Fraunhofer-Institut für Produktionsanlagen und Konstruktionstechnik IPK

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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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Verbundprojekt SmartStream: Intelligente Bearbeitung durch die Verwendung schaltbarer Fluide

2019 , Schmiedel, C. , Bierwisch, C. , Uhlmann, E. , Menzel, P. , Mohseni-Mofidi, S. , Breinlinger, T. , Nutto, C.

Strömungsschleifen und Hydroerosiv (HE)-Verrunden sind einzigartige Verfahren, die sich dadurch auszeichnen, dass sie funktionelle Oberflächen im Inneren eines Bauteils bearbeiten können, die sonst mechanisch nicht zugänglich sind. Jedoch unterliegen die Verfahren Begrenzungen aufgrund der Gesetzmäßigkeiten der Strömungsmechanik. Daher können die Verfahren nicht bei allen Anwendungen für eine technisch sowie wirtschaftlich sinnvolle Bearbeitung genutzt werden. Im Verbundprojekt SmartStream werden Möglichkeiten zur Überwindung bisher geltender Verfahrensgrenzen untersucht. Zur lokalen Beeinflussung der Zerspanungsleistung der auf die Oberflächen wirkenden Abrasivmedien werden diese durch ein externes magnetisches Feld schaltbar gemacht. Mit Hilfe des angelegten Magnetfeldes lassen sich zum einen strömungsmechanisch ungünstig gelegene Bereiche des Werkstücks bearbeiten und zum anderen die Zeitspanvolumina lokal gezielt steuern. Im vorliegenden Beitrag werden erreichte Entwicklungsziele am Beispiel des Strömungsschleifens vorgestellt.

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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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Manufacturing of graphite electrodes with high geometrical requirements

2019 , Uhlmann, E. , Kuche, Y. , Polte, J. , Polte, M.

Graphite is widely used for the die-sinking electrical discharge machining (EDM) process, especially for the roughing process. For the manufacturing of graphite electrodes the milling process is mainly used. The process enables fast processing times tP and high geometrical flexibility. In consequence of the cutting behaviour of graphite micro-components with geometrical features can be manufactured. In this contribution the manufacturing of micro-pins and bridges with aspect ratios of A = 1:50 were machined with diamond coated milling tools. By variation of the depth of cut ap and the width of cut ae it can be shown that the influence of the depth of cut ap is quite bigger than the influence of the width of cut ae. This results in consequence of the higher stability of the geometrical features by improved force distribution.

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Verfügbarkeitssteigerung durch gezielte Datenanalyse

2020 , Uhlmann, E.

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Safety of slim tool extensions for milling operations

2019 , Uhlmann, E. , Thom, S. , Barth, E. , Pache, T. , Prasol, L.

The development of 5-axis machine tools (MT) allows complete machining of complex workpiece geometries. In order to counteract lacking operation space and to improve the accessibility of the workpiece, slim tool extensions (STE) are applied. Operating errors, e.g. by crash, can cause plastic deformation of STE during machining operation and therefore lead to an increased moment of inertia, and thus to rotational energy due to the spindle speed control of machine tools. Currently applied machine tool enclosures are not designed for such failures with corresponding kinetic energies EKIN. The described failure implies a risk potential for operators and a high damage potential for machine tools. In this paper, the failure scenario is identified and modeled. This includes the calculation of elastoplastic deformations of STE based on finite element analysis and analytical calculation of kinetic energies EKIN considering deformed STE. Based on the described model a parameter study is carried out considering the geometry of the STE as well as the spindle speed nS. The safety of existing machine tool enclosures is evaluated according to DIN EN 12417 in order to identify safe operating conditions. Finally, the authors suggest possible solutions addressing both, the STE and machine tool enclosure. The research presented in this paper is funded by the German Machine Tool Builders Association (VDW).

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Rheological and Mechanical Gradient Properties of Polyurethane Elastomers for 3D-Printing with Reactive Additives

2019 , Wang, P. , Auhl, D. , Uhlmann, E. , Gerlitzky, G. , Wagner, M.H.

Polyurethane (PU) elastomers with their broad range of strength and elasticity are ideal materials for additive manufacturing of shapes with gradients of mechanical properties. By adjusting the mixing ratio of different polyurethane reactants during 3D-printing it is possible to change the mechanical properties. However, to guarantee intra-and inter-layer adhesion, it is essential to know the reaction kinetics of the polyurethane reaction, and to be able to influence the reaction speed in a wide range. In this study, the effect of adding three different catalysts and two inhibitors to the reaction of polyurethane elastomers were studied by comparing the time of crossover points between storage and loss modulus G' and G'' from time sweep tests of small amplitude oscillatory shear at 30°C. The time of crossover points is reduced with the increasing amount of catalysts, but only the reaction time with one inhibitor is significantly delayed. The reaction time of 90% NCO group conversion calculated from the FTIR-spectrum also demonstrates the kinetics of samples with different catalysts. In addition, the relation between the conversion as determined from FTIR spectroscopy and the mechanical properties of the materials was established. Based on these results, it is possible to select optimized catalysts and inhibitors for polyurethane 3D-printing of materials with gradients of mechanical properties.

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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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Application of laser surface nanotexturing for the reduction of peri-implantitis on biomedical grade 5 Ti-6Al-4V dental abutments

2019 , Uhlmann, E. , Schweitzer, L. , Cunha, A. , Polte, J. , Huth-Herms, K. , Kieburg, H. , Hesse, B.

The annual revenue of dental implants is estimated on 33 billion USD in 2019 and the efforts to keep the teeth functionality and aesthetics is continuously growing over the years. However, loosening of dental implants induced by infection is still a critical and common problem worldwide. In this scenario, the development of new implant manufacturing strategies is of utmost importance. Every surface exposed in the oral cavity, both the tooth and the implant surface, are covered by a layer of salivary proteins, the so-called pellicle. The initial formation of a pellicle is followed by the attachment of bacterial cells onto it. Well-developed biofilms on dental implant surfaces become the main source of pathogenic microbes causing Peri-Implantitis, which is one of the main causes of dental implant failure. The surface topography and chemical composition of an implant are key factors in controlling surface wettability, which directly affects the formation of the biological films. In this sense, ultrafast laser surface nanotexturing rises as a promising advanced technology for controlling implant surface biological properties. Laser-processing parameters such as laser wavelength l, fluence F and number of pulses N are essential for surface texturing. Thus, this paper presents promising results on the influence of different laser induced periodic surface structures (LIPSS) on the composition of the pellicle and the biofilm formation on biomedical grade 5 Ti-6Al-4V dental abutments. Moreover, a biofilm reactor was built and adapted to assess the effect of the LIPSS on the biofilm formation.

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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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