Fraunhofer-Institut für Produktionsanlagen und Konstruktionstechnik IPK

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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.

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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.

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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.

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Heat Transfer Study for Oil-in-Water Emulsion Jets Impinging onto hot Metal Surface

2022 , Nabbout, Kaissar , Pasternak, Lars , Sommerfeld, M. , Bock-Marbach, Benjamin , 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.

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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.

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Replication of Functional Surfaces Micro-Structured by EDM

2022 , Uhlmann, Eckart , Polte, Mitchel , Ludwig, Jonas , Bolz, Robert

Functional surfaces are applied in a broad range of industries ranging from automotive over aerospace to medical technology. In this paper, the manufacturing of molds micro-structured by sinking electrical discharge machining (sEDM) and the surface replication on polycarbonat (PC) is discussed. The presented analysis shows the ability to replicate hydrophobic and hydrophilic effects on PC samples from micro-structured molds fabricated by sEDM.

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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.

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Automated defect detection of CT projection image data using Monte Carlo simulation

2022 , Uhlmann, Eckart , Hein, Christoph , Fehlhaber, Felix , Wang, Yifan , Dürre, Gregor

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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Fundamental study on embedded displacement sensor arrays for ultrasonic-assisted ultraprecision machining

2022 , Uhlmann, Eckart , Polte, Mitchel , Bulla, Benjamin , Dambon, Olaf , Dicke, Clemens , Hocke, T. , Thißen, Kai , Heper, M.

Ultraprecision machining is a key technology for manufacturing complex steel moulds with dimensional accuracies in sub-micrometer range for mass production of optical components using micro-injection moulding. According to the state of the art, during the machining of carbide-forming metals, such as steel alloys, used single crystal diamond tools suffer from excessive tool wear. In order to overcome this technological und economical limitation, ultrasonic-assisted ultraprecision machining is applied successfully in a broad range of industrial and scientifically applications. Based on the reduction of the contact time between the tool and the workpiece excessive chemical and related tribological tool wear can be avoided. Nevertheless, the cutting speed is strictly limited to deceed critical contact times. Therefore, the monitoring of the tool vibration characteristic and thus the process control is a major challenge and of current industrial and scientifically interest. To overcome these challenges a method for in-situ measurement of the ultrasonic vibration is currently being developed and first results are shown. Using the sophisticated ultrasonic system, developed by SON-X GMBH, Aachen, Germany, up to a frequency fUS= 100 kHz the application of a dedicated eddy current sensor enabled the determination of the real path lines and the exact position of the cutting edge during the whole process with a displacement amplitude AD= 1 µm. The results were subsequently verified by laser vibrometer measurements. As a result of the investigation, an elliptical path movement of the cutting edge in the longitude direction AD,y= ± 1.0 µm and in z-direction AD,z= ± 0.34 µm could be determined using a frequency fUS= 100 kHz. Based on this new measurement method, the vibration characteristic can be specifically varied and adapted to the application. In addition, a comprehensive scientifical knowledge of the process can be gained and used to improve tool wear models.

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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.

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