Fraunhofer-Institut für Produktionsanlagen und Konstruktionstechnik IPK

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  • Publication
    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.
  • Publication
    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.
  • Publication
    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.
  • Publication
    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.
  • Publication
    Selection of diamond coated silicon nitrides for use as ceramic end mills when machining glass and carbon fiber reinforced plastics
    ( 2021)
    Stawiszynski, Bartek
    ;
    Protz, Falk
    ;
    Uhlmann, Eckart
    The machining of advanced materials is challenging the tooling technology. To cope this, new cutting materials and geometries are developed. In this case, four types of silicon nitride based ceramics are investigated after coating with CVD-diamond for the use as ceramic end mills. To assess the wear resistance, model wear tests and damage evaluation were carried out and evaluated. After subsequent summary of the results, ceramic and cemented carbide substrate were selected for milling of glass and carbon fiber reinforced plastic (GFRP/CFRP) The determined force distribution and wear properties of the tools are presented and discussed. The diamond coated substrates are qualified by their wear profile and the measured constant cutting forces for use in the machining of GFRP/CFRP. Finally, the crack formation progress for diamond coated silicon nitrides when machining glass and carbon fiber reinforced plastics was demonstrated.
  • Publication
    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.
  • Publication
    Measurement and Modeling of Contact Forces during Robot-guided Drag Finishing
    ( 2021)
    Uhlmann, Eckart
    ;
    Kopp, Marco
    Robot-guided drag finishing is a free abrasive grinding operation that is used for polishing and deburring of workpieces with complex shaped geometries. The workpiece is attached to a robot and moved through a bulk of abrasive particles. The motion of abrasive particles during contact with the workpiece is the basis of the material removal mechanisms. To investigate the motion of abrasive particles during contact, a force measurement system was used to determine contact forces. The experimental setup was replicated in a numerical simulation based on the discrete element method (DEM). Based on the comparison of experimental and simulative results the qualitative validity of the DEM model was concluded. With the presented DEM model, the characteristic particle behavior during contact with the workpiece can be modeled which allows the prediction of resulting processing marks. Consequently, the DEM model can be used to design free abrasive grinding operations without using the time and cost intensive trial and error approach.
  • Publication
    Modeling of the wet immersed tumbling process with the Discrete Element Method (DEM)
    ( 2021)
    Uhlmann, Eckart
    ;
    Fürstenau, J.-P.
    ;
    Kuche, Yves
    ;
    Yabroudi, Sami
    ;
    Polte, Julian
    ;
    Polte, Mitchel
    Immersed tumbling is an industrially established process for finishing of components made of metal, ceramic or plastic. In this process, the components are completely surrounded by a wet, abrasive medium, which allows burrs to be removed and surfaces to be polished. In order to gain specific insights into the influence and flow properties of the abrasive media used in this process, numerical approaches using the Discrete Element Method (DEM) with the Rocky DEM software are presented within these investigations. A complete process simulation could be realised by means of a digital machine tool. The immersed tumbling process with cone-shaped polymer abrasive media is implemented by use of a liquid bridge model. The results were validated by experiments with an industrially used immersed tumbling machine tool and for the first time allow sound statements about the contact conditions and interactions of the abrasive media with the workpiece.
  • Publication
    Numerical investigation on the process behavior of a closed-loop internal cooling system for turning operations
    ( 2021)
    Uhlmann, Eckart
    ;
    Meier, P.
    The development of sustainable manufacturing processes and the associated reduction of operating materials such as cooling lubricants represent key focuses on recent production technology. Thus, a novel tool system with a closed-loop internal cooling system for turning operations is presented in this study. The system design is based on numerical investigations of the heat flow Q⋅ with consideration of the thermomechanical load of the cutting tool and flow characteristics of the cooling fluid. The process behavior of the proposed system shows a significant dependence of the flow rate V⋅ and tool thickness tT in terms of tool temperature reduction DTHT.
  • Publication
    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.