Increasing complexity due to functional integration of components in moving systems is still overshadowed by requirements for lightweight construction. From a production technology perspective, major challenges also lie in high energy and material costs. For large series parts, forming manufacturing processes are therefore preferred when the geometry is suitable. For components with high complexity, small wall thicknesses and high geometric requirements, machining production is often unavoidable, as it enables production with final dimensions without the challenge of high process forces. Since exclusively forming production is usually not possible for complex components and exclusively machining does not make sense for efficiency reasons, combined process chains are used in industrial environments in which different manufacturing processes are used.
During their production, the preliminary product is first produced by cup extrusion, from which the target geometry is then created by turning and milling. Due to the material flow and the inhomogeneous stress states, residual stresses remain in the pressed part after forming. These are distributed over the component volume with different signs and amounts and are in balance with one another. If component areas subject to internal stress are removed, for example through subsequent machining steps, a new state of equilibrium is formed in the remaining material. As a result, distortion can occur, particularly on flanges or with small wall thicknesses, which results in rejects due to non-compliance with the required geometric specifications. Machining post-processing steps lead to an extension of the process chain and reduce the material efficiency of the manufacturing process. Reducing the machining volume through near-net-shape processes, i.e. forming close to the final shape, therefore makes sense from both ecological and economic points of view.
The results developed as part of the 2013 priority program prove that the residual stress state of the component resulting from extrusion can be fundamentally influenced by the process control. Against this background, the overarching goal of the present research project is to identify general residual stress-relevant processes in the production of cup extruded parts and to use them in industry-related process chains to improve the component's residual stress state.
Research projects
Prediction of tool fatigue in cold forging processes
(Third Party Funds Group – Sub project)
Term: 1. April 2025 - 30. September 2027
Funding source: Bayerische Forschungsstiftung
Cold forging has been pioneering for more than 2000 years. In order toaddress current ecological and economic challenges and reduce CO2 emissions, technical components areprimarily produced using cold forging. This combines advantages such as theelimination of energy-intensive heat treatment and surface scaling. In order tomeet diverse requirements such as high load-bearing capacity and eco-friendlyproduction, the use of tools with complex internal geometries is necessary toenable the production of near-net-shape components. High contact pressures andtensile stresses due to high yield stresses lead to high loads on tools. Thiscan lead to fatigue failure, resulting in economic disadvantages that areassociated with an inhibition threshold for the use of efficient cold forgingprocesses.
The goal of the project partners is to develop concepts forextending tool life of cold forging tools. Using numerical simulation models,it is possible to analyse tool loads in detail. To achieve this objective,geometric and mechanical component properties are analysed and used as adatabase for tool stress. Integrated into a simulation model, this data is usedto determine the tool life. In order to validate the accuracy of thepredictions, the methods are transferred to industrial processes.
The calculation and subsequent extension of tool lifecontribute to more economical production of cold forged components and promotethe spread of eco-friendly manufacturing technologies in Bavaria as a businesslocation.
Forming tailored hybrid semi-finished products - Tailored Additive Blanks
(Third Party Funds Group – Sub project)
Term: 1. October 2024 - 30. September 2027
Funding source: Bayerische Forschungsstiftung
The load-specific design of functional components is a promising way of responding to the increasing demands in terms of sustainability and resource efficiency. Tailored blanks have therefore become increasingly important in the field of sheet metal forming in recent years. The semi-finished product properties are customised to meet the final requirements. From an industrial perspective, it is of great interest to additionally increase the geometric flexibility and customisability of these tailored blanks by specifically combining forming technology methods with additive manufacturing. The technological advantages of the two processes complement each other perfectly and enable the efficient production of components with locally customised geometric and mechanical properties that clearly stand out from the state of the art. However, the interaction of the two processes under industry-related boundary conditions is still largely unknown.
The aim of TP 3 is therefore to develop a holistic understanding of the material-efficient production and forming of customised, hybrid semi-finished sheet metal products. The integration of the hybrid manufacturing approach into generative design enables a continuous, economical product development process, which also allows the reduced CO2 footprint of the technology to be quantified by recording the process data in advance.
Basic research and determination of process limitations in bulk forming processes of microgears from sheet metal - phase 2
(Third Party Funds Single)
Funding source: DFG-Einzelförderung / Sachbeihilfe (EIN-SBH)
There is a trend towards miniaturization of technical systems in numerous industries. This trend is characterized by minimizing geometric dimensions while increasing functionality and quality. These products include miniaturized drive systems with geared micro components, which have been used in a wide variety of industries for many years. Given the increasing demand for microgears, research into efficient manufacturing processes that enable economical and precise production of metal microgears is necessary. Cold solid forming processes offer technological, economic and ecological advantages compared to other manufacturing processes. However, at the current state of the art, the production of micro gears using cold solid forming processes for modules smaller than 0.2 mm is not possible due to high tool stress, size effects and handling problems.
Theobjective of the second project phase is the fundamental analysis of anextended process chain for the manufacturing of microgears with a module of0.1 mm. This includes the investigation of functional interactions ofsingle process steps as well as the forming-related properties on theapplication behavior of the microgears. Based on the findings of the firstproject phase with regard to the three-stage process chain, the process chainwill be extended in the second phase by an additional VFP stage and by theextrusion of a cup as a gear holder. The aim of the process extension by amulti-stage VFP is to identify effects and interactions between the influencingvariables punch diameter and penetration depth in order to analyze the effectson the material flow and the homogeneity of the deformation on the basis of theeffect mechanism determined in the first phase. The process understandinggained will subsequently be used to adjust required pin properties throughtargeted material flow control for subsequent forming of the gear holder, aswell as to reduce the process forces identified as critical in the first phase.Another sub-objective is to develop a substantial process understanding formulti-stage microforming process chains through the integration of cup formingas well as through the final separation from the sheet metal strip. For thispurpose, a suitable forming strategy for the integration of a cup extrusion isdeveloped and interactions between the forming stages are identified, resultingin a fundamental process knowledge. In addition, the forming possibilities ofthe process chain and the component spectrum will be significantly expanded. Afurther sub-objective is to evaluate the application behavior of the impactextruded microgears on the basis of the analysis of runnability in a practical laboratorytest on a gear test rig. Finally, functional relationships are determined andthe findings from both phases are evaluated to derive a process window anddevelop a detailed understanding of the process.
Analysis of the elastic-plastic material behavior of higher-strength steel materials under cyclic and swelling loading depending on the relaxation behavior
(Third Party Funds Single)
Funding source: DFG-Einzelförderung / Sachbeihilfe (EIN-SBH)
The objective of the research project isto analyze the elastic-plastic material behavior under cyclic and discontinuousloading of high-strength steel materials. In addition to a pronouncedBauschinger effect, these materials exhibit nonlinear elastic material behaviorunder swelling loading. By modeling these properties and investigating theunderlying cause-effect relationships, the numerical prediction of sheet metalforming processes with high-strength steels will be improved. Both effects havea significant influence on the springback occurring after a forming process,but have so far only been taken into account independently of each other in asimulative design of components in basic scientific investigations.Metal-physical approaches exist to explain both effects, although research intothe interrelationship of the two characteristics is necessary for clearassignment. The analysis of a possible correlation of both mechanisms as wellas the influence of relaxation effects, i.e. a time-dependent stress behaviorunder constant load application, represent key aspects for improving theunderstanding of materials and thus the numerical description. The hypothesisof the project is that there is a systematic relationship between materialproperties, such as nonlinear elasticity, the Bauschinger effect and relaxationprocesses. In the first phase of the project, the mechanical behavior of thematerial is analyzed under cyclic and pulsating loads, with continuous anddiscontinuous load application, in order to investigate the functionalrelationships between the aforementioned effects in the subsequent workpackages. Here, the material-specific influence of the stress state, theanisotropy, the pre-strain as well as the load and unload phases will beinvestigated. In order to be able to determine the causes of identifiedinteractions, microstructural characterizations will also be carried out withthe aid of scanning electron microscopy and X-ray diffraction investigations.The evaluation of the results in work phase 2 with regard to the occurringmechanisms of action will improve the understanding of the material. Furthermore,mechanical parameters for the description of the Bauschinger effect and therelaxation behavior will be derived, which will provide new approaches forplastomechanical modeling. The subsequent significance evaluation of theeffects as well as the adaptation of existing material models should improvethe numerical prediction of the springback. Finally, the validity of thederived conclusions and modeling approaches will be verified in a near-processlaboratory test.
Investigation of internal stress-relevant mechanisms along the process chain of the production of cup extruded parts
(Third Party Funds Single)
Funding source: DFG-Einzelförderung / Sachbeihilfe (EIN-SBH)
Increasing complexity due to functional integration of components in moving systems is still overshadowed by requirements for lightweight construction. From a production technology perspective, major challenges also lie in high energy and material costs. For large series parts, forming manufacturing processes are therefore preferred when the geometry is suitable. For components with high complexity, small wall thicknesses and high geometric requirements, machining production is often unavoidable, as it enables production with final dimensions without the challenge of high process forces. Since exclusively forming production is usually not possible for complex components and exclusively machining does not make sense for efficiency reasons, combined process chains are used in industrial environments in which different manufacturing processes are used.
During their production, the preliminary product is first produced by cup extrusion, from which the target geometry is then created by turning and milling. Due to the material flow and the inhomogeneous stress states, residual stresses remain in the pressed part after forming. These are distributed over the component volume with different signs and amounts and are in balance with one another. If component areas subject to internal stress are removed, for example through subsequent machining steps, a new state of equilibrium is formed in the remaining material. As a result, distortion can occur, particularly on flanges or with small wall thicknesses, which results in rejects due to non-compliance with the required geometric specifications. Machining post-processing steps lead to an extension of the process chain and reduce the material efficiency of the manufacturing process. Reducing the machining volume through near-net-shape processes, i.e. forming close to the final shape, therefore makes sense from both ecological and economic points of view.
The results developed as part of the 2013 priority program prove that the residual stress state of the component resulting from extrusion can be fundamentally influenced by the process control. Against this background, the overarching goal of the present research project is to identify general residual stress-relevant processes in the production of cup extruded parts and to use them in industry-related process chains to improve the component's residual stress state.
Tailor Alloyed Blanks - Manufacturing of high-strength process-adapted semi-finished parts by a local laser-based adaption of the alloying system
(Third Party Funds Single)
Funding source: DFG-Einzelförderung / Sachbeihilfe (EIN-SBH)
The aim of the proposed research project is theextension of the forming limits and the defined adjustment of the mechanicalproperties of high-strength aluminum alloys by a tailored local adaption of thealloying system prior to forming. In order to improve the elastic-plasticproperties of high-strength 7xxx aluminum alloys, metallurgical as well as methodsof laser material processing are used to perform a local microstructuremodification over the entire depth of the semi-finished product. Targetedconcentration reduction through element evaporation and the addition ofalloying elements should allow a local adaptation of the chemical compositiontowards 6xxx aluminum alloys, since this alloy class exhibits higher forminglimits. Since primarily the high zinc content in combination with magnesium inalloys of the 7000 series leads to a lower forming capacity than grades withlower strength, it is necessary to locally reduce the concentration of theseelements and to replace them, if necessary, with other alloying elements.Specifically, this requires magnesium and zinc evaporation as well as siliconinput in order to avoid a critical silicon concentration of 0.8% by weight,which promotes hot cracking. In addition, a minimum magnesium concentrationshould be sought to reduce the strength. This can be attributed to thedecreasing number of vacancies, which have a high binding energy to magnesiumatoms, and thus favor the transformation. This represents a significantinnovation to the current state of research, which has actually been limited tothe extension of the design limits of high-strength aluminum alloys by means ofwarm-forming or hot-forming processes or a local heat treatment. Theprerequisite for a successful local adaption of the alloying system is thefundamental scientific determination of interactions in the element evaporationof low-boiling alloying elements in combination with the insertion ofadditional elements, as well as the influence of laser material processing onthe resulting mechanical properties. Furthermore, the reworking of the alloyzone as well as the diffusion behavior of the introduced alloying elements formthe further focal points of the research project. On the basis of acharacterization of the resulting mechanical properties, the simulative designof a forming process ultimately takes place in order to verify the methodologyon the basis of a demonstrator component.
Investigations on the process combination of DED-LB/M and forming
(Third Party Funds Single)
Funding source: DFG-Einzelförderung / Sachbeihilfe (EIN-SBH)
The primary aim of the research project is to develop a fundamental understanding of the process combination of DED-LB/M and forming with alternating application of the two steps. This can be used for future research to produce tailored components using DED-LB/M and forming. Due to the novelty of this approach, the project content relates to process control and, in particular, to the analysis of thermal and mechanical interactions in the application of the two manufacturing processes. One aim is to quantify the influences of different process strategies on the material properties as well as the temperature fields and profiles in DED-LB/M. In addition, the influence of the combination of the two processes on work hardening and mechanical properties will be analyzed. Based on this, the extent to which the strain hardening introduced during forming can be influenced by recovery or recrystallization during DED-LB/M will be investigated. In addition, the aim is to determine the relationships between the mechanical properties of the as-built test specimen, the formability and the resulting geometric component properties, also in alternating process sequences. This should generate a deep understanding of the forming behavior of structures manufactured using DED-LB/M, which can be used for the design of the combined production chain.
Data-based identification and prediction of the die surface condition and interactions in sheet bulk metal forming processes from coil
(Third Party Funds Group – Sub project)
Term: 1. November 2023 - 31. October 2026
Funding source: DFG / Schwerpunktprogramm (SPP)
Joining by forming of two-shear aluminum-steel-joints by shear-clinching
(Third Party Funds Single)
Funding source: DFG-Einzelförderung / Sachbeihilfe (EIN-SBH)
Optical strain rate control in material characterization
(Third Party Funds Group – Overall project)
Term: 1. February 2023 - 31. July 2025
Funding source: Bayerische Forschungsstiftung
URL: https://forschungsstiftung.de/Projekte/Details/Optische-Dehnratenregelung-in-der-Werkstoffcharakterisierung.html
A fundamental knowledge of material behavior is necessary for the targeted forming of metallic materials. Characterization tests, such as the tensile test, are used to determine specific material parameters such as yield stress, tensile strength, uniform elongation and elongation at break. In addition, the elastic-plastic material behavior can be analyzed. Through the appropriate choice of a material model, this material behavior is mapped in a simulation. Formingsimulations represent the manufacturing process and are used for the design of tools and sheets and contribute to the safe and resource-saving design of parts.
Most metallic materials exhibit strain rate sensitivity. This means that the material behavior changes depending on the forming speed. In particular, quasi-static characterization tests carried out at low strain rates, which hardly ever occur in real forming processes, lead to deviations from the real material behavior. Thus, the consideration of the actual strain rate sensitivity leads to an improved material modeling and thus simulative representation of the material behavior.
The aim of the research project is therefore to develop, in cooperation with the project partners, a robust method for carrying out optically strain-rate-controlled tests and to analyze the influence on the prediction quality of simulations. This will reduce the difference between the nominally selected strain rate and the actual strain rate. By this method, more accurate material parameters are measured, which in turn enables an improved component and process design.
Notch Rolling and Cyclic Bending - Basic Investigations for the Production of Bulk Materials with a Low Aspect Ratio out of Strip Material
(Third Party Funds Single)
Funding source: DFG-Einzelförderung / Sachbeihilfe (EIN-SBH)
Inorder to increase the productivity of the production process of steel wires,the process chain of notch rolling and cyclic bending is fundamentallyanalyzed. During notch rolling, notches are formed on both sides of a sheetmetal strip, in whose areas the material fatigues and forms cracks during thesubsequent fulling process. The numerical and experimental implementation ofboth process steps enables the identification of relevant influencingparameters and their interactions. Parameters taken into account are, amongothers, the notch radius, notch angle and web thickness in notch rolling, andthe bending angle and number of cycles to breakage or to the desired residualweb thickness in cyclic bending. Numerical and experimental studies of ductiledamage are required to evaluate material separation.
Mechanical joining without auxiliary elements
(Third Party Funds Group – Sub project)
Term: 1. July 2019 - 30. June 2027
Funding source: DFG / Sonderforschungsbereich / Transregio (SFB / TRR)
URL: https://trr285.uni-paderborn.de/
The aim of this project is to conduct fundamental scientific research into joining without auxiliary element using metallic pin structures produced by forming technology, which are pressed into the joining partner or caulked after insertion into a perforated joining partner, and the joint properties that can be achieved with this. This includes the development of a fundamental understanding of the acting mechanisms with a focus on feasibility in phase 1, the optimisation of the pin structure with regard to geometry and arrangement as well as the joining process for the targeted adjustment of joining properties in phase 2 and the transferability of the technology to an extended range of applications in phase 3. The aim in phase 1 is therefore to develop a fundamental understanding of the extrusion of defined metallic pin geometries from the sheet plane using local material accumulation in order to be able to determine local changes in the material properties, such as strength. Simultaneously, different process control strategies for joining metal and FRP as well as different metals will be fundamentally researched and process windows will be derived.In the case of FRP, various process routes will be investigated with a focus on fibre-friendly injection of the pin structures or hole forming for caulking of the pin structures without delamination of the FRP. Ultrasound, vibration, infrared radiation or combinations of these methods are used to melt the matrix with the goal of identifying suitable process routes and generating an understanding of the mechanisms at work. Based on the findings of the pin manufacturing and the results regarding the joining processes, a fundamental understanding of the process will be developed, which will allow the further development of the pin geometry and the definition of suitable simple, regular pin arrangements and dimensions in the next step. In order to meet the different requirements of the pin manufacturing process and the joining method, the adaptability of the tool and joining technology is essential. Accordingly, the adaptation on the tool side and the specific process control during pin production will be investigated in order to demonstrate the possible variations. In addition, the adaptability of the joining operation will be achieved by adapting the process control, especially in the case of metal-FRP joints, in order to react to different conditions, such as the fibre layer and layer structure of the FRP. Finally, the direction-dependent joint properties and the application behaviour of the multi-material joints joined with the developed pin geometries will be characterised and evaluated depending on the pin dimensioning and arrangement in order to identify the decisive influencing factors on the joint properties.
Center for Nanoanalysis and Electron Microscopy
(FAU Funds)
CENEM was established in 2010 to provide a forefront research center for the versatile characterization of materials and devices with state-of-the-art instrumentation and expertise and to intensify the interdisciplinary research. The big CENEM network represents the strong collaborations within the University of Erlangen-Nürnberg as well as the collaboration with other universities, dedicated research institutes and industry.
The support of the core facility CENEM by the German Science Foundation (DFG) and the Cluster of Excellence EXC 315 “Engineering of Advanced Materials” is gratefully acknowledged.
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