Enrico Bruder

Properties of UFG HSLA Steel Profiles Produced by Linear Flow Splitting

Linear flow splitting is a new cold forming process for the production of branched sheet metal structures. It induces severe plastic strain in the processing zone which results in the formation of an UFG microstructure and an increase in hardness and strength in the flanges. Inbuilt deformation gradients in the processing zone lead to steep gradients in the microstructure and mechanical properties. In the present paper the gradients in the UFG microstructure and the mechanical properties of a HSLA steel (ZStE 500) processed by linear flow splitting are presented, as well as a calculation of local strength from hardness measurements on the basis of the Ludwikequation. In order to investigate the thermal stability of the UFG microstructure heat treatments below the recrystallization temperature were chosen. The coarsening process and the development of the low angle to high angle grain boundary ratio in the gradient UFG microstructure were monitored by EBSD measurements. It is shown that heat treatment can lead to a grain refinement due to a strong fragmentation of elongated grains while only little coarsening in the transverse direction occurs. A smoothing of the gradients in the UFG microstructure as well as in the mechanical properties is observed.

The effect of deformation texture on the thermal stability of UFG HSLA steel

The microstructures of ultrafine grained (UFG) metals processed by severe plastic deformation are far from the thermodynamic equilibrium thus being prone to undergo coarsening processes. Theoretical and experimental investigations revealed that the stability against discontinuous grain growth in UFG metals with high stacking fault energy strongly depends on the fraction of high angle grain boundaries (HAGBs). This means that discontinuous grain growth does not occur if the fraction of HAGBs exceeds a certain level. The present work focuses on the impact of strong deformation textures on the thermal stability of UFG microstructures in a ferritic steel processed by linear flow splitting. It shows that the expected correlation between thermal stability and fraction of HAGBs is valid up to moderate texture intensities, whereas a strong deformation texture promotes discontinuous grain growth in spite of a high fraction of HAGBs. EBSD measurements reveal that this behavior is attributed to a strain-induced grain boundary migration causing a progressive orientation pinning effect with ongoing grain growth. Thereby, a large fraction of HAGBs is transformed into low angle grain boundaries (LAGBs) with low mobility. Consequently, a microstructure with a majority of LAGBs evolves being unstable against discontinuous grain growth.

UFG-microstructures by linear flow splitting

Linear flow splitting is a new continuous cold forming process where the edge of a sheet metal is formed into two flanges by splitting and supporting rolls. Thus the production of bifurcated profiles from sheet metal without lamination of material becomes feasible. The production of such structures takes place incrementally in a modified roll forming machine. Experimental investigateons on a HSLA steel show, that even at a surface increase of the sheet edge of about 1800% no cracks were nucleated in the profiles. EBSD measurements in the splitting centre reveal that similar to other SPD processes UFG microstructures develop in the processing zone. Thus a steady state is reached in the processing zone where increasing strain has no more (or little) influence on the materials properties i.e. its deformability, as it is typical for SPD-processes. The formation of UFG microstructures is considered to be a mandatory condition for the linear flow splitting process, as it improves the formability of the material to the extremely high level required for this process. The mechanical properties of profiles produced by linear flow splitting are characterised by large gradients, depending on the local deformation and the resulting microstructure. Very high hardness is measured at the former processing zone, i.e. the splitting centre and the flange surface, where severe plastic deformation takes place and UFG microstructures are present. In direction to lower deformation i.e. with increasing distance to the splitting ground or flange surface the hardness decreases close to the level of the undeformed material. In the present paper the linear flow splitting process is introduced and the microstructural development in the process zone is discussed on the base of EBSD measurements on profiles of the steel ZStE 500. The repartition of mechanical properties in a bifurcated profile is demonstrated by detailed hardness measurements.

Severe Plastic Deformation by Equal Channel Angular Swaging

Equal Channel Angular Swaging (ECAS) is a new severe plastic deformation process which combines the conventional equal channel angular pressing (ECAP) and the incremental bulk forming process rotary swaging. The tool system consists of two rotary swaging dies with an angled channel that contains four shear zones, generating severe plastic strain per pass. The crucial advantages compared to conventional ECAP are a significant reduction of friction and axial forces plus the potential to be extended to continuous processing. Thus, ECAS has high potential for a cost-efficient production of bulk UFG materials. In the present paper the principles of ECAS are introduced and first experimental results for the processing of copper are presented.

Severe Plastic Deformation and Incremental Forming for Magnetic Hardening

The magnetic hardening of ARMCO® and FeCo17 in a severe plastic deformation and an incremental forming process is presented. The enhancement of the coercivity, which depends on the strain induced by the forming process, is investigated. Strain induced during the incremental forming process are analysed in FE-simulations.

Manufacturing Integrated Design

One of the key challenges faced by engineers is finding, concretizing, and optimizing solutions for a specific technical problem in the context of requirements and constraints (Pahl et al. 2007). Depending on the technical problem’s nature, specifically designed products and processes can be its solution with product and processes depending on each other. Although products are usually modeled within the context of their function, consideration of the product’s life cycle processes is also essential for design. Processes of the product’s life cycle concern realization of the product (e.g., manufacturing processes), processes that are realized with the help of the product itself (e.g., use processes) and processes at the end of the product’s life cycle (recycling or disposal). Yet, not just product requirements have to be considered during product development, as requirements regarding product life cycle processes need to be taken into account, too. Provision for manufacturing process requirements plays an important role in realizing the product’s manufacturability, quality, costs, and availability (Chap. 3). Further life cycle demands, such as reliability, durability, robustness, and safety, result in additional product and life cycle process requirements. Consequently, the engineer’s task of finding optimal product and process solutions to solve a technical problem or to fulfill a customer need is characterized by high complexity, which has to be handled appropriately (Chaps. 5 and 6).The book gives a systematic and detailed description of a new integrated product and process development approach for sheet metal manufacturing. Special attention is given to manufacturing that unites multidisciplinary competences of product design, material science, and production engineering, as well as mathematical optimization and computer based information technology. The case study of integral sheet metal structures is used by the authors to introduce the results related to the recent manufacturing technologies of linear flow splitting, bend splitting, and corresponding integrated process chains for sheet metal structures.One of the key challenges faced by engineers is finding, concretizing, and optimizing solutions for a specific technical problem in the context of requirements and constraints (Pahl et al. 2007). Depending on the technical problem’s nature, specifically designed products and processes can be its solution with product and processes depending on each other. Although products are usually modeled within the context of their function, consideration of the product’s life cycle processes is also essential for design. Processes of the product’s life cycle concern realization of the product (e.g., manufacturing processes), processes that are realized with the help of the product itself (e.g., use processes) and processes at the end of the product’s life cycle (recycling or disposal). Yet, not just product requirements have to be considered during product development, as requirements regarding product life cycle processes need to be taken into account, too. Provision for manufacturing process requirements plays an important role in realizing the product’s manufacturability, quality, costs, and availability (Chap. 3). Further life cycle demands, such as reliability, durability, robustness, and safety, result in additional product and life cycle process requirements. Consequently, the engineer’s task of finding optimal product and process solutions to solve a technical problem or to fulfill a customer need is characterized by high complexity, which has to be handled appropriately (Chaps. 5 and 6).

Computer-Integrated Engineering and Design

Virtual product development aims at the use of information modeling techniques and computer-aided (CAx-) tools during the product development process, to represent the real product digitally as an integrated product model (Anderl and Trippner 2000). Thereby, data related to the product as well as product properties are generated and stored as result of the product development process (e.g., product planning, conceptual design) (Pahl et al. 2007; VDI 2221 1993). Within virtual product development CAx process chains have been established. They comprise the concatenating of the applied tools and technologies within the steps of the virtual product development process enabling the consistent use of product data (Anderl and Trippner 2000). The computer-aided design (CAD) technology aims at the integration of computer systems to support engineers during the design process such as design conceptualization, design, and documentation. It provides the geometry of the design and its properties (e.g., mass properties, tolerances) which is abstracted to be used in computer-aided engineering (CAE) systems (e.g., finite element method (FEM)) for design analysis, evaluation, and optimization. The computer-aided process planning (CAPP) technology provides tools to support process planning, Numerical Control (NC) programming, and quality control (Hehenberger 2011; Lee 1998; Vajna 2009). The advantages are continuous processing and refinement of the product model, minimizing the modeling efforts regarding time as well as costs and avoiding error sources. In addition, all relevant data and information related to the product can be provided for subsequent processing (Anderl and Trippner 2000). CAx technologies have been widely established within the product development processes in industry. They have been further developed in the last years; however efforts to integrate and to automate them are still a topic of research. Especially, with the introduction of innovative manufacturing technologies such as linear flow and bend splitting require new methods and tools for the virtual product development process. These technologies enable the production of a new range of sheet metal products with characteristic properties (e.g., Y-profile geometry, material properties) that are not addressed in state-of-the-art methods and tools.

The CRC666 Approach: Realizing Optimized Solutions Based on Production Technological Innovation

Finding technical solutions for given problems is one of a designer’s key challenges. The task is especially demanding since the designer tries to find not only one possible solution but also the best possible solution, taking all existing conditions, limitations, and requirements into account (Pahl et al. 2007). There are many product development approaches that support the designer in this. The focus and drivers of the approaches differ: Reduction of complexity (Suh 1998) Integration of product development in company processes (Ehrlenspiel and Meerkamm 2013) Methodical approach based on analysis and synthesis steps (VDI 2221 1993) Cross-domain development of systems with a focus on mechatronic systems (VDI 2206 2004) Sustainable product design (Birkhofer et al. 2012) Effectiveness and efficiency (Lindemann 2009) Flexibility (Lindemann 2009) Cost and time reduction; quality improvement (Eder and Hosnedl 2010) Computer-aided automatization (Weber 2005)

Manufacturing Induced Properties: Determination, Understanding, and Beneficial Use

Based on its procedural principle, every manufacturing technology affects a variety of properties of the workpiece or product in a characteristic way (Sect. 2.3). The sum of all those properties which comprise geometrical as well as material-related ones is considered as manufacturing-induced properties. While the geometric manufacturing-induced properties are often the reason why a specific technology is chosen by the designer for the manufacturing of a certain product, the material-related manufacturing-induced properties are often seen as by-products of the process. With regard to metal forming, all manufacturing processes inherently influence the mechanical properties of the manufactured material. In many cases, these mechanical manufacturing-induced properties are merely regarded in terms of restrictions in product development. However, with respect to a manufacturing-integrated product development approach, the mechanical properties are of special interest, since we aim at utilizing their full potential to maximize the product performance.