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
    ;
    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
    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
    Characterization and investigation of binderless nanopolycrystalline diamond turning tools for precision machining
    ( 2022)
    Uhlmann, Eckart
    ;
    Sturm, Heinz
    ;
    Polte, Mitchel
    ;
    Hocke, T.
    ;
    Polte, C.
    ;
    Polte, Julian
    Cemented carbide is used in a wide range of industrial applications as a wear-resistant material, e.g. in mould making and forming industry. At state of the art, the machining of cemented carbide is severely limited because of the hardness, high strength and the resulting wear resistance of the material. Due to the brittle-hard character cemented carbide materials suffer from surface cracks during the machining. The brittle-hard character and the related phenomena result in high tool wear. A promising approach for the machining of cemented carbide is the use of the novel cutting material binderless nanopolycrystalline diamond (NPD) with a dedicated cutting edge design. Within this work, laser machined tools with a corner radius of rε = 400 µm are fully characterized, investigated by Raman spectroscopy regarding the condition of the diamond and applied for first cutting experiments. Cutting investigations were carried out using specimens with a tungsten carbide content of cC = 88 %, a cobalt content of cCo= 12 % and a grain size of dg= 0.5 µm. Prior to these investigations, the condition of the diamonds and possible changes due to the lasered cutting edges were examined by Raman spectroscopy. During the cutting investigations, the brittle-ductile transition as well as the minimum chip thickness were identified by scratching tests. It could be shown that a hydrostatic stress state can be used to achieve ductile chip formation using cemented carbide as workpiece material.
  • Publication
    Residual stresses in additive manufactured precision cemented carbide parts
    ( 2022)
    Polte, Julian
    ;
    Polte, Mitchel
    ;
    Hocke, T.
    ;
    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
    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
    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
    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
    Application of Uncertainty-Aware Sensor Fusion in Physical Sensor Networks
    (IEEE, 2022)
    Gruber, Maximilian
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    Pilar von Pilchau, Wenzel
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    Gowtham, Varun
    ;
    Koutrakis, Nikolaos-Stefanos
    ;
    Schönborn, Nicolas
    ;
    Eichstädt, Sascha
    ;
    Hähner, Jörg
    ;
    Corici, Marius-Iulian
    ;
    Magedanz, Thomas
    ;
    Polte, Julian
    ;
    Uhlmann, Eckart
    Modern industrial processes often collect redundant information from multiple sensors. It is of interest to leverage this information to form a more accurate or robust estimate of an observed quantity utilizing a sensor fusion operation. To be able to comply with quality requirements on the fused value, preservation of traceability is required. Moreover, the sensor fusion needs to be implemented within suitable digital architectures for Industrial Internet of Things (IIoT) environments. In a continuation of previous work, this is achieved by the usage of digital twins that represent the entities of two IIoT testbeds and the adoption of a method for uncertainty-aware homogeneous sensor fusion, which is presented in full detail. Metrological traceability of the fused value is established by propagating the measurement uncertainty of the input sensor according to metrological standards. The method is implemented as a modular service connected to an existing IIoT architecture. The flexibility of the method is shown by application to two different scenarios with only minimal adaption efforts. The fused sensor values are (as indicated by earlier work) robust to outliers and perform well in practical scenarios within the chosen IIoT architecture.
  • Publication
    Cutting edge preparation of monolithic ceramic milling tools
    ( 2021)
    Uhlmann, Eckart
    ;
    Polte, Mitchel
    ;
    Polte, Julian
    ;
    Hocke, Toni
    Due to international competition, continuous increases in productivity, product quality and reduction of production costs are required. Especially, the development of milling tools made of innovative cutting materials and application-specific tool geometries for the machining of brittle materials are in focus to overcome these challenges. One approach to improve the performance and the tool behaviour concerning milling of graphite is the use of monolithic ceramic milling tools. Unfortunately, the high brittleness of the ceramic leads to breakouts on the cutting edge during the grinding process. This results in an increased maximum chipping of the cutting edge, which has a significant influence on the milling process. To improve the breakout behaviour, a cutting edge preparation with the immersed tumbling process was applied. To enable a process reliable cutting edge preparation, a suitable lapping medium, the influence of the processing time as well as the depth of imme rsion were investigated. Besides the maximum chipping of the cutting edge, the rounded cutting edge radius was also analysed. The results show that a process reliable cutting edge preparation of monolithic ceramic milling tools with a maximum chipping of the cutting edge RS,max ⤠3 µm and a rounded cutting edge radius of rβ ⤠7 µm could be realised. In future investigations, the experimental applicability of monolithic ceramic milling tools will be proved.
  • Publication
    Sensor integration in hybrid additive manufactured parts for real-time monitoring in turbine operations
    ( 2021)
    Uhlmann, Eckart
    ;
    Polte, Julian
    ;
    Kersting, Robert
    ;
    Brunner-Schwer, Christian
    ;
    Neuwald, Tobias
    Real-time monitoring of operation conditions such as tempeatures and vibrations enables efficiency enhancement for maintenance tasks. In energy industry monitoring of critical components such as turbine blades is essential for the operation safety. But the effective recording of critical process data is a challenging task due to the extreme operating conditions. With a hybrid processing approach combining two additive manufacturing technologies new classes of self-monitoring components become possible allowing data acquisition directly inside the component. Using the example of a turbine blade, the hybrid process chain is described. The turbine blade blank is produced via Laser Powder Bed Fusion (L-PBF) with channels for the integration of high temperature sensors. After integration cavities were closed by Laser Directed Energy Deposition (L-DED) followed by classical milling operations for part finishing. The data acquisition is integrated in state-of-the-art product l ifecycle monitoring (PLM) software to create a digital twin. Evaluation shows that temperature could be successfully monitored at conditions of Π= 550°C.