Fraunhofer-Institut für Produktionsanlagen und Konstruktionstechnik IPK

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  • Publication
    Semi-automatic process control for efficient refurbishment of turbine blades
    ( 2023-06-16)
    Uhlmann, Eckart
    ;
    Polte, Julian
    ;
    Mühlich, Christopher
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    Mönchinger, Stephan
    ;
    Ebrahimi, Puya
    The refurbishment of turbine blades requires the precise removal of damaged surface coatings. In manufacturing companies, this usually involves time-consuming activities such as detecting residual coatings and adapting process settings to varying turbine blade geometries. The use of automated systems therefore opens up opportunities to improve the efficiency of turbine blade refurbishment processes by replacing manual tasks. This paper presents an conceptual approach for a semi-automatic decoating process of turbine blades that integrates abrasive blasting technology into a closed loop process control system. The experimental setup consists of a robot for guiding the turbine blade in a blast machine and a nozzle system for local removal of residual coatings using abrasive material. Based on image processing the residual coatings of a turbine blade are labeled by a neural network and mapped to a 3D model of the turbine blade, which is used by a software control system to coordinate the decoating process. Using a prototype setup this paper investigates the applicability of the proposed approach and evaluates its feasibility.
  • Publication
    Framework of an experimental setup to enable an adaptive process control based on surrogate modelling
    ( 2022)
    Uhlmann, Eckart
    ;
    Polte, Julian
    ;
    Bösing, Manuel
    ;
    Schuler, Niklas
    Numerical simulations can help to reduce the necessity of experimental studies. Nevertheless, these simulations are costly in terms of their computational effort resulting in significant expenditure of time and hence prevent a flexible adaption to continuously changing process conditions in real time. To address this shortcoming, the paper describes a framework for the application of surrogate models to enable an adaptive process control in real time. Following, an experimental setup to validate the general framework is designed for a laser metal deposition process. In particular, the component distortion shall be simulated and the results are then used to train the surrogate models. By measuring the final component distortion the quality of the surrogate models can be assessed.
  • Publication
    Heat Transfer Study for Oil-in-Water Emulsion Jets Impinging onto hot Metal Surface
    ( 2022)
    Nabbout, Kaissar
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    Pasternak, Lars
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    Sommerfeld, M.
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    Bock-Marbach, Benjamin
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    Kuhnert, Jörg
    ;
    Barth, Enrico
    ;
    Uhlmann, Eckart
    The purpose of this work is to analyse numerically as well as experimentally liquid jets impinging at different angles (30°, 60° and 90°) and different velocities (4.7 m/s, 7.0 m/s and 9.7 m/s) onto a hot circular plate made of Inconel 718. Liquids used in the experiments are water and oil-in-water emulsion with 8% concentration of the mineral oil Adrana AY 401 from Houghton Deutschland GmbH. An infrared camera is used to measure the black-coated rear face of the plate during the jet cooling process. The temperature field obtained is then used as input to estimate the heat transfer coefficient. The heat transfer coefficient is estimated by solving an Inverse Heat Transfer Problem (IHTP). In addition, the transient growth of the wetting area is also shown for both liquids. The heat transfer coefficient obtained from the experiments are utilised as input in numerical simulations with the Finite-Pointset-Method (FPM). Comparison between experiments and simulations is done to validate the recently implemented evaporation modelling in the MESHFREE software.
  • Publication
    Process behaviour of segmented and actuated tool electrodes for variable shaping in sinking EDM
    ( 2022)
    Uhlmann, Eckart
    ;
    Thißen, Kai
    ;
    Schulte Westhoff, Bela
    ;
    Streckenbach, Jan
    ;
    Ludwig, Jonas
    ;
    Maas, Jürgen
    In sinking electrical discharge machining (S-EDM), many applications such as the manufacturing of injection moulds require numerous tool electrodes due to tool wear compensation. The manufacturing of tool electrodes causes a high cost and time expenditure in the entire process chain. This paper aims for a novel approach to a segmentation of the tool electrode in order to shape it variably. The shaping is realized by actuation of single tool electrode segments (STES) using miniaturized linear actuators. In the future, the roughing process in S-EDM could be carried out by segmenting and variably shaping of the tool electrode. To investigate the process behaviour of a segmented tool electrode in S-EDM, different geometry configurations of the tool electrodes are compared. Experimental results show a similar material removal rate for the different tool electrode configurations. The relative linear wear of a segmented tool electrode is only 7.7 % of the relative linear wear of a monolithic tool electrode. In order to dynamically position the STES, a miniaturized electrical linear drive is developed and constructed. The outer diameter of the actuator must not exceed the edge length of an STES. In the machine tool an actuated STES is tested and the material removal rate and the relative linear wear for different Z-axis lifting motions are analysed. The material removal rate could be increased by 37 % applying actuated Z-axis lifting motions compared to the process without Z-axis lifting motion. In this context the relative linear wear increased slightly. The results of this paper are used for the further development of the system to enable more efficient process chains in the EDM process.
  • Publication
    Investigation of additive manufactured tungsten carbide-cobalt tool electrodes for sinking EDM
    ( 2022)
    Uhlmann, Eckart
    ;
    Polte, Mitchel
    ;
    Hörl, Robert
    ;
    Braun, Thomas
    ;
    Bolz, Robert
    Increasing product complexity and continuous developments in related tool and mould making industry require ongoing advances in manufacturing processes like electrical discharge machining (EDM). To meet the increasing requirements, the development of adapted EDM processes and tool designs is necessary. Additive manufacturing (AM) enables the manufacturing of complex tool electrode geometries with interior flushing channels for EDM processes with very few restrictions regarding the design. This accounts even for tungsten carbide-cobalt (WC-Co), which is a suitable material for EDM tool electrodes with various advantages, e.g. thermal and mechanical stability. This paper shows first results of additive manufactured WC-Co tool electrodes for the use in sinking EDM and the related development process.
  • Publication
    Residual stresses in additive manufactured precision cemented carbide parts
    ( 2022)
    Polte, Julian
    ;
    Polte, Mitchel
    ;
    Hocke, T.
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    Blankenburg, Malte
    ;
    Lahoda, Christian
    ;
    Uhlmann, Eckart
    Due to the good strength properties and high hardness, components made of cemented carbide are used in various industrial sectors as key components, e.g. mould making and matrices. Precision cemented carbide parts are mainly machined by milling and electrical discharge machining (EDM). Nevertheless, long machining times and excessive tool wear are remaining challenges at the state of the art. A promising approach to overcome these challenges is the machining of precise cemented carbide parts using a process chain consisting of near-net-shape laser powder bed fusion (LPBF) and subsequent finishing using a dedicate diamond slide burnishing process. Within previous investigations a geometrical accuracy of ag ≤ 10 µm and a reduction of the surface roughness by Ra = 89 % could be achieved. Within this work plastic deformation induced by the diamond slide burnishing and the effects on the material properties in the surface area were investigated, e.g. residual stresses. For this purpose, the lattice distortion of the metallic cobalt phase was measured by X-ray diffraction using high-energy synchrotron radiation. In addition, the height profile of the residual stresses was also recorded in distances of d = 3 µm to obtain information about the depth effect of the diamond slide burnishing process. Based on the investigations an increase of the residual compressive stresses could be obtained. This shows a particularly positive effect especially for additively manufactured components, as these often show a slight porosity and higher surface roughness as conventional manufactured components. In this way, crack propagation can be prevented and the fatigue strength can be increased.
  • Publication
    DEM simulation of centrifugal disc finishing
    ( 2022)
    Uhlmann, Eckart
    ;
    Polte, Julian
    ;
    Kuche, Yves
    ;
    Landua, Fabian
    The finishing of small components with complex geometries is a major industrial challenge. One process that is suitable for targeted post-processing is centrifugal disc finishing with wet and dry media. In this process, the workpieces float as bulk material together with the abrasive particles in a container and are completely surrounded by the abrasive medium. As shown in previous studies, the Discrete Element Method (DEM) is suitable for investigations of grinding processes with specified workpiece motions. To simulate unpredictable workpiece motion, a new approach is being tested in which the workpieces themselves are treated as particles. Within this research paper, results for the post-processing of centrifugal disc finishing with the software ROCKY DEM are presented. The investigation results show good correlation between the numerical determined pressures and the analysis results of the rounded workpiece edges on test components made of mould-steel X13NiMnCuAl4-2-1-1.
  • Publication
    Zirconium dioxide-reinforced aluminium oxide ceramic for micro-milling of graphite
    ( 2022)
    Uhlmann, Eckart
    ;
    Polte, Mitchel
    ;
    Polte, Julian
    ;
    Hocke, T.
    ;
    Wendt, M.
    Tool and mould making is one of the most important sectors for production of complex parts with highest economic efficiency. Particularly the milling process is a key technology for the manufacturing of tool electrodes for electrical discharge machining (EDM). Beside copper, graphite is the most industrial relevant tool electrode material for sinking-EDM. According to the state of the art the machining of graphite results in high tool wear in consequence of strong chemical and abrasive effects. Currently, uncoated and cost intensive diamond coated cemented carbide tools are used for industrial applications. High tool costs and short tool life have a negative impact on the economic efficiency of the manufacturing process and increase the overall production costs. To reduce the production costs, the needs for innovative cutting materials and dedicated manufacturing processes are high. The zirconium dioxide-reinforced aluminium oxide ceramic used in this investigation shows a great potential because of the high hardness H, the missing binder phase and the covalent bond. The aim of this investigation is the examination of the application behaviour of ceramic cutting tools during the machining process of graphite. Therefore, dedicated milling tests in partial and full cut were carried out. For evaluation of the application behaviour of the ceramic tools, the surface quality of the machined graphite depending on the wear of the tools was considered. The results show that a minimum surface roughness of Ra = 0.80 µm and average surface roughness of Rz = 6.55 µm could be achieved in first milling tests. Due to a strong sharpening effect of the cutting edge during the machining, the possibility was provided to produce complex components with highest precision and without chipping behaviour. The machining of graphite using ceramic milling tools shows extensive advantages compared to conventional milling tools, which may positively affect the economic efficiency of machining graphite in the future.
  • Publication
    Precision Finishing of Additive Manufactured Ti-Al-components Using Diamond Slide Burnishing
    ( 2022)
    Polte, Julian
    ;
    Polte, Mitchel
    ;
    Lahoda, Christian
    ;
    Uhlmann, Eckart
    Due to the increasing importance of lightweight design in terms of resource management, titanium aluminium (Ti-AI) alloys are gaining more and more significance. To fully exploit light weight design potentials additive manufacturing (AM) has the ability to shift state of the art product design towards maximised resource efficiency and physically minimized weight. Next to material standardization and qualification processes, major limitations for mass scale industrialization of additive manufacturing are high surface roughness values in a range of 5 μm ≤ Ra ≤ 15 urn and remaining tensile residual stress states. A promising approach to overcome these challenges shows a process chain consisting of near-net-shape laser powder bed fusion (LPBF) and subsequent finishing using a dedicate diamond slide burnishing (DSB) process [1]. Within this work plastic deformation induced by DSB and the effects on the workpiece material properties were investigated.
  • Publication
    Surface optimization of dental implants with laser surface texturing and silver coating
    ( 2022)
    Uhlmann, Eckart
    ;
    Brehmer, Annika
    ;
    Schneider, Peter
    ;
    Hein, Christoph
    ;
    Souza Schweitzer, Luiz Guilherme De
    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.