Fraunhofer-Institut für Produktionsanlagen und Konstruktionstechnik IPK

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Wolframschmelzcarbidbasierte MMC-Schichten für den industriellen Einsatz im Formenbau

2022 , Langebeck, Anika , Jahnke, Christian , Wünderlich, Tim , Hein, Christoph , Bohlen, Annika , Uhlmann, Eckart

Zur Steigerung der abrasiven Verschleißbeständigkeit können Oberflächen lokal mit Hartpartikeln verstärkt werden. Diese sogenannten Metal-Matrix-Composit(MMC)-Schichten können mittels Laserstrahldispergieren gefertigt und durch Mikrofräsen nachbearbeitet werden. Im hier vorgestellten Forschungsvorhaben wurde als Grundwerkstoff verwendete Aluminiumbronze (CuAl10Ni5Fe4) mit Wolframschmelzcarbid verstärkt. Der Hartpartikelgehalt kann dabei durch eine Steigerung des Pulvermassenstroms bis zur Packungsdichte des unverarbeiteten Pulvers erhöht werden. Über eine temperaturbasierte Leistungsregelung kann eine gleichbleibend homogene MMC-Schicht mit konstanter Dicke und Tiefe dispergiert werden. Durch das Mikrofräsen mit optimierten Parametern können qualitativ hochwertige MMC-Oberflächen für den industriellen Einsatz in Spritzgusswerkzeugen hergestellt werden. Dabei wurde vor allem der Zahnvorschub fz als kritischer Prozessparameter identifiziert.

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Numerical investigation into cleanability of support structures produced by powder bed fusion technology

2022 , Campana, Giampaolo , Uhlmann, Eckart , Mele, Mattia , Raffaelli, Luca , Bergmann, André , Kochan, Jaroslaw , Polte, Julian

Purpose: Support structures used in laser powder bed fusion are often difficult to clean from unsintered powder at the end of the process. This issue can be significantly reduced through a proper design of these auxiliary structures. This paper aims to investigate preliminary the airflow within differently oriented support structures and to provide design guidelines to enhance their cleanability, especially the depowdering of them. Design/methodology/approach: This study investigates the cleanability of support structures in powder bed fusion technology. Digital models of cleaning operations were designed through computer-aided engineering systems. Simulations of the airflow running into the powder entrapped within the thin walls of auxiliary supports were implemented by computational fluid dynamics. This approach was applied to a set of randomly generated geometrical configurations to determine the air turbulence intensity depending on their design. Findings: The resul ts, which are based on the assumption that a relationship exists between turbulence and powder removal effectiveness, demonstrated that the maximum cleanability is obtainable through specific relative rotations between consecutive support structures. Furthermore, it was possible to highlight the considerable influence of the auxiliary structures next to the fluid inlet. These relevant findings establish optimal design rules for the cleanability of parts manufactured by powder bed fusion processes. Originality/value: This study presents a preliminary investigation into the cleanability of support structures in laser powder bed fusion, which has not been addressed by previous literature. The results allow for a better understanding of the fluid dynamics during cleaning operations. New guidelines to enhance the cleanability of support structures are provided based on the results of simulations.

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Ex Situ Residual Stress Analysis of Chemical Vapor Deposited Diamond Coated Cutting Tools by Synchrotron X-Ray Diffraction in Transmission Geometry

2021 , Hinzmann, Daniel , Böttcher, Katrin , Reimers, Walter , Uhlmann, Eckart

When machining difficult-to-cut, nonferrous materials, chemical vapor deposited (CVD) diamond-coated cutting tools are applied. The tools' favorable mechanical property profile is based on the hardness of the coating as well as the adaptability of the substrate. Nevertheless, the reproducibility of machining results and process stability are limited by insufficient coating adhesion. The resulting cutting tool failure is based on coating delamination initiated by crack development. By assessing residual stress as an influence of coating adhesion, an analysis of CVD diamond-coated tools is performed using synchrotron X-ray diffraction in transmission geometry. Investigation of a nanocrystalline and multilayer morphology on cobalt-based tungsten carbide (WC-Co) and a silicon nitride-based ceramic (Si3N4) provides the distribution of the principal in-plane residual stress tensor component s22 depending on the coating morphology and substrate material. Contrary to microcrystalline CVD diamond, nanocrystalline layers decrease the compressive residual stress. In addition, the CVD diamond coating deposited on the Si3N4 substrate material tends to induce an overall initial tensile residual stress that leads to increased tool performance compared to WC-Co-based coated tools. Variation of the coating morphology as well as the substrate material offers the possibility to extend the current model for residual stress-dependent tool failure.

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Effects on part density for a highly productive manufacturing of WC-Co via laser powder bed fusion

2021 , Polte, Julian , Neuwald, Tobias , Gordei, Anzhelika , Kersting, Robert , Uhlmann, Eckart

The additive manufacturing of parts made from difficult-to-weld materials through the usage of preheating temperatures of up to Î0 ⤠500 °C is enabled by newest L-PBF machine tools, such as the RenAM 500Q HT from the company RENISHAW PLC, Wottun-under-Edge, UK. This work aims to delevop processing parameters for the dense and crack-free manufacturing of tungsten-carbide cobalt (WC-Co) via this off-the-shelf machine tool. Therefore the laserpower and scanning speed were varied between 80 W ⤠PL ⤠350 W and 140 mm/s ⤠vS ⤠650 mm/s respectively. Furthermore the influence of a continuous and pulsed laser mode was analysed. A focus was set on the identification of parameters that enable a highly productive manufacturing while maintaining a high part density. A parameter set for relative density rel. > 94 % and a buildup rate v = 0.59 mm3/s was developed.

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In situ microstructure analysis of Inconel 625 during laser powder bed fusion

2022 , Schmeiser, Felix , Krohmer, Erwin , Wagner, Christian , Schell, Norbert , Uhlmann, Eckart , Reimers, Walter

Laser powder bed fusion is an additive manufacturing process that employs highly focused laser radiation for selective melting of a metal powder bed. This process entails a complex heat flow and thermal management that results in characteristic, often highly textured microstructures, which lead to mechanical anisotropy. In this study, high-energy X-ray diffraction experiments were carried out to illuminate the formation and evolution of microstructural features during LPBF. The nickel-base alloy Inconel 625 was used for in situ experiments using a custom LPBF system designed for these investigations. The diffraction patterns yielded results regarding texture, lattice defects, recrystallization, and chemical segregation. A combination of high laser power and scanning speed results in a strong preferred crystallographic orientation, while low laser power and scanning speed showed no clear texture. The observation of a constant gauge volume revealed solid-state texture changes without remelting. They were related to in situ recrystallization processes caused by the repeated laser scanning. After recrystallization, the formation and growth of segregations were deduced from an increasing diffraction peak asymmetry and confirmed by ex situ scanning transmission electron microscopy.

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Advances in Modeling of the Kerf Formation considering the Primary and Deflection Jets for the Abrasive Water Jet Technology

2021 , Uhlmann, Eckart , Kruggel-Emden, Harald , Männel, Constantin , Barth, Enrico , Markauskas, Darius

Processing of difficult to machine materials is a promising application for abrasive water jet kerf cutting and milling. However, due to the large number of interactions of an energy-bound cutting process, a precise prediction of the material removal is crucial for its application. Based on an analytical approach, a material removal simulation model is introduced considering the primary and deflecting jet impacts to rapidly predict various cutting situations. The model describes fundamental cutting mechanisms considering the water jet's material removal rate and is calibrated for titanium aluminides. The model allows for a comprehensive kerf prediction and thus potentially accelerates the process design improving the productivity and quality for abrasive water jet kerf cutting and milling.

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Analysis of influencing factors for the dressing process in double side face grinding

2021 , Uhlmann, Eckart , Lichtschlag, Linus

In grinding, the design of the dressing process is an essential part of work preparation and restoration of the grinding wheel's profile and cutting ability. In contrast to most grinding processes, the choice of dressing parameters in double face grinding with planetary kinematics has so far only been experience-based. As a consequence, the dressing process causes a higher degree of tool wear than the machining of the workpieces. A focused design of the dressing process based on a scientific data could help to improve the ecological and the economic efficiency by reducing tool wear and the amount of dressing tools used. In this paper, methods for determining the wear condition and the result of the dressing process, including macro- and microscopic characteristic are presented. This includes a correlation analysis between parameters of wear characteristics and workpiece surface quality. Furthermore, technological investigations are carried out in order to systematically limit the main influencing factors on the dressing process. As a result, the parameters dresser grain size dgd, rotational speed ratio nld and the machined dresser height ∆hd are identified as significant for dressing. The knowledge about their principal influence on the dressing result could provide the basis for further research.

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Optimizing the sharpening process of hybrid-bonded diamond grinding wheels by means of a process model

2022 , Uhlmann, Eckart , Muthulingam, Arunan

The grinding wheel topography influences the cutting performance and thus the economic efficiency of a grinding process. In contrary to conventional grinding wheels, super abrasive grinding wheels should undergo an additional sharpening process after the initial profiling process to obtain a suitable microstructure of the grinding wheel. Due to the lack of scientific knowledge, the sharpening process is mostly performed manually in industrial practice. A CNC-controlled sharpening process can not only improve the reproducibility of grinding processes but also decrease the secondary processing time and thereby increase the economic efficiency significantly. To optimize the sharpening process, experimental investigations were carried out to identify the significant sharpening parameters influencing the grinding wheel topography. The sharpening block width lSb, the grain size of the sharpening block dkSb and the area-related material removal in sharpening VâSb were identi fied as the most significant parameters. Additional experiments were performed to further quantify the influence of the significant sharpening parameters. Based on that, a process model was developed to predict the required sharpening parameters for certain target topographies. By using the process model, constant work results and improved process reliability can be obtained.

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Fully coupled wet cylindrical turning simulation using the Finite-Pointset-Method

2021 , Uhlmann, Eckart , Barth, Enrico , Quellhorst, Alexander , Seifarth, Tobias , Kuhnert, Jörg , Nabbout, Kaissar , Sommerfeld, Martin

In industrial machining operations, many turning processes are carried out under wet conditions. In contrast, most simulation tools are only suitable for dry cutting processes due to challenges of modeling fluid-structure-interactions (FSI). In this paper, a wet, fully coupled cutting simulation using the Finite-Pointset-Method (FPM) is presented and validated for industrially relevant cylindrical turning. To facilitate the required reduction of the calculation effort, different routines like adaptive numerical discretization are applied. The results indicate different cutting fluid effects like evaporation areas around the chip.

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Concept for an actuated variable tool electrode for use in sinking EDM

2021 , Uhlmann, Eckart , Streckenbach, Jan , Thißen, Kai , Schulte Westhoff, Bela , Masoud, Abd Elkarim , Maas, Jürgen

Typically, a large number of individual tool electrodes has to be used in sinking electrical discharge machining (sinking EDM) to successfully machine a single workpiece. Due to non-uniform wear and insufficient flushing of the working gap electrode geometries have a significant effect on the process efficiency. This paper discusses the use of an actuated variable tool electrode for sinking EDM to reduce the number of required tool electrodes and to increase the overall process efficiency. A miniaturised linear actuator was developed to individually move electrode segments to form the target shape for the tool electrode. The coordinated actuation of bundled electrode segments introduces new methods for the active flushing within the working gap, which cannot be implemented in conventional sinking EDM. Intelligent sinking strategies can further improve process efficiency by creating and sinking sub-geometries into the workpiece offering improved flushing conditions compa red to the original geometry.

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