Fraunhofer-Institut für Produktionsanlagen und Konstruktionstechnik IPK

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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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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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Niobcarbid statt Wolframcarbid Alternativer Schneidstoff in der Drehbearbeitung

2019 , Kropidlowski, K. , Uhlmann, E. , Woydt, M. , Theiler, G. , Gradt, T.

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Application of niobium carbide based cutting materials for peripheral milling of CFRP

2019 , Uhlmann, E. , Meier, P. , Hinzmann, D.

Due to its inherent material properties, the implementation of niobium carbide (NbC) as hard phase in cutting materials represents a promising alternative to machining. Recent investigations show equivalent tool life in metal cutting compared with cemented carbides based on tungsten carbide (WC). Besides metal cutting, the machining of high-performance composite materials poses an increasing importance due to its growing demand in the automotive and aeronautical sector. NbC and its wear resistance against abrasion can be suitable for this specific application. Additionally, the low density of NbC indicates an advantageous dynamic behaviour. Thus, this study focuses on the milling of carbon fiber reinforced plastics (CFRP). Complex tool geometries are implemented in a peripheral milling strategy. The machining trials are conducted with uncoated NbC-based cutting materials in CFRP with varying cutting speeds vc. The utilized NbC compositions (NbC-10TiC)-6Ni7.5VC and (NbC-15TiC7N3)-5Ni7.5WC2.5Mo2C embedded in a Nickel (Ni) matrix were applied and compared towards their performance with an industrial available cemented carbide (WC-Co). As tool life criteria, a tool diameter reduction of Dd = 0.1 mm and a cutting path of lc = 10.000 mm were defined. Apart from tool life performance, the workpiece quality was assessed. An inferior performance was identified with (NbC-10TiC)-6Ni7.5VC in terms of tool life compared to WC-Co, which can be attributed to microstructure issues. Yet, (NbC-15TiC7N3)-5Ni7.5WC2.5Mo2C shows a competitive performance in machining with an achieved cutting path lc identical to WC-Co. It can be stated, that NbC-Ni systems can accomplish an equivalent performance in comparison to WC-Co when machining CFRP.

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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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Verfügbarkeitssteigerung durch gezielte Datenanalyse

2020 , Uhlmann, E.

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Increasing the productivity and quality of flute grinding processes through the use of layered grinding wheels

2019 , Uhlmann, E. , Schroer, N. , Muthulingam, A. , Gulzow, B.

Due to the increasing relevance of resource efficiency, the production of cutting tools is exposed to increasing demands in regard to productivity and quality. Flute grinding is of particular significance within the various grinding operations used in tool manufacturing. Apart from the rake face, the flute grinding process determines the quality of the cutting edges. However, the grinding wheels typically used for flute grinding are not designed to take the complex contact conditions of this process into account. This paper presents a method for designing application-oriented grinding wheels to improve the productivity and the quality of grinding processes. Firstly, a model is presented which is used to simulate the contact conditions. The results show the significance of the grinding wheel edge in flute grinding. Based on that, grinding wheels with different layers over its width were developed to compensate the varying and complex contact conditions. To verify this approach technological experiments were carried out.

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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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3-Achs-Portalfräsmaschine als Demonstrator für ein modulares Werkzeugmaschinengestell

2019 , Uhlmann, E. , Polte, M. , Blumberg, J. , Peukert, B.

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Tool wear modelling using micro tool diameter reduction for micro-end-milling of tool steel H13

2019 , Manso, C.S. , Thom, S. , Uhlmann, E. , Assis, C.L.F de , Conte, E.G del

Micro components have been demanded increasingly due to the global trend of miniaturization of products and devices. Micro milling is one of the most promising processes for micro-scale production and differs from conventional milling due to the size effect introducing phenomena like the minimum chip thickness, making the prediction of micro milling process hard. Among challenges in micro milling, tool life and tool wear can be highlighted. Understanding tool wear and modelling in micro milling is challenging and essential to maintaining the quality and geometric tolerances of workpieces. This work investigates how to model the diameter reduction of a tool caused by tool wear for micro milling of H13 tool steel. Machining experiments were carried out in order to obtain cutting parameters affecting tool wear by considering the diameter reduction. Dry full slot milling with TiAlN (titanium aluminium nitride)-coated micro tools of diameter d = 400 mm was performed. Three levels of feed per tooth (fz = 2 mm, 4 mm and 5 mm) and two spindle speed levels (n = 30,000 rpm and 46,000 rpm) were used and evaluated over a cutting length of lc = 1182 mm. The results show that lower levels of feed per tooth and spindle speed lead to higher tool wear with a total diameter reduction over 22%. The magnitude of the cutting parameters affecting tool wear was determined by ANOVA (analysis of variance), and the model validation meets the statistical requirements with a coefficient of determination R2 = 83.5% showing the feasibility of the approach to predict tool wear using diameter reduction modelling in micro milling.

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