bluuebunny/crossref_metadata_2025 huggingface dataset:
On the Performance of Welded, Riveted and Adhesive Bonded Al/Mg Sheet Metal Joints
Authors: Alfano Marco , Ambrogio Giuseppina , Filice Luigino , Furgiuele Franco , Gallus Enrico , D'Antuoni Domenico
Published: March 2011

Aluminum (Al) and Magnesium (Mg) alloys are nowadays widely employed in order to produce lightweight automotive and aeronautical components and to gain fuel saving and reduced emissions. However, the joining of Al and Mg alloys poses well known technical problems and the application of conventional joining techniques, e.g. welding, may be ineffective. On the other hand, adhesive bonding may be considered as a candidate replacement of the traditional techniques and for this reason it has been recently proposed as an alternative technology for Al/Mg joints. In particular, it has been demonstrated that adhesive bonding, in conjunction with state-of-the-art surface treatments, can provide Al/Mg joint with enhanced strength. However, in order to evaluate the potential of adhesive bonding to outperform the conventional joining techniques a systematic comparative analysis is needed. Therefore, the aim of this work is to supplement the existing studies on Al/Mg bonding providing a comparative analysis between Al/Mg joints prepared using gas metal arc (MIG) welding, riveting and adhesive bonding. Probably, the use of adhesive bonding as complementary joining process will be the industrial answer to the hybrid joints performance needs.
Identification of Post-Necking Hardening Behaviour of Sheet Metal: a Practical Application to Clinch Forming
Authors: Coppieters Sam , Lava Pascal , Sol Hugo , van Houtte Paul , Debruyne Dimitri
Published: March 2011

Clinching is a mechanical joining technique which involves severe local plastic deformation of two or more sheet metal parts resulting in a permanent mechanical interlock or joint. The required forming load and energy can be determined with the aid of the finite element method. However, a good knowledge of the elasto-plastic properties is of utmost importance to perform a sufficiently accurate simulation. This paper presents two alternative material tests to identify the hardening behaviour of sheet metal beyond the point of maximum uniform elongation. In addition, the material tests were applied to DC05 and the identified material behaviour is evaluated through the prediction of the forming load during clinching.
Light Metal in High-Speed Stamping Tools
Authors: Hirsch Martin , Demmel Peter , Golle Roland , Hoffmann Hartmut
Published: March 2011

The required number of punched and blanked parts in the electronic industry, such as leadframes, contact pins or plugs often reach several million pieces. According to this, the production process has been sped up to frequencies up to 2000 parts per minute. At this production rate parts of thin steel or copper sheets are produced with high-speed stamping presses and blanking tools. Because of the high gating velocities in the blanking tool there is a recurring acceleration at the moment, when the blank holder contacts the sheet metal. A second shock in the blanking tool arises, when the sheet cracks. This is also known as the impact shock during the blanking process. Trough these two impulses and through the cycle of the plunger movement a periodic oscillation arises in the tool. Horizontal vibrations can lead to an undefined position between punches and die-plate, while vertical movement leads to increased wear because of friction forces between the blanked surface and the lateral area of the punches. The goal of this project was to minimize these oscillations in cutting tools by the usage of lightweight materials in the flux of forces. An experimental cutting tool was designed with alternative top and bottom plates for the comparison of the oscillation status in the cutting process when using plates of steel, aluminium or magnesium. The centre plate of the tool remains constant. Experiments were accomplished for several velocities and tool setups with different plate materials. To determine the influence of the materials with different density and elasticity acceleration, force and acoustic emission sensors were integrated in the tool. The set of problems was investigated by analyzing the measured data and by determining the wear in practical tests.
Small Batch Laser Welding Using Light Fasteners and Laser Tack Welding
Authors: Rasmus Milla , Mäntyjärvi Kari , Karjalainen Jussi A.
Published: March 2011

Laser welding is known for its low heat input compared to arc welding methods. This could enable laser welding of sheet metals with lighter fastening solutions and less time-consuming tack welding alternatives. A feasibility study was carried out to study four different corner joint types for 2 mm thick cold rolledcold-rolled steel sheet by using filler-free laser welding. The aim of the research was to get more experimental knowledge about the laser welding of corner joints. Also possible benefits concerning faster manufacturing times and smaller costs by developing fastening applications for small batch laser welding was to be studied in practice. The 170 mm long joints were welded without air gap or pressing. All corner joint types proved to be weldable with a continuous wave Yb:YAG diode-pumped disk laser. It was also found during the With the experiment it was also found out that laser welding enables the use of light and inexpensive fasteners such as magnetic holders in steadinstead of traditional clamps and fixturing. With some joint types, the insufficient fastening power of magnetic fasteners against distortions was compensated by making a spot-like laser tack weld toat the end of the weld before welding the actual seam. This showed that it is possible to make precise and small tack welds with a laser and to use laser -tacking in sheet metal assembly.
Application of Servo Presses to Sheet Metal Forming
Authors: Mori Kenichiro
Published: March 2011

Mechanical AC servo presses having high flexibility for control of motion have been recently developed. In these presses driven by servo motors, the slide motion is accurately controlled by real-time feedback of ram position measured with sensors like the conventional machine tools, and thus complicated motion is attainable. The application of servo presses to sheet metal forming processes is reviewed in the present paper. The springback in bending was reduced by bottoming and re-striking. In deep drawing, the forming limit of high strength steel sheets was improved by detaching tools from the sheet, and the wrinkling was prevented by applying a stepwise motion. A hot stamping process using rapid resistance heating and a servo press was developed to produce ultra-high strength steel parts.
Application of the Finite Element Methods on the Staking Process of Staking Fasteners
Authors: Tofall Miriam , Merklein Marion , Plettke Raoul
Published: March 2011

The increasing use of new materials with varying thicknesses within the automotive industry creates high demands on joining elements such as staking fasteners. Simultaneously statements about the feasibility of the design with joining elements already in the early stage of the development are necessary. The challenge is to define suitable element geometry, tool geometry and process parameters. To meet those requirements, a good understanding of the staking process is inevitable. According to the state of the art the examinations regarding the performance of staking fasteners under different conditions are totally conducted experimentally. This trial-and-error procedure leads to an extensive financial effort and to long development times for new elements. It is furthermore not possible to observe all influences of different process parameters. In the field of mechanical engineering the use of numerical simulation for complex constructions is a common technique. This paper deals with the applicability of the finite element method (FEM) on the joining of sheet metals with staking fasteners. In this matter the FEM is used to get scientific insights in the staking process and is also used to identify influencing variables and their interactions.
Size Effects in Micro Forming
Authors: Vollertsen Frank
Published: March 2011

Size effects are effects which might occur, if the dimensions of a forming process are scaled up or down. They might enable or disable the application of a process in the micro range. Based on the systematic order of size effects, which defines density, shape and structure effects, one example for each group is given. A density effect, which occurs in Tiffany structures, explains the changes in forming behavior of foils with respect to the forming limit diagram. The feasibility of a new heading process only in the micro range is due to a shape effect, driven by the surface energy. The changes in the tribology in deep drawing by a structure effect, known as closed an open lubricant pocket model, can be explained only if one takes the temperature dependence of the viscosity of the lubricant into account.
Thickness Effect on the Formability of AZ31 Magnesium Alloy Sheets
Authors: Forcellese Archimede , Gabrielli Filippo , Simoncini Michela , El Mehtedi Mohamad
Published: March 2011

The thickness effect on formability of AZ31 magnesium alloy sheet has been widely investigated by means of uniaxial tensile tests, performed in the temperature range from 250 to 350°C, with strain rates varying from 10-4 to 10-1 s-1, using samples with different thickness values (from 1.5 to 3.2 mm). A preliminary microstructural study has shown that grain size and morphology are not significantly affected by both sheet thickness and heating just before the deformation step. The experimental results of tensile tests have been analysed in terms of flow curve shape, flow stress and strain to failure levels. They show that, in general, flow stress increases and ductility decreases with increasing sheet thickness even if such influence is strongly related to the temperature and strain rate conditions Finally, the analysis of the Zener-Hollomon parameter vs. peak flow stress data showed that the same mechanisms are operative in the investigated sheets.
A Theoretical Study on Forming Limit Diagram Predictions Using Viscoplastic Polycrystalline Plasticity Models
Authors: Serenelli Mariano , Bertinetti María , Turner Pablo , Signorelli Javier
Published: March 2011

The Forming Limit Diagrams (FLDs) of textured polycrystalline sheet metals were investigated using micro-macro averaging and two types of grain-interaction models: Full-Constraint (FC) and Self-consistent (SC) schemes, in conjunction with the Marciniak–Kuczynski (MK) approach. By referring to previous FLD studies based on the FC-Taylor model ─ Wu and coworkers [Effect of an initial cube texture on sheet metal formability, Materials Science and Engineering A, 364:182–7, 2004] and Inal and coworkers [Forming Limit comparison for FCC and BCC sheets, International Journal of Plasticity, 21:1255-1266, 2005] ─ we found that the MK-FC strategy leads to unrealistic results. In the former case, the researchers found that an increasing spread about the cube texture produces unexpectedly high limit strains. In the latter work, Inal et al. predicted a remarkably low forming-limit curve for a FCC material and an extremely high forming-limit curve for a BCC material, in the biaxial-stretching range. Our investigations show that simulations performed with the MK-VPSC approach successfully predict more reliable results. For the BCC structure, the MK-VPSC predictions do not give the extreme values predicted when calculations are carried out with the MK-FC approach. In the FCC case, with decreasing textural intensity ─ from the ideal cube texture, through dispersions around the cube texture with increasing cut-off angles, to a random texture ─ a smooth transition in increasing limit strains was obtained. Furthermore, these results suggest that the selected constitutive model is critical for predicting the behavior of materials that exhibit a qualitative change in crystallographic texture, and hence, evolve anisotropically during mechanical deformation.
Influence of the Processing of Magnesium Alloys AZ31 and ZE10 on the Sheet Formability at Elevated Temperature
Authors: Stutz Lennart , Bohlen Jan , Kurz Gerrit , Letzig Dietmar , Kainer Karl Ulrich
Published: March 2011

The substitution of conventional materials such as aluminium alloys and steels with the lightest structural metal magnesium and its alloys can yield significant weight saving in the transportation industry and hence, reduce vehicle weight and greenhouse gas emissions. Producing magnesium sheets by conventional hot rolling is expensive due to the large number of rolling passes to final gauge and annealing steps at elevated temperatures between the rolling passes. Twin roll casting is a well established processing route for aluminium sheets which can reduce the necessary rolling passes to a bare minimum to reduce the production costs. This process is receiving increasing attention for the production of magnesium sheets. This study reveals first hand results of sheet metal forming experiments on magnesium sheets rolled from twin roll cast strip as well as conventional DC cast slabs. Two different alloys, AZ31 (Mg-3Al-1Zn-Mn) and rare earth element containing ZE10 (Mg-1Zn-RE) were investigated. It is known that these alloys show significant differences in the microstructure development during conventional rolling as a result of recrystallisation. For hot rolled AZ31, distinct textures are formed with the majority of basal planes oriented in the sheet plane and hence, unfavourably for basal slip. Conventionally rolled ZE10 commonly shows a much weaker texture. Forming limit diagrams are presented and discussed with respect to the initial texture of the sheets. Strain response to various strain paths and plastic anisotropy are evaluated. Results of twin roll cast sheets are compared with conventionally hot rolled sheet of the same alloys. Competitive formability can be achieved at 200°C for all tested sheets. While conventionally rolled sheets show a generally higher formability than their twin roll cast counterparts, ZE10 outperforms AZ31 for both processing routes.
Methods for Determination of Residual Stress of a Formed Plate Using Laser Ablation, Wire EDM and Milling
Authors: Lämsä Janne , Mäntyjärvi Kari , Järvenpää Antti , Grüner Martin , Merklein Marion , Karjalainen Jussi A.
Published: March 2011

In this work laser ablation was used for the determination of residual stress of a formed plate. Manufacturing processes, like bending, create residual stresses in the product and those can be very disadvantageous for fatigue durability. Residual stresses that are generated during the manu-facturing of products can cause distortions, dimensional errors or can even break the products. The research material was ultra-high-strength steel (UHSS) with a yield strength of 1100 MPa. Speci-mens with a 90 degree bent angle were made by air bending using a press brake. Air bending causes variable residual stress patterns in the cross section of the material. The residual stresses of the formed area were determined by removing material and measuring strains caused by the release of stresses. A slot with the width of 1 mm has been manufactured parallel to the edge, both on the outer and on the inner side of the bend. True residual stress distribution can be calculated from the measured strains. A pumped 1064 nm Nd:YVO4 ablation laser, whose pulse length is 90 ns, was used for the removal of material. This process creates a negligible heat affected zone (HAZ) and laser ablation doesn’t increase stresses in the specimen. The results were compared with those ob-tained when slots were produced by milling and wire-EDM, as well as with the stress values meas-ured by X-ray diffraction.
Innovative Machine Concepts for 3D Bending of Tubes and Profiles
Authors: Hermes Matthias , Staupendahl Daniel , Becker Christoph , Tekkaya A. Erman
Published: March 2011

The paper deals with two new processes and developed special machines for profile and tube bending. The first process is a new roll-based machine for three-dimensional bending of profiles with symmetrical and asymmetrical cross-sections that has been developed. Compared to conventional processes like stretch bending, the advantage of Torque Superposed Spatial (TSS) Bending is the kinematic adjustment of the bending contour, leading to higher flexibility and cost efficiency especially in small batch production. The second process is the new process of Incremental Tube Forming (ITF). This process is based on a combination of a spinning process and kinematic free form bending of tubular semi-finished products. It is suitable for bending tubes two- and three-dimensionally to arbitrary contours and for manufacturing tailored tubes. The combined spinning and bending process leads to low bending forces with the possibility of a significant springback reduction.
On the Development of Novel Light Weight Profiles for Automotive Industries by Roll Forming of Tailor Rolled Blanks
Authors: Beiter Philip , Groche Peter
Published: March 2011

Due to continuously increasing demands on safety, comfort and ecological performance, different lightweight construction concepts have been searched for and applied by the automotive industry lately. This paper focuses on the development of novel light weight profiles by roll forming of tailor rolled blanks (TRBs). It covers analytics, experiments and FE analysis. At the beginning, state of the art tools were used for a fundamental process layout. The results show, that their application with respect to the varying sheet thicknesses within the blanks is generally acceptable. However, it may be concluded that TRBs as semi-finished products for roll forming operations call for a well adapted pre-cut of the blank. In a second step, roll forming of TRBs to a symmetrical U-profile with constant roll gap was investigated. For this purpose, experiments on a conventional roll forming line and corresponding FE simulations were conducted. Both show very similar results for the final bending angle of the part. Nevertheless, variability in bending angle of up to 14.3° is witnessed between the areas of different sheet thickness on one part. Thus, one may conclude, that a sheet thickness dependent adaptation of the roll gap is necessary for closer tolerances. A vertical and horizontal adjustability of the rolls seems appropriate to meet this purpose. With respect to these findings, two different tool kit concepts were developed and investigated by means of FE analysis. Both aim at a real-time adjustment of the roll gap to the actual sheet thickness within the stand. On the one hand, a force-driven self-positioning of the rolls was simulated. On the other hand the positioning of the rolls was preset in accordance to the feed of the sheet and its thickness distribution. Both concepts are discussed by their effect on the final bending angle of the roll formed U-profile.
On the Study of Constitutive Parameter Identification of Advanced Yield Criteria
Authors: Aydin M.S. , Canpolat Aykut , Gerlach Jörg , Kessler Lutz , Tekkaya A. Erman
Published: March 2011

Recently, an alternative inverse-analysis approach was proposed to obtain the material parameters of the advanced yield criteria by employing tensile and cup drawing tests [1]. In this paper, the applicability of this strategy will be investigated for a mild steel grade by means of cruciform, plane strain tension and hydraulic bulge tests. Other than this, the impact of the strain rate on the hydraulic bulge tests will be one another aspect of this work.
Development of a Microscopic Damage Model for Low Stress Triaxiality
Authors: Achouri Mohamed , Germain Guenael , dal Santo Phillippe , Boude Serge , Lebrun Jean Lou , Saidane Delphine
Published: March 2011

This work dealsa contribution to ductile damageof High-Strength Low-Alloy (HSLA) steel under low stress triaxiality. This work is based on micrographics observations and in-situ shear tests to examine the evolution of microstructure in this kind of loading and to identify the damage process associated. Numerical simulations by finites elements has been performed to simulate the material behavior of nucleation mechanism and the interaction between cavities during the coalescence phase, as well as the effect of the relative position of the inclusions in the shear plane.The model used as a reference in this work is the Gurson-Tvergaard- Needleman (GTN) model. It has been recently improved in order to take into account the effects of low triaxiality during shearing. A new modelisunderdevelopmentto takeintoaccounttheeffects oflowtriaxiality stresses (or loading) during shearing.
The Simulation of Metal Foams Forming Processes
Authors: D'Urso Gianluca Danilo , Longo Michela , Maccarini Giancarlo , Giardini Claudio
Published: March 2011

Metal foams are two-phase compounds of a gas and a solid with several interesting physical and mechanical properties; in particular they have very low density, good rigidity, excellent energy absorption, high vibration damping. At now, the final shape of foamed devices is directly obtained through the foaming process itself and no further shaping steps are expected. Anyway, the plastic formability of metal foams, in order to both characterize the material itself and to produce more complex parts, seems to be useful for several industrial applications. Since metal foams are quite new products, the basic aspects ruling plastic deformation processes are still partially unknown and FEM methods may represent a valid tool for deepening these topics. This work deals with the formability of Aluminum Foam Sandwich (AFS) panels and it is focused on the FEM simulation of a compression processes. A numerical model was set up by using the FEM code Deform 2D v10.1. Foam behaviour was simulated by means of a compressible (porous) material model and the foam cracking was simulated using a damage model based on the foam density parameter. Some FEM routines were implemented into the FEM code to take into account both the non-homogeneous distribution and the strain hardening effect of the foam cells. An experimental campaign based on the compression of AFS panels made of close cells foam was carried out to fine tune and to validate the model. In particular, experimental data regarding load stroke curves and foam density were used to optimize the material description. An innovative solution, based on a non-linear relation between foam density and effective strain of the foam, was implemented into the FEM code.
Numerical Inverse Method for Friction Coefficient Estimation in Tube Hydroforming
Authors: Fiorentino Antonio , Marzi Roberto , Ceretti Elisabetta , Giardini Claudio
Published: March 2011

Friction plays an important role in forming processes, in fact it influences the material flow and therefore it affects the process and part characteristics. In particular, friction is a very influencing factor in Tube Hydroforming (THF), where high die-part contact pressure and area make the material sliding very difficult. As a consequence, the material hardly flows to the expansion zones and the part formability can be compromised. To obtain sound parts, FEM models allow to study the process and optimize its parameters, but they require the right definition of the friction at tube-die interface. For these reasons, friction represents a key-point in THF processes and its knowledge and prediction are very important even if, nowadays, a comprehensive friction test for THF is not available in literature. With this paper, the Authors want to propose a novel approach to estimate friction for THF processes. In particular it will be described a numerical inverse method that allows to estimate the Coulombian friction coefficient combining experimental test and FE simulation results. The method is based on the effects of friction on the tube final thickness distribution when it is pressurized and compressed by two punches under different lubrication conditions without expansion. In particular, it will be shown how the use of few and fast FE simulations allows to estimate an analytical function that takes into account the process conditions and that can be used in combination with experimental results in order to estimate the friction coefficient in THF processes.
Simulation of Hot Sheet Metal Forming Processes Based on a Micro-Structural Constitutive Model
Authors: Farzin Mahmoud , Jafari Nedoushan Reza , Mashayekhi Mohammad
Published: March 2011

A constitutive model is proposed for simulations of hot forming processes. Dominant mechanisms in hot forming including inter-granular deformation, grain boundary sliding and grain boundary diffusion are considered in the constitutive model. A Taylor type polycrystalline model is used to predict inter-granular deformation. Previous works on grain boundary sliding and grain boundary diffusion are extended to drive three dimensional macro stress-strain rate relationships for each mechanism. In these relationships, the effect of grain size is also taken into account. It is shown that for grain boundary diffusion, stress-strain rate relationship obeys the Prandtl-Reuss flow rule. The proposed model is used to simulate step strain rate tests and the results are compared with experimental data. It is concluded that the model can be used to predict flow stress for various grain sizes and strain rates. The proposed model can be directly used in simulation of hot forming processes and as an example the bulge forming process is simulated and the results are compared with experimental data.
Numerical and Experimental Study of the Effect Pressure Path in Tube Hydroforming Process
Authors: Elyasi Majid , Khanlari Hassan , Bakhshi-Jooybari Mohammad
Published: March 2011

In this paper, the effect of pressure path on thickness distribution and product geometry in the tube hydroforming process is studied by finite element simulation and experimental approach. In simulations and experiments, low carbon stainless steel (SS316L) seamless tubes were used. The obtained results indicated that with increasing of the initial pressure, the bulge value of the part increases and the wrinkling value decreases. In addition, if the initial pressure is highly decreased, then bursting may occur.
Investigation on the Effect of Pulsating Pressure on Tube-Hydroforming Process
Authors: Khalili Khalil , Ahmadi-Brooghani Seyed Yousef , Ashrafi Amir
Published: March 2011

Tube hydroforming process is one of the metal forming processes which uses internal pressure and axial feeding simultaneously to form a tube into the die cavity shape. This process has some advantages such as weight reduction, more strength and better integration of produced parts. In this study, T-shape tube hydroforming was analyzed by experimental and finite element methods. In Experimental method the pulsating pressure technique without counterpunch was used; so that the internal pressure was increased up to a maximum, the axial feeding was then stopped. Consequently, the pressure decreased to a minimum. The sequence was repeated until the part formed to its final shape. The finite element model was also established to compare the experimental results with the FE model. It is shown that the pulsating pressure improves the process in terms of maximum protrusion height obtained. Counterpunch was eliminated as being unnecessary. The results of simulation including thickness distribution and protrusion height were compared to the part produced experimentally. The result of modeling is in good agreement with the experiment. The paper describes the methodology and gives the results of both experiment and modeling.
Constitutive Modelling of Anisotropy, Hardening and Failure of Sheet Metals
Authors: Vladimirov Ivaylo N. , Kiliclar Yalin , Tini Vivian , Reese Stefanie
Published: March 2011

The paper discusses the application of a newly developed coupled material model of finite anisotropic multiplicative plasticity and continuum damage to the numerical prediction of the forming limit diagram at fracture (FLDF). The model incorporates Hill-type plastic anisotropy, nonlinear Armstrong-Frederick kinematic hardening and nonlinear isotropic hardening. The numerical examples investigate the simulation of forming limit diagrams at fracture by means of the so-called Nakajima stretching test. Comparisons with test data for aluminium sheets display a good agreement between the finite element results and the experimental data.
Numerical Prediction of Damage Evolution in Sheet Metal Forming Processes with Nonlinear and Complex Strain Paths
Authors: Jamshidi Babak , Haji Aboutalebi Farhad , Farzin Mahmoud , Forouzan Mohammad Reza
Published: March 2011

Various thin-walled parts with fairly complex shapes are produced from sheet metals such as automotive panels and other structural parts. In these processes, damage and fracture may be observed on the work piece, and formability plays a fundamental role. Therefore, determination of forming limits and prediction of rupture modes in these operations is very important for process design engineers. In this paper, first, based on plane stress elasto-plasticity and finite strain theories a fully coupled elastic-plastic-damage model is used to predict damage evolution in one sheet metal forming process with nonlinear and complex strain paths. As the plane stress algorithm is valid for thin sheet metals and finite strain theory is recommended for large deformations or rotations, the model is able to quickly predict both deformation and damage behaviour of the parts with nonlinear and complex strain paths. The numerical simulations are compared with experimental tests. Comparison of the numerical and experimental results shows that the proposed damage model is accurate for various forming conditions. Hence, it is concluded that finite element method combined with continuum damage mechanics, can be used as a reliable and rapid tool to predict damage evolution in sheet metal forming processes with nonlinear and complex strain paths.
A Simulation Approach for Chaining the Forming-Welding-Crash Behaviour of Sheet Metal Structures
Authors: Papadakis Loucas , Schober Alexander , Zaeh Michael F. , Demosthenous George
Published: March 2011

In recent years the simulation of manufacturing chains and of the crash behaviour of automotive sheet metal structures has gained more ground on its way to be established in accompanying the overall product cycle. In the automotive press and welding plants high accuracy and quality of sheet metal structures is essential in order to achieve the intended passive crashworthiness of the overall vehicle body. So as to describe the manufacturing process chain more precisely and to predict the structural behaviour at early stages of product and production planning, an interlinking of forming, welding and crash models within a structural computation chain is necessary. Considering the structural properties of sheet metal parts after the forming process for simulating welding tasks and finally the crash behaviour requires a multifaceted modelling method. In this paper a practicable strategy of realising the simulation chain forming-welding-crash of sheet metal structures is introduced by means of shell element models. The complete computed results of a forming process simulation, such as residual stresses, plastic strains and material thinning are transferred onto a prepared shell mesh based on the CAD geometry of the component, which satisfies the requirements of a welding computation. Further on, the structural properties after forming, the thermal distribution due to the welding process and the mechanical clamping conditions are combined in a thermo-mechanical computation of the welding effects to calculate the final shape, residual stresses and material thinning of the manufactured sheet metal structure. Finally, the attained structural results are converted into the required data-format by means of a developed conversion routine, which enables the setup of a crash model considering the entire preliminary manufacturing chain. In this contribution the structural behaviour along the introduced simulation chain is analysed step by step and the rendered results are discussed and compared with performed measurements.
Optimisation of Condition in Hot Gas Bulging of Aluminium Alloy Tube Using Resistance Heating Set into Dies
Authors: Maeno Tomoyoshi , Mori Kenichiro , Unou Chihiro
Published: March 2011

A hot gas bulging process of an aluminium alloy tube using resistance heating set into a die was developed. In the developed process, the tube was heated during the forming, and thus the drop in temperature was prevented. The control of the hot gas bulging was simplified by sealing air in the tube. The tube was bulged by thermal expansion of the air sealed in the tube without control of internal pressure during the forming. Hot gas bulging of an aluminium alloy tube without and with the axial feeding was performed. The deformation behaviour of the tube in the die was observed by a heatproof glass plate inserted in the die. The timing of the axial feeding, the feeding velocity and the amount of the axial feeding were optimised.
Identification of the Characteristics of Hydroformed Structures Using Optimization Methods
Authors: Radi Bouchaib , Ayadi A. , Cherouat Abel , Giraud-Moreau Laurence , El Hami A.
Published: March 2011

In this study, we present an experimental/numerical methodology which aims to improve 3D thin sheet hydroforming. The experimental study is dedicated to the identification of stress-strain flow by using the Nelder-Mead simplex algorithm optimization from the global measure of displacement and force. Applications are made to the simulation of thin sheet hydroforming using different die geometry to show the efficiency of the proposed methodology to localize plastic instability, thinning of the blanks and damage initiation under different forming condition.
A Methodology for Optimization of the Direct Laser Metal Deposition Process
Authors: Angelastro Andrea , Campanelli Sabina L. , Casalino Giuseppe , Ludovico Antonio D. , Ferrara Simone
Published: March 2011

Direct Laser Metal Deposition (DLMD) is actually one of the most attractive techniques in the group of Material Accretion Manufacturing (MAM) processes. In fact, the DLMD technology is able to realize, to repair and restore, objects, moulds and tools, directly from the 3D CAD model in a rapid and economic way. A great variety of metals, including those very difficult to work with the conventional techniques, can be shaped in a large number of complex geometries. This technique is also well suited to produce very hard coatings. The metallic parts, which are obtained through melting coaxially fed powders with a laser, present very good mechanical properties, with minimum porosity and good adhesion to the substrate. The objective of this work was to optimise the scanning velocity of the laser beam in order to maximize the density of DLMD parts. The optimization procedure was worked out with a mathematical model together with an experimental analysis to study the shape of the track clad generated melting coaxially fed powders with a laser. The material tested was Colmonoy 227-F, a nickel alloy specially designed for manufacturing moulds. The presented methodology has permitted to select the better combination of parameters that produce almost full density parts, free of cracks and well bonded to the substrate sintered parts.
Multivariate Adaptive Regression Splines as a Tool to Improve the Accuracy of Parts Produced by FSPIF
Authors: Verbert Johan , Behera Amar Kumar , Lauwers Bert , Duflou Joost R.
Published: March 2011

Feature Assisted Single Point Incremental Forming (FSPIF) is a technique to increase the accuracy of the SPIF process. FSPIF generates an optimized toolpath based on the features detected in the workpiece geometry and using knowledge of the behavior of these features during incremental forming. Using this optimized toolpath, parts can be formed with higher accuracy. The prediction of the dimensional deviations occurring in different features during forming as a function of their type (e.g. planar, ruled, freeform or ribs ) and various process parameters, such as sheet thickness, wall angle, tool diameter, rolling direction, etc., is an important step in the FSPIF method. Due to the great number of parameters and combinations that are possible, a mathematical tool should be used in order to automate the prediction process. One such tool is MARS or Multivariate Adaptive Regression Splines, a fast, non-parametric multivariate regression technique with automatic variable selection, which generates continuous surfaces as a response function. In this paper, the authors describe and validate the use of MARS as a tool to predict deviations in uncompensated tests by training the MARS model using only a limited number of experiments. Using this validated model, compensation strategies are developed and implemented, which have shown significant improvements in accuracy in new test cases.
On the Formability and Microstructural Characteristics of AISI 301 Parts Formed by Single-Point Incremental Forming
Authors: Lonardelli Ivan , Bosetti Paolo , Bruschi Stefania , Molinari Alberto
Published: March 2011

The present work focuses on the correlation between the material tendency to be deformed by incremental sheet forming and the microstructural features that appear during the process itself. The material object of the study is the stainless steel AISI 301L. Single-point incremental forming (SPIF) experiments were carried out and the material formability evaluated. X ray diffraction (XRD) analysis was utilized to determine the fraction of transformed martensite along the wall of formed parts at different levels of thickness reduction. TEM analysis was then employed to analyze the microstructure developed during the SPIF process. Two fundamental deformation mechanisms are observed, which could explain the remarkable material formability achievable during the SPIF process: strain induced martensitic transformation, and deformation twinning. Particularly, deformation twinning (instead of dislocation slip) appears to be the preferred plastic deformation mode of austenite at the early stage of the process, leading to the formation of multiple nano-twins in coarse grains that are responsible for the material ductility enhancement.
Machines and Tools for Sheet-Bulk Metal Forming
Authors: Merklein Marion , Tekkaya A. Erman , Brosius Alexander , Opel Simon , Kwiatkowski Lukas , Plugge Björn , Schunk Sebastian
Published: March 2011

The demand on closely-tolerated and complex functional components in the automotive sector, like e.g. synchronizer rings, leads to the development of a new process-class named “sheet-bulk metal forming”. Within this technology bulk metal forming operations are applied on sheet metals. In the following two novel approaches considering machines and tools for sheet-bulk metal forming are presented. The first approach aims on a technology based on rolling, which is suitable for mass production. The second one is an incremental forming solution for low batch production. Both machine concepts allow the application of different forming strategies to manufacture individual tailored semi-finished products in term of a pre-distribution of material. These products feature variable sheet thicknesses and mechanical properties, which can be adapted to their case of applica-tion. Depending on the individual batch size, the blanks can be finished to functional parts by sub-sequent forming processes like deep drawing and upsetting, extrusion or incremental forming. In this paper the case of an incremental tooth-forming is mainly considered. Forming sequences and resulting loads are modeled and calculated by finite elements simulations for all discussed processes to serve as a basis for the design and dimensioning of the machine components and forming tools.
Enhanced Requirements for Surface Quality of Outer Car Body Shells According to Thermal Manufacturing Processes
Authors: Albiez Christoph , Liewald Mathias , Görres Andreas , Regensburger Jochen
Published: March 2011

Challenging automotive design in the interaction of modern lightweight strategies to reduce car body weight as well as legislative regulations, impose higher requirements for future car body development. This trend leads to thinner sheet metal blanks and indicates higher requirements for narrow process windows in the entire manufacturing process to ensure the surface quality of outer shell panels. Especially, thermal loads within the coating process might cause local shape deviation in the startup phase of a new product. Further developments in multi-material-design for car body components induce material configurations with a complex deformation behavior due to different thermal expansion characteristics of the materials involved. For these reasons, there is a need to improve the prediction of the surface quality in the early car development process using numerical simulation methods. The influence of process parameters affecting the surface quality is shown and integrated into the process simulation.
Reduction of Charge Trapping Sites in Al2O3/SiO2 Stacked Gate Dielectrics by Incorporating Nitrogen for Highly Reliable 4H-SiC MIS Devices
Authors: Hosoi Takuji , Kagei Yusuke , Kirino Takashi , Mitani Shuhei , Nakano Yuki , Nakamura Takashi , Shimura Takayoshi , Watanabe Heiji
Published: March 2011

Superior flatband voltage (Vfb) stability of SiC-based metal-insulator-semiconductor (MIS) devices with aluminum oxynitride (AlON) gate dielectrics was demonstrated. MIS capacitors with gate insulators consisting of a thick pure aluminum oxide (Al2O3) and a thin underlying SiO2 layer fabricated on n-type 4H-SiC substrates showed a positive Vfb shift due to substrate electron injection depending on the applied gate bias and the thickness of the SiO2 interlayer. This large Vfb shift was greatly suppressed for devices with AlON/SiO2 stacked gate dielectrics, suggesting that electron trapping sites in Al2O3 film were mostly compensated for by nitrogen incorporation. This finding is helpful in realizing highly reliable SiC-based MIS field-effect-transistors (MISFETs) in terms of threshold voltage stability.
An Experimental Study of High Voltage SiC PiN Diode Modules Designed for 6.5 KV / 1 KA
Authors: Peters Dethard , Thomas Bernd , Duetemeyer T. , Hunger T. , Sommer R.
Published: March 2011

The paper describes first results of 6.5 kV SiC PiN diode modules which are designed as neutral point valves for medium-voltage power inverters rated for 1000 A. The power module consists of 4 AlN DCB substrates soldered on an AlSiC base plate. Each DCB is equipped with 20 SiC PiN diodes operating in parallel. The total active area of all 80 diode chips is 5.68 cm². At the rated current of 2 x 500A the forward voltage drops from 4.1 V at room temperature to 3.9 V at an averaged junction temperature of 125°C. The switching experiments show a very low reverse recovery charge of about 30 µC only. The conduction loss is comparable to the corresponding 6.5 kV silicon diode whereas the dynamic loss is marginal with respect to the forward conduction loss if the switching frequency is held below 10 kHz.
Thin Film Stress and Texture Analysis at the MCX Synchrotron Radiation Beamline at ELETTRA
Authors: Ortolani Matteo , Azanza Ricardo Cristy Leonor , Lausi Andrea , Scardi Paolo
Published: March 2011

The main instrumental characteristics of MCX, the new beamline at the Italian synchrotron Elettra in Trieste, are presented. Design and geometrical set-up are well suited to the X-ray diffraction stress and texture analysis of thin films and surfaces, and are such to guarantee a full control of the main instrumental errors. Besides exploiting the typical features of synchrotron radiation, like high brilliance, tuneable beam energy and optimal beam geometry, MCX can also host tools for in-situ studies, like X-ray diffraction during four point bending. A few examples of current applications are shown.
Thickness Effect on Microstructure and Residual Stress of Annealed Copper Thin Films
Authors: Vayrette Renaud , Rivero Christian , Blayac Sylvain , Inal Karim
Published: March 2011

In this work, coupled effects of thickness and annealing temperature on both microstructure and residual stress of electroplated copper thin films are studied. Microstructure is investigated by Electron Backscattered Diffraction (EBSD) and residual stress is estimated from samples curvature. All films exhibit highly twinned grains. Except for several microns films, median crystallite size grows with both film thickness and annealing temperature. Concerning residual stress, it decreases, first as the increase of film thickness, and secondly as the decrease of annealing temperature. The comparison between experiments and stress models demonstrates that the root mechanisms of residual stress generation change with annealing temperature. As well as annealing temperature, film thickness determines the level of residual stress through control of microstructure. Furthermore, EBSD investigations confirmed that the relevant microstructural length to define mechanical properties of thin copper films is the median crystallite size.
Evaluation of Arc Evaporated Coatings on Rounded Surfaces and Sharp Edges
Authors: Bohlmark Johan , Blomqvist Helen , Landälv Ludvig , Amerioun Shahrad , Ahlgren Mats
Published: March 2011

This paper presents measurements and cutting tests related to coating features on sharp cutting edges and rounded objects. One typical feature of plasma based deposition processes is the formation of a sheath region around the object to be coated. The formation of the sheath has some implications on the coating of three dimensional objects, since rounded surfaces and edges are subjected to different ion flux density as compared to a flat surface. Solid carbide drills of different diameters were coated with a TiAlCrSiN coating by cathodic arc evaporation. It is noted the deposition rate increases with decreasing drill diameter, and the fraction of elements with high expected mean ionization charge state is higher for a small as compared to a large diameter drill. The observations are explained by Coulomb attraction of ions from the plasma in combination with the sheath to tool radius ratio in combination with resputtering and scattering in the gas/plasma phase. Solid carbide end mills were coated with TiAlN at three different substrate biases; -10, - 40, and - 80 V. It is observed that the coating stresses increase drastically with increasing bias, and the corners of the tools have different stress levels than the flatter areas. In addition, the fraction of Ti in the coating around the corners is increased significantly when the bias increases. The end mills were tested in a machining test, and the best performer was the variant deposited at - 40 V.
Residual Stress Analysis Using the Hole-Drilling Method and Geometry-Specific Calibration Functions
Authors: Sobolevski Enrique Garcia , Nau Andreas , Scholtes Berthold
Published: March 2011

Due to the fact that no analytical solution exists to determine residual stresses in components with geometrical deviations from an ideal plate with the well known semi-destructive incremental hole-drilling method, calibration functions are required. Currently, such available functions, generated in an experimental or numerical manner are strictly speaking only valid for the reference case of a wide and thick plate and are only applicable if the surrounding field of the geometry at the measurement point is similar to the ideal one. Consequently, accuracy and reliability of assessing residual stresses by means of the incremental hole-drilling method can be improved if geometry specific calibration functions adapted to real geometries are used. This work deals with the determination of specific calibration functions by means of numerical simulations according to the MPA II standard (differential method) for three different components, violating the geometric restrictions of the reference.