Marion Merklein

Friedrich-Alexander Universität Erlangen-Nürnberg, Erlangen, Bavaria, Germany

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Publications (106)70.79 Total impact

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    ABSTRACT: Demonstrated that textured tool possessed a lower friction coefficient than the nontextured tool.•Demonstrated that the amount of reduction depends on the relative orientation between the sliding direction and the sheet orientation.•The flat-on-cylindrical test apparatus effectively simulated the critical bending area in the sheet metal stamping operation.
    Tribology International 01/2015; 81. · 2.12 Impact Factor
  • Marion Merklein, Sebastian Suttner, Adam Schaub
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    ABSTRACT: The requirement for products to reduce weight while maintaining strength is a major challenge to the development of new advanced materials. Especially in the field of human medicine or aviation and aeronautics new materials are needed to satisfy increasing demands. Therefore the titanium alloy Ti-6Al-4V with its high specific strength and an outstanding corrosion resistance is used for high and reliable performance in sheet metal forming processes as well as in medical applications. Due to a meaningful and accurate numerical process design and to improve the prediction accuracy of the numerical model, advanced material characterization methods are required. To expand the formability and to skillfully use the advantage of Ti-6Al-4V, forming processes are performed at elevated temperatures. Thus the investigation of plastic yielding at different stress states and at an elevated temperature of 400°C is presented in this paper. For this reason biaxial tensile tests with a cruciform shaped specimen are realized at 400°C in addition to uniaxial tensile tests. Moreover the beginning of plastic yielding is analyzed in the first quadrant of the stress space with regard to complex material modeling.
    Key Engineering Materials 09/2014; 622-623:273-278.
  • Sebastian Suttner, Marion Merklein
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    ABSTRACT: Increased requirements for sheet metal parts and the use of advanced high-strength steels and other materials with lightweight potential set new standards for material characterization methods. Especially in the automotive sector with complex, multi-stage forming processes, new challenges are placed to model the real material behavior numerically. Thus, the requirements can be met to the numerical design of forming processes, advanced knowledge in the field of material characterization is needed. Therefore characterization methods under cyclic load are used. Two possibilities to investigate the cyclic behavior of the material are the tension-compression test and the cyclic shear test. The differences in the material properties of sheet metals during a reversal of load are marked by the Bauschinger effect and lead to a decrease of the beginning of plastic yielding. In this paper, the cyclic material behavior of different materials is characterized with experimental tension-compression tests and compared to the results of cyclic shear tests from a modified ASTM simple shear test preparation. The aim is the analysis of the Bauschinger effect through the identification of the kinematic hardening model according to Chaboche and Rousselier for the investigated materials. Moreover an estimation of the characteristic of the Bauschinger effect is presented.
    IDDRG 2014 Conference; 06/2014
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    ABSTRACT: The on-going trend in product miniaturization, together with the increasing quality and reduction of costs of micro-components, leads to the need of a robust process design, which might additionally avoid the occurrence of defects in the workpiece. Processes like microforming are affected by variations which can be foreseen but not totally mastered in the design stage. One approach is seen in an adaptive control system based on a metamodel processing the data of online measuring. This approach is grounded on in-depth knowledge based on correct and precise process modelling. This paper presents both experimental and simulative study of a microforging process, part of a more complex forming chain. It consists of six parallel ribs on metal strip. The ribs have a width of 250 µm and are spaced by a gap of 150 µm. The process has been studied by different punch forces, analyzing the final geometry of the workpiece. In particular the rib height is considered as critical to quality parameter. The simulations show reliable results that can be used for the design of the model interfacing measurement and control of the whole microforming process.
    Key Engineering Materials 05/2014; 611-612:565-572.
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    ABSTRACT: Mixed-Materials parts have great light-weight potential for the automotive application to reduce the carbon footprint. But the joining of fibre composite plastic sheets to metal sheets is in practical application limited to adhesive bonding or mechanical joining with additional fastener elements due to the large differences in physical properties. A new process chain based on plastic joining without fastener elements is proposed and first results on the mechanism and on the achievable strength of the new joints are shown. The process chain consists of three steps: First joining pins are added to the sheet metal by an additive manufacturing process. In a second step these pins are pierced through the fibre composite sheet with a local heating of the thermoplastic in an overlap setup. In the third and last step the joint is created by forming the pins with the upsetting process to create a shape lock. The shear strength of the joined specimens was tested in a tensile testing machine. The paper shows that even with a non-optimized initial setup joints can be realised and that the new process chain is a possible alternative to adhesive bonding.
    Key Engineering Materials 05/2014; 611-612:1468-1475.
  • Kolja Andreas, Marion Merklein
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    ABSTRACT: Cold forging enables mass production of steel based components. High loads within cold forging presuppose high loadable tool materials. This is why apart from tool steels cemented carbides are mainly used as tool materials. Due to brittleness of these materials, fatigue is one of the major limits of tool life. Tool manufacturing requires a combination of hard machining and subsequent machining steps. For hard machining of complex tool geometries electrical discharge machining (EDM) represents the industrial standard. The thermal influenced surface layer has to be removed by post and fine machining steps. The resulting surface integrity has a major influence on the internal strength of a tool. Correlations between tool manufacturing, surface properties and tool behavior will gain knowledge for an optimized tool production. In this context, scope of the present paper are the investigation and description of the interactions between tool manufacturing and resulting surface properties for tools made of cemented carbide and tool steel. Within the article, the surface properties caused by a conventional process chain consisting of EDM and polishing are quantified. In addition, these results are compared to an adapted process chain with an integrated peening process. The results reveal that the conventional and the adapted process chain lead to similar surface topographies and roughness values. However, the integration of a peening process shifts the residual stress level towards higher compressive stresses.
    Production Engineering 03/2014; 8(1-2).
  • Sebastian Rösel, Marion Merklein
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    ABSTRACT: Within this paper a new approach to enhance the process window in sheet metal hydroforming processes will be presented. The key idea of the technology is the local adaption of the properties of the active fluid medium. In this case the magnetorheological fluid (MRF) Basonetic® 5030 is used and the fluid behavior is changed due to a partially applied external magnetic field. Based on the new property distribution the medium can be used as forming and sealing medium at the same time. The results are compared to the values reached with mineral oil. The presented work covers all necessary steps for a successful application of the technology. After the presentation of the used fluids, a material characterization and the tools, which are developed for this reason, as the sealing limits for two different configurations are determined. Based on these investigations forming operations are carried out at the related process parameters to show up the potential of the MRF. At the end a numerical model is built up and validated for both fluids used to offer a qualified tool for process design.
    Production Engineering 03/2014; 8(1-2).
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    ABSTRACT: Tailored Blanks is the collective for semi-finished sheet products which are characterised by a local variation of the sheet thickness, sheet material, coating or material properties. With these adaptions the tailored blanks are optimised for a subsequent forming process or the final application. In principle four different approaches can be distinguished to realise tailored blanks: joining materials with different grade, thickness or coating by a welding process (tailor welded blanks), locally reinforcing the blank by adding a second blank (Patchwork blanks), creating a continuous variation of the sheet thickness via a rolling process (tailor rolled blanks) and adapting the material properties by a local heat treatment (tailor heat treated blanks). The major advantage of products made from tailored blanks in comparison to conventional products is a weight reduction. This paper covers the state of the art in scientific research concerning tailored blanks. The review presents the potentials of the technology and chances for further scientific investigations.
    Journal of Materials Processing Technology 02/2014; 214(2):151–164. · 1.95 Impact Factor
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    ABSTRACT: The Laser Beam Melting (LBM) process technology within the family of Additive Manufacturing technology is characterized by its ability to fabricate fully dense 3D structures directly from micro-sized metal powder. With the current state of the art, Ti-6Al-4V has been processed using LBM machine systems constituting a laser with a beam diameter of about 100 μm. In order to fabricate structures with smaller wall thicknesses, processing of Ti-6Al-4V is attempted on the LBM machine system, Realizer SLM 50 consisting of a laser with a beam diameter 10 μm. The proposed paper presents the development of process parameters for fabricating fully dense Ti-6Al-4V 3D structures using the LBM machine system, Realizer SLM 50. Further experiments are carried out to determine the wall thickness and mechanical properties achievable using the selected process parameters. Analysis and scientific arguments are presented to explain the influence of building direction and heat treatment on mechanical properties.
    Physics Procedia 01/2014; 56:90–98.
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    ABSTRACT: The paper deals with the testing and modelling of metals response when subjected to sheet forming operations. The focus is both on the modelling of hardening behaviour and yield criteria and on the description of the sheet metal formability limits. Within this scope, the paper provides a critical review of the models available today for predicting the material behaviour at both industrial and scientific level, and the tests needed to identify the models’ material parameters. The most recent advances in the field are also presented and discussed with particular emphasis on the challenges the sheet metal forming community is now facing.
    CIRP Annals - Manufacturing Technology 01/2014; · 2.54 Impact Factor
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    ABSTRACT: Mit der Entwicklung neuer Leichtbauwerkstoffe, wie höherfester Stahlwerkstoffe und Aluminiumlegierungen, ist der Anspruch an die Materialmodellierung in komplexen Blechumformsimulationen stark gestiegen. Einen wesentlichen Ansatz zur Verbesserung der Vorhersagegenauigkeit bildet in diesem Zusammenhang die numerische Abbildung des kinematischen Verfestigungsverhaltens. In dieser Arbeit wird am Beispiel des höherfesten Stahlwerkstoffs DP600 eine Methodik vorgestellt, um die Robustheit im Identifikationsprozess des kinematischen Modells nach Chaboche und Rousselier zu erhöhen. Basierend auf experimentellen Zug-Druck-Versuchen werden unterschiedliche Auswertestrategien analysiert. Abschließend erfolgt die Validierung und Bewertung der identifizierten Parameter durch den Abgleich eines Simulationsmodells des Wechselbiegeversuchs mit Realversuchen. The development of new lightweight materials such as high strength steels or aluminum alloys leads to an increasing demand on the material modelling in the simulation of complex sheet metal forming processes. The numerical mapping of the kinematic hardening behavior is an auspicious approach to improve the quality of the simulation results. This work introduces a strategy to enhance the robustness of the identification process of the kinematic hardening law according to Chaboche and Rousselier on the the advanced high strength steel DP600. For this purpose different evaluation strategies are executed on the data of tension-compression experiments and finally validated with the comparison of numerical simulations and experi-mental results of a cyclic bending test.
    DVM Tagung Werkstoffprüfung, Berlin; 01/2014
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    ABSTRACT: With respect to multistage forming processes the material behaviour and the history of the strain path during the process is of special interest for the improvement of the numerical prediction of forming processes. While different researchers investigated the Bauschinger effect during a load reversal and biaxial loading with pre-strained specimens, in this paper the yield locus evolution in the first quadrant of the principles stress space under biaxial loading of a modified cruciform specimen without test interruption is presented. The movement of the yield surface centre caused by kinematic hardening is approximated by an alternative approach based on experimental results.
    CIRP Annals - Manufacturing Technology 01/2014; · 2.54 Impact Factor
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    Kolja Andreas, Marion Merklein
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    ABSTRACT: In forming industry the tool is fundamental for the profitability, as it determines efficiency of cold forging process. In this regard, the tool surface has a distinctive influence on the tribological conditions and thus on the occurring tool stresses. The present study investigates the influence of different fine machining strategies on the tribological performance of cold forging tools made of WC-Co cemented carbide by applying the double cup extrusion test.The results reveal that a peened surface causes higher friction in the forming process compared to polished tool surfaces up to 100%. For polishing a minimum in friction is found for the diamond grit D 6 μm with a friction factor of m = 0.03.
    Procedia CIRP. 01/2014; 13:61–66.
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    ABSTRACT: Simple shear tests are widely used for material characterization especially for sheet metals to achieve large deformations without plastic instability. This work describes three different shear tests for sheet metals in order to enhance the knowledge of the material behavior under shear conditions. The test setups are different in terms of the specimen geometry and the fixtures. A shear test setup as proposed by Miyauchi, according to the ASTM standard sample, as well as an in-plane torsion test are compared in this study. A detailed analysis of the experimental strain distribution measured by digital image correlation is discussed for each test. Finite element simulations are carried out to evaluate the effect of specimen geometries on the stress distributions in the shear zones. The experimental macroscopic flow stress vs. strain behavior shows no significant influence of the specimen geometry when similar strain measurements and evaluation schemes are used. Minor differences in terms of the stress distribution in the shear zone can be detected in the numerical results. This work attempts to give a unique overview and a detailed study of the most commonly used shear tests for sheet metal characterization. It also provides information on the applicability of each test for the observation of the material behavior under shear stress with a view to material modeling for finite element simulations.
    International Journal of Solids and Structures 12/2013; · 2.04 Impact Factor
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    ABSTRACT: Accumulative roll bonding (ARB), as a method for production of ultrafine grained materials, is frequently supposed to be easily transferable to established industrial production lines. In literature, however, common sheet dimensions used for ARB in a laboratory scale are between 20 and 100 mm in width. In order to quantify the potential of upscaling the ARB process to a technological relevant level, sheets of AA1050A with an initial sheet width of 100–450 mm were accumulative roll bonded up to 8 cycles. In this regard, three different rolling mills of distinct dimensions were used for processing of the sheet material. The influence of process parameters and the reproducibility of the process, in terms of mechanical properties and homogeneity of the sheets, were studied by means of mechanical and microstructural characterization. Both appear to be largely independent on the sheet size and the rolling mill utilized for production. Only small deviations after the first cycles could be detected, vanishing in subsequent cycles due to the features of microstructural evolution. The finally obtained results indicate a high potential for industrial application of ARB and illustrate the possibility to upscale the process to a level necessary for that purpose.
    Journal of Materials Science 12/2013; 48(24). · 2.31 Impact Factor
  • Tobias Gnibl, Sebastian Suttner, Marion Merklein
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    ABSTRACT: In order to predict the warm formability of friction stir welded aluminum sheets, a new approach for the mechanical characterization at elevated temperature is presented in this paper. Based on warm tensile test and biaxial tensile test local properties of base material and weld nugget material were determined by using specimens with reduced measuring areas. Special characterization specimens are designed according to the weld zone dimensions and numerically optimized to guarantee homogeneous stress distribution. Identified material parameters were used to build up local material models based on approximated flow curves and an anisotropic yield function. The ability of predicting the formability performance of welded sheets was finally evaluated by the validation of numerical simulations with experimental results in dome stretching tests.
    AIP Conference Proceedings; 12/2013
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    ABSTRACT: Within the scope of the investigations carried out in a joint research project microstructures were designed for the tribological system of a camfollower contact, as a representative of highly loaded revolving sliding contacts, with the purpose of friction reduction. For this type of friction contacts the effects of microstructures are not yet fully understood. For gaining nterdisciplinary results the design of microstructures by numerical simulations, the accuracy of the manufacturing process and the tribological behavior of microstructured components were investigated. For manufacturing of microstructures the process of microcoining was focused due to ist perspective for mass production, which was compared to micro laser Ablation regarding its accuracy. For microstructured bucket tappets a significant reduction of friction was achieved in a component test bench compared to polished surfaces.
    Tribologie und Schmierungstechnik 11/2013; 61(1):21-28.
  • T. Kroiß, U. Engel, M. Merklein
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    ABSTRACT: In this paper a comprehensive approach is presented for the consideration of the interactions between process, tool and machine during the design of cold forging tools and processes by simulation. The interactions occur due to the high forming loads in cold forging and yield considerable deflections of press and tooling system. These, in turn, influence the workpiece dimensions. The entire approach comprises an efficient determination of the deflection characteristic of stroke-controlled press and tooling system and its condensed modeling in combination with the FE simulation of a cold forging process. Building on that, an analytic process model is developed that is based on a set of variant simulations. It permits an optimization of the values of influencing parameters to achieve high workpiece accuracy without subsequent adjusting effort. Initially, the analytic process model required a high number of variant simulations. By acquiring knowledge on the specific process behavior in an analysis of effects and interactions a considerable reduction of simulation runs by a factor of almost 12 was achieved in the case study on full forward extrusion. The approach is supplemented by an analytic model of the die load. In addition, scatter and uncertainties of target values depending on the ones of the influencing parameters can be estimated by applying the Monte Carlo method to the analytic process model.
    Journal of Materials Processing Technology 07/2013; 213(7):1118–1127. · 2.04 Impact Factor
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    ABSTRACT: Titanium alloys, such as Ti-6Al-4V, offer favorable characteristics as significant strength, biocompatibility and metallurgical stability at elevated temperatures. These advantages afford the application of parts out of Ti-6Al-4V in a wide field within aerospace, astronautic and medical technologies. Most applied shaping operations for parts out of titanium alloys are forging, casting, forming and machining. In order to develop and improve forming operations numerical simulations are applied during preprocessing. For that purpose mechanical properties of the material such as yield stress and Lankford parameter have to be determined. Due to the two-phase (α + β) microstructure of Ti-6Al-4V, forming operations have to be carried out at elevated temperatures to reduce the required forming force and extend forming limits. Taking the temperature and stress state dependency of the material into consideration, uniaxial tensile and compression tests are accomplished at elevated temperatures, ranging from 400 to 600 °C. Furthermore, the experimentally determined yield stress and Lankford parameter are approximated with the yield loci model proposed by Barlat 2000. The model predicts the flow response of the material, thus provides input data for the finite element analysis of forming processes at different temperature levels.
    Key Engineering Materials 06/2013; 554-557:29-32.
  • Martin Grüner, Marion Merklein
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    ABSTRACT: Aluminium alloys show a great potential for lightweight constructions due to their high strength and low density but the production of this material is very energy consuming. Also the recycling of aluminium alloys, e.g. chips from the milling process, shows different challenges. Beside contamination by cooling lubricant and oxidation of the surface of the chips the melting and rolling process for new semi finish products needs a high amount of energy. TEKKAYA shows a new approach for recycling of aluminium alloy chips by an extrusion process at elevated temperatures producing different kinds of profiles. A new idea is the production of components directly out of chips using severe plastic deformation for joining of the chips similar to the accumulative roll bonding process in sheet metal forming. In a first approach aluminium alloy chips out of a milling process were uniaxial compressed with different loads inside an axisymmetric tool installed in a universal testing machine. The compressed chip disks subsequently were tested with two experiments to gain information on their stability. First experiment is a disk compression test with the disk standing on its cylindrical surface, giving information on the stability perpendicular to the compression direction. Second experiment is a stacked disk compression test with three disks to investigate the stability parallel to compression direction. During all three tests force and displacement values are recorded by the universal testing machine. These data are also processed to calculate or identify input parameters for the numerical investigations. For numerical simulation ABAQUS in conjunction with the Drucker-Prager-Cap material model, which is often used for sintering processes, seems to be a good choice. By numerical simulation of the experiments and comparison with the experiments input parameters for the material model can be identified showing good accordance. This material model will be used in future numerical investigations of an extrusion process to identify tool geometries leading to high strains inside the material and by this to an increased stability of the parts.
    Key Engineering Materials 06/2013; 554-557:630-637.