bluuebunny/crossref_metadata_2025 huggingface dataset:
Influence of Grinding on the Surface Properties of Cemented Carbides
Authors: Andreas Kolja , Engel Ulf , Merklein Marion
Published: February 2012

The increased demand for manifold industrial goods requires superior manufacturing techniques. In the field of steel products, cold forging has gained importance for the last sixty years. Within cold forging the tool takes a key role as it determines both accuracy and efficiency of forming process. For forming processes with high demands regarding wear resistance WC-Co cemented carbides are increasingly used as tool materials. The manufacturing process of the tool requires a combination of hard and fine machining. In order to reduce the effort of subsequent fine machining process, surfaces with low roughness are preferred. As grinding leads to high surface qualities, it is a common method in tool machining. Grinding is accompanied by compressive residual stresses in the surface which have a positive influence on the tool life. The absolute value of residual stresses is determined by the machining parameters. The present study investigates the influence of feed and in-feed on the topography and the near surface residual stresses. While the surface roughness is correlated with both parameters, the feed has a major influence on the residual stresses in the surface of cemented carbides.
Processing of New Solar Absorbers in Steel Design Based on Partially Cold Roll Bonded Hybrid Semi-Finished Parts
Authors: Steinbach Frank , Koch Lotta , Hermann Michael , Witulski Jörg , Tekkaya A. Erman
Published: February 2012

The conventional manufacturing of solar absorbers has the disadvantage that only simple pipe branch channel geometries are possible. For this reason, a new approach of manufacturing solar absorbers is presented with which it is possible to design the channel geometry as a quasi-fractal structure (FracTherm®, developed by Fraunhofer Institute for Solar Energy Systems) and which reduces the pressure drop and the required energy for the pump. To manufacture these new absorbers, a fast, nearly continuous production process was developed which consists of partial cold roll bonding and subsequent hydroforming, similar to symmetric hydroforming of sheet metal pairs. Various channel geometries, which are developed by Fraunhofer ISE, within the hybrid sheet metal, can be applied. Therefore, three technologies are combined to manufacture a new type of solar absorber. A special look is taken at cold roll bonding. By this process, the material for the new solar absorbers (copper-steel-copper/copper-steel-copper hybrid sheet material) is produced using a suitable release agent to avoid the bonding process along the subsequent water channels. To establish manufacturing guidelines, the characterization of the material is necessary. A peel test like ISO 11339 is used to determine the strength of the layers of the hybrid material. At least the forming characteristics of the hybrid material are dominated by the basic material, in this case steel. A further look is given to the hydroforming of the material. Different cross-section geometries have been tested by a simplified experiment to find out the best geometry for the absorber channels, and have been compared with simulation results, too. Hence, for a crack-free forming operation the choice of the die radius and corner radius is decisive as they are within the same range. To show the feasibility of the hydroforming process and validate the process chain, a small demonstrator was manufactured. Finally it is possible to manufacture a steel based solar absorber with a quasi-fractal structure by combining partial cold roll bonding and hydroforming. All these results are used as guidelines for the production of a new absorber with quasi-fractal structure (FracTherm®).
Application of Mechanical Vibration in the Machine Building Technology
Authors: Sędek Piotr , Weglowski Marek S.
Published: February 2012

The application of mechanical vibration has been known for many years, but some controversy still exists. According to some ideas the mechanical vibration reduces the technological stresses by summation of technological stress and stress from external loads (vibration). But on the other hand, the mechanical vibration causes more complicated phenomena (micro-relaxation) resulting in dimensional stability close to natural seasoning effects. In the present study authors present results of research into mechanical vibration from the experimental and practical point of view, proving that this process can be used to obtain dimensional stability. The results has also indicated that the reduction of the technological stresses is highly questionable.
Numerical Simulations of Clay Tiles Compression
Authors: Vignes Jérémie , Schmidt Fabrice , Dusserre Gilles , De Almeida Olivier , Dalmasso Jean Frédéric
Published: February 2012

During the pressing step, the clay tiles undergo stresses which result in the appearance of defects. A rheological study, based on free compression tests, allowed to confirm the Elasto-visco-plastic behaviour of the clay. The different constitutive parameters were estimated by fitting the force-displacement experimental curves using the optimisation algorithm (ES Metamodel) implanted in the commercial software Forge 2009®. The influence of the tribological parameters was studied using squeezing numerical simulations of a full tile. The numerical model was validated with experimental squeezing test of technological specimen with a tile lug. Then, we have compared experimental force with the numerical one and deduced that the clay/tool interface is not perfectly sliding. A friction Tresca’s law was used to model the clay/tool interface. Numerical results showed that the actual geometry of tile lug didn’t allow to form correctly the tile. Several areas undergo tensile stress, air traps ,... A new geometry of tile lug was proposed in order to limit this phenomenon. Using a simplified defect criteria (Latham and Cockroft), the numerical model allowed to locate the areas where there is a risk of crack.
Computer Aided Design of Manufacturing of Fasteners - Selection of the Best Production Chain
Authors: Skóra Mariusz , Weglarczyk Stanislaw , Kusiak Jan , Pietrzyk Maciej
Published: February 2012

Computer aided design of the manufacturing technology for the fasteners is presented the paper. The particular objectives of the work were twofold. The first objective is evaluation of applicability of various materials for fasteners. Analysis of different technological variants is the second objective of the research. In the material part, bainitic steels are considered as an alternative for the commonly used carbon-manganese steels. This is a continuation of [1,2]. Possibility of elimination of the heat treatment was evaluated. Main features of the new generation of bainitic steels are discussed briefly in the paper. Rheological models for all steels investigated in the project were developed. The models were implemented into the finite element code for simulations of drawing and multi stage forging. Simulations of various variants of manufacturing chain were performed and the best alternative was selected. Criteria for the selection composed dimensional accuracy and tool life. Industrial trials were performed for the selected cycle and the efficiency of this cycle was evaluated. Finally, the optimization task was formulated. However, solution of the optimization problem is costly at this stage and improvement of the efficiency of the formulation will be the objective of further research. References 1. Kuziak R., Skóra M., Węglarczyk S., Paćko M., Pietrzyk M., Computer aided design of the manufacturing chain for fasteners, Computer Methods in Materials Science, 11, 2011, 243-250. 2. Kuziak R., Pidvysots’kyy V., Węglarczyk S., Pietrzyk M., Bainitic steels as alternative for conventional carbon-manganese steels in manufacturing of fasteners - simulation of production chain, Computer Methods in Materials Science, 11, 2011, 443 – 462.
Determination of Forming Limit Strains Using Marciniak-Kuczynski Tests and Automated Digital Image Correlation Procedures
Authors: Vysochinskiy Dmitry , Coudert Terence , Reyes Aase , Lademo Odd Geir
Published: February 2012

Forming limit strains are used to construct a forming limit diagram (FLD), which is a diagram in the principal strain space, traditionally used for designing forming operations of sheet metals. A line indicating the boundary between safe and unsafe strains is often called the forming limit curve (FLC). FLDs are also used to evaluate results from finite element simulations. Therefore consistency and reproducibility are important. This paper deals with the experimental determination of forming limit strains from Marciniak-Kuczynski (MK) tests. The material tested is AA6016 aluminum alloy in three different conditions: virgin material and material subjected to 5% and 8% deformation by rolling. Strains were measured by the use of digital image correlation (DIC) technique. Forming limit strains were determined by the use of two automated methods. The results from the two methods are compared and evaluated regarding their applicability to the Marciniak-Kuczynski test and ability to capture actual forming limit strains.
Compound Forging of Hybrid Powder-Solid-Parts Made of Steel and Aluminum
Authors: Behrens Bernd-Arno , Kosch Klaus Georg , Frischkorn Conrad , Vahed Najmeh , Huskic Adis
Published: February 2012

Compound forging is a technology to successfully manufacture hybrid parts by applying resource-saving process steps. During compound forging of steel-aluminum parts the formation of intermetallic phases is benefited. The thickness of these intermetallic phases influences the bonding and thus the global part quality. According to literature, specific coating elements reduce the phase seam thickness. In powder-metallurgically manufactured parts it is possible to selectively insert specific elements in the surface area. Therefore, a time intensive coating process can be avoided. The applicability of combining the technologies of powder-metallurgy and compound forging is discussed in this paper. Powder-metallurgically manufactured and solid parts made of steel and aluminum are compound forged and the influences on deformation behavior and the joining zone are investigated.
Hydroforging of Thick-Walled Hollow Aluminum Profiles
Authors: Müller Karsten , Stonis Malte , Lücke Michael , Behrens Bernd Arno
Published: February 2012

Lightweight design of cars is one way to reduce fuel consumption and increase the range of cars. This is an important factor to attain the EU limit values for CO2 emissions for vehicles and so to escape penalties for exceeding these limits as of the year 2012. The increasing uses of high-strength steels or of lightweight structures are adequate means to reducing weight. At IPH – Institut für Integrierte Produktion Hannover gGmbH a method to produce hollow profiles made of aluminum was developed. The method combines flashless forging and tube hydroforming. This is called hydroforging. With this method it is possible to produce thick-walled hollow aluminum profiles with undercuts without complex tool kinematics. The forging is supported by an active medium. A tool concept has been developed that uses the drives of a hydraulic press with die cushion. With this tool various component geometries were produced and analysed. To produce the tools interior pressure and the forming pressure liquid tin as incompressible active medium was used. The forming is initiated by an upsetting of the aluminum profiles and supported by the active medium, so that the profile is pushed against the engraving of the dies. The process was designed based on simulations and verified by practical experiments. This paper describes the development of the forging process with active medium and the discussion of the forging experiment results.
Analysis of Non-Crimp Fabric Composite Reinforcements Forming
Authors: Bel Sylvain , Hamila Nahiene , Boisse Philippe
Published: February 2012

Abstract Two experimental devices are used for the analysis of the deformation mechanisms of biaxial non-crimp fabric composite reinforcements during preforming. The bias extension test, commonly use for the shear behaviour characterisation of woven fabrics, allows to highlight the sliding between the two plies of the reinforcement. This sliding is localized in areas of high gradient of shearing. This questions the use of bias extension test in determining the shear stiffness of the studied reinforcement. Then a hemispherical stamping experiment, representative of a preforming process, allows to quantify this sliding. The slippage is defined as the distance, projected onto the middle surface, of two points initially opposed on both sides of the reinforcement. For both experiments, the characteristic behavior of the non-crimp fabric reinforcement is highlighted by comparison with a woven textile reinforcement. This woven fabric presents only a very little sliding between warp and weft yarns during preforming. This aspect of the deformation kinematics of the non-crimp fabric reinforcement must be considered when simulating the preforming.
Characterization and Finite Element Modeling of Unidirectional Non-Crimp Fabric for Composite Manufacturing
Authors: Petrov Alexander , Sherwood James A. , Fetfatsidis Konstantine A.
Published: February 2012

A hybrid finite element discrete mesoscopic approach is proposed to model the forming of composite parts using a unidirectional glass prepreg non-crimp fabric (NCF). The tensile behavior of the fabric is represented using 1-D beam elements, and the shearing behavior is captured using 2-D shell elements. The material is characterized using tensile and shear frame tests. These properties are then incorporated into an ABAQUS/Explicit finite element model via user-defined material subroutines. The shear frame characterization test is simulated using a finite element model of the fabric, and the finite element results are compared to experimental data as a validation of the methodology. The thermostamping of a double-dome geometry, which has been used in an international benchmarking program, is modeled as a demonstration of the capabilities of the proposed methodology.
Forming of Thermoplastic Composites
Authors: Haanappel Sebastiaan P. , Sachs Ulrich , ten Thije Rene H.W. , Rietman Bert , Akkerman Remko
Published: February 2012

Design and production guidelines for UD reinforced thermoplastic composites are highly desirable. Therefore, forming experiments and simulations with a realistic complex shaped product were conducted. Thermoforming experiments with quasi-isotropic UD carbon/PEEK and 8HS woven glass/PPS composites showed a clear difference in formability. Many wrinkles develop near doubly curved areas for the considered UD composites, whereas significant in-plane shear is observed for the woven composites. Forming prediction tools can be utilised to optimise the product design with respect to formability. A forming prediction methodology is shown, which encompasses finite element modelling in combination with material models that describe major deformation mechanisms. Characterisation methods were developed to describe inter-ply friction and in-plane shear. Forming simulations are able to indicate the critical areas for the UD composites, as is concluded from the comparison of wrinkling and in-plane shear distributions within the formed specimens. Forming experiments and predictions match qualitatively well and this tool can successfully be utilised in the product design phases.
First Steps on the Modeling and Simulation of Thermoplastic/Thermoset Phase Separation
Authors: Lamari Hajer , Ammar Amine , Leygue Adrien , Chinesta Francisco
Published: February 2012

Matrices employed in composites parts of aeronautic structures consist of a thermoset / thermoplastic mixture. Thermoplastic is introduced in low concentration in order to improve the mechanical properties, in particular the ones related to choc resistance. However, there are two antagonist mechanisms, the one related to energy that leads to demixing and the one related to entropy that tends to mix. These effects are strongly coupled with the elasticity of thermoplastic, the evolution from a newtonian fluid to a viscoelastic one of thermosets, the presence of reinforcement fibers, … and are nowadays bad understood despite the significant impact that these effects have on the composite microstructure and then on its mechanical properties. This work constitutes a first attempt to understand these complex physics.
On the Improvement of Formability and the Prediction of Forming Limit Diagrams at Fracture by Means of Constitutive Modelling
Authors: Kiliclar Yalin , Engelhardt Marcus , Vladimirov Ivaylo N. , Pietryga Michael P. , von Senden genannt Haverkamp Hermann , Reese Stefanie , Bach Friedrich Wilhelm
Published: February 2012

Sheet metal forming processes are well-established in production technology for the manufacturing of large quantities. To increase the formability, the processing limit of a single forming process can be enhanced by a combination of quasi-static and high-speed forming process. The forming limits for both operations for the aluminum alloy EN AW 6082 T6 obtained via simulations and experiment are investigated in a research cooperation between the Institute of Materials Science (IW) and the Institute of Applied Mechanics (IFAM). Significant changes in forming limits with higher strain rates are indicated by the experimental results. Here, the forming limit curves move to the lower right hand side. The processes are simulated and the FLD at fracture are predicted by means of finite element analysis. The constitutive model is based on the multiplicative split of the deformation gradient. It is coupled with ductile damage and combines nonlinear kinematic and isotropic hardening. The kinematic hardening component represents a continuum extension of the classical rheological model of Armstrong–Frederick kinematic hardening. The coupling of damage and viscoplasticity is carried out following the well-known concept of effective stress and the principle of strain equivalence. Using these powerful tools the simulation of dynamic effects and the prediction of forming limit diagrams at fracture shows good correlation with the experiments.
Manufacturing Processes for Combined Forming of Multi-Material Structures Consisting of Sheet Metal and Local CFRP Reinforcements
Authors: Schmidt Hans Christian , Damerow Ulf , Lauter Christian , Gorny Bernhard , Hankeln Frederik , Homberg Werner , Troester Thomas , Maier Hans Jürgen , Mahnken Rolf
Published: February 2012

A new and promising approach to the reduction of greenhouse gas emissions is the use of improved lightweight constructions based on multi-material systems comprising sheet metal with local carbon fibre reinforced plastic (CFRP) reinforcements. The CFRP is used to reinforce highly stressed areas and can be aligned to specific load cases. The locally restricted application of CFRP means that the material costs can be effectively reduced by comparison to parts made entirely of CFRP on account of the expensive production process requiring the use of an autoclave. These parts are thus only used in high-priced products. The production of hybrid CFRP steel structures in a mass production process calls for an efficient production technology. Current research work within the scope of a collaborative research project running at the University of Paderborn is concentrating on the development of manufacturing processes for the efficient production of automotive structural components made up of sheet metal blanks with local CFRP patches. The project is focusing especially on basic research into the production of industrial components. The aim of the investigation is to create an efficient and controlled process for producing CFRP reinforced steel structures from semi-finished hybrid steel-CFRP material. This includes tool concepts and an appropriate process design to permit short process times. The basis of an efficient process design is an in-depth knowledge of the material behaviour, and hence a thorough characterisation was performed. Material parameters were determined for both simulation and forming. For this, monotonic tensile, shear and bending tests were conducted using both uncured prepregs and cured CFRP specimens. To achieve an accurate simulation of the forming process, a special material model for carbon fibre prepregs has been developed which also includes the anisotropic material behaviour resulting from fibre orientation, the viscoelastic behaviour caused by the matrix and the hardening effects that prevail during curing. Recent results show good qualitative agreement and will be presented in this paper. In order to control the properties of the hybrid components, four different tool concepts for the prepreg press technology have been developed and tested. The concepts are presented and the results of experimental investigations are discussed in this paper.
Forming Simulation Sensitivity Study of the Double-Dome Benchmark Geometry
Authors: Rietman Bert , Haanappel Sebastiaan P. , ten Thije René H.W. , Akkerman Remko
Published: February 2012

Simulations of manufacturing processes are of utmost importance in order to check on process feasibility of composites products already during the design phase. In order to benchmark the different software for (thermo)forming simulations of textiles and composites a benchmark geometry was agreed during previous Esaform conferences. Round 2 results have led to the insight that a stronger definition of the benchmark was needed, see [1]. The geometry, referred to as double-dome, combines doubly curved regions with steep walls and small radii. Therefore it may be considered critical with respect to forming behavior. As testing material a Twintex comingled glass/PP both as plain and twill weave woven fabric were chosen [2]. This paper addresses the simulation of the double-dome with the finite-element software Aniform. Shear angles, draw-in and the possible presence of wrinkles will be taken into account and compared to round 2 results of other participants. Additionally, a numerical sensitivity study of material and process parameters will be presented in order to identify major influences on the forming results. The paper concludes with a number of recommendations for further research as well as possible improvements for numerical modeling. [1] Sargent et.al., “Benchmark study of finite element models for simulation the thermostamping of woven-fabric reinforced composites”. Proceedings of the 13th Esaform Conference, Brescia 2010. [2] Cao et.al., “Characterisation of mechanical behaviour of woven fabrics: experimental methods and benchmark results”, Composites Part A: Applied Science and Manufacturing, 2008.
Tailored Heat Treated Profiles - Enhancement of the Forming Limit of Aluminum Profiles under Bending Load
Authors: Merklein Marion , Lechner Michael , Schneider Thomas , Plettke Raoul
Published: February 2012

Aluminum profiles are well-established components in lightweight constructions. However, these profiles have a small forming capability in comparison to steel profiles, which leads to a limitation in their application. Within this paper a new and innovative approach for the enhancement of the forming limit of aluminum profiles under bending load called Tailored Heat Treated Profiles (THTP) is presented. With THTP the mechanical properties of the material are locally modified by a short-term heat treatment. By this local modification the material flow during the following cold bending operation can be influenced. For the design of the heat treatment layout, the correlation between the heat treatment parameters and the material properties has to be investigated. Tensile specimens were cut out of the profile and were subsequently completely heat treated with a laser. The changes of the mechanical properties caused by the heat treatment were analyzed by tensile tests. However, with a complete softening of the profile, the formability could not be improved. To increase the formability a local heat treatment, which leads to partial softening of the profile, has to be investigated. In order to characterize the heat-affected zone (HAZ) of the laser treatment, thermal camera and microhardness measurements were carried out. Appropriate heat treatment layouts have to be found to enhance the forming limit. Different layout strategies were developed and afterwards validated by the heat treatment and forming of profiles. This paper will present the findings of this investigation and show that THTP can be used to improve the formability of aluminum profiles for bending operations.
Analytic Prediction of the Process Parameters for Form-Fit Joining by Die-Less Hydroforming
Authors: Gies Soeren , Weddeling Christian , Marré Michael , Kwiatkowski Lukas , Tekkaya A. Erman
Published: February 2012

The Commission of the European Communities aims for a reduction of new car CO2 emissions of 120 grams per kilometer in 2012. As a result of the omnipresent efforts of the automotive industry to hit these tighter emission standards innovative lightweight strategies, e.g. the use of lightweight materials are developed. This entails new joining techniques that are appropriated to the new lightweight materials. The die-less hydroforming process is a joining method for tubular joints which meets the new demands of lightweight strategies. Since there is no need for any additional connection elements or filling material, it is an interesting alternative to conventional welding and riveting processes. The present paper describes the basic principle of the die-less hydroforming joining technology with a special focus on form-fit connections. An analytical model, based on the membrane theory with an additional local consideration of bending stresses is developed. This analytic approach can be used to calculate the working fluid pressure, required to bulge the tube material into the groove of the outer joining partner. Taking into account the material parameters as well as the groove and tube geometry, this model allows a reliable process design. Additionally, validation of the model by experimental investigations will be provided.
Free Surface Modeling of Contacting Solid Metal Flows Employing the ALE Formulation
Authors: van der Stelt A.A. , Bor T.C. , Geijselaers Bert , Akkerman R. , Huétink J.
Published: February 2012

In this paper, a numerical problem with contacting solid metal flows is presented and solved with an arbitrary Lagrangian-Eulerian (ALE) finite element method. The problem consists of two domains which mechanically interact with each other. For this simulation a new free surface boundary condition is implemented for remeshing of the boundary elements. It uses explicitly that the integral of the convective velocity along a boundary element remains zero. Steady state solutions are obtained only if the integral of the convective velocities along each free surface boundary element remains zero. The new remeshing option for the free surface is tested on a cladding problem employing friction stir welding (FSW). The problem describes two elasto-viscoplastic aluminum material flows which mechanically interact.
Real Time Simulation of Non-Linear Solids by PGD Techniques
Authors: Niroomandi Siamak , Gonzalez David , Alfaro Iciar , Bordeu Felipe , Leygue Adrien , Cueto Elías , Chinesta Francisco
Published: February 2012

We analyse here how Dynamic Data Driven Application Systems (DDDAS) can constitute a valuable tool in the field of forming processes. Simulation tools in the field of DDDAS are required to provide a response in real-time, a requisite that is often too severe for complex problems. Here, we consider that of hyperelasticity, commonly used in different fields such as rubber manufacturing or surgery, for instance. We analyse here how model reduction techniques, and particularly Proper Generalized Decompositions (PGD) methods can provide a suitable response to the strong requirements posed by DDDAS. We will consider two different approaches to the problem. The first one is an explicit approach that nevertheless provides with good results. The second one is based on the use of Asymptotic Numerical Method.
Identification of Process-Based Limit Stress States Applying a Stretch-Bending-Test
Authors: Hezler Christian , Merklein Marion , Hecht Joachim , Griesbach Bernd
Published: February 2012

The evaluation of forming simulation by using the forming limit curve has only limited validity if it is applied on car body components with non-linear strain paths. If modern high strength materials are used, the forming limit criteria can also provide invalid predictions. Especially high strength multiphase steels show a specific behaviour in forming, necking and crack initiation. If bending loads are applied to these materials, the onset of cracking occurs partially not within the range of the forming limit curve (FLC). The stress limit indicates the failure beginning more accurate. It is independent of the forming history and should be less sensitive to the behaviour of high strength steels. In the post processing of a simulation it could be used similar to the forming limit. A limit curve applied on the in-plane-stress-diagram of an analysed component defines areas that are more vulnerable for cracking. The required stress limit curve will be obtained in this research by applying a stretch-bending-test. It is selected in order to reach loads, which are comparable to the forming process in the components’ production. The forming state that is affecting the specimen is a combination of bending and stretching load. Different load conditions can be applied at the test by altering the stamp-radius and the specimen geometry. Since stresses cannot be measured directly in the experiment, the test is modelled in the simulation where the stresses can be calculated for a given material model. Finally the stress limit criterion was applied on the test parts’ stress distribution diagram. Occurring stresses above the stress limit curve are displayed on the simulation. Thereby it is possible to show a good correlation in critical areas between the failure prediction in the simulation and occurring rupture on the test component.
Metal Flow in Two-Hole Extrusion of Al-Alloys Studied by FEA with Experiments
Authors: Kandis Janis , Valberg Henry
Published: February 2012

Forward two-hole extrusion of Al has been investigated with the purpose of studying how metal flow inside the billet is influenced by the location of the holes in the dies, i.e. whether they are position near to or far apart from each other. The study has been conducted by means of finite element analysis (FEA) using the software DEFORM 3D® and validation of simulation results are done by comparison with grid pattern experiments performed long time ago by one of the authors. The analysis shows that the experimental conditions are well reproduced by FEA. New insight into the metal flow phenomena in two-hole extrusion is also gained thanks to the analysis. It is shown, for instance, that moving the holes far apart from each other brings about a distinct shift in the metal flow. The deformations subjected to the peripheral outer shear zones of the billet material then become much more localized than when the two holes are close.
Comparison between FEM Simulations and Analytical Calculations of Required Force for Al Extrusion
Authors: Torabzadeh Khorasani Sepinood , Valberg Henry
Published: February 2012

In this study the cold extrusion of Al alloys will be investigated by finite element analysis (FEA) using DEFORM 2D. Besides, theoretical calculations to find the required extrusion force will be done. Several FE-simulations have been performed for two different extrusion geometries and for different conditions of friction including high and low friction, to quantify the influence of friction on the extrusion force. The results from FEA and theory for cold extrusion are compared to see if there is good agreement. The correlation between the data obtained by theory and FEA is discussed.
Effect of Porthole Design and Welding Chamber Dimensions on Material Flow and Weld Deformability of Extruded Aluminium Profiles
Authors: Donati Lorenzo , Ben Khalifa Nooman , Tomesani Luca , Tekkaya A. Erman
Published: February 2012

Aim of the work is to investigate different strategies in balancing material flow during direct extrusion through porthole dies. Two AA6082 hollow profiles were simultaneously extruded by a single die with different portholes extrusion ratio, dissimilar welding chambers and different bearing lengths. A strict process control was realized by measuring thermal conditions in the die by means of 6 thermocouples and on the profiles by a self calibrating pyrometer for aluminum alloy applications. Several billets were extruded at different ram speeds (2 to 7 mm/sec) and the effect of die design on surface quality, profile lengths and thermal field was recorded. The profiles were then sectioned and the position of the seam welds in the profiles identified and compared also with the profiles tip.
Determination of Flow Curves under Equibiaxial Stress Conditions
Authors: Mulder J. , Vegter Henk , Ha Jin Jin , van den Boogaard Ton
Published: February 2012

Three experimental methods have been used to establish flow curves for a low carbon steel under biaxial stress conditions: the hydraulic bulge test, the stack compression test and the biaxial tensile test. The individual tests are discussed and the results for a DC06 IF steel grade compared. Initially the results appear to be different but after compensation, including strain rate and temperature correction, the true hardening curves are coinciding.
Frictional Behaviour of Environmentally Friendly Lubricants for Sheet Metal Forming Processes
Authors: Sgarabotto Francesco , Ghiotti Andrea
Published: February 2012

In last decades, national legislations have become even more restrictive with respect to the application and the disposal of hazardous lubricants in sheet metal forming. The introduction and the continuous improvement of environmental friendly solutions has seen a continuous growth and attention, but today the usage of traditional hazardous lubricants is still significant, requiring expensive cleaning operations and harmful cleaning agents to remove them. The use of solid organic lubricants can reduce or eliminate this drawback, despite their performances may be significantly affected by specific process parameters and the presence of debris. In this paper the performances of a solid organic lubricant have been compared to traditional liquid lubricants applied to sheet metal forming applications. Different surface topographies have been reproduced and the effects in terms of frictional behaviour have been investigated.
Benchmarking of Direct and Indirect Friction Tests in Micro Forming
Authors: Eriksen Rasmus Solmer , Calaon M. , Arentoft Mogens , Bay Nils
Published: February 2012

In this study the application of a simulative sliding friction test at micro scale is suggested. Two work piece specimens are upset against opposing sides of a flat tool element. The tool element is then pulled out while the resulting friction force F is measured. The test principle offers several advantages when compared against the DEC-test, including easy visual inspection of tool and work piece surfaces, continuous measurement of friction coefficient over the complete sliding length and less sensitivity to mechanical tolerance deviations of work piece and tool elements.
Prediction of Texture Evolution in Rolled Sheet Metals by Using Homogenization Schemes
Authors: Jöchen Katja , Böhlke Thomas
Published: February 2012

This work deals with comparing the prediction of the development of rolling textures by using a homogenization method that is based on a homogeneous reference material. The proposed homogenization scheme, assuming constant stress polarisations in each phase, has in a natural way the potential to model the transition between Taylor- and Sachs-type textures. Therefore, the stiffness ef the hemogeneous reference material has to be varied between infinitely stiff and infinitely compliant. In the present study, texture evolution during rolling is simulated, showing that the application of different comparison materials in the homogenization scheme leads to the development of different main texture characteristics (Cube, Cu, Bs, Goss) in the orientation distribution function. For efficiently carrying out the rolling simulations using the proposed method, the measured texture information of the bulk aluminum sample is representatively reduced by using a partitioning technique of the orientation space.
Unconditionally Convex Yield Functions for Sheet Metal Forming Based on Linear Stress Deviator Transformation
Authors: Aretz Holger , Barlat Frédéric
Published: February 2012

Two non-quadratic orthotropic yield functions called Yld2011-18p (containing 18 param-eters) and Yld2011-27p (containing 27 parameters) are proposed. The formulations are based on theestablished concept of linear transformations operating on the stress deviator. Application examplesreveal the capabilities of both yield functions to accurately describe complex plastic anisotropy ofsheet metals.
Smart Components through Rotary Swaging
Authors: Brenneis Matthias , Groche Peter
Published: February 2012

The parts of smart components consisting of structural and smart materials are conventionally produced separately and assembled in additional processes afterwards. An alternative approach to combine the forming of metallic parts and the assembly of components in one process step is proposed in this paper. Numerical and experimental investigations are carried out to investigate the influence of the axial clamping of the tube during the integration of a ring part through rotary swaging. The experiments also demonstrate the producibility of smart components by incremental forming processes without damaging the sensitive functional parts, which is proven by a functioning test.
Process Mechanics in Friction Stir Welding of Magnesium Alloys: Experimental and Numerical Analysis
Authors: Buffa Gianluca , Fratini Livan , Gnibl Tobias , Wieland Michael , Merklein Marion
Published: February 2012

Light weight construction is a major task within automotive and aircraft industry due to lower fuel consumption or increase the possible payload. Structural or exterior shell components are more and more manufactured out of aluminum alloys for this reason. A further weight reduction could be achieved by the substitution of aluminum alloys by magnesium alloys. Also the application of blanks with a varying thickness is a possibility to realize light weight design. To combine the advantages of weight reduction by the use of magnesium alloys and tailored welded blanks (TWBs), an effective joining technique is required. Friction Stir Welding can be used for difficult to be welded magnesium alloys to manufacture magnesium TWBs. During this process the different thickness of the two sheets can cause an unequal heat distribution below the tool, affecting material flow and therefore components strength. In the paper the main results of a numerical and experimental campaign on Friction Stir Welding of AZ31 magnesium alloy tailored blanks are presented. The numerical simulation was validated by experimental observations and the occurring bonding conditions have been analyzed in both approaches.
Comparison of Bending of Automotive Steels in Roll Forming and in a V-Die
Authors: Weiss Matthias , Marnette Jascha , Wolfram Preston , Larrañaga Jon , Hodgson Peter D.
Published: February 2012

Bending in a V-die has been used to indicate the outcome of bending in cold roll forming, although little direct correlation has been performed. In this work direct comparison of the springback in both processes was performed using six samples of automotive steels in a conventional roll forming line where the transverse springback is measured. A bend of similar radius was formed in a V-die and the springback determined. In general, the springback in V-die forming was greater than in roll forming, in some cases by a factor of 2. The theoretical springback angle was determined for all steels using a simple and approximate analytical equation and compared to the experimental roll forming and bending results. While for the roll forming process good agreement was achieved the theoretical values significantly underestimated springback in the V-bending process.
Influence of Predetermined Surface Defect to the Bendability of Ultra-High-Strength Steel
Authors: Määttä Antti , Järvenpää Antti , Jaskari Matias , Mäntyjärvi Kari , Karjalainen Jussi A.
Published: February 2012

The use of ultra-high-strength steels (UHS) has become more and more popular within last decade. Higher strength levels provide lighter and more robust steel structures, but UHS-steels are also more sensitive to surface defects (e.g. scratches). Practically this means that the critical crack size decreases when the strength increases. The aim of the study was to study if the formula of critical crack size is valid on forming processes of UHS-steels. Surface cracks with different depths were created by scratching the surface of the sheet by machining center. Effect of the scratch depth was determined by bending the specimens to 90 degrees. Bents were then visually compared and classified by the minimum achieved bending radius. Test materials used were direct quenched (DQ) bainitic-martensitic UHS steels (YS/TS 960/1000 and 1100/1250). Results from the bending tests were compared to the calculated values given by the formula of critical crack size.
A New Tool Concept for Rotary Peen Forming with Defined Impact Positions
Authors: Russig Christoph , Bambach Markus , Hirt Gerhard
Published: February 2012

Rotary peen forming (RPF) has been developed as a new peen forming process in which the shot is held by a flexible connection and moved on a circular trajectory (see Fig. 1 below). The main advantage compared to a traditional shot peen forming (SPF) processes is that RPF does not need refeed of shot particles. Hence, RPF offers a compact machine design and a flexible use. The RPF process causes localized plastic deformation just as in traditional shot peen forming but involves tangential components which can create shear deformation in the plastic layer. These tangential components depend on the connection used for the setup. Compared to traditional shot peen forming, RPF shows different process characteristics in terms of coverage and the shape of indentations created on the surface of the workpiece. In this paper, a new tool concept for rotary peen forming is evaluated using experiments and numerical investigations of the process. The set-up uses a spring-attenuator system, which leads to more deterministic impact positions than previously used wire-based impactor concepts.
Goal Oriented Error Control for Frictional Contact Problems in Metal Forming
Authors: Blum Heribert , Rademacher Andreas , Schröder Andreas
Published: February 2012

In this note, techniques for goal oriented error control of finite element discretizations are proposed for frictional contact problems. The finite element discretization is based on a mixed method, where Lagrange multipliers are introduced to capture the geometrical and frictional contact conditions. A posteriori error estimates for user-defined, probably non-linear quantities of interest are derived using the dual weighted residual method (DWR). Numerical results substantiate the applicability of the presented techniques to the simulation of metal forming processes.
Grain Boundary Embrittlement and De-Embrittlement in Age Hardenable Iron Alloys
Authors: Heo Yoon Uk , Lee Hu Chul
Published: February 2012

Grain boundary embrittlement and de-embrittlement observed in age hardening iron alloys were reviewed. Fe-Mn-Ni and Fe-Ni-Ti alloys show excellent hardening response during aging treatment. However these alloys all suffer grain boundary embrittlemnt and show no tensile ductility even after very short aging treatment. Precipitation of intermetallic phases, θ-MnNi in Fe-Mn-Ni alloys and η-Ni3Ti in Fe-Ni-Ti alloys, at grain or lath boundaries was suggested as the reason for the weakening of grain boundary strength. Grain boundary strength recovered when these precipitates transform to austenite after extended aging. Dislocation glide or dislocation climb did critical role in conversion of these grain boundary precipitates to austenite.
Production of DMR 249A Steel at SAIL, Bokaro Steel Plant
Authors: Mallik Subrata , Minz Biswasi Sunita , Mishra Basudev
Published: February 2012

Low alloy steels are an attractive option for high performance structural applications due to cost and availability factors. A low carbon low alloyed steel, DMR 249A, was developed for strategic applications by Indian Navy at Steel Melting Shop II, Bokaro Steel Plant (SMS II, BSL). This paper enumerates the detail process variables modified for this development. DMR 249A grade was having the specified gas contents of hydrogen <2 ppm in final product for the avoidance of detrimental phenomenon like “Hair Line Cracks”. So the Hydrogen content of liquid steel was to be less than 3 ppm and this demand vacuum treatment of the steel. In absence of any Degassing unit at SMS II, BSL, making of DMR 249A steel was a challenging task. The hydrogen content of steel was controlled through restriction of hydrogen in input raw materials, control in degree of deoxidation during tapping, slag basicity at ladle furnace, argon rinsing regime and cooling of slabs i.e. control over diffusion of H2. The steel was produced with the existing infrastructure at Bokaro Steel Plant with various alloying elements and processed suitably to obtain the desired yield strength, toughness and gaseous content. The control was exercised at various stages of steel making and hot strip rolling to enable achievement of a higher degree of consistency in mechanical properties and microstructure. Quality fulfillment was a great challenge without vacuum degasser unit but Bokaro successfully made the steel with 100% customer satisfaction.
Manufacturing of Inconel 718 Based Honeycomb Panels for Metallic Thermal Protection Systems
Authors: Baluragi Hanamantray , Anil Kumar V. , Narasaiah K. , Gopinath Shibu , Sinha P.P.
Published: February 2012

Metallic thermal protection system (MTPS) offers significant improvements over the ceramic based TPS for reentry applications. Space shuttle refurbishment time is estimated to be around 17000 man hours between flights. Metallic based TPS can be fabricated easily and provides wide range of design options for TPS. Adaptability and robustness of metallic thermal protection systems offers the potential for reusability. In this work, a unique manufacturing process has been evolved to realize light weight honeycomb panels through corrugation, laser welding and diffusion brazing of faceplates, where in 50 micron thick Inconel718 foil is used for making honeycomb core and 0.2mm thick Inconel718 foil as faceplates. The compression and three point bend test on these panels have shown no debond between faceplates and honeycomb core. 150x150x5mm size honeycomb panels were coated with YSZ and NiCrAlY based Thermal Barrier Coatings (TBC) and high temperature tests have shown thermal resistance of around 570 °C with front wall temperature of 1186 °C and back wall of 533 °C. Also these panels have been characterized for reusability by the testing of same panel at different heat flux levels. Though it is found that honeycomb panel has shown its integrity without debond a certain acceptable level of degradation in coating is observed. Thus Inconel718 based honeycomb panels with TBC coating are proved for use as thermal protection system for reusable launch vehicle systems.