµm showed a reduction of germ number ngr = 99.6 %. It concluded that the disinfection of technical fluids by a rotor-stator assembly is a biocide-free alternative. In addition to defined process parameters such as shear gap gS, temperature Ï, frequency frot and time of machining process tmp, also the peripheral speed vp, rotational speed vrot, flow rate fr and shear stresses Ï were used to assess the machining result and to develop an overall concept for disinfection of technical fluids.
PublicationTool wear prevention in ultra-precision polymer machining( 2020)
;Uhlmann, E. ;Fang, F. ;Polte, J. ;Hein, C. ;Lai, M. ;Dörr, M.Jahnke, C.Polymers become more relevant in the field of optical components as their optical properties, like refractive index n and wavelength dependent dispersion n = f(Î»), 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.
PublicationIncreased efficiency and accuracy in ultra-precision machining through adapted CAM software( 2020)
;Uhlmann, E. ;Polte, J. ;Hein, C. ;Kuche, Y.Dörr, M.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.
PublicationMicro-cutting of a MMC-composite for enhanced injection moulds( 2019)
;Uhlmann, E. ;Polte, M. ;Hein, C. ;Polte, J.Jahnke, C.Tools for micro-injection moulding are currently made of hardened steel. These tools are exposed to high local loads, which significantly reduce the injection moulding tool life time tT. Furthermore, the occurring wear of the milling tool during machining of hardened steel leads to reduced surface roughness Ra and geometrical accuracy GF. Copper and aluminium alloys as mould materials provide an alternative to hardened steel with advantages regarding material removal rate QW and wear of the milling tool, but with a significantly reduced life time of the injection moulding tool tT. Until now, the combination of a good machinability and high wear resistance cannot be achieved. The approach, presented in this paper consists of an easy to machine material and the development of a wear resistant metal-matrix-composite (MMC) material layer with a hardness of up to 3,000 HV. Therefore, the pre-machined test specimens made of aluminium-bronze are coated by laser dispersing with wolfram-carbide-particles W2C-WC. Furthermore, for the finishing machining of the coated moulds, a cutting technology for the machining of W2C-WC-particles was developed. The verification of the developed technology was performed with an injection moulding process based on carbon-fibre reinforced thermoplastic material. By means of documented machining efforts, the quality indicators geometrical accuracy GF and surface roughness Ra as well as occurring tool wear, the feasibility of the developed technology was demonstrated.
PublicationMeasurement of in-mould shear rates by x-ray particle image velocimetry( 2017)
;Uhlmann, E. ;Hein, C.Oberschmidt, D.The manufacturing of large quantities of polymeric optical and micro-optical components becomes more and more important regarding industrial applications as MEMS devices, customer electronics or micro imaging systems. The relevant parameters for the qualification of polymeric micro optics as surface roughness, shape and positional tolerances, refractive index, molecular orientation, injection moulding process induced deviations and their connection to injection moulding parameters are largely known. The manufacturing of micro optics by micro injection moulding and associated with that, micro injection moulding machine tools with highly complex plastification and injection systems is far less understood. In particular, the influence of shear loads and temperature deviation on replication quality has not been fully investigated. The occurring shear rates during injection moulding lead to mechanical damage of the polymer on a molecular level and reduced optical functionality. This work presents an approach for in mould shear rate measurement by the use of a metrological computed tomography system. Using metal powder with a particle size 3 mm < dp < 5 mm as tracer particles, Polyetheretherketon (PEEK) as mould material, a Zeiss Metrotom 800 computer tomography system and a Babyplast injection unit, streamlines of polymer flow could be visualized. In accordance to optical particle image velocimetry (PIV), for each frame a matrix including particle position was calculated. The temporal shift of these positions lead to velocity gradients that allow the calculation of shear-rates . By reproducing relevant elements of injection units and mould structures, this works enables the profound investigation of fluid dynamics regarding micro injection moulding and the correlation between shear loads and polymer characteristics.
PublicationGenerative tool manufacturing for the replication of micro-optical components( 2014)
;Uhlmann, E. ;Hein, C. ;Bergmann, A.Oberschmidt, D.