Now showing 1 - 10 of 59
  • Publication
    Semi-automatic process control for efficient refurbishment of turbine blades
    ( 2023-06-16) ; ;
    Mühlich, Christopher
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    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
    Process behaviour of segmented and actuated tool electrodes for variable shaping in sinking EDM
    ( 2022) ;
    Thißen, Kai
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    Schulte Westhoff, Bela
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    Streckenbach, Jan
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    Ludwig, Jonas
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    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
    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
    Fundamental study on embedded displacement sensor arrays for ultrasonic-assisted ultraprecision machining
    ( 2022) ; ;
    Bulla, Benjamin
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    Dambon, Olaf
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    Dicke, Clemens
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    Hocke, T.
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    Thißen, Kai
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    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.
  • Publication
    Precision Finishing of Additive Manufactured Ti-Al-components Using Diamond Slide Burnishing
    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) ;
    Brehmer, Annika
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    Schneider, Peter
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    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.
  • Publication
    Automated defect detection of CT projection image data using Monte Carlo simulation
    ( 2022) ; ; ;
    Wang, Yifan
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    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.
  • Publication
    Replication of Functional Surfaces Micro-Structured by EDM
    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.
  • Publication
    DEM simulation of centrifugal disc finishing
    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
    Residual stresses in additive manufactured precision cemented carbide parts
    ( 2022) ; ;
    Hocke, T.
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    Blankenburg, Malte
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    Lahoda, Christian
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    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.