Modernengineering structures increasingly rely on hybrid material systems in whichdifferent materials are combined according to their specific properties. Theresulting increase in material diversity places high demands on adaptable andresource-efficient joining technologies. Pin joining offers a novel approachfor creating robust joints between dissimilar materials without the need foradditional auxiliary joining elements.
In pinjoining, metallic pins are locally formed directly from the base material byforward extrusion. These integral structural elements are subsequently used tojoin a counterpart material – within the scope of this project, eitheraluminium or fibre-reinforced polymers (FRP). Different joining strategies canbe applied: the formed pins may be pressed directly into the joining partner orinserted through pre-drilled holes and subsequently caulked. In both cases, acombined force- and form-fit joint is created, whose mechanical properties arestrongly influenced by the pin geometry, local material hardening, and theinteraction between pin and joining partner.
The firstphase of the project focused on the fundamental investigation of single-pinjoints. The objective was to systematically analyse the underlying mechanismsand develop a comprehensive understanding of the relevant process–structurerelationships. To this end, manufacturing processes, achievable pin geometries,local material modifications, and load-bearing capacities as well as failuremechanisms were investigated experimentally. In addition, different processstrategies were evaluated with regard to their influence on joint quality andmechanical and geometrical properties.
Thecurrently ongoing second phase transfers these findings to more complexmulti-pin joints. Particular emphasis is placed on the interactions betweenneighbouring pins and their influence on load transfer, stress distribution,and the overall load-bearing capacity of the joint. The aim is to establish aprofound understanding of pin interaction effects in order to enable the load-and material-specific design of multi-pin joints and to predict and tailortheir mechanical behaviour.
Pin joiningtherefore offers considerable potential as a resource-efficient, adaptable, andauxiliary-element-free alternative to conventional joining technologies. Inparticular, the process opens up new opportunities for the realisation ofhigh-performance and sustainable hybrid lightweight structures.
Research projects
Development of a data driven method for the process design of thermally aided forming processes with additional component evaluation for hot stamping
(Third Party Funds Single)
Term: 1. April 2026 - 31. March 2029
Acronym: ME 2043/126-1
Funding source: DFG-Einzelförderung / Sachbeihilfe (EIN-SBH)
Thermally assisted forming processes, such as hot stamping, are technologically particularly demanding production processes with a large number of possible process parameter settings. The effects on the material properties in terms of process-structure-property relationships are not fully known. Process control based on classic methods for estimating material behavior with the aim of producing components with tailored material properties is only possible to a limited extent. The research approach is therefore based on the hypothesis that the synthesis of testing and characterization, modelling and simulation as well as new methods from the field of machine learning make it possible to establish new types of process-structure-property relationships. These in turn make it possible to generate efficient process models for process design and component evaluation in thermally assisted forming processes. The objectives of the project are to develop cause-effect relationships and to develop, apply and evaluate machine learning methods for the improved description of hot stamping processes with the following focal points: 1. a plant-related process model, which is used within the project for process design. The process model can be used to efficiently predict the microstructure and mechanical properties of the material (strength and hardness) at the end of the process for specified process parameters (thermal load path). The plant-related process model is therefore suitable for use in optimizing the process parameters with regard to the desired microstructure and associated properties in the process. 2. a hybrid material model for simulation-supported process design, which allows efficient FEM simulation of the entire hot forming process. The aim of the hybrid material model is to use the advantages of machine learning in material modelling where classical, physically motivated modelling has major challenges. Microstructural processes (such as austenitisation with subsequent quenching with different microstructural states, diffusive processes, phase transformations, etc.), which are very complicated from a physical modelling perspective, are leartned using experimental data. The methodology is developed and validated using the hot stamping process. The goal is to transfer the developed approaches to other materials, alloys and processes.
Elaboration and qualification of a versatile process chain consisting of a pre-hole and joining process for industrial application (T07#)
(Third Party Funds Group – Sub project)
Project leader: Michael Lechner, Marion Merklein
Term: 1. January 2026 - 31. December 2027
Acronym: SFB/TRR 285 T07
Funding source: DFG / Sonderforschungsbereich / Transregio (SFB / TRR)
The project comprises the elaboration and qualification of a versatile process chain for the mechanical joining of pin structures in a previously shear-cut pre-hole. The aim is to transfer scientific conclusions from project C01 to an industry-oriented process chain for the production of a bicycle cassette. The use of a crossover aluminum alloy developed by AMAG in this process chain is expected to make a significant contribution. The aim of the investigation is to identify the process limits and develop a process window for the design of load-appropriate joints.
Expansion of the joinability and improvement of the joint properties in mechanical joning processes by tailor heat treated aluminum semi-finished parts
(Third Party Funds Single)
Term: 1. October 2025 - 30. September 2027
Funding source: DFG-Einzelförderung / Sachbeihilfe (EIN-SBH)
The increasing demands on the automotive industry to reduce the vehicle weight and to increase crash safety at the same time require the extensive use of modern high-performance materials as well as the production of car bodies with a multi-material design. This results in new challenges for joining technologies. This applies in particular to the joining of dissimilar, high-strength materials. Against this background, within the first phase of the project, the focus was to extend the process limits for shear-clinching high-strength aluminum alloys of the 7000 series by means of a tailored short-term heat treatment. The localization of the heat treatment enables the targeted setting of strength gradients in the sheet and thus the influencing of the material flow in the joining process with the aim of improving the properties of the joints. Within the second phase, the findings are to be transferred to joining with auxiliary joining parts. For this purpose, the investigations will be carried out using semi-tubular self-piercing riveting as an example. Furthermore, the control of the cooling rate during the retrogression of precipitation-hardenable aluminum makes it possible to influence the aging behavior and thus the resulting mechanical properties of the alloys. This circumstance is to be used to achieve not only an improvement of the joint geometry by the local heat treatment, but also to influence the resulting application properties by the complete control of the local temperature-time curves. With the aid of numerical simulation, the interaction between the heat treatment layout and the resulting material flow in the semi-tubular punch riveting process is investigated. After cold and artificial aging of the specimens, the resulting application properties are determined by varying the heat treatment layout and the realized cooling rate. In particular, the focus is on the strength under cyclic loading and the susceptibility of the alloy to stress corrosion cracking. It is known from the literature that retrogression followed by re-aging has a beneficial effect on corrosion behavior. The influence of such a heat treatment on the application properties of mechanical joining points is therefore to be analyzed as part of the research project.
Roll-formed profiles of high-strength aluminum alloys for semifinished products and complex component geometries (High-strength Al profile components)
(Third Party Funds Single)
Term: 1. August 2025 - 31. July 2027
Acronym: 01|F23805N
Funding source: andere Förderorganisation
URL: https://www.lft.fau.de/rollgeformte-geschlossene-profile-aus-hochfesten-aluminiumlegierungen-fuer-halbzeuge-und-komplexe-bauteilgeometrien-hochfeste-al-profilbauteile/
As part of the IGF projecttitled "High-Strength Aluminium Profile Components – Roll-Formed, ClosedProfiles Made of High-Strength Aluminium Alloys for Semifinishe and ComplexComponent Geometries," an efficient process strategy is being developedfor producing complex component geometries from high-strength, closed aluminiumprofiles using hydroforming. The profiles are manufactured through roll formingand high-frequency induction welding, offering the advantage of a continuousproduction process and improved cost efficiency compared to traditionalextrusion methods. The project's objective is to implement this process chainfor high-strength aluminium alloys in the 6000 and 7000 series and to assessthe formability of the profiles—including the weld seam and the heat-affectedzone, which undergo microstructural changes—using IHU.
Key scientific questionsconcern the formability and weldability of the alloys, the quality andmanufacturability of the weld seams, and the assessment of process-relatedmaterial properties through tube expansion testing. In addition toexperimentally investigating and optimizing individual process steps, theresults will be used to validate the simulation models of the entire processchain. An innovative aspect of the project involves managing input and outputparameters of the simulations via a centralized data platform. This platformenables statistical correlation and targeted optimization of processparameters, semi-finished product characteristics, and component quality. It isreferred to as a digital shadow, based on a simplified digital twin. Finally,the new process routes will be compared and evaluated against establishedmanufacturing methods from both economic and environmental perspectives,including the use of alloys with high recycled content. The goal is to supportresource-efficient and cost-effective production of high-strength,dimensionally stable lightweight profile components at scale.
Prediction of tool fatigue in cold forging processes
(Third Party Funds Group – Sub project)
Project leader: Marion Merklein
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.
Improvement of the formability and joining strength of hot-formed, custom-made sheet metal semi-finished products
(Third Party Funds Single)
Term: 1. December 2024 - 30. November 2026
Acronym: Mass-Presshärten
Funding source: AIF Arbeitsgemeinschaft industrieller Forschungsvereinigungen
Forming tailored hybrid semi-finished products - Tailored Additive Blanks
(Third Party Funds Group – Sub project)
Project leader: Marion Merklein
Term: 1. October 2024 - 30. September 2027
Acronym: FORAnGen
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)
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.
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. July 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.
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 - 30. June 2026
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.
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)
Project leader: Marion Merklein
Term: 1. November 2023 - 31. October 2026
Funding source: DFG / Schwerpunktprogramm (SPP)
In-situ characterization of a locally carburized complex phase steel for manufacturing of tailored semi-finished products
(Third Party Funds Single)
Term: 1. October 2021 - 31. March 2028
Funding source: DFG-Einzelförderung / Sachbeihilfe (EIN-SBH)
Hot stamping has established itself as a manufacturing process for safety-critical components. A further improvement in passenger safety can be achieved by locally adjusting the mechanical properties. This is based on the combination of high-strength zones for penetration protection in the interior and ductile zones, which enable energy absorption due to the higher residual deformation capacity. One method of tailoring is the local carburization of the semi-finished product. Due to the regional modification of the chemical composition, this process offers several advantages over welding- and temperature-based methods. For example, the design of the zones to be adjusted is very flexible due to the small transition areas. In addition, the process is independent of complex furnace and tool technology and is therefore particularly suitable for tailoring the properties of small series components. In addition to the strength-enhancing function of the additionally absorbed carbon, it also influences the phase transformation temperatures of the steel. This property is still uninvestigated in tailored carburization. Based on this effect, a greater gradation between carburized and non-carburized areas can be achieved by a suitable setting of the austenitizing temperature.
The overall aim of the project is therefore to develop a fundamental scientific understanding of the process. Therefor, the influence of the carburizing parameters on the transformation temperatures is to be analyzed first. Based on this, a process corridor of the austenitization temperature can be identified as a function of the respective carburization. On the basis of this, the effect of varying the carburization parameters and the austenitization temperature on the mechanical properties of carburized and non-carburized samples will be investigated. The obtained results in combination with the in-situ characterization of the microstructural changes via laser ultrasound measurments will be used to identify a process window. In addition, the prediction accuracy of the numerical simulation is to be improved based on the in-situ characterization and the hot flow behavior, taking into account the process-specific influencing variables. The extended material models will be validated and verified using real demonstrator components. Furthermore, the demonstrator components, which have different carburized zones and were manufactured with various process parameters, are to be examined with regard to their energy absorption capacity using three-point bending tests and crash tests. Finally, a process evaluation and guidelines are to be derived with regard to the achievable grading using the method examined.
Mechanical joining without auxiliary elements
(Third Party Funds Group – Sub project)
Project leader: Dietmar Drummer, Marion Merklein
Term: 1. July 2019 - 30. June 2027
Acronym: TRR 285 C01
Funding source: DFG / Sonderforschungsbereich / Transregio (SFB / TRR)
URL: https://trr285.uni-paderborn.de/
Modernengineering structures increasingly rely on hybrid material systems in whichdifferent materials are combined according to their specific properties. Theresulting increase in material diversity places high demands on adaptable andresource-efficient joining technologies. Pin joining offers a novel approachfor creating robust joints between dissimilar materials without the need foradditional auxiliary joining elements.
In pinjoining, metallic pins are locally formed directly from the base material byforward extrusion. These integral structural elements are subsequently used tojoin a counterpart material – within the scope of this project, eitheraluminium or fibre-reinforced polymers (FRP). Different joining strategies canbe applied: the formed pins may be pressed directly into the joining partner orinserted through pre-drilled holes and subsequently caulked. In both cases, acombined force- and form-fit joint is created, whose mechanical properties arestrongly influenced by the pin geometry, local material hardening, and theinteraction between pin and joining partner.
The firstphase of the project focused on the fundamental investigation of single-pinjoints. The objective was to systematically analyse the underlying mechanismsand develop a comprehensive understanding of the relevant process–structurerelationships. To this end, manufacturing processes, achievable pin geometries,local material modifications, and load-bearing capacities as well as failuremechanisms were investigated experimentally. In addition, different processstrategies were evaluated with regard to their influence on joint quality andmechanical and geometrical properties.
Thecurrently ongoing second phase transfers these findings to more complexmulti-pin joints. Particular emphasis is placed on the interactions betweenneighbouring pins and their influence on load transfer, stress distribution,and the overall load-bearing capacity of the joint. The aim is to establish aprofound understanding of pin interaction effects in order to enable the load-and material-specific design of multi-pin joints and to predict and tailortheir mechanical behaviour.
Pin joiningtherefore offers considerable potential as a resource-efficient, adaptable, andauxiliary-element-free alternative to conventional joining technologies. Inparticular, the process opens up new opportunities for the realisation ofhigh-performance and sustainable hybrid lightweight structures.
Center for Nanoanalysis and Electron Microscopy
(FAU Funds)
Term: 1. January 2010 - 3. March 2038
Acronym: CENEM
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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