bluuebunny/crossref_metadata_2025 huggingface dataset:
Effect of Moisture on the Behaviour of an Extruded Clay Paste
Authors: Vignes Jérémie , Schmidt Fabrice , Dusserre Gilles , Dalmasso Jean Frédéric
Published: June 2013

In the industrial process, the moisture of the clay sheet obtained by extrusion and pressed to form a tile varies in time. It depends on the nature and the mixing of the raw materials during the production. In order to model and undersand the influence of the moisture on the pressing step, it is necessary to determine the parameters of the rheological and tribological laws. A study of the rheological behaviour, based on free compression tests on cylinder samples, allowed to use an elasto-visco-plastic behaviour for the extruded clay paste. The different constitutive parameters were estimated by an inverse analysis based on the experimental force/displacement curves. The identification was performed with the optimisation algorithm implemented in the commercial software Forge® 2009. The influence of the water content in the paste on the rheological parameters was identified and fitted using linear models. The friction factor was measured from tests on a rectilign tribometer. To understand the influence of the moisture, we simulated a compression test, using Forge® involving the shaping of a tile lug. This geometry is representative of the state of stress during the pressing of the tile, in an area currently sujected to defects. The numerical model show that an increase of eighteen percent of the moisture allows to decrease by half the pressing force.
Earing Prediction in Drawing and Ironing Processes Using an Advanced Yield Criterion
Authors: Barros Pedro Daniel , Oliveira Marta C. , Alves José Luis , Menezes Luis Filipe
Published: June 2013

This work aims to contribute to the understanding of the role/influence of advanced yield criteria on the earing profile prediction after drawing and ironing, for a cylindrical cup benchmark proposed at the NUMISHEET 2011 conference [1]. Two typical materials used for can-making were considered and studied: an AA5042 aluminum alloy and an AKDQ steel. The drawing and ironing operations are performed on a special die which allows drawing and ironing in one single punch stroke in order to simplify the real process. The benchmark results report include, for each material: (i) the earing profile after drawing and ironing, presenting the cup height evolution with the angle from the rolling direction, and (ii) the evolution of punch force with punch stroke. This work presents a comparison between experimental and numerical results obtained for the aforesaid benchmark with DD3IMP in-house solver, using two sets of parameters for the Cazacu and Barlat 2001 [2] yield criterion, identified based on uniaxial tensile, equi-biaxial tension and disc compression test results. The first set uses the initial yield stress values while the second one used the flow stress values for an accumulated plastic work of 20 MPa. The results highlight the different impact of the experimental data in the earing prediction for both materials: the results for the second set are slightly improved for the AKDQ steel while for AA5042 the effect is negligible. The improved earing prediction obtained with the second set for the AKDQ steel seems to result from a better description of the stress states that occur in the flange zone.
Optimization Analysis of A7075 Bicycle Stem Forging Process
Authors: Chen Dyi Cheng , Shiu Jiun Ru , Lin Jheng Guan
Published: June 2013

This research analyzes an innovative forging mold design for the various bicycle stem. The paper used the rigid-plastic finite element analysis software and structural analysis to investigate the plastic deformation behavior of aluminum alloy A7075 workpiece for forging process. Under various forging conditions, it analyses the effective strain, the effective stress, the temperature changing, surface pressure, mold radius load distribution, stress analysis of billet and mold. Moreover the paper used the Taguchi method combine the algorithm method of artificial neural network to find out the best design parameters. The paper hoped to offer some tolerance um precision forging manufacture knowledge for industry.
Analysis of Incremental Sheet Forming Parameters and Tools Aimed at Rapid Prototyping
Authors: Silva Pablo J. , Leodido Leonardo M. , Silva Cosme Roberto Moreira
Published: June 2013

The incremental sheet forming allows the production in high quality of extremely complex pieces of steel, aluminum, titanium and many other materials, in order to reduce time and costs of production and cost of tooling used in low production. Working with tools of various diameters and a suitable machine programming is possible to produce complex parts of small lots in few hours, which in conventional stamping process would take days. This paper aims to introduce process parameters and analyze results from practice tests and computational analysis by changing the rotation, advancement in XY and Z advancement, tooling options, fixture plate and forming tool for producing pieces of varying size and complexity in the shortest time and at the highest quality possible. Thus, presents the incremental sheet forming as an alternative for rapid prototyping, as well as its devices and tools.
Improving Surface Based Clamping Simulations by Measuring the Position of Active Surfaces during the Clamping Process
Authors: Drossel Welf Guntram , Wahl Martin , Schulz Frank , Mauermann Reinhard , Schützle Wilhelm , Ackert Patrick
Published: June 2013

The manufacturing process of body parts starts with the step of sheet metal forming. The single parts, produced at the press shop, are put into clamping devices in order to align and to fix them. The fixation takes part before further operations like joining can be carried out. In order to simulate the process chain of add-on body parts realistically, the clamping process (closing the clamping device) has to be taken into account. The stationary surfaces of a clamping device are called passive and the moveable surfaces are called active surfaces. If the clamping process is calculated by means of active surfaces, their positions need to be measured in the state of a closed clamping device. While the passive surfaces of a body construction device can be measured with high reproducibility, the measurement of active surfaces in the state of a closed device is impracticable because of the loss of accessibility. Furthermore, if the parts to be clamped or the position of the clamping device differ from their designed position, the assembly works like a flat spring against the clamping device force in all spatial directions. The active surface does not reach the position which was measured before. In order to take these facts in clamping simulations into account, the end position of the active surfaces should be known. A clamping device concept on the basis of a measuring probe for optical measurement systems was developed. It is possible to determine the position of active surfaces with high reproducibility while the parts are clamped. It can be shown, that the presented clamping device concept contributes to significantly better results of clamping simulations. Thus a better starting basis for further simulations along the process chain is offered.
Simulation of Electromagnetic Forming of a Cross-Shaped Cup by Means of a Viscoplasticity Model Coupled with Damage at Finite Strains
Authors: Kiliclar Yalin , Demir O. Koray , Vladimirov Ivaylo N. , Kwiatkowski Lukas , Reese Stefanie , Tekkaya A. Erman
Published: June 2013

In the field of sheet metal forming traditional forming processes are used. However, a quasi-static forming process combined with a high speed forming process can enhance the forming limits of a single one. In this paper, the investigation of the process chain quasi-static deep drawing – electromagnetic forming by means of a new coupled damage-viscoplasticity model for large deformations is performed. The finite strain constitutive model, used in the finite element simulation combines nonlinear kinematic and isotropic hardening and is derived in a thermodynamically consistent setting. The anisotropic viscoplastic model is based on the multiplicative decomposition of the deformation gradient in the context of hyperelasticity. The kinematic hardening component represents a continuum extension of the classical rheological model of Armstrong–Frederick kinematic hardening. Hill-type plastic anisotropy is modelled by expressing the yield surface as a function of second-order structure tensors as additional tensor-valued arguments. The coupling of damage and plasticity is carried out in a constitutive manner according to the effective stress concept. The constitutive equations of the material model are integrated in an explicit manner and implemented as a user material subroutine in the commercial finite element package of LS-Dyna with the electromagnetical modul. Aim of the work is to show the increasing formability of the sheet by combining quasi-static deep drawing processes with high speed electromagnetic forming process.
Multi-Scale Modeling of Microstructure Evolution Induced Anisotropy in Metals
Authors: Yalcinkaya Tuncay
Published: June 2013

This paper presents two crystal plasticity based computational constitutive models for the intrinsic formation of plastic microstructure during monotonic loading and its altered evolution under strain path changes in metal forming operations. The formation step is modeled via a non-convex strain gradient crystal plasticity framework which could simulate the intrinsic development of the plastic microstructures. The evolution under strain path changes is modeled via phenomenologically based constitutive equations incorporated into crystal plasticity framework. The latter is capable of simulating the transient anisotropy effects (e.g. cross hardening, Bauschinger effect) depending on the change in the strain path. The paper discusses the unification of such models for the continuous modeling of microstructure formation and evolution processes.
Influence of Anisotropic Yield Functions on Parameters of Yoshida-Uemori Model
Authors: Kano Hirotaka , Hiramoto Jiro , Inazumi Toru , Uemori Takeshi , Yoshida Fusahito
Published: June 2013

Yoshida-Uemori model (Y-U model) can be used with any types of yield functions. The calculated stress strain response will be, however, different depending on the chosen yield function if the yield function and the effective strain definition are inappropriate. Thus several modifications to Y-U model were proposed in the 10th International Conference on Technology of Plasticity. It was ascertained that in the modified Y-U model, the same set of material parameters can be used with von Mises, Hill’s 1948, and Hill’s 1990 yield function. In this study, Yld2000-2d and Yoshida’s 6th-order polynomial type 3D yield function were examined and it was clarified that the same set of Y-U parameters can be used with these yield functions.
Development of a Damage Prediction System for Bending and Cutting of High Strength Steels
Authors: Vatter Peter Horst , Hildering Sven , Tsoupis Ioannis , Merklein Marion
Published: June 2013

Abstract. The application of modern high strength low alloyed steels (HSLA) and advanced high strength steels (AHSS) for structural and safety relevant components in the automotive industry offers the advantage of combining low specific weight with high material strength. Typical manufacturing processes for these steel grades are bending and cutting operations. The forming and cutting potential of these innovative steel grades is different to conventional steels as the process and the damage behaviour is changing. In bending operations cracks occur at the outer bending edge, whereas in cutting operations delamination can appear at the sheared edge. These damages, even though they are small, can initiate the component to fail. For a reliable use of such materials in industrial application a method for the process design is essentially needed. In particular, damages have to be predicted at an early stage. In industrial application damage is detected by a trial-and-error approach causing significant work and a high failure rate. A system for an offline assessment of the risk of failure is unknown so far. In the scope of this work, a method is presented to describe the damaging behaviour of both, bending and cutting operations, by theoretical metamodels. In order to generate a database experiments were carried out using different high strength steels. The main influence factors have been varied, such as the rolling direction, the punch-to-die clearance and the cutting contour in the cutting operation. The bending was investigated using an air-bending process varying the bending angle, the bending radius and the rolling direction. To calculate further sampling points a finite element model has been developed and validated against the experimental data. The damage criterion of Lemaître has been applied. The necessary parameters were determined by reverse identification by means of the major strain for the bending operation and by the punch force-punch stroke curve for the cutting operation. To build up a system for the prediction of the damage the gained data basis was approximated by mathematical functions. An error analysis was carried out showing good accordance. In doing so, a metamodel for the occurrence of damages could be established. The functions are implemented in a software tool which allows the user to determine the failure probability for a given parameter set.
Application of Combined Casting-Forging Process for Production of Durable Lightweight Aluminum Parts
Authors: Dedov Stanislav , Lehmann Gunter , Kawalla Rudolf
Published: June 2013

Due to the constant development in the automotive industry, where high performance shared with the maximal comfort and safety at low car body weight are the primary goals, gains the lightweight construction in importance. Materials with light weight, high strength and toughness are being engaged. With this background the material aluminum and its alloys become highly attractive to manufacturers. There are mainly two ways of forming the metal materials: casting or forming. Apart from substitution of one method by another there are also many examples of combining of casting and forging processes in practice. Such approach allows using the advantages of both methods, shortening the process chains and saving energy and resources at the same time. Furthermore the form flexibility can be increased and the product quality can be improved. For higher process efficiency a direct transition from casting to forging operation should be applied, so that the heat loss decreases and no additional heat treatment between these operations is necessary. There are processes known, which allow producing the final parts by casting and forging from one a single heat. The application of such processes requires materials, which have simultaneously good casting and forging properties. The Institute of Metal forming TU Freiberg works intensively on development of combined casting-forging technologies for lightweight aluminum parts. A technological chain for this coupled process followed by precipitation hardening heat treatment was developed (Figure 1). Heat treatable aluminum cast and wrought alloys with 1 – 7 % silicon were applied. By the variation of silicon content the optimal cast, forging and hardening properties were achieved. This technology with high energy efficiency allows producing durable light weight parts from aluminum alloys while the mechanical properties of the final parts are equal to or even higher than those in the conventional processes.
Die and Process Design for Hot Forging of a Gear Wheel – A Case Study
Authors: Henke Thomas , Bambach Markus , Hirt Gerhard
Published: June 2013

Gearing components are an example for widely used machining parts in engines. Nowadays the development and optimization of materials and process chains are driven towards a concurrent improvement of final product properties and production efficiency. Excellent mechanical properties needed for gearing components e.g. high load capacity and high fatigue resistance depend on a fine homogeneous microstructure in the final product. Efficiency in gear manufacturing can be optimized by increasing the temperature during processing, which allows for lower forging loads and lower die stresses, thus improving die life in terms of mechanical fatigue. Additionally, increasing the temperature during case hardening reduces the process duration significantly. Hence process efficiency also increases. To meet the need of a fine homogenous microstructure, dynamic recrystallization has to be initiated during hot forging and grain growth has to be avoided during dwell times and case hardening. This grain size control can be achieved by applying micro-alloying concepts. Recently, an Nb-Ti-based alloying concept for case hardening steels was introduced, which increases fine grain stability and therefore potentially allows for higher forging and case hardening temperatures, leading to improved process efficiency [1]. In this paper a 25MoCr4-Nb-Ti steel grade is characterized in terms of flow resistance and microstructure evolution by hot compression tests and annealing experiments. The processing limits of this material in terms of abnormal grain growth are determined and a JMAK-based microstructure model considering these limits is presented and implemented in the FE-Software DEFORM 3dTM. The model is used in a case study to design a laboratory scale forging process for lowest possible die stresses and finest possible grain sizes. Experimentally measured grain sizes and forging loads from forgings at the laboratory scale are used to evaluate the process design. It is shown that considering microstructure evolution in process design is absolutely necessary to jointly optimize for process efficiency and final properties. The application of the Nb-Ti-based micro-alloying concepts allows for lower die stresses and thus seems to reduce mechanical fatigue of the dies compared to conventional case-hardening steels. [1] S. Konovalov et. al.: Testcase gearing component. In: G. J. Schmitz, U. Prahl (Ed.): Integrative Computational Materials Engineering, Wiley-VCH Verlag GmbH & Co. KGaA, 2012, ISBN 978-3-527-33081-2
Accurate Evaluation Method for the Hydraulic Bulge Test
Authors: Mulder J. , Vegter Henk , Aretz Holger , van den Boogaard Ton
Published: June 2013

Optical measuring systems provide much more detail on the deformation of the blank in the bulge test than conventional contact height measuring systems. A significant increase in accuracy of the stress-strain curve can be achieved by fitting the surface to more complicated equations than the traditional spherical surface and by considering the local strain data to approximate the curvature for the midplane. In particular an ellipsoid shape is shown to be very accurate in describing the surface of the blank. Contact height measuring systems provide insufficient data to fit a surface to an ellipsoid shape and to establish local strain data. Pragmatic equations are proposed using the work hardening coefficient from the tensile test to approximate the same accuracy in stress-strain curves as obtained by optical measuring systems using the before mentioned evaluation method.
Beta Forging of Ti-6Al-4V: Microstructure Evolution and Mechanical Properties
Authors: Astarita Antonello , Ducato Antonino , Fratini Livan , Paradiso Valentino , Scherillo Fabio , Squillace Antonino , Testani Claudio , Velotti Carla
Published: June 2013

Titanium alloys are finding an increasing use in the aeronautical field, due to their characteristics of high mechanical properties, lightness and corrosion resistance. Moreover these alloys are compatible with the carbon fibre reinforced plastics that are also finding a wide use in the aeronautical field. On the other hand the use of these alloys implies some drawbacks, for example titanium alloys are often considered more difficult to form and generally have less predictable forming characteristics than other metallic alloys such as steel and aluminum. In this paper was studied both the microstructure evolution and the mechanical properties of a Ti-6Al-4V rolled bar after hot forging. The thermo-mechanical response of a Ti-6Al-4V alloy was studied in elevated temperature compression tests (CT). Furthermore numerical simulations were carried out in order to do a comparison between numerical data and experimental results. The simulations were carried out using an implicit commercial code able to conduct coupled thermo-mechanical-microstructural analysis of hot forming processes of metal alloys.
Simulation of Composite Forming at Meso Scale
Authors: Gatouillat S. , Barregi A. , Vidal-Sallé Emmanuelle , Boisse Philippe
Published: June 2013

The forming simulation of woven reinforcements allows accessing to information such as fibre position after forming but also deformation state as well as predicting defects such as wrinkles, yarn sliding, and fibre/yarn fracture. The proposed model consists in a mesoscopic description of the reinforcement. It is simple enough to render the simulation of the forming preform possible but describes also properly the main phenomena occurring during the forming. A geometrical model where each yarn is modelled using shell elements in contact-friction with its neighbours is proposed. A hypoelastic behaviour specific of the yarn is used. Identification and validation of the model are done using standard characterisation tests for fabrics. Forming simulations illustrate the capabilities of the proposed approach. A main interest of such modelling is the possibility for the simulation to exhibit large sliding between warp and weft yarns when the tensile loads are too important.
Identification of Fibre Degradation due to Friction during the Weaving Process
Authors: Florimond Charlotte , Ramezani-Dana Hossein , Vidal-Sallé Emmanuelle
Published: June 2013

In order to be able to properly evaluate the in-use mechanical properties of high performance composite materials, it is useful to identify all the critical operations of the forming process which can degrade the row materials (i.e. the yarns for continuous fibre reinforcements). Those degradations begin during the weaving process which is the main topic of the present paper. The weaving operation has been proved to be particularly critical, especially when the weaving parameters are not correctly tuned. For glass fibre reinforcements, the travel followed by both the warp and weft yarns inside the weaving loom is observed and several zones are identified as particularly critical: the contact between warp yarns and heddles, between yarns and the beater, between yarns … For each zone, the loading has been reproduced in laboratory devices in order to quantify its effect on the final resistance of the yarn. In parallel, the friction parameters have been measured for several friction configurations: friction between yarns in several directions, friction between yarns and various metallic parts of the loom. The objective is the identification of a forming window in terms of yarn tension, the shed opening, the beater for… This work is realised with the financial support of the French National Agency for Research (ANR) in the framework of project ANR- 09-MAPR-0018 (NUMTISS)
Forming of a Non-Crimp 3D Orthogonal Weave E-Glass Composite Reinforcement
Authors: Pazmino Juan , Carvelli Valter , Lomov Stepan , Verpoest Ignaas
Published: June 2013

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Analysis of the Blank Holder Force Effect on the Preforming Process Using a Simple Discrete Approach
Authors: Najjar Walid , Legrand Xavier , Dal Santo Philippe , Soulat Damien , Boude Serge
Published: June 2013

Simulation of the dry reinforcement preforming, first step of the Resin Transfer Moulding process, become necessary to determine the feasibility of the forming process, compute the fiber directions in the final composite component, and optimize process parameters during this step. Contrary to geometrical approaches, based on fishnet algorithms, finite element methods can take into account the actual physical parameters, the real boundary conditions and the mechanical behavior of the textile reinforcement. The fabric can be modeled either as continuum media with specific material behavior [5, 6], or using discrete structural elements to describe the textile structure at the mesoscopic scale. A semi-discrete approach, which is a compromise between the above continuous and discrete approaches, is also used for simulation. A discrete approach for the simulation of the preforming of dry woven reinforcement has been proposed and presented in a previous paper. This modelling is based on a “unit cell” formulated with elastic isotropic shells coupled to axial connectors. The connectors, which replace bars or beams largely studied in other discrete approaches, reinforce the structure in the yarn directions and naturally capture the specific anisotropic behavior of fabric. Shell elements are used to take into account the in-plane shear stiffness and to manage contact phenomena with the punch and die. The linear characteristic of the connectors, has been extended to a non linear behaviour in the present paper to better account for fabric undulation. Using this numerical model, we propose, in this work to study the effect of process parameters on the woven fabric deformation during the performing step. The emphasis will be placed on the analysis of the influence of the blank holder pressure on the shear angle distribution.
Validation of Macroscopic Forming Simulations of a Unidirectional Pre-Impregnated Material through Optical Measurements
Authors: Margossian Alexane , Dumont François , Beier Uwe
Published: June 2013

Presenting interesting aspects such as a high strength-to-weight ratio, Carbon Fibre Reinforced Plastic components are frequently used in the aerospace industry. The forming step, which conforms the reinforcement to a specific geometry, is a sensitive phase of the manufacturing process. In order to detect the occurrence of defects prior to any trial, forming methods are often simulated via finite element software. The presented work will detail the simulation validation of a double curved helicopter frame forming out of a unidirectional carbon fibre pre-impregnated material (M21E, Hexcel®). The finite element model was based on an explicit approach at a macroscopic level and developed via the commercially available software Visual-Crash PAM (ESI®) [1]. The validation was carried out on six different preforms. Measurements of the top layers were performed by an enhanced version of a 4D measuring system, originally developed for non-woven fabric [2], able to make reproducible photographic and height measurements (Fig. 1). Experimental results were then compared to simulated ones. Due to material specificities, the photo quality reached for non-crimp fabrics could not be achieved [2]. After hardware and software modifications, measurements and analyses were eventually successfully completed. The validation of the simulation reached an accuracy of 1° to 3° depending on the geometrical features of the preform (Fig. 2).
Characterization of Cured Composite Materials for Wind Turbine Blades
Authors: Mitchell Cynthia J. , Sherwood James A. , Fetfatsidis Konstantine A. , Dangora Lisa M.
Published: June 2013

NCFs (Non-Crimp Fabrics) infused with epoxy resin are popular in the design of wind turbine blades and other complex systems due to their ability to conform to complex shapes. Past work in the development of a combination beam-shell modeling approach to simulate the forming of NCF composites has been demonstrated to capture the change in the orientations of the yarns during a forming process. The structural performance of these manufactured blades is often analyzed using finite element simulations that consider the material properties of the fibers and of the resin based on the rule of mixtures and orthotropic shells where the model is sectioned into zones that account for changes in the material properties due to variations in the orientations of the lamina and number of layers. With the availability of the beam-shell model, the use of zones can be removed if the individual contributions of the yarns (beam elements) and resin (shell elements) can be characterized and the orientations of the yarns resulting from a forming simulation can be used to account for the variations in the material properties of the composite throughout the blade. This research uses a combination of static flexure tests and impact modal tests to ascertain the material properties of the fibers and resin in a unidirectional and biaxial non-crimp fabric laminate plates. The material properties are used in a finite element model of the plate and the model is analyzed in flexure and in a free-free modal configuration to compare to experimental results. Two different approaches are used in the commercially available software Abaqus to model the plate. One approach uses a combination of beam and shell elements to represent the fibers and the resin, respectively. The other approach uses orthotropic shell elements to capture the unbalanced behavior of the fiber/resin composite. The beam/shell modeling approach better represents the overall behavior of a single-layer plate and can be extended to consider multiple plies.
Finite Element Modeling of Unidirectional Non-Crimp Fabric for Manufacturing of Composites with Embedded Cabling
Authors: Petrov Alexander S. , Sherwood James A. , Fetfatsidis Konstantine A. , Mitchell Cynthia J.
Published: June 2013

A hybrid finite element discrete mesoscopic approach is used 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 into an ABAQUS/Explicit finite element model via a user-defined material subroutine. The forming of a hemisphere is simulated using a finite element model of the fabric, and the results are compared to a thermostamped part as a demonstration of the capabilities of the used methodology. Forming simulations using a double-dome geometry, which has been used in an international benchmarking program, were then performed with the validated finite element model to explore the ability of the unidirectional fabric to accommodate the presence of interlaminate cabling.
Application of X-Ray Microtomography to Quantify the Liquid Fraction of M2 Steel for Semi-Solid Forming Process
Authors: Gu Guo Chao , Pesci Raphaël , Becker Eric , Langlois Laurent , Bigot Régis
Published: June 2013

Thixoforging, one variant of semi-solid metal processing in which the metallic alloys are processed at low liquid fraction (0.1< Fl < 0.3), is used to produce complex parts with high mechanical properties. Steel thixoforging faces more challenges as compared to that of low melting point materials due to high processing temperature and lack of understanding of the thermomechanical behavior of materials in the given conditions. It is crucial to study the microstructure at the semi-solid state to improve the understanding of the thixoforging process since the material behavior strongly depends on main parameters: the liquid fraction, its distribution as well as the coherence of the solid skeleton. The microstructure has a great influence on the viscosity of the material, on the flows and finally on the final shape and mechanical properties of the thixoforged parts. Here, the characterization of the volume percentage and distribution of liquid fraction at the semi-solid state with high energy 3D X-ray microtomography was investigated on M2 steel grade as a ‘model’ alloy. The obtained results have been compared to 2D observations using EDS technique in SEM on heated and quenched specimens. They showed a good correlation making both approaches very efficient for the study of the liquid zones at the semi-solid state.
Advances in the Twin-Roll Strip Casting of Strip with Profiled Cross Section
Authors: Vidoni Michele , Daamen Markus , Hirt Gerhard
Published: June 2013

Direct thin strip casting is an economically end energetically smart process for the production of steel strip. In a single process step, liquid steel can be cast and directly rolled to hot strip in thicknesses ranging from one to four millimeters. With the use of specifically profiled casting rolls it is possible to produce strip with optimized cross-sections, allowing this process to compete with tailor welded and tailor rolled blanks for the production of a class of products already widely applied in industry. Numerical and experimental studies proved the feasibility of this concept and additional simulations were used to optimize the profile to be used for the experiments. A thickness variation of one millimeter from the edge to the center could be successfully achieved. However, the dimensional precision and the roughness distribution along the cross section of the produced strip were not satisfactory. Additional profiles were applied for the experimental analysis leading to better roughness distribution and geometrical accuracy. In order to further improve the uniformity of properties along the profiled section it is necessary to increase the homogeneity of the microstructure. The coating and surface preparation of the casting rolls play a very important role in the strip casting process as they strongly affect the solidification behavior. This observation lead to the idea of selectively coating the casting rolls, applying a less conductive layer on the areas where the casted profile is thinner. Thus, a more homogeneous solidification front can be obtained. The effect of a locally modified casting roll coating on the solidification is numerically investigated and the results applied for the selection of the coating parameters to be used for the experiments.
Thixoforging of Ultrasound Treated 6060 Aluminum Alloy
Authors: Pola Annalisa , Attanasio Aldo , Ceretti Elisabetta , La Vecchia Giovina Marina
Published: June 2013

In the last years researches on thixotropic materials have been developed in order to introduce this new technology in manufacturing processes. For instance, when considering high pressure die-casting, several applications are present in literature mainly related to low melting point alloys (Al and Mg) because of the limited die life experienced when casting higher melting materials. In this case, semi-solid metal forming allows to work at lower temperature with subsequent increase in die life and reduction in production costs, combined with lower porosity level in the casting. On the other hand, in the case of conventional forging, semi-solid processing needs higher performance materials and/or coatings for the mould because of the working temperatures; however, the advantages of obtaining near net shape part in a single step, with reduced machining and finishing costs, make the semi-solid technology competitive. The present paper deals with the thixoforging of aluminum 6061 alloy, whose semi-solid feedstock material was obtained by ultrasound treatment. The application of ultrasonic waves to liquid or solidifying alloys has been already demonstrated to be an effective technique for the obtainment of globular microstructure. Along with a refining effect, ultrasound can also produce a series of beneficial effects, such as hydrogen degassing or oxide and non-metallic inclusion removal, which all improve mechanical properties of the component. The aim of this research was to investigate the influence of process parameters on final forged part quality. The solid fraction percentage as a function of temperature was measured by differential scanning calorimetric analysis. The geometry of the die was properly designed and optimized by FEM simulation in order to be suitable for forging semi-solid material, allowing a comparison with conventional forging process. 14 K-type thermocouples were used for monitoring the temperature of top and bottom dies; an instrumented 100 ton press was also equipped with load cells to acquire the forging force. A deep metallurgical analysis of the forged parts was performed in order to evaluate their mechanical properties and quality.
Groove Filling Characteristics and Strength of Form-Fit Joints Produced by Die-Less Hydroforming
Authors: Gies Soeren , Weddeling Christian , Kwiatkowski Lukas , Tekkaya A. Erman
Published: June 2013

The manufacturing of modern lightweight structures and the implementation of multi material concepts, for example in automotive engineering, entails appropriate joining technologies. The absence of additional connection elements or filling materials as well as the possibility to join dissimilar metals are basic requirements in this field of application to reach the aspired weight reduction. In case of tubular joints the die-less hydroforming process meets these demands and thus makes it an interesting alternative to conventional welding and riveting processes. The present work focuses on form fit joints produced by die-less hydroforming. It provides a verification of a previously presented analytical approach that allows the calculation of the working fluid pressure required to bulge the tube material into the groove of the outer joining partner. For that purpose, the groove filling characteristics of joined specimens with different groove geometries are analyzed. Here both joining partners were made of the aluminum alloy EN AW-6060. Additionally the connection strength of the joined specimens are determined using tensile tests. The results prove that the groove angle is the main influencing factor on the connection strength and that it can be used for an ordinal comparison of different groove geometries.
Toward a Real Time Control of Toolpath in Milling Processes
Authors: Poulhaon Fabien , Rauch Matthieu , Leygue Adrien , Hascoet Jean Yves , Chinesta Francisco
Published: June 2013

Real-time control of manufacturing processes is a challenging issue for nowadays industry. The need for ever more efficient production requires new strategies in order to make correct decisions in an acceptable time. In a large number of cases, operators working on a CNC machine tool have a reduced number of possibilities for interacting in real-time with the machine. Numerical simulation based control is in that sense an appealing alternative to the conventional approach since it provides the operator with an additional source of information, confirming his choices or in reverse suggesting a more adapted strategy. The main goal of this work is to propose a method to move from a bilateral approach (operator and CNC controller) to a trilateral one where the simulation is an active component of the manufacturing process. This paper focuses on a simple issue sometimes encountered in milling processes: how to remove a constant thickness of material at the surface of a part whose exact geometry is unknown The difficulty lies in the choice of an appropriate trajectory for the tool. So far the method which is employed consists in acquiring the geometry of the part thanks to a palpation step made prior to milling. However, this step has to be repeated for each part and can become rather fastidious as the size of the part increases. The approach presented here gets rid of the palpation step and makes use of online measurements for identifying the real geometry and correcting the trajectory of the tool in accordance. By monitoring the forces applying on the tool (directly on the NC), we have access to the milling depth and therefore to the geometry of the part at several locations along the trajectory of the tool. This information is used as an input data for our numerical model running on an external device, which finally derives an approximation for the geometry. An optimized trajectory is then obtained and is updated on the machine. This procedure is repeated as the tool moves forward and it allows for a fast and robust on-line correction of the toolpath.
Crystal Plasticity Finite-Element Simulation of Deformation Behavior during Unloading under Compression in Magnesium Alloy Sheet
Authors: Hama Takayuki , Kitamura Naoya , Fujimoto Hitoshi , Takuda Hirohiko
Published: June 2013

Magnesium (Mg) alloys are the lightest metals that can be used for structural components, and the press forming of Mg alloy sheets has recently attracted attention in automobile and electrical industries. To increase the number of applications of the press forming, it is crucial to understand mechanical properties of Mg alloy sheets. Because Mg alloys are hexagonal close-packed (hcp) materials, mechanical properties of Mg alloy sheets are significantly different from those of conventional structural sheet metals that have cubic structures. Crystal plasticity models can analyze numerically the interaction between mesoscopic crystalline and macroscopic deformation in metals; thus the models are powerful tools to further understand the mechanical properties of Mg alloy sheets. In the present study, the nonlinear response that arose during unloading under in-plane compression of a rolled magnesium alloy sheet was investigated using a crystal-plasticity finite-element method, focusing on the effects of twinning and detwinning. The mechanism that the nonlinear response was more pronounced under in-plane compression than that under in-plane tension was also discussed. In the simulation, a twinning and detwinning model that has originally been proposed by Van Houtte (1978) and recently extended to the detwinning process by the authors [Hama and Takuda, 2012] was employed. From numerical experiments, it was confirmed that, as already pointed out in literature, the activity of detwinning played an important role on the nonlinear response during unloading. On the other hand, it was also found that the basal slip systems could be very active during unloading because of the dispersion of crystal orientations owing to the activity of twinning during loading, which increased the nonlinear response. It was concluded that the nonlinear response during unloading was more pronounced under in-plane compression than that under in-plane tension owing to these two factors that did not present under in-plane tension.
Direct 3D Simulation of Powder Sintering by Surface and Volume Diffusion
Authors: Pino Muñoz Daniel , Bruchon Julien , Drapier Sylvain , Valdivieso François
Published: June 2013

Within the general context of solid-state sintering process, this work presents a numericalmodelling approach, at the grain scale, of ceramic grain packing consolidation. Typically, the sinteringprocess triggers several matter diffusion routes that are thermally activated: surface, grain boundaryand volume diffusions. Including this physics into a high-performance computing framework wouldpermit to investigate and to track the changes occurring into a granular packing during sintering. Inperforming this kind of simulations, one will face several challenges: the strong topological changesappear during sintering simulation at the grains scale, the evolution of the structure is mainly drivenby the surface tension phenomena through the Laplace's law, and the mechanical properties of thegrains could, possibly, be different. The proposed numerical simulations are carried out within anEulerian Finite Element framework and the Level-Set method is used to cope with changes in themicrostructure. The results obtained with this numerical strategy are compared with success to theusual geometrical models.
Improvement on CAE Model Considering Surface Deformation of Tools in Contact with Blank Sheet for Accurate Torsional Springback Prediction in High Strength Steel Part Forming
Authors: Ishiwatari Akinobu , Hiramoto Jiro , Inazumi Toru
Published: June 2013

It is difficult to predict springback, particularly in torsion, with high accuracy by FE simulation. Generally, more accurate springback prediction havs been achieved mainly by the improvement of material modeling such as Baushinger effect and plastic anisotropy models. It is also proved that tool deformations can greatly influence on the accuracy of torsion springback prediction as shown in the authors’ study [Esaform 2012]. The study shows that FE simulation using elastic tool model has 30% more accuracy in predicting torsional spring back in a curved hat shape than that by rigid tool model. But full elastic tool modeling is tedious work and FE calculation with the elastic tool model needs enormous time.There are two kinds of tool deformation during a press forming: tool deflection as a whole, and surface deformation where the tool is in contact with the steel sheet. Three forming experiments were carried out with an insert block of different stiffness, which touch steel sheets directly, in this study. The results revealed that surface deformation of a tool has great influence on torsion springback of a curved hat shape. Based on the results, a new tool modeling is proposed in this study. In the model, the part of a tool in direct contact with a blank sheet is elastic and the other part is rigid. That means the model deals with only surface deformations of tools in FE simulation. By the new model, the accuracy of torsion springback prediction of a curved hat shape was improved with less calculation time.
Surface Evolution and Lubricant Distribution in Deep Drawing
Authors: Ludwig Manuel , Volk Sebastian , Groche Peter
Published: June 2013

Deep drawing is one of the most important processes applied in industrial production. Here the Finite-Element-Method (FEM) is an important tool in the development and optimization process. One aspect to optimize simulations is to consider real friction behavior. Thus the friction phenomenon has to be describable. In addition to contact normal pressure and velocity the surface topography and the lubricant amount have a great influence on friction. This paper illustrates the influence of surface evolution in real, inhomogeneous processes on the lubricant distribution. For this a rectangular cup with four different corner radii is used to evaluate local surface topographies and lubricant amounts in deep drawing. The lubricant amount is measured by fluorescence technique and the surface topography is evaluated by a confocal white-light microscope. Due to hydrodynamic effects the lubricant is squeezed out and displaced to adjacent regions. Further hydrostatic pressures built up in closed lubricant pockets force the lubricant to stay in the forming zone to bear a part of the load. In free forming zones without contact between the sheet and tool the surface roughens due to grain dislocations in the microstructure. This paper also presents the results of lubricant distribution and surface evolution by varying the initial lubricant amounts and drawing depth. It can be recognized that the different corner radii of the rectangle cup have a great influence on the surface evolution and lubricant distribution. Moreover it can be clearly seen that surface parameters correlate with the lubricant amount. By means of the described evaluation it is also possible to correlate these values with load histories consisting of contact pressures and strain evolution, evaluated in FEM. All the results contribute to a better understanding of the friction behavior in deep drawing and point out the inhomogeneous character of friction.