bluuebunny/crossref_metadata_2025 huggingface dataset:
Considerations on the Reliability of Advanced Squeeze Casting Process
Authors: Rosso Mario , Peter Ildiko
Published: February 2012

This paper presents an analysis of an advanced squeeze casting process suitable for the manufacturing of high performance industrial components more quickly and cheaply. After a short description of the process, some produced components are considered. The components, in A380 alloys, have been T6 heat treated and their soundness has been certified by non destructive tests. All considered components have been designed for advanced application in the automotive field, in particular for quite important sport cars. Standard samples for tensile and impact tests have been machined directly from the previous components. After the execution of the tests the fracture surface of samples has been observed by SEM in order to analyze details and to evaluate the influence of the process and of the alloy on the fracture behavior. On polished transverse sections of samples the microstructure of the alloy has been observed, highlighting a mainly globular shaped microstructure as expression of the attained semi-solid conditions during the processes. A critical analysis has been developed to evaluate the real potential and to present some criticism of the process.
Cold Backward Extrusion of Titanium Billet with Pulsating Lubricant Supply on Servo Press
Authors: Matsumoto Ryo , Sawa Shinkichi , Utsunomiya Hiroshi
Published: February 2012

To prevent seizure in backward extrusion of holes for lightweight structural components, an extrusion method utilizing a punch having an internal channel for supplying liquid lubricant to the punch nose was applied to forming of pure titanium billet using a servo press. On the servo press, the punch was pushed into the billet in a manner combining pulsed and stepwise modes. The sufficient amount of the liquid lubricant was pulsating supplied to the cavity formed at the bottom of the hole. Appropriate punch ram motion and forming limit for preventing seizure are determined from the surface observation of the formed hole and the punch.
Analytical and Numerical Approaches to Predict the Flow Characteristics of a Magnetorheological Fluid in Rotational Symmetric Cross Sections
Authors: Rösel Sebastian , Merklein Marion , Grüner Martin
Published: February 2012

For a better understanding of the hydroforming process using magnetorheological fluids as a medium it is necessary to gain basic information for an analytical and numerical description of the fluid behaviour under process relevant conditions. Therefore an experimental setup is build up, which consists of a pressure chamber and a rotational symmetric outlet. Different parameters like feed rate and magnetic flux density are varied. Afterwards an analytical approach and a numerical model are developed. To get the relevant material input data for the fluid description an additional numerical simulation of the created magnetic flux density with flux lines perpendicular to the symmetry line of the outlet is performed. The leakage rates, which are observed for the experiments, are compared to the analytically calculated ones and to the results of the numerical simulation.
Observation of Welded Interface of SPCC/A1100-O Tailored Blanks Made by Butt Laser Welding
Authors: Iizuka Takashi , Itani Ryo
Published: February 2012

Welding properties and formabilies of a tailored blank which consists of dissimilar metals are interesting because of the possible benefits for lightening of materials. Especially, the combination of mild steel and aluminum or aluminum alloy is expected as a representative of such a light hybrid material. Until now, some successful examples about welding of steel and aluminum using friction stir welding and laser roll welding have been reported. Recently, our research team has developed a butt laser welding method using CO2 laser. It was already confirmed that, by using this method, it was possible to obtain SPCC/A1100 O-tailored blanks with almost equal joint strength to the tensile strength of base aluminum. However, it has not been reported what was made in welded interfaces of the hybrid sheets. In this study, the welded interface of SPCC/A1100-O tailored blank obtained by butt laser welding was observed and analyzed using FE-SEM and EDS. Furthermore, fractured site in some formability tests were also observed, and it was identified where fracture occurred. In the experiments, the welded interface of steel/aluminum tailored blank, which has joint strength of 80MPa-90MPa, was observed. In the observation of low magnification, no clear intermetallic compound layers were seen. In the observation of higher magnification, it was confirmed that some intermetallic layers existed. From results of EDS analysis, it was indicated that this intermetallic compound layer consisted of FeAl3, Fe2Al5, FeAl, Fe2Al and Fe3Al. Thin Fe2Al5 layers of about 3 micro meters mainly existed between steel side and aluminum side. From this layer, some dendritic FeAl3 layers appeared into the aluminum side. In the steel side, relatively wide FeAl layers and Fe3Al layers were seen in turn. According to references, because welded sheet of steel and aluminum with good mechanical properties has intermetallic layers less than 4 micro meters, it was confirmed that butt laser welding method developed by our team had possibility to provide good steel/aluminum tailored blanks. In the fractured site by Erichsen test, Fe2Al5 layered were left in both steel side and aluminum side. Thus, it was indicated that a crack spread along the Fe2Al5 layer. From results of these experiments, it was confirmed that butt laser welding method developed by our team provided steel/aluminum tailored blanks with thin Fe2Al5 layers of about 3micro meters. And, it was indicated that this Fe2Al5 layer brought about early fracture.
Explicit Simulation of Forming Processes Using a Novel Solid-Shell Concept Based on Reduced Integration
Authors: Pagani Mara , Reese Stefanie , Perego Umberto
Published: February 2012

The contribution deals with the simulation of sheet metal forming processes by means of a recently developed hexahedral solid-shell finite element. In contrast to this earlier work, we pursue here explicit integration. The element formulation has the following features. In order to avoid undesired effects of locking an enhanced assumed strain (EAS) concept using only one EAS degree-of-freedom has been implemented. In addition, by means of the assumed natural strain (ANS) method an excellent performance in bending situations is obtained. A key point of the element formulation is the construction of the hourglass stabilization by means of different Taylor expansions. This procedure leads to the important advantage that the sensitivity of the results with respect to mesh distortion is noticeably reduced. Further the hourglass stabilization is in this way designed that locking is eliminated and numerical stability guaranteed. The finite strain material model for plastic anisotropy and non-linear kinematic and isotropic hardening is motivated by a rheological model including Armstrong-Frederick kinematic hardening. The element formulation has been implemented into the academic code FEAP. Some standard benchmark examples are computed.
Improvement on CAE Model for Accurate Torsional Springback Prediction in High Strength Steel Part Forming
Authors: Ishiwatari Akinobu , Kano Hirotaka , Hiramoto Jiro , Inazumi Toru
Published: February 2012

It is difficult to predict springback, torsion in particular, with great accuracy by FE simulation. In this study, the effects of anisotropic yield functions of the blank and elastic deformation of the tools on springback are investigated in order to improve the accuracy of torsional springback prediction in high strength steel part forming. The effects of anisotropic yield functions on the torsional springback in curved hat forming were compared, using parameter sets derived from various experimental methods: uniaxial tensile tests only; hydrostatic bulge tests and uniaxial tension tests; uniaxial and biaxial tensile tests. FE analysis of press forming taking account of tool deformations was carried out and the results were compared with the ones of FE simulation with rigid tools and experimental results. It is demonstrated that FE simulated torsional springback with deformable tool model has better correlation with experimental one than with rigid tool model.
Modeling Induced Flow Anisotropy and Phase Transformations in Air Hardening Steels
Authors: Barthel Clemens , Klusemann Benjamin , Denzer Ralf , Clausmeyer Till , Svendsen Bob
Published: February 2012

In this work a material model for hardening development in sheet metals during forming processes involving loading path changes is formulated. In particular, such hardening development is due to the formation and interaction of dislocation microstructures in the material, resulting in an evolution in the size, center and shape of the yield surface. Such yield surface evolution is accounted for in the current model with the help of an evolving structure tensor. The model is intended for an air hardening steel and takes therefore thermomechanics into account in particular phase transformations from ferrite to austenite and from austenite to martensite. As numerical examples a tension shear test and a heating-cooling sequence are simulated.
Remapping Method for Transferring Data between Two Meshes Using a Modified Iterative SPR Approach for Parallel Resolution
Authors: Kumar Sushil , Fourment Lionel
Published: February 2012

In metal forming simulations, the transfer of data from one mesh to another can be very often required such as, in ALE formulation at each time step or in Lagrangian formulation at each remeshing step. Its accuracy is one of the main concerns for researchers, since the accumulation of generated diffusion can lead to larger numerical error and create convergence problems. Since 1992, the Super convergent Patch Recovery method (SPR) introduced by Zienkiewicz & Zhu [1], was a major breakthrough for the methods to estimate errors in FE solution. Later, it has also been used to recover nodal fields from integration points, in order to transfer data between two meshes [10]. The original method raises some difficulties to treat the domain boundaries. They have not quite properly been handled, in particular in the frame of parallel implementation, despite the fact that, surface phenomena, such as contact and friction, play such an important role in metal forming applications. In the present paper, it is presented a modified iterative SPR method which deals with boundary points with the same order of accuracy as the interior points. It does not require increasing the patch size and it is easier to implement in parallel environment. Also, when interpolating the field on new mesh, a new and consistent technique (P0+ transport) of enriched field has been used. It involves building a P1+ field by mixing the recovered SPR nodal field with the known field at integration points. Results are presented in form of convergence rate and L2 error norm, for several analytical functions for a SPR based transfer operator against a simple volumetric based transfer operator, before being applied to an actual metal forming problem. All computations presented here have been done by using four processors in parallel environment.
A First Approach Toward a Proper Generalized Decomposition Based Time Parallelization
Authors: Poulhaon Fabien , Chinesta Francisco , Leygue Adrien
Published: February 2012

Many models encountered in computer science remain intractable because of their tremendouscomplexity. Among them, the numerical modeling of manufacturing processes involving severalcharacteristic times is a challenging issue. Classical incremental methods often fail for solving efficientlysuch transient models. In that sense model reduction based simulation appears to be a verypromising alternative. Multidimensional parametric models can be solved within the context of theProper Generalized Decomposition (PGD). It opens new horizons regarding time parallelization. Indeed,by no more considering the initial condition of a transient problem as a static input data butas an extra- coordinate similarly to space and time, we demonstrate that it is possible to parallelizeefficiently the computation and even reach real-time in some cases.
Effect of Process Parameters on Seam Weld Quality of ZM21 Tubes
Authors: Segatori Antonio , Reggiani Barbara , Donati Lorenzo , Pinter Tommaso , Rami Y. , Tomesani Luca
Published: February 2012

The increasing attention to magnesium alloys in extruded profiles, especially in the transportation industry, is related to their low density associated with good mechanical properties and complete recyclability. This allows to push towards both increasing efficiency and pollution restrictions. However, these advantages are negatively balanced by the production rates drop in relation to dangerous profile temperatures increasing that force to keep low velocities. In this context, a novel porthole die has been purposely designed for magnesium alloys allowing an increasing of the process velocity up to four times with respect to past solutions. The mandrel consisted of three ports made by 120° bridges that created an equal number of seam welds. The extruded tubes, made in ZM21, were 50 mm in diameter and 2 mm in thickness and were tested under different process conditions. In the present work, the quality of the seam welds has been investigated in relation to each process condition by means of the rubber plug testing method that allowed to applied an hydrostatic tensile state.
Tribological Behaviour of PVD Coatings for Sheet Metal Forming Tools: Laboratory and Industrial Evaluation
Authors: Sgarabotto Francesco , Ghiotti Andrea
Published: February 2012

In the last decades, Physical Vapour Deposition (PVD) and Chemical Vapour Deposition (CVD) processes have been significantly improved and optimized for the applications on dies for sheet metal forming processes. However, due to the different contact conditions at dies-blank interfaces, and the wide range of applied contact pressures, the selection of the correct coating may be still affected by trials-and-error approaches. Although many methods to evaluate the tribological performances of such coatings can be found in scientific literature, they often suffer of limitations in reproducing the interface conditions typical of industrial processes. The objective of the present research work is to investigate the tribological behaviour of two coatings deposited by PVD magnetron sputtering technique. Both investigations in laboratory and industrial conditions were performed: the former to evaluate their tribological characteristics, the latter to test the performances of coatings in production lines. The results, in terms of wear resistance, outline the comparison of the new technology with the performances of traditional dies.
Sliding Wear Behaviour of Al-7075 Based Metal Matrix Composite: Effect of Processing Parameters
Authors: Dasgupta Rupa , Das Satyabrata , Jha Amol Kumar
Published: February 2012

Metal Matrix Composite made from Al-7075 based alloy dispersed with 10% SiC particles through the liquid metallurgy route were evaluated for their sliding wear properties under different loads and for a length of sliding distance. The volume loss and wear rate under different experimental conditions were compared between the following conditions for both the alloy and composite (i) cast (ii) aged (iii) extruded. Attempts have been made to arrest wear of the alloys that experience seizure under the mildest of experimental conditions through the above processing techniques and explain the experimental results through worn surface studies. The extent of success attained through each process has been discussed. It is felt that the cumulative effect of the different processing techniques including composite making, ageing and extrusion can open up new avenues for this alloy system, which in general is not used for wear resistant applications.
Biaxial Tensile Test of High Strength Steel Sheet for Large Plastic Strain Range
Authors: Hakoyama Tomoyuki , Kuwabara Toshihiko
Published: February 2012

Deformation behavior of high strength steel with a tensile strength of 590 MPa under biaxial tension was investigated for a work equivalent plastic strain range of 0.002 0.16. The test material was bent and laser welded to fabricate a tubular specimen with an inner diameter of 44.6mm and wall thickness of 1.2 mm. Using a servo-controlled tension-internal pressure testing machine, many linear stress paths in the first quadrant of stress space were applied to the tubular specimens. Moreover, biaxial tensile tests using a cruciform specimen were performed to precisely measure the deformation behavior of the test material for a small strain range following initial yielding. True stress-true plastic strain curves, contours of plastic work in stress space and the directions of plastic strain rates were measured and compared with those calculated using selected yield functions. The plastic deformation behavior up to an equivalent plastic strain of 0.16 was successfully measured. The Yld2000-2d yield function most closely predicts the general work contour trends and the directions of plastic strain rates of the test material.
Influence of Punch Velocity on Spring Back in Micro Forming
Authors: Wielage Hanna , Hu Zhen Yu , Vollertsen Frank
Published: February 2012

In macro forming it is already known, that the punch velocity has an influence on the deep drawing process. This influence is considerably induced by the velocity dependent friction behavior between sample and tool. A further influence is the strain rate dependent forming behavior of the material. In micro range, the influence of punch velocity on the deep drawing process could, due to the size effects, be different from that in macro range, for example the spring back behavior. In this article the influence of punch velocity on the spring back behavior in micro deep drawing is investigated using strip drawing test with two different widths (1 mm and 2 mm). Experiments with aluminum strips with a thickness of 50 µm were performed with punch velocities ranged from 1 mm/s to 1000 mm/s. The strain behavior, which occurs with different punch velocities are investigated on the basis of microsections. The spring back of all samples was measured by an optical measurement system and compared with each other. From the reported work it can be concluded, that with increasing punch velocity the spring back of the complete system is increasing, while the spring back at cup wall stays constant. As reasons can be cited mass inertia effects due to the high velocities and the velocity dependent friction.
Optimization of Forging Preforms by Using Pseudo Inverse Approach
Authors: Halouani Ali , Li Y.M. , Abbès Boussad , Guo Y.Q. , Meng F.J. , Labergère Carl , Lafon Pascal
Published: February 2012

A simplified method called “Pseudo Inverse Approach” (PIA) has been developed for axi-symmetrical cold forging modelling. The approach is based on the knowledge of the final part shape. Some intermediate configurations are introduced and corrected by using a free surface method to consider the deformation paths without classical contact treatment. A new direct algorithm of plasticity is developed using the notion of equivalent stress and the tensile curve, which leads to a very fast and robust plastic integration procedure. Numerical tests have shown that the Pseudo Inverse Approach is very fast compared to the incremental approach. In this paper, the PIA will be used in an optimization loop for the preliminary preform design in multi-stage forging processes. The optimization problem is to minimize the effective strain variation in the final part and the maximum forging force during the forging process. The numerical results of the optimization method using the PIA are compared to those using the classical incremental approaches to show the efficiency and limitations of the PIA.
Statistical Analysis of Forming Processes as a First Step in a Process-Chain Analysis: Novel PRO-CHAIN Components
Authors: Steffes-Lai Daniela , Clees Tanja
Published: February 2012

This paper presents a new approach for statistical analysis of process chains, including a parameter sensitivity analysis of each process step as a basis for dimension reduction, and an efficient interpolatory metamodel in order to predict new designs. A Monte Carlo alike evaluation of this metamodel results in the requested statistical information, e.g. quantiles of the output functionals. Numerical results are presented for the forming process of a ZStE340 metal blank of a B-pillar. Additionally, a brief overview of results of the process chain forming to crash is given.
Cazacu and Barlat Criterion Identification Using the Cylindrical Cup Deep Drawing Test and the Coupled Artificial Neural Networks – Genetic Algorithm Method
Authors: Aguir Hamdi , Alves José Luis , Oliveira Marta C. , Menezes Luis Filipe , BelHadjSalah Hedi
Published: February 2012

This paper deals with the identification of the anisotropic parameters using an inverse strategy. In the classical inverse methods, the inverse analysis is generally coupled with a finite element code, which leads to a long computational time. In this work an inverse analysis strategy coupled with an artificial neural network (ANN) model is proposed. This method has the advantage of being faster than the classical one. To test and validate the proposed approach an experimental cylindrical cup deep drawing test is used in order to identify the orthotropic material behaviour. The ANN model is trained by finite element simulations of this experimental test. To reduce the gap between the experimental responses and the numerical ones, the proposed method is coupled with an optimization procedure based on the genetic algorithm (GA) to identify the Cazacu and Barlat’2001 material parameters of a standard mild steel DC06.
Evaluation of Associated and Non-Associated Flow Metal Plasticity; Application for DC06 Deep Drawing Steel
Authors: Safaei Mohsen , De Waele Wim , Zang Shun Lai
Published: February 2012

In this paper the capabilities of Associated Flow Rule (AFR) and non-AFR based finite element models for sheet metal forming simulations is investigated. In case of non-AFR, Hill’s quadratic function used as plastic potential function, makes use of plastic strain ratios to determine the direction of effective plastic strain rate. In addition, the yield function uses direction dependent yield stress data. Therefore more accurate predictions are expected in terms of both yield stress and strain ratios at different orientations. We implemented a modified version of the non-associative flow rule originally developed by Stoughton [1] into the commercial finite element code ABAQUS by means of a user material subroutine UMAT. The main algorithm developed includes combined effects of isotropic and kinematic hardening [2]. This paper assumes proportional loading cases and therefore only isotropic hardening effect is considered. In our model the incremental change of plastic strain rate tensor is not equal to the incremental change of the compliance factor. The validity of the model is demonstrated by comparing stresses and strain ratios obtained from finite element simulations with experimentally determined values for deep drawing steel DC06. A critical comparison is made between numerical results obtained from AFR and non-AFR based models
On the Modeling of Evolving Elastic and Plastic Anisotropy in the Finite Strain Regime – Application to Deep Drawing Processes
Authors: Vladimirov Ivaylo N. , Pietryga Michael P. , Tini Vivian , Reese Stefanie
Published: February 2012

In this work, we discuss a finite strain material model for evolving elastic and plastic anisotropy combining nonlinear isotropic and kinematic hardening. The evolution of elastic anisotropy is described by representing the Helmholtz free energy as a function of a family of evolving structure tensors. In addition, plastic anisotropy is modelled via the dependence of the yield surface on the same family of structure tensors. Exploiting the dissipation inequality leads to the interesting result that all tensor-valued internal variables are symmetric. Thus, the integration of the evolution equations can be efficiently performed by means of an algorithm that automatically retains the symmetry of the internal variables in every time step. The material model has been implemented as a user material subroutine UMAT into the commercial finite element software ABAQUS/Standard and has been used for the simulation of the phenomenon of earing during cylindrical deep drawing.
Influence of Different Pre-Stretching Modes on the Forming Limit Diagram of AA6014
Authors: Werber Alexandra , Liewald Mathias , Nester Winfried , Grünbaum Martin , Wiegand Klaus , Simon Jörg , Timm Jürgen , Bassi Corrado , Hotz Walter
Published: February 2012

In order to evaluate the formability of sheet materials forming limit diagrams (FLD) are recorded which represent the values of major and minor strain when necking occurs. FLDs are recorded based on the assumption that exclusively linear strain paths occur. In real forming parts, however, particularly in those with complex shapes, predominantly non-linear strain paths occur which reduce the accuracy of the failure prediction according to a conventional FLD. For this reason forming limits after loading with non-linear strain paths have to be investigated. In this contribution a systematic analysis of the forming limits of a conventional AA6014 alloy after loading with non-linear strain paths is presented. This material is pre-stretched in uniaxial, plane strain and biaxial direction up to several levels before performing Nakajima experiments in order to determine FLDs. During the pre-stretching process as well as during the Nakajima experiment the strain distribution can be measured online very precisely with the optical deformation measurement systems GOM Aramis or VIALUX. The gained curves are compared to the FLD of the as-received material. The results prove a significant influence of the pre-stretching condition on the forming limits of the used aluminum alloy. For a low pre-stretching in uniaxial as well as in biaxial direction the FLDs show a slightly reduced formability while after higher pre-stretching levels the forming limit can be improved such as for biaxial loading after uniaxial pre-stretching. The formability after pre-stretching in plane strain direction was changed. Also, a shift of the FLD depending on the direction of pre-stretching can be observed.
Laser Heat Treatment Effects on Roller Hemming in Aluminum Alloys
Authors: Kleeh Tobias , Merklein Marion , Roll Karl
Published: February 2012

Especially for bending/hemming operations, aluminum alloys lack sufficient formability. The aim is to use them in the same way as other structural materials such as conventional steel. In this study, a combined laser-assisted roller hemming process is set up. For this, a 4000 W Nd:YAG-laser with a wave-length of 1096 nm is used. Several parameters are defined and the effects of heat treatment on the hemming ability of AA6014 were investigated. Taking into account the kinds of components that are expected to be formed, the experiment is set up with two flexible robots that can rotate on six axes. One moves the roller for the forming process and the other guides the laser system. Radiation tests by the laser were conducted before the forming processes. Sheets were irradiated with a laser energy level between 10 J/mm and 40 J/mm. The heat-treat condition was confirmed by micro-hardness tests. Roll (in/out) for straight contours after final hemming were measured and the effect from the heat treatment was investigated. Furthermore, the influence of the applied heat on the final hem geometry was investigated. Limitations of the conventional roller hemming process were highlighted and the transition to laser-assisted roller hemming defined.
Experimental Analysis of the Influence of Process Parameters on Residual Stress in AA2024-T3 Friction Stir Welds
Authors: Carlone Pierpaolo , Palazzo Gaetano S.
Published: February 2012

Friction stir welding (FSW) is an innovative joining technique, in which a solid state weld is obtained by means of frictional heating and plastic deformation of the processing material. In recent years, an increasing application of the FSW process has been observed, however, for the effective implementation of the technique in safety-critical components and to predict the fatigue behavior of FSWed assemblies, an accurate knowledge of the process-induced residual stress is needed. In this paper results, provided by an experimental analysis on the influence of process parameters on the residual stress in 4mm AA2024-T3 butt joints are reported and discussed. The contour method has been applied to evaluate the residual stress. An asymmetric stress distribution has been found in all samples. A significant dependence of the tensile and compressive stress peaks on the feed rate has been found, while a non monotonic influence of the rotating speed has been evidenced.
Quality Analysis of Friction Stir Welded Butt Joints by Means of Experiments and Simulations
Authors: D'Urso Gianluca Danilo , Longo Michela , Giardini Claudio , Ceretti Elisabetta
Published: February 2012

Friction Stir Welding (FSW) is a solid-state welding process introduced and developed in last decades. In this process a rotating tool is pressed on the two parts to be welded (mainly two plates), driven into the material and then translated along the parts interface. Academic and industrial interest is focused on the characteristics of the joined part in terms of mechanical resistance and fatigue resistance of the joints. These characteristics are heavily related to the process parameters chosen since the material stirring and the material temperature greatly depend on the pin rotating and translating speed. In fact, the stirring phenomena and the friction acting between the shoulder of the pin and the sheets, greatly increase the part temperature so that the material greatly changes its structural characteristics due to softening effect: grain dimensions, local hardness, grain orientation. Moreover, due to the physical material movement different types of defects (mainly voids) can be present in the welded zone (nugget). In particular three different areas can be identified: the heat affected zone (HAZ), the thermo-mechanical affect zone (TMAZ) and the nugget. The extension and the characteristics of these zone are very important in order to define the joint quality. These investigations are very important especially when FSW is applied in industrial fields such as aerospace, automotive and naval. To cut and to investigate an experimentally obtained joint is interesting for understanding the weld quality, but FEM simulation of the process can add very useful information in defining how the process parameter influence the joint behaviour and the three different zone extensions. As an example the heat flux, and consequently the temperature distribution inside the material, depend on the combination of rotation and welding speeds. For this reason, in the last years several efforts were oriented to the numerical simulation of the process, in order to investigate thermo-mechanical aspects, stress and strain distributions, thermal flow, residual stresses. The present paper deals with the set up of a FE model for the simulation of the FSW process whose results are correlated with the experimental observations carried out when joining AA6060-T6 aluminium alloy plates 5mm thick with a cylindrical tool with flat shoulder. The experimental campaign was performed under different welding conditions varying the tool rotational speed and the welding speed. A three-dimensional piezoelectric load cell was used to measure the welding forces in the main directions. The numerical model was developed and set up in DEFORM 3D environment. The information obtained from the model helped in the understanding of the welding phenomena.
Extension of a Failure Criterion for Hemming Applications in the FEM Simulation
Authors: Zubeil Martin , Roll Karl , Merklein Marion
Published: February 2012

In the FEM calculation of sheet metal forming processes to determine the failure case, the forming limit diagram is basically used. To determine the failure case at bending condition, the forming limit diagram can not be used. This behaviour was shown by many authors. Bending tests with an aluminium material (AC170PX) have shown that a high deformation ratio can be achieved without failure. Based on the loading conditions and the previous strain path through the deep-drawing process, a resulting bendability at a certain point can be obtained. Depending on the pre-damage and the mentioned loading conditions of the material failure will be occurring during bending at different times. Current developments of failure criteria consider the failure as in ductile fracture or shear fracture, which must be considered separately in the simulation. To rule out a separate analysis of the mode of failure in the post-processing, an existing failure criterion is extended and will be presented in this work. For the applications flanging and hemming the following extension of a stress-based failure criterion is proposed. Based on the triaxiality and the equivalent plastic strain a monitoring of the stress ratio is implemented in the FEM simulation. During the forming simulation the monitoring system observe the stress ratio based on the principal stresses resulted from the integration (Gauss) point of the shell element. According to the evaluation of the stress ratio evolution, a relevant definition will take into account how the damage will be accumulated. If the critical value of damage in the integration point of the shell element is reached, failure will be occur based on the position of the sheet thickness.
Simulation of Hybrid Joining Technologies Using the Example of Clinch-Bonding
Authors: Etemadi Sirous , Hahn Ortwin , Roll Karl
Published: February 2012

In this paper a method for simulating hybrid joining processes will be described. The simulation of joining processes with adhesives is necessary because mechanical joining processes are mostly applied in combination with adhesives. However, the simulation of hybrid joining processes is not state of the art. The reason is the Fluid-Structure-Interaction between the adhesive and the plates, which occurs due to the highly uneven stiffness of the materials. This problem is minimized by the use of an elastic‑plastic material model and a Lagrange formulation for the adhesives. The parameters for the material formulation and the friction have been evaluated by conducting a design of experiment. The correlation between simulation and experiment is ensured by an evaluation of the geometrical distribution of the adhesives within the clinch‑bonding point and the force-displacement diagram. Considering the very low computing time of approximately thirty minutes, the obtained result is very satisfying.
Investigation of Thick Sheet AHSS Springback in Combined Bending under Tension
Authors: Chalal Hocine , Racz Sever Gabriel , Balan Tudor
Published: February 2012

This contribution investigates the springback behavior of several advanced high-strength sheet steels (TRIP, Dual-Phase, ferrite-bainite) with thicknesses up to 4 mm. Samples were tested by means of the bending-under-tension (BUT) test. This test proved very useful to discriminate constitutive models, while avoiding the interference of friction in the springback investigations [1,2]. However, the interpretation and numerical simulation of the test have to be carefully performed [3,4]. The applicability of several guidelines from the literature was investigated experimentally and numerically, in the context of thick AHS sheets. The monotonic decrease of springback as back force increased was confirmed for this category of sheet steels, and a general trend for the non-linear influence of the tool radius was observed. The influence of numerical factors on the predicted values of springback was investigated. Conclusions and simple guidelines are drawn from the analysis with industrial sheet forming applications in mind. References [1] T. Kuwabara, S. Takahashi, K. Akiyama, Y. Miyashita, SAE Technical paper 950691 (1995) 1-10. [2] I.N. Vladimirov, M.P. Pietryga, S. Reese, Prediction of springback in sheet forming by a new finite strain model with nonlinear kinematic and isotropic hardening, Journal of Materials Processing Technology 209 (2009) 4062-4075. [3] W.D. Carden, L.M. Geng, D.K. Matlock, R.H. Wagoner, Measurement of springback, International Journal of Mechanical Sciences 44 (2002) 79-101. [4] K.P. Li, W.P. Carden, R.H. Wagoner, Simulation of springback, International Journal of Mechanical Sciences 44 (2002) 103-122.
An Analytical Method for Prediction of Cross-Sectional Deformations in Stretch Bending
Authors: Welo Togeir
Published: February 2012

Abstract. A method for the prediction of cross-sectional distortions of hollow sections under the action of combined bending and stretching has been developed. The model is based on classical deformation theory of plasticity combined with detailed interpretations, making the simplifications necessary to develop a practical closed-form solution while retaining basic mechanisms. The model provides the ability to assess the effect of material properties, tool and section geometry on deformation of individual cross-sectional members. The applicability of the model has been verified with a series of carefully controlled laboratory experiments done in an industry-type rotary stretch bending machine. The findings show that the main parameter with respect to (magnitude of) nominal deformations is the width of the cross section, whereas flange thickness is the main parameter with respect to controlling dimensional accuracy. Comparing the experimental and analytical results, the agreement is remarkably good - in most cases comparable to what could be achieved with more elaborate FE analyses - despite the simplifications necessary to develop the model. A new tool design concept denoted Flatness Limit Curve has been introduced, and used to demonstrate the general applicability of the approach.
Warm Incremental Forming of Magnesium Alloys Using Hot Fluid as Heating Media
Authors: Galdos Lander , Sáenz de Argandoña Eneko , Ulacia Ibai , Arruebarrena Gurutze
Published: February 2012

Industrial application of magnesium alloys is increasing in the last decade due to the very high mechanical strength to weight ratio they present. Typical applications are aeronautic parts but their use in the automotive industry is also growing. The bigger the reduction of the vehicle weight is, which can be obtain using these alloys, the bigger the energy saving will be in the near future. However, the formability of these alloys is poor and they are very difficult to be formed at room temperature. Several works have been presented by different authors on the positive influence the temperature increase has to form magnesium alloys. Normal process temperature is about 200-250°C. In this paper warm incremental forming of magnesium alloys is investigated. The work focuses in the formability limits of the alloys and the identification of the optimal process parameters. Aiming to obtain a homogeneous temperature in the forming areas, hot fluid is used as heating media. Experimental results for different temperatures are presented and final microstructures are related to the possible deformation mechanism.
Towards Energy Efficiency in Incremental Forming of Titanium
Authors: Ambrogio Giuseppina , Gagliardi Francesco , Filice Luigino , Aghinelli Odetta
Published: February 2012

Incremental sheet metal forming (ISF) had a great interest in the scientific community, in the last years. A common opinion is that ISF has not to be considered as an alternative to conventional stamping but has to be regarded as a process able to work materials in a new way. Furthermore, ISF could be a suitable alternative to manufacture some “hard to work materials”. Among them, Titanium plays a relevant role. Today Titanium is usually worked by superplastic forming (SPF) or hot forming (HF) in case of simple shapes. However, both the processes are very slow and expensive. In a previous work the authors showed how it is possible to form Titanium alloys using ISF combined with a local heating. However, heating suggests also to analyze energy consumption. The process does not requires large forces but is really slow. Thus, the different heating sources can have a deep impact on the global energy performance. The paper is a first attempt to consider the process in a wider view, looking at the energy consumption as a primary issue. In particular, a comparison among different heating methods was carried out.
In-Process Hardening in Laser Supported Incremental Sheet Metal Forming
Authors: Mohammadi Amirahmad , Vanhove Hans , Behera Amar Kumar , van Bael Albert , Duflou Joost R.
Published: February 2012

The effect of localized laser hardening on the dimensional accuracy of incrementally formed steel sheets has been studied. By dynamically heating by means of laser beam scanning (500W Nd:YAG) the temperature of the sheet reaches the austenization temperature and by subsequent self-quenching a hard martensitic structure will form. Using FE modeling, a laser power setting of 202 W, scanning velocity of 600 mm/min and beam diameter of 6 mm were selected as optimum processing parameters for transformation hardening. Hardness tests were performed in order to investigate the hardness profile along the depth and width of the laser hardened zone. Experimental results reveal that generation of a selectively hardened martensitic band, formed by transformation hardening, can increase the accuracy of the incrementally formed part.
Evolution of Roughness on Straining of Interstitial Free – IF Steel Sheet
Authors: Unfer Ricardo Kirchhof , Bressan José Divo
Published: February 2012

This study aims to assess the evolution of surface roughness and waviness parameters with plastic strain in Interstitial Free – IF steel sheet. For the achievement of this study, it was considered various roughness and waviness profile parameters such as: arithmetic average roughness (Ra), maximum distance peak-valley (Rt), average waviness (Wa) and waviness of the total height peak-valley (Wt). Tensile test specimens of IF steel at 0º, 45º and 90º to the direction of rolling were fabricated. After preparing the sheet proof specimens, it was performed simple tensile tests and measurements of roughness and waviness of the specimen surface at various strain stages resulting in a large quantity of data. During the tensile test, it has been measured the following plastic strain to indicate the incremental step: (e1) longitudinal strain and (e2) transverse strain. From these data, it was possible to obtain points needed to plot the curves of roughness and waviness parameters versus strain and to determine the material behavior using equations of the equivalent strain. From the curves drawn it was possible to see how the material roughness and waviness behaves during the straining in the uniaxial tensile state, with the possibility to predict the influence of plastic strain on roughness and waviness parameters and the onset of local necking of IF steel sheet. The waviness parameters Wt is the best for characterizing the onset of local necking.
An Upper-Bound Prediction of Tangential Force in Single Point Incremental Forming
Authors: Mirnia Mohammad Javad , Mollaei Dariani Bijan
Published: February 2012

In the present work, the upper-bound approach is used to study the deformation zone of single point incremental forming of truncated cones. The velocity field and the dissipated power of the process are achieved using an assumed deformation zone and streamlines defined by Bezier curves. The tangential force acting on the tool is attained by optimizing the presented upper-bound solution. Then, influences of the effective parameters including vertical pitch, initial thickness, tool diameter, and wall angle on the tangential force are investigated. In order to validate the presented upper-bound solution, predicted tangential forces are compared with experimental data available in literature. The comparison shows an appropriate agreement between them.
Any Effect of Processing History on Precipitation Hardening of Metastable Austenitic Stainless Steels
Authors: Saha S. , Datta Kanykumari , Mitra Manoj Kumar , Lindgren L.E. , Post J.
Published: February 2012

The strain induced martensite formation is known to be sensitive to the stress state [1]. The amount of martensite formed varies if the same amount of load is applied in different states of stress. For example, martensite formed is maximum in tension, minimum in compression and somewhere in between, in shear. Martensite could also originate due to elastic stress, or in absence of any mechanical energy, solely, by change in temperature (thermal martensite). Thus, it is the aim of this project to understand the different kinds of martensite that originate due to different processing paths and then, to understand how the precipitation behaviour is affected by the process of arriving at the martensite. Basically, it is to understand how the dislocation substructure varies under various stress states and thermal states, and how it affects the kinetics and type of precipitation in metastable austenitic stainless steels. This work is carried out with a high alloy, metastable and precipitation hardenable stainless steel called Sandvik NanoflexTM. Formation of strain induced martensite in semi austenitic metastable stainless steels is strongly a function of strain rate. It is also a function of stress state: in this study a planer planar shear state and an axial tensile state of stress are compared. The morphology of martensite formed in tension is different from that in shear. Predominantly sheared samples show rippled structures with ridges and valleys where as predominantly tensile deformation creates samples with planer planar laths separated by crevasse-like boundaries. The morphological difference in the martensite formed under different stress-states, creates different shape of precipitates in semi austenitic metatstable stainless steels. The predominantly sheared samples show roundish precipitates where as predominantly tensile deformed samples show precipitates with a core. Difference in the dislocation substructure is thought to be the root cause of such morphological differences in the martensite and precipitates formed through different stress states.
Ludwik’s Model Parameter Identification for V-Bending Simulations with Ti64 and MS1200
Authors: Mendiguren Joseba , Galdos Lander , Sáenz de Argandoña Eneko , Silvestre E.
Published: February 2012

Flow curves coming from tensile tests together with constant young modulus are widely used by industry when modelling sheet metal bending processes. Unfortunately this modelization strategy based on previous mentioned variables is not accurate enough and leads to big errors due to the springback of the material. This drawback is even more important when high strength steels are bended. Aiming to reduce the springback errors, Ludwik’s hardening material models under bending deformation have been obtained for a Ti6Al4V alloy and for a MS1200 martensitic ultra high strength steel and their accuracy has been compared to the classical models obtained from tensile tests. First of all, classical Ludwik’s hardening models are obtained from tensile tests. Then, using a V-Bending test and inverse simulation, Ludwik hardening model parameters for bending are calculated using a Von Mises yielding criteria. As a result, a model able to represent the bending behaviour of these two materials more accurately without complex code modifications is achieved.