Fraunhofer-Institut für Produktionsanlagen und Konstruktionstechnik IPK

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Influence of superimposed low frequency oscillations on single-pass honing of long-chipping steel

2022 , Uhlmann, E. , Rozek, André

Single-pass honing is used as a finishing process to meet high demands regarding form and dimensional accuracy of drilled bores. The disadvantages of single-pass honing compared to the conventional long-stroke honing are high process forces and torques as well as an increased risk of chip space clogging of the abrasive stones. A significant reduction in process forces and torques can be achieved by superimposing the axial movement with oscillations. In this work the kinematic basics of different oscillation parameters and their effects on single-pass honing of long-chipping steel are analyzed. It can be concluded that by superimposing low frequency oscillations in single-pass honing, the process forces and torques as well as the specific energy consumption can be reduced significantly without a decline in surface quality and form accuracy.

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Effects on the distortion of Inconel 718 components along a hybrid laser-based additive manufacturing process chain using laser powder bed fusion and laser metal deposition

2021 , Uhlmann, E. , Düchting, J. , Petrat, T. , Krohmer, E. , Graf, B. , Rethmeier, M.

The combination of laser powder bed fusion (LPBF), known for its geometrical freedom and accuracy, and the nozzle-based laser metal deposition process (LMD), known for its high build-up rates, has great potential to reduce the additive manufacturing times for large metallic parts. For the industrial application of the LPBF-LMD hybrid process chain, it is necessary to investigate the influence of the LMD process on the LPBF substrate. In addition, the build plate material also has a significant impact on the occurrence of distortion along the additive manufacturing process chain. In the literature, steel build plates are often used in laser-based additive manufacturing processes of Inconel 718, since a good metallurgical bonding can be assured whilst reducing costs in the production and restoration of the build plates. This paper examines the distortion caused by LMD material deposition and the influence of the build plate material along the hybrid additive manufacturing process chain. Twin cantilevers are manufactured by LPBF and an additional layer is subsequently deposited with LMD. The distortion is measured in the as-built condition as well as after heat treatment. The effect of different LMD hatch strategies on the distortion is determined. The experiments are conducted using the nickel-base alloy Inconel 718. The results show a significant influence of LMD path strategies on distortion, with shorter tool paths leading to less distortion. The remaining distortion after heat treatment is considerably dependent on the material of the build plate.

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Einfluss der Schärfparameter auf die Schleifscheibentopographie

2019 , Uhlmann, E. , Muthulingam, A.

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Modelling of Abrasive Water Jet Cutting with Controlled Depth for Near-Net-Shape Fabrication

2019 , Uhlmann, E. , Männel, C.

Near-net-shape fabrication of difficult to machine materials is a promising application for the abrasive water jet technology. An effective implementation can be achieved by controlling the kerf depth and cutting off defined material fragments. A model for controlled cutting is introduced to make the machining process design more effective for different materials. An empirical model was combined with the process' physical behavior, allowing the prediction of the kerf geometry using a minimum number of predictors and thus initial trials. The model tested with metal matrix composites, reveals the capability of transferring knowledge to new materials using few initial trials.

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Residual stress assessment during cutting tool lifetime of CVD-diamond coated indexable inserts

2022 , Uhlmann, E. , Hinzmann, Daniel

Insufficient coating adhesion limits reproducibility regarding tool lifetime as well as workpiece quality during the application of CVD-diamond coated cutting tools. Depending on the combination of tungsten carbide substrate material, coating thickness as well as coating morphology, individual residual stress conditions exist within CVD-diamond coated cutting tool specifications. The application of these tools is accompanied by coating delamination as primary cutting tool failure. The tool lifetime of the respective cutting tool composition depends on the corresponding residual stress condition until crack development within the CVD-diamond coating initiates tool failure. During external cylindrical turning of hypereutectic aluminium silicon alloy AlSi17Cu4Mg-T6 the residual stress condition of a CVD-diamond coated cutting tool is assessed along the cutting edge, the rake face as well as flank face throughout the respective tool lifetime. Consequently, the progression of the residual stress condition until cutting tool failure regarding coating delamination is observed. During the tool lifetime of the investigated CVD-diamond cutting tools, compressive residual stress ∆σR,c shifts to tensile residual stress ∆σR,t underneath the cutting edge corner. The approximated residual stress difference of ∆σR ≈ 5 GPa indicates stress peak relaxation processes, such as crack initiation, within the CVD-diamond coating.

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Verfügbarkeitssteigerung durch gezielte Datenanalyse

2020 , Uhlmann, E.

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Ecological and functional optimization of the pretreatment process for plasma based coatings of cutting tools

2019 , Uhlmann, E. , Riemer, H. , An, S. , Fröhlich, M. , Paschke, H. , Petersen, M.

Increasing demands in machining of high-tech materials and dry machining lead to higher thermal and mechanical loads on cutting tools. In response to these challenges, enhanced coating solutions are applied to increase performance and life of cutting tools. However, during the production process the cemented carbide substrates are contaminated with grinding oils and residues of organic material. For the subsequent physical vapor deposition (PVD) coating process an intensive and high-quality cleaning process is necessary. In this contribution, plasma electrolytic polishing (PEP) is used as a novel alternative to conventional ecologically harmful cleaning baths. Apart from the ecological advantage, the surface of the substrate can be optimized with regard to the coating adhesion. To examine the performance of the different cleaning processes, machining tests were performed at the IWF to evaluate the layer adhesion and tool life of the tools.

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Acoustic emission-based process monitoring in the milling of carbon fibre-reinforced plastics

2022 , Uhlmann, E. , Holznagel, Tobias

Milling of fibre-reinforced plastics is a challenging task. The highly abrasive fibres lead to high tool wear and coating failures, which cause increasing process forces and temperatures. Machining with a worn tool, in turn, can result in unwanted workpiece damages such as delamination or fibre protrusion. Reliable monitoring of the process must therefore be able to detect damages to the milling tool and the workpiece alike. The presented process monitoring approach measures the acoustic emission generated by the milling tool cutting edge entering the workpiece with a sensor attached to the tool holder. Specific acoustic emission frequency spectra and waveforms are emitted in the cutting zone for different tool wear states. Coating failures as well as other acoustic emission events due to workpiece damages can be robustly detected and distinguished by feature extraction and signal processing as well. The developed setup, the monitoring parameterisation techniques and signal processing algorithms as well as experimental and monitoring results are presented and discussed in this paper.

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Reconfiguring machine tool behavior via smart building block systems

2019 , Uhlmann, E. , Peukert, B.

The reconfigurability of manufacturing systems is conventionally increased by utilizing concepts of modularization and platforms. At this moment, the actual reconfigurability is often limited to a priori designed reconfiguration variants for the production within single part families. There is only a little research on reconfiguring the mechanical behavior of machine tool frames. This paper presents an innovative approach for reconfiguring the mechanical behavior based on smart building block systems. Topologically optimized polyhedral building blocks are mechanically bolted to form different machine tool frame configurations. A high grade of modularization allows for the assembly of individualized topologies for different manufacturing scenarios "as needed when needed". The increase in reconfigurability results from the high geometric flexibility of the proposed building block system. However, successful implementation relies on quick and robust simulation approaches for calculating the machine tool frame characteristics before the actual assembly process. Within this paper, a time-efficient approach based on the sub-structuring methodology is utilized. The presented approach consists of forming superelements by performing a GUYAN reduction on the building blocks to extract the stiffness behavior. A Component Mode Synthesis is used to extract modal information. The ANSYS Parametric Design Language is then used to automatically couple the modules according to a customized descriptive machine tool language. A simple joint model is implemented and experimentally fitted with a two-block configuration. The two-block configuration is then extrapolated to a full machine tool frame portal. An example of changing the modal characteristics of this machine tool frame portal is presented in the form of numerical results.

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Thermal and technological aspects of double face grinding of Al2O3 ceramic materials

2019 , Deja, M. , List, M. , Lichtschlag, L. , Uhlmann, E.

Double face grinding with planetary kinematics is a process to manufacture workpieces with plan parallel functional surfaces, such as bearing rings or sealing shims. In order to increase the economic efficiency of this process, it has to be advanced permanently. The temperature in the contact zone of most grinding processes has a huge influence on the process efficiency and the workpiece qualities. In contrast to most grinding processes these influences are unknown in double face grinding with planetary kinematics. The application of standard measuring equipment is only possible with high effort due to the inaccessibility of the working space during the machining process. Furthermore, measurement of the workpieces temperature in the considered machining system is not reported. Due to that fact, the intensive cooling has so far been the only method to avoid the occurrence of thermal defects especially in case of brittle ceramic materials. The influence of the mean cutting speed, the tools' cutting performance and the coolant flow on the temperature change of the workpieces made of Al2O3 ceramic materials was investigated with the use of a newly developed method. The first empirical approach to predict the change in temperature of the ceramic workpieces while processing is proposed. The developed measuring method can be used for obtaining experimental temperature data in other processes, such as polishing and lapping for which only theoretical models exist.

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