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Forming tailored hybrid semi-finished products - Tailored Additive Blanks
(Third Party Funds Group – Sub project)
Overall project: FORAnGen - Bavarian research association for the design of sustainable products using generative design
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.
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Basic research and determination of process limitations in bulk forming processes of microgears from sheet metal - phase 2
(Third Party Funds Single)
Term: 1. July 2024 - 30. June 2026
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.
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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)
Term: 1. March 2024 - 28. February 2026
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.
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Investigation of internal stress-relevant mechanisms along the process chain of the production of cup extruded parts
(Third Party Funds Single)
Term: 1. February 2024 - 31. January 2026
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.
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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)
Term: 1. January 2024 - 31. December 2025
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.
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Investigations on the process combination of DED-LB/M and forming
(Third Party Funds Single)
Term: 1. December 2023 - 30. November 2025
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.
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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)
Overall project: Datengetriebene Prozessmodellierung in der Umformtechnik
Term: 1. November 2023 - 31. October 2026
Funding source: DFG / Schwerpunktprogramm (SPP)
Manufacturing by forming offers the advantage of a material utilization of up to 100 %. Sheet bulk metal forming processes from coil can overcome current ecological and economic challenges through the efficient production of functionally integrated components. The production of defective components due to tool wear counteracts the high material utilization and thus reduces the energy efficiency. This results in increased product costs and environmental impact, as scrap costs have to be allocated to the good parts and defective components have to be disposed of and recycled. Online detection of signs of wear offers the potential to intervene in the process within a batch’s production and thus keep scrap levels low while positively influencing the environmental balance of the overall process. However, this requires a system that uses machine data in a knowledge model as part of an information model to predict tool wear and, thus, deviating component properties at an early stage. The aim of this research project is therefore to develop a tool wear model based on a full back extrusion process from the strip. Moreover, the correlation strengths between process parameters are to be determined from the automatic monitoring of the process by sensors, optical analysis and the microscopic examination of tool and component samples. These, in combination with a causal model constructed by experts, allow the generation of a quantified cause-effect graph. Additionally, experts may uncover previously unknown causal relations based on strongly correlated parameters that are validated experimentally and simulatively. The resulting quantified cause-effect graph is part of an information model formalized as an ontology, for product, process and the machine resource, including varying tools. With the help of an assistance system to be developed in the project, the information model can be interacted with in order to explain "backwards" observed deviations at product or tool by process variables acting on them and to predict "forwards" the effects of changes on dependent variables. Based on the extended parameter understanding, an intervention in the forming process within running batches and, thus, an increased resource efficiency shall be enabled.
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Joining by forming of two-shear aluminum-steel-joints by shear-clinching
(Third Party Funds Single)
Term: 1. July 2023 - 30. June 2025
Funding source: DFG-Einzelförderung / Sachbeihilfe (EIN-SBH)
Besides the use lightweight materials, the lightweight principle is realized by function integration and the load-specific design of components. This requires the joining of dissimilar materials as well as the joining of multi-layer sheets. Latter is a challenge, not only for welding technologies, but also for mechanical joining processes, since the additional sheet layer and contact surface obstructs the process design. Process limits of well-established mechanical joining processes also apply for the joining of multi-layer sheets. Therefore, high-strength material can only be joined with additional fasteners. Moreover, there are no systematic investigations on the influence of the mechanical properties of the joining partners, their thickness and the order for the joining by forming of multi-layer sheets. Therefore, the aim of the research project is the enhancement of process limits of joining by forming of dissimilar, multi-layer materials through the qualification of the shear-clinching technology for the joining of three-layer sheets. For this purpose, the shear-clinching process is fundamentally investigated for the joining of two-shear joints and the basic mechanisms are derived. The effect of the additional sheet is systematically analyzed in dependence of influences from the mechanical properties of the joining partners and the tool geometry. By the analysis of the cutting behavior and the material flow, the interaction of each layer is identified, laying the foundation for the adaption of prevailing tool systems for the changed process conditions. The suitability of the solution is confirmed by the analysis of the joint characteristics.
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Improvement of the mapping accuracy in the material modeling by considering the yield locus under plane strain
(Third Party Funds Single)
Term: 1. April 2023 - 31. March 2025
Funding source: DFG-Einzelförderung / Sachbeihilfe (EIN-SBH)
Nowadays, forming processes are analyzed,evaluated and designed using simulation. Precise material modelling is animportant factor in improving the mapping accuracy of a forming process in thesimulation. Due to the growing computing power and increasing progress inmaterial characterization, material models with a high number of degrees offreedom can be used. In contrast a huge number of tests are required.
Conventional material models, suchas Hill'48, Yld2000-2d or BBC05, are implemented in commercial FE software andoffer comparatively short calculation times. However, these material modelscannot directly model the stress states of plane strain and shear. These areonly approximated on the basis of the input data and therefore are subject to ahigh degree of scatter. In the first project phase, it was demonstrated thatthe integration of the real material behavior under plane strain in the rollingdirection significantly improved the accuracy of the simulation. Now thequality of the prediction is to be analyzed by implementing additional characteristicvalues, such as the plane strain perpendicular to the rolling direction or theshear stress. The yield locus exponent offers great potential for this, as itis determined as a function of the material without reference to the laws ofmetal physics. The roundness of the yield locus curve can be varied by theyield locus exponent, whereby an additional material parameter can beintegrated into the material modelling (see figure).
In addition, it is to beinvestigated whether parameter identification at increased true plastic strainsleads to an improvement in the mapping accuracy between numerically calculatedand experimentally produced components in the case of distorsionally hardeningmaterials. With the aid of a subroutine, all material parameters are modelledas a function of strain. Finally, the determined yield loci are to be verifiedand evaluated using two demonstrator components, a cruciform cup and aB-pillar.
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Optical strain rate control in material characterization
(Third Party Funds Group – Overall project)
By improving the accuracy with which material behavior is represented in simulations, components and manufacturing processes can be designed more resourceefficiently. Thus, material characterization plays a central role in the implementation of new lightweight design strategies and the achievement of better vehicle crash behavior.
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.
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Improvement of the application characteristics of multi-layered sheet material for forming technology produced via Accumulative Roll Bonding (continued)
(Third Party Funds Single)
Term: 1. February 2023 - 31. January 2025
Funding source: DFG-Einzelförderung / Sachbeihilfe (EIN-SBH)
Accumulative roll bonding enablesstrenghtening of sheet materials accompanied by a reduction in ductilitythrough the formation of an ultrafine-grained microstructure. However, theformability and in particular the failure behavior of the multilayeredsemi-finished products is also dependent on the bond strength between theindividual layers. In the project, the cause-effect relationships between theprocess input parameters and the resulting interface properties areinvestigated. Based on a reproducible pretreatment, correlations betweensurface, bonding and forming properties are analyzed with the aim of improvingthe formability of accumulatively rolled aluminum products by suitable processmeasures.
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FE-based springback prediction of sheet metal forming processes from lightweight materials considering anisotropic hardening (continued)
(Third Party Funds Single)
Term: 1. February 2023 - 31. January 2025
Funding source: DFG-Einzelförderung / Sachbeihilfe (EIN-SBH)
The overall objective in the second project phase is to improve thenumerical design of deep drawing processes at elevated temperatures as afunction of the strain rate. According to previous investigations, aluminiumalloys of the 7000 series show both a tensile-compression asymmetric andstrain-rate sensitive material behaviour. These aspects influence not only thetemperature but also the hardening and springback behaviour. For this reason, aphenomenological material model is being developed, taking into account theanisotropic hardening as a function of the temperature and the strain rate, inorder to be able to numerically represent the specific material behaviour ofhigh-strength aluminium alloys. Based on the results from the first projectphase, it is only possible to a limited extent to investigate the stress-statedependent forming behaviour of AA7020-T6 and AA7075-T6 at temperatures above100 °C with the given test setups. It is therefore necessary to modify the testsetups in order to investigate the material behaviour in a temperature rangerelevant for 7000 aluminium alloys. Using this analysis, the material model tobe developed in the first phase will be extended by one term as a function ofstrain rate and temperature. By modelling the anisotropic hardening behaviourin correlation to the forming rate and forming temperature an improvedrepresentation of the material behaviour is given. In order to validate thematerial model, deep-drawing tests with a circular cup at elevated temperaturesand different forming speeds are performed. The validation is based on thesheet thinning and the force-displacement curve during the deep drawingprocess. In addition, the springback behaviour with open cross profiles andopen T-profiles are to be determined. Since the friction between tool andworkpiece influences the deep drawing process, the corresponding frictioncoefficients are determined in the strip drawing test. Thus, after successfulvalidation of the material model as a function of the forming speed andtemperature, the numerical mapping accuracy and prediction quality of warm andhot forming processes can be improved with regard to the springback behaviour.As a result, process design time is saved, because expensive experimentaliteration loops are avoided.
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Experimental investigation and modeling of heat transfer during hot stamping
(Third Party Funds Single)
Term: 1. January 2023 - 31. December 2024
Funding source: DFG-Einzelförderung / Sachbeihilfe (EIN-SBH)
The hotstamping process has been established as a manufacturing process for theproduction of ultra-high-strength components. The process is based on amartensite transformation when quenching rates exceed a theoretical value of 27K/s. Investigations have already shown that the process-side parameters cansignificantly influence the critical cooling rate and thus the resultingmicrostructure formation. The goal of the research project is to develop afundamental understanding of the heat transfer mechanisms involved in hotstamping and the dominant influencing variables in order to derive a physicallybased model. This is the basic prerequisite for the precise representation ofall relevant sub-processes in hot stamping and will enable the transfer andapplication of simulation models and results to thermally assisted material processingmethods in the future.
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Manufacturing of helical-toothed functional components from sheet metal by developing and analyzing a forming process of sheet bulk metal forming
(Third Party Funds Single)
Term: 1. January 2023 - 31. December 2024
Funding source: DFG-Einzelförderung / Sachbeihilfe (EIN-SBH)
The overarching objective is to determine the basiccausal relationships between component and process parameters and to derivecausalities in the manufacture of helical components using sheet metal forming.The process-specific challenges, a robust process window and the process limitsare to be worked out for a process chain consisting of deep drawing, extrusionand upsetting. In order to enable the industrial use of sheet metal forming forthe production of helical components in the medium term, the process must befundamentally researched and a continuous understanding of the process must begenerated from process design to the production of ready-to-use components. Inthe present project, a parameter-dependent process window with the achievablecomponent properties is to be derived on the basis of an extensive processanalysis. Furthermore, the extension of the component functionality that can berealized by forming helical gears with different modules and helix angles onsemi-finished sheet metal products by sheet metal forming is fundamentallyinvestigated. A two-stage process chain consisting of deep-drawing/extrusionand upsetting is used as part of the investigations. With the help of anumerical process model, a comprehensive process analysis is carried out andbasic causal relationships between the influencing parameters are determined.Based on these findings, the design of the reference process and theexperimental implementation are carried out. The simulation model is validatedusing process and component-specific parameters such as process force, geometryand hardness distribution. Parameter-dependent process limits are identifiedthrough the detailed investigation of the influence of the gear geometry andthe materials used on the resulting component properties and the tool stress.At the end of the first funding period, a number of sub-goals are being aimedfor. Process-specific challenges with regard to the flow paths that can beachieved and the resulting mold filling are identified. In addition, ananalysis of the influence of the material flow specific to helical gears on thecomponent properties relevant to use, such as strain hardening and gearquality, is to be carried out. Finally, an adapted process control to avoidsubsequent machining is developed
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Use of versatile joining processes for the production of hybrid component structures in an industrial environment
(Third Party Funds Group – Sub project)
Overall project: Method development for mechanical joinability in versatile process chains
Term: 1. January 2022 - 31. December 2024
Funding source: DFG / Sonderforschungsbereich / Transregio (SFB / TRR)
The subject of the transfer project is the analysis and transferability of the methodology of the transformability of a wobbling semi-hollow punch riveting process from sub-project C02 "Adaptable joining with auxiliary joining part" under industrial boundary conditions and an extension in the Transregio 285 collaborative research center (SFB/TRR285) "Method development for mechanical joinability in versatile process chains". through targeted adjustment of relevant process parameters. The central goal of the research project is the transfer of basic scientific findings for the targeted production of geometric characteristics of joints such as undercuts in wobbling semi-tubular punch riveting to the new approach of joining by tumbling.
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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)
Term: 1. April 2020 - 31. March 2026
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.
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Mechanical joining without auxiliary elements
(Third Party Funds Group – Sub project)
Overall project: Method development for mechanical joinability in versatile process chains
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.
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Forming and joining of semitubular self-piercing rivets made of high-strength steel with adapted mechanical properties and numerical analysis of the process chain
(Third Party Funds Single)
Term: 1. January 2018 - 30. November 2024
Funding source: DFG-Einzelförderung / Sachbeihilfe (EIN-SBH)
Joining is an important method of productionengineering, for which reason the efficiency of such manufacturing processes ishighly relevant. Self-piercing riveting is a mechanical joining process, usinga rivet as fastener to join two or more sheets. This makes it possible to joindissimilar materials and to realize multi-material design. However, the rivetproduction is a time-consuming process, including the steps hardening andcoating in order to achieve an adequate strength and a high ductility as wellas corrosion resistance. The use of high strain hardening materials as rivetmaterials, such as high nitrogen steels, shows a huge potential concerning thereduction of production steps and thus a shortening of the rivet manufactureprocess chain since the conventional hardening, tempering and coating steps afterforming are not necessary anymore. However, the challenging high tool loadsduring cold bulk forming of high nitrogen steels represent a major challengefor the manufacturing process.
The objective is to investigate fundamentalinfluencing factors on the forming process for manufacturing rivets using highstrain hardening materials, the resulting rivet properties, the joining processand the achievable joint properties. The LFT is working on this project incollaboration with the Laboratory for material and joining technology (LWF) at Paderborn University. At the LFT, the projectfocus is on the development of the forming tools and appropriate formingstrategies in order to realise the forming process despite the high tool loads.In this context, fundamental correlations between the forming temperature, theachievable die filling during forming and the mechanical properties of theformed rivets are investigated. By choosing a suitable forming strategy and rivetgeometry, the mechanical properties of the rivets are to be adapted accordingto the requirements of the joining process.
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Center for Nanoanalysis and Electron Microscopy
(FAU Funds)
Term: 1. January 2010 - 3. March 2038
The Center for Nanoanalysis and Electron Microscopy (CENEM) is a facility featuring cutting-edge instrumentation, techniques and expertise required for microscopic and analytical characterization of materials and devices down to the atomic scale. CENEM focuses on several complementary analysis techniques, which closely work together: Electron Microscopy, X-ray Microscopy, Cryo-TEM, Scattering Methods, Scanning Probes and Atom Probe Microscopy. With the combination of these methods new materials, particles, structures and devices are characterized not only microscopically and analytically on all length scales even down to the atomic scale but also by various in situ investigations and 3D methods. The knowledge gained through the versatile characterization methods is then used to further develop and improve materials and devices.
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.
Research projects
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)
Improvement of the mapping accuracy in the material modeling by considering the yield locus under plane strain
(Third Party Funds Single)
Funding source: DFG-Einzelförderung / Sachbeihilfe (EIN-SBH)
Nowadays, forming processes are analyzed,evaluated and designed using simulation. Precise material modelling is animportant factor in improving the mapping accuracy of a forming process in thesimulation. Due to the growing computing power and increasing progress inmaterial characterization, material models with a high number of degrees offreedom can be used. In contrast a huge number of tests are required.
Conventional material models, suchas Hill'48, Yld2000-2d or BBC05, are implemented in commercial FE software andoffer comparatively short calculation times. However, these material modelscannot directly model the stress states of plane strain and shear. These areonly approximated on the basis of the input data and therefore are subject to ahigh degree of scatter. In the first project phase, it was demonstrated thatthe integration of the real material behavior under plane strain in the rollingdirection significantly improved the accuracy of the simulation. Now thequality of the prediction is to be analyzed by implementing additional characteristicvalues, such as the plane strain perpendicular to the rolling direction or theshear stress. The yield locus exponent offers great potential for this, as itis determined as a function of the material without reference to the laws ofmetal physics. The roundness of the yield locus curve can be varied by theyield locus exponent, whereby an additional material parameter can beintegrated into the material modelling (see figure).
In addition, it is to beinvestigated whether parameter identification at increased true plastic strainsleads to an improvement in the mapping accuracy between numerically calculatedand experimentally produced components in the case of distorsionally hardeningmaterials. With the aid of a subroutine, all material parameters are modelledas a function of strain. Finally, the determined yield loci are to be verifiedand evaluated using two demonstrator components, a cruciform cup and aB-pillar.
Optical strain rate control in material characterization
(Third Party Funds Group – Overall project)
Term: 1. February 2023 - 31. January 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.
Improvement of the application characteristics of multi-layered sheet material for forming technology produced via Accumulative Roll Bonding (continued)
(Third Party Funds Single)
Funding source: DFG-Einzelförderung / Sachbeihilfe (EIN-SBH)
Accumulative roll bonding enablesstrenghtening of sheet materials accompanied by a reduction in ductilitythrough the formation of an ultrafine-grained microstructure. However, theformability and in particular the failure behavior of the multilayeredsemi-finished products is also dependent on the bond strength between theindividual layers. In the project, the cause-effect relationships between theprocess input parameters and the resulting interface properties areinvestigated. Based on a reproducible pretreatment, correlations betweensurface, bonding and forming properties are analyzed with the aim of improvingthe formability of accumulatively rolled aluminum products by suitable processmeasures.
FE-based springback prediction of sheet metal forming processes from lightweight materials considering anisotropic hardening (continued)
(Third Party Funds Single)
Funding source: DFG-Einzelförderung / Sachbeihilfe (EIN-SBH)
The overall objective in the second project phase is to improve thenumerical design of deep drawing processes at elevated temperatures as afunction of the strain rate. According to previous investigations, aluminiumalloys of the 7000 series show both a tensile-compression asymmetric andstrain-rate sensitive material behaviour. These aspects influence not only thetemperature but also the hardening and springback behaviour. For this reason, aphenomenological material model is being developed, taking into account theanisotropic hardening as a function of the temperature and the strain rate, inorder to be able to numerically represent the specific material behaviour ofhigh-strength aluminium alloys. Based on the results from the first projectphase, it is only possible to a limited extent to investigate the stress-statedependent forming behaviour of AA7020-T6 and AA7075-T6 at temperatures above100 °C with the given test setups. It is therefore necessary to modify the testsetups in order to investigate the material behaviour in a temperature rangerelevant for 7000 aluminium alloys. Using this analysis, the material model tobe developed in the first phase will be extended by one term as a function ofstrain rate and temperature. By modelling the anisotropic hardening behaviourin correlation to the forming rate and forming temperature an improvedrepresentation of the material behaviour is given. In order to validate thematerial model, deep-drawing tests with a circular cup at elevated temperaturesand different forming speeds are performed. The validation is based on thesheet thinning and the force-displacement curve during the deep drawingprocess. In addition, the springback behaviour with open cross profiles andopen T-profiles are to be determined. Since the friction between tool andworkpiece influences the deep drawing process, the corresponding frictioncoefficients are determined in the strip drawing test. Thus, after successfulvalidation of the material model as a function of the forming speed andtemperature, the numerical mapping accuracy and prediction quality of warm andhot forming processes can be improved with regard to the springback behaviour.As a result, process design time is saved, because expensive experimentaliteration loops are avoided.
Experimental investigation and modeling of heat transfer during hot stamping
(Third Party Funds Single)
Funding source: DFG-Einzelförderung / Sachbeihilfe (EIN-SBH)
The hotstamping process has been established as a manufacturing process for theproduction of ultra-high-strength components. The process is based on amartensite transformation when quenching rates exceed a theoretical value of 27K/s. Investigations have already shown that the process-side parameters cansignificantly influence the critical cooling rate and thus the resultingmicrostructure formation. The goal of the research project is to develop afundamental understanding of the heat transfer mechanisms involved in hotstamping and the dominant influencing variables in order to derive a physicallybased model. This is the basic prerequisite for the precise representation ofall relevant sub-processes in hot stamping and will enable the transfer andapplication of simulation models and results to thermally assisted material processingmethods in the future.
Manufacturing of helical-toothed functional components from sheet metal by developing and analyzing a forming process of sheet bulk metal forming
(Third Party Funds Single)
Funding source: DFG-Einzelförderung / Sachbeihilfe (EIN-SBH)
The overarching objective is to determine the basiccausal relationships between component and process parameters and to derivecausalities in the manufacture of helical components using sheet metal forming.The process-specific challenges, a robust process window and the process limitsare to be worked out for a process chain consisting of deep drawing, extrusionand upsetting. In order to enable the industrial use of sheet metal forming forthe production of helical components in the medium term, the process must befundamentally researched and a continuous understanding of the process must begenerated from process design to the production of ready-to-use components. Inthe present project, a parameter-dependent process window with the achievablecomponent properties is to be derived on the basis of an extensive processanalysis. Furthermore, the extension of the component functionality that can berealized by forming helical gears with different modules and helix angles onsemi-finished sheet metal products by sheet metal forming is fundamentallyinvestigated. A two-stage process chain consisting of deep-drawing/extrusionand upsetting is used as part of the investigations. With the help of anumerical process model, a comprehensive process analysis is carried out andbasic causal relationships between the influencing parameters are determined.Based on these findings, the design of the reference process and theexperimental implementation are carried out. The simulation model is validatedusing process and component-specific parameters such as process force, geometryand hardness distribution. Parameter-dependent process limits are identifiedthrough the detailed investigation of the influence of the gear geometry andthe materials used on the resulting component properties and the tool stress.At the end of the first funding period, a number of sub-goals are being aimedfor. Process-specific challenges with regard to the flow paths that can beachieved and the resulting mold filling are identified. In addition, ananalysis of the influence of the material flow specific to helical gears on thecomponent properties relevant to use, such as strain hardening and gearquality, is to be carried out. Finally, an adapted process control to avoidsubsequent machining is developed
Use of versatile joining processes for the production of hybrid component structures in an industrial environment
(Third Party Funds Group – Sub project)
Term: 1. January 2022 - 31. December 2024
Funding source: DFG / Sonderforschungsbereich / Transregio (SFB / TRR)
The subject of the transfer project is the analysis and transferability of the methodology of the transformability of a wobbling semi-hollow punch riveting process from sub-project C02 "Adaptable joining with auxiliary joining part" under industrial boundary conditions and an extension in the Transregio 285 collaborative research center (SFB/TRR285) "Method development for mechanical joinability in versatile process chains". through targeted adjustment of relevant process parameters. The central goal of the research project is the transfer of basic scientific findings for the targeted production of geometric characteristics of joints such as undercuts in wobbling semi-tubular punch riveting to the new approach of joining by tumbling.
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.
Forming and joining of semitubular self-piercing rivets made of high-strength steel with adapted mechanical properties and numerical analysis of the process chain
(Third Party Funds Single)
Funding source: DFG-Einzelförderung / Sachbeihilfe (EIN-SBH)
Joining is an important method of productionengineering, for which reason the efficiency of such manufacturing processes ishighly relevant. Self-piercing riveting is a mechanical joining process, usinga rivet as fastener to join two or more sheets. This makes it possible to joindissimilar materials and to realize multi-material design. However, the rivetproduction is a time-consuming process, including the steps hardening andcoating in order to achieve an adequate strength and a high ductility as wellas corrosion resistance. The use of high strain hardening materials as rivetmaterials, such as high nitrogen steels, shows a huge potential concerning thereduction of production steps and thus a shortening of the rivet manufactureprocess chain since the conventional hardening, tempering and coating steps afterforming are not necessary anymore. However, the challenging high tool loadsduring cold bulk forming of high nitrogen steels represent a major challengefor the manufacturing process.
The objective is to investigate fundamentalinfluencing factors on the forming process for manufacturing rivets using highstrain hardening materials, the resulting rivet properties, the joining processand the achievable joint properties. The LFT is working on this project incollaboration with the Laboratory for material and joining technology (LWF) at Paderborn University. At the LFT, the projectfocus is on the development of the forming tools and appropriate formingstrategies in order to realise the forming process despite the high tool loads.In this context, fundamental correlations between the forming temperature, theachievable die filling during forming and the mechanical properties of theformed rivets are investigated. By choosing a suitable forming strategy and rivetgeometry, the mechanical properties of the rivets are to be adapted accordingto the requirements of the joining process.
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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