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It is impossible to obtain the forming limit curve (FLC) by full zone hydraulic forming test under quasi-static (QS) condition since the liquid will leak from the notches of the specimen once the pressure increases. In this study, a novel method is proposed to investigate the frictionless full zone hydraulic FLC of AA5A06 under high strain rate (HSR) condition based on the impact hydroforming technology (IHF). It is found that the FLC is increased significantly by IHF compared with the quasi-static rigid punch (QS-R) forming and the quasi-static hydraulic (QS-H) forming. Differentiating with the QS-H, the increase amounts of FLC at the biaxial tension zone and the tension-compression zone are notably different for IHF. Additionally, the theoretical calculations of FLC is conducted by using M-K model combining with Hill48 anisotropic yield criterion under QS and HSR conditions. The results calculated by the M-K model reasonably agree with the ones obtained from experimentation under QS and HSR condition, and a higher initial thickness ratio is assigned for HSR considering the neck postponing effect of inertia.

Laser shock hydroforming is a novel microforming method that adopts laser energy as the driving force and liquid as the medium to transmit pressure. The method combines the advantages of laser shock forming and micro hydroforming. Previous research has demonstrated that this method can deform thin sheets into complex shapes at high strain rates. We know that the formability of materials is improved at high strain rates, but experimental analysis on this method alone cannot examine the deformation process. Therefore, this study first conducted free- and die-forming experiments of laser shock hydroforming to characterise the features of the deformation process and understand the factors that may contribute formability enhancement. Experimental results were discussed to uncover the formability of thin sheets under different conditions, including the laser energy and the effect of the die. Then, a numerical model was established considering fluid–solid interaction. The deformation process, sheet velocity, contact stress and strain rate were investigated through numerical means, and these indicators explain the mechanism of formability improvement in this method. Furthermore, the numerical results indicate a positive phenomenon—pressure equalisation—which might be due to the reflection of pressure off the rigid side wall of the liquid chamber.

This work presents an experimental study of aluminum sheet forming. It shows the performances of a steam hydroforming process. The new forming technique is based on both temperature and pressure to make a sheet form. These parameters are linked to the water vaporization process into a cavity covered by the blank. The performances are deduced by comparing the results obtained from the steam tests with those acquired at room temperature. Performances are expressed in terms of forming loads, surface creation, and forming limits. The experimental results show that the use of the steam temperature as a factor could decrease the limit loads necessary for the forming operation and increase the surface creation. On top of improving forming loads and surface creation, increasing steam temperature induces a clear improvement of forming limits.

In this article, a newly developed method for forming metal sheets together with long fiber-reinforced thermoplastics (LFT) to hybrid parts is presented. The idea of combining two different materials in one part is nothing new, but most of the existing processes use at least separate production techniques for each material and an additional joining operation. The special characteristic of this new process is realized by a combined forming tool for both sheet metal and LFT to create a hybrid part with only one necessary and simultaneously executed process step. Besides contact to the punch, the metal sheet is also formed by the molten LFT material, which behaves like a hydraulic fluid in hydroforming processes. With this method, it is possible to reduce the thickness of sheet metal components by adding a LFT reinforcement structure. The interface connection between the metal sheet and LFT is realized by using a bonding agent, which is previously applied to the metal sheet via coil or powder coating. To achieve this hybrid forming process, new tool and sealing concepts have been developed and the corresponding process parameters were identified and optimized. As a result, the innovative process offers a cost- and time-efficient solution for multi-material lightweight design.

This paper presents the first academic study of a hydroforming process known as edging. An edging process allows a smaller radius to be produced with a lower pressure than a standard sheet hydroforming process and is currently developed by trial and error that relies heavily on operator experience. This paper reports the first systematic investigation of the edging process that concludes in a new analytical model which can be used to enable the design of edging processes. It was found that in each of the three aerospace nickel alloys tested, the edging technique was effective in sharpening the flange radius from 10 mm to 4 mm or from 6 mm to 2 mm in thicknesses of 2.1 mm and 1.2 mm respectively. This radius is equivalent to between 1.5 and 1.8 times the material thickness (1.5 t to 1.8 t). These results were achieved by using edging heights of between 2.5 to 5 mm (2.5 t to 3 t). At the limits of successful edging operations, (under 2 t) three different kinds of phenomena were observed: crushing of the top of the component, radii which were pushed inwards, and the generation of an underside lip which protruded from the bottom of the samples. This paper discusses the benefits of hydroforming with an edging operation, explores the limitations of the edging process, derives an equation which can be used to estimate the sharpness of an edged radius and finally defines a model which enables the design of an edging operation. The work reported here is particularly relevant to aerospace applications because it will enable lighter components to be formed with lower pressures with nickel based superalloys.

For the existence of bending deformation during low pressure tube hydroforming(LPTH), springback is unavoidable and deteriorate the forming accuracy. In this paper, an analytical model of springback for LPTH was proposed. The simulation and experiment were carried out to investigate the effects of the main factors on the springback, such as internal pressure, corner radius and thickness. The results indicate that, different from expansion deformation, bending forming is the main and basic deformation for tube forced into the required shape during the LPTH. Consequently, springback appears. However, the deformation type has great dependence on the internal pressure, which ensures the internal pressure of the function to reduce the springback. There is a critical pressure which would induce pure bending deformation and result in the largest springback. Consequently, it need try to avoid the critical pressure for the LPTH. On the contrary, whatever the internal pressure is less or bigger than the critical pressure, springback are all decreased. In contrast, it is more effective to decrease the springback when pressure is bigger than the critical pressure. In addition, bigger corner radius can also contribute to decrease the springback because of a much larger tensile force introduced under the same internal pressure. For a definite component, improving internal pressure is the only method to decrease the springback.

International audience; It is now well recognized that the material data obtained from a tensile test is less appropriate than those from a Tube Bulging Test (TBT) for a finite element simulation of tube hydroforming. However, the manufacturers still use classical data (often tensile test data) for designing metal operations due to the lack of standard for the TBT and a more complex post processing analysis of experimental measures. Getting the hardening curve from the tube bulging test requires the use of an analytical or numerical model. In this paper, three models for post-processing measures obtained from the TBT are compared based on the same experimental procedure. Thanks to a preliminary step, consisting of the validation of the analytical models through the use of finite element simulations of the TBT, it highlights that the results obtained for the local (stress and strain) and global components (the thickness distribution along the tube and the deformed tube profile) are very close, whatever the models. The test configuration (die radius and free length) seems to have no significant impact on the resulting stress-strain curve for the three models. The three models are used for post processing tube bulging tests performed on AISI304, INCONEL and Copper tubes validating their capacity for tube characterization on different materials. Finally, this study demonstrates that the Boudeau-Malécot Model can be used to obtain hardening curve from TBT without a loss of accuracy compared to more complex post-processing models and with an important gain of quality compared to tensile test.

Due to the continuous weight reduction effort in the automotive sector, formability enhancement of aluminum alloys in forming and hydroforming processes is gathering much attention from research institutes and industries. During sheet forming processes, large deformations are desired to obtain complex shapes but these are limited by the appearance of defects such as wrinkling and cracks. To avoid these issues, intermediate annealing heat treatments are often applied as a possible solution. Nevertheless in large components where small details have to be created, local heat treatment through lasers can be cost effective over the furnace treatment of the whole part and it would limit possible geometrical distortion in large components. The following article presents fiber laser process parameters definition on deformed sheets made of Al6060 alloy. Grain structure variation and hardness decrease were studied to correctly select process parameters (laser power, feeding speed and overlapping among subsequent passes) to increase material formability. In addition, a systematic comparison between fiber laser and furnace heat treatment was assessed proving the equivalence of the two methods in terms of achieved mechanical proprieties.

The purpose of this study is to predict forming limit diagrams (FLDs) for AA6063 and AA6065 aluminum seamless extruded tubes. The Modified Marciniak and Kuczynski (M-K) method is used with Barlat’s 1989 anisotropic yield function and Voce equation. Furthermore, a new calibration method for FLD determination based on the modified M-K method is also applied. The predicted forming limits correlate well with experimental data. It is shown that in comparison to other methods, this method is able to predict necking in tube hydroforming with more accuracy. Therefore, this method can be used to predict bursting in a wide range of practical tube hydroforming of aluminum alloys.

Being light weight and superior in characteristics, hybrid materials such as fiber metal laminate (FMLs) and functionally graded structures (FGS) are becoming increasingly popular in aeronautical, automobile and military industries. In the present work, an innovative methodology which hereafter will be named as “3A method” has been proposed to replace complex shaped, monolithic, metallic sheet parts with hybrid parts. This method is based on simultaneous forming of any number of multiple metallic blanks in required shape by applying hydroforming (HF) technology. Based on numerical simulations, forming limit diagrams (FLDs) are established for three types of blanks forming hemispherical shaped parts using Barlat 2000 yield criteria/DYNA Form/LS Dyna. To validate the simulation results, experimental study is accomplished and optimal process parameters are determined by varying the cavity pressure under constant die-binder gap. Effects of number of layers and thickness of blanks on thinning, wrinkling and punch force have been well studied for three types of blanks and a comparative analysis is made to investigate various failure modes. To achieve a composite layered structure, post forming procedure has been devised and implemented to get a final hybrid part. Furthermore, limitations of the 3A method in terms of final shape of parts are discussed. Good agreement can be found between numerical and experimental research. The new methodology is capable of employing any types of resins and composite materials at any required place in parts for desired characteristics. Elimination of repeated heating and solidification of blank assembly as well as precise punch force and speed requirements make this multilayer blank forming method more efficient, economical and user friendly for manufacturing of FMLs and FGSs at commercial scales.

An enhanced unfolding inverse finite element method (IFEM) has been used together with an extended strain-based forming limit diagram (FLD) to develop a fast approach to predict the feasibility of tube hydroforming process of concept part and determine where the failure or defects can occur. In tube hydroforming, the inverse IFEM has been used for estimating the initial length of tube, axial feeding and fluid pressure. The already developed IFEM algorithm used in this study is based on the total deformation theory of plasticity. Although the nature of tube hydroforming is three-dimensional deformation, in this article a modeling technique has been used to perform the computations in two-dimensional space. Therefore, compared with conventional forward finite element methods, the present computations are quite fast with no trial and error process. In addition, the solution provides all the components of strain. Using the extended strain-based forming limit diagram, the components of strain can lead us to measure the potentials for failures during the deformation. The extended strain-based FLD based on the Marciniak and Kuczynski (M-K) model has been computed and used to predict the onset of necking during tube hydroforming. The extended strain-based FLD is built based on equivalent plastic strains and material flow direction at the end of forming. This new forming limit diagram is much less strain path dependent than the conventional forming limit diagram. Furthermore, the use and interpretation of this new diagram is easier than the stress-based forming limit diagram. The results of analysis for free bulging and square bulging have been compared with some published experimental data and the results obtained by conventional commercial software. The results indicate that the fluid pressure estimated by this method is 2.7 % greater than the results obtained by the experiment in the square bulging sample. In addition, the fluid pressure estimated in the free bulge sample is 5.6 % greater than the experimental results.

The formability can be improved in warm/hot sheet hydroforming due to two important factors of temperature and through thickness normal stress. An extension of the M-K model was presented in this paper with the liquid pressure induced through thickness normal stress taken into account. The through thickness normal stress was introduced by using the general form of the Hill48 criterion. The combined effect of temperature and through thickness normal stress on the increase of FLD0 is achieved by applying a proposed temperature dependent constitutive equation for 5A06 aluminum alloy (a Chinese designation of Al-Mg alloy, corresponding to the ASTM designation of 5056 aluminum alloy) into the M-K approach. The Newton–Raphson method is used in the numerical procedure and it is proved to be stable and correct. The yield loci show a significant dependence on temperature and through thickness normal stress. Both size shrinking caused by the elevated temperature and location shifting due to the increasing thickness normal stress of the yield loci are observed. Comparison of the experimental FLDs of AISI-1012 low carbon steel (an AISI designation of steel) at plane stress and room temperature, STKM-11A steel (a Japanese designation of Steel Tube Kozo Machine) for tube hydroforming at room temperature and 5A90 aluminum alloy (a Chinese designation of Al-Li alloy) at plane stress and elevated temperature with the theoretical results show good agreements. The effect of key parameters, such as inhomogeneity factor f0, n value, m value and initial thickness T0, grain size d, initial surface roughness R0, show a strong dependence on FLDs and increase of FLD0. The increase of FLD0 is formulized in a full quadratic form, which is a function of temperature and through thickness normal stress. The left quadrant of FLD was determined by the cylindrical warm hydromechanical cup deep drawing, which shows a good accordance with the predicted results by using the modified M-K model.

The efficiency and safety of vehicles represent today one of the most important lines of developing in the automotive industry, for example by the introduction of new materials. In fact, the investment in advanced materials represents one of the most important strategies to reduce injury among vehicle occupants in traffic accidents. Associated with the development of safety systems, there is also the possibility of improving efficiency by the introduction of materials that lead to weight reduction, having a direct impact on fuel consumption and carbon dioxide emissions. Metallic foams are one of these materials, due to the excellent ratio between mechanical properties and density. The main goal of this investigation is to study the mechanical behaviour of aluminium sandwich structures, composed by a metallic foam core with two outer layers of metallic sheets. With this work, the authors intend to contribute to a better understanding and consequently to provide design guidelines for the plastic forming of these composites. In order to correctly characterize the mechanical behaviour of the sandwich structure, the foam core and sheets were tested separately. For the aluminium sheet a series of tensile tests were performed, using samples obtained along three different angles to the rolling direction. For the metal foam core, uniaxial compression tests were used. Finally, with the numerical model defined considering isotropic and anisotropic constitutive models, a set of numerical and experimental bulge tests were performed to evaluate the capacity of forming of these panels, using hydroforming processes.

Pre-bending is a critical process required prior to hydroforming. The bending has an effect on the tube thickness and strain which will use up a portion of the formability of the as-received tube. To compensate for this loss of formability, a multi-objective optimization method was applied to improve the hydroforming process after pre-bending. A multi-objective genetic algorithm (MOGA) and Kriging surrogate model were used to optimize the loading path. The Kriging model was used to replace the finite element simulation in constraint handling. The optimal loading parameters in the hydroforming process were obtained for a tube that was previously bent 90°, and showed an improvement in reducing the corner radii of the part at the extrados and intrados of the bend (8.73 mm and 11.24 mm for the extrados and intrados of the bend, respectively). The corresponding corner fill expansion (CFE) was improved by 16.7% (or 1.79 mm) compared to the maximum expansion of 10.73 mm obtained experimentally.

An optimization of load paths in hydroforming of angled tubes are investigated through statistical methods in conjunction with FEA and simulated annealing algorithms. The main aim of this study is to improve the tube formability by applying the optimal load parameters. A new method to design the optimal load paths is represented and it is applied to optimize the load curves in hydroforming of X- and Y- tube shapes. By the aid of proposed method, the tube is formed with good formability indicators and lower capacity of equipments. Comparing the results of this study with the experimental data confirm the effectiveness of the method.

From classical hydraulic bulging of a circular diaphragm, a new method of recording a stress-strain curve is derived named modified hydraulic bulging on the sphere. New method allows more accurate determination of membrane stress in the deforming material. Assumption on the bulk geometry is no longer needed since modification, using sphere as an obstacle, determines the radius of curvature needed in acquisition of membrane stress. Performing modified hydraulic bulging upon just one test specimen, yields three points of stress-strain curve. Experimentally obtained points have different strains, covering different areas; small, medium and large deformations, within a single experiment. Use of the small transducer integrated in apparatus, enables acquisition of force and thus reliable stress acquisition upon the known (spherical) geometry. Likewise, the obtained stress-strain curve can be used in a finite element model of the modified hydraulic bulging on the sphere that is now under development.

A successful approach to achieve a reduction of a car’s total weight is the implementation of lightweight strategies in the design process, e.g. using lightweight materials. An interesting alternative to conventional welding and riveting processes is joining by die-less hydroforming. This work describes an analytical model which can be used to calculate the strengths of these joints, taking into account the material parameters, joint geometry and process parameters. Additionally, validation of the model by both finite element simulations and experiments will be provided. Furthermore, investigations were carried out to implement the described methodology for a multi-joint used in a space frame structure.

The aim of this research is to study the feasibility of vases with tube hydroforming, identifying the limits of this technology. The goal of the simulation study was the identification of the maximum pressure needed to realize vases with big diameter and length. Initially the attention was focused on the realization of a square vase geometry. The initial tubes have a high diameter of 120 mm. Many simulations were conducted to optimize process parameters for this square geometry, namely actuators stroke and water pressure, but it wasn’t possible to completely achieve the die shape at the protrusion edges due to the big diameter expansion and to the rib geometries (thickness, height and fillet radii). Different vase geometries characterized by lower diameter expansion and same dimension of the ribs, were tested. The formability results were improved but there are still problems when the material is filling the ribs (material breakage). In order to realize a safe square part, it was necessary to optimize the rib geometrical dimensions. Other simulations were conducted for a round vase geometry, to check the maximum diameter expansion. Some general design rules were finally summarized.

Sheet metal hydroforming is a forming technology for the production of complex parts. The forming operation is performed by a pressurized fluid. The inner contour of the part has no contact to the tool. This offers high potentials with regard to the forming of stringer-stiffened sheet metals. However, the hydroforming process requires cost-intensive tooling, which makes it inflexible in adapting to short-term changes of the part geometry or producing batches of similar but not identical parts. Incremental forming processes are highly flexible because they reduce or even spare the need of dedicated tooling. In order to manufacture individually shaped sheet stringer parts, the process chain of hydroforming can be extended with an additional incremental forming step. Large batches can be produced costefficiently by hydroforming, upon which single parts can be modified according to particular specifications by means of incremental forming. In this paper investigations of a newly developed process chain for manufacturing sheet stringer parts are described. Their focus was to analyze the feasibility of incrementally forming surface structures with stiffeners both out of flat sheets and out of pre-forms produced by hydroforming. The examined process chain consists of laser welding and hydroforming, followed by incremental driving of the stringers. During the incremental step, the stringers are shaped through local stretching of selected areas. Thus using a simple universal tool set sheets of one millimeter thickness with stringers in varying constellations have been formed successfully. The radii of such curvatures could be changed along a stringer by modifying selected process parameters creating complexly curved surfaces in the sheet.

This paper deals with different aspects of the hydroforming technology and its relevance for the automotive industry. Starting from a brief description of tube hydroforming and sheet hydroforming, the paper shows the progressive developments of both technologies, using results of R&D projects, prototypes and serial production parts as examples. Considerations on the future trends and chances of the hydroforming technologies will close the paper.

The hydroforming process is characterized in these recent years by the remarkable development to compare with other processes manufacturing such as deep drawing and bending... Hydroforming is a reliable process that improves the resistance and rigidity of parts with the geometrical and dimensional tolerances allowing for lower costs tool and therefore an overall cost of manufacturing reduced. The success of hydroforming process requires the control simultaneously of various parameters such as used material properties, thickness, internal pressure,... In this paper, we introduce our model based in a neural approach (ANN) compared to the numerical simulation and experimental results. This method allows a better thickness distribution during Tee extrusion tube hydroforming process (THF) and the optimization of the final part geometry. A multilayer’s neural networks (MNN) program is used to control the tube wall thickness variation, so the loading paths (axial feeding and the internal pressure) are used like inputs for our networks, the thickness is the output.

Tube hydroforming (THF) technology is receiving much interests in automotive and pipe industry thanks to its advantages in terms of final part quality and manufacturing costs. In THF a tube is placed in a die and is expanded by means of high pressure filled-in media. The sealing and the material feeding are guaranteed by two punches that plastically deform and then push the tube edges. To obtain sound parts, the tube expansion zones still represent a criticalness in THF, in fact the severe thinning the tube can undergo in those areas leads to bursting before the die is completely filled. Consequently, the high friction acting on the tube prevents the material flow towards the expansion zones. In this work, an experimental test campaign will show how unbalanced friction conditions can influence the material flow and the geometry of the expanded material in Y-Joint pipes hydroforming. In fact, studying a semi-free expansion of the tubes using different feeding zones length, the tube expansion will follow its free evolution that depends on the imposed unbalanced conditions at the tube edges.

In this paper, uniaxial tensile tests are firstly conducted to evaluate the flow stress of AZ61 magnesium alloy at different temperatures and strain rates. A commercial finite element code of DEFORM 3D is used to simulate the plastic deformation of AZ61 magnesium alloy tube during a y-shape hydroforming process at elevated temperatures. The effects of loading paths with different feeding speed ratios and initial tube positions on the contact area at the counter punch surface at the bulge stage are discussed. The effects of friction coefficient on the contact area at the counter punch surface are also investigated. Finally, using a testing machine with a capacity of 40 tons of axial feeding, 30 MPa of internal pressure and 300oC of maximum temperature, y-shape hydraulic forming experiments of AZ61 magnesium alloy tubes at elevated temperatures are carried out. The analytical flow line patterns and thickness distribution of the formed product are compared with the experimental results.

Nowadays the global warming and the shortage of resources represent big challenges. To cope with these deviances it is the duty of the automotive industry, to build up light weight constructions for high efficient vehicles. For example forming parts as components of exhaust systems or chassis components could be realized by hydroforming, a new flexible technology, which enables the realisation of undercuts and increases the forming limits. Thereby comparatively complex part geometries can be produced. Using this process the blank is deformed by gases or fluids as pressure media. In this case a magnetorheological fluid could be used. The key property of magnetorheological media is an increasing viscosity under magnetic fields. Thus they can not only serve as a pressure medium, but also act as a sealing in the flange area to prevent leakage. For a better understanding of the process a basic characterisation has to be done. Therefore an experimental setup is built up. Different parameters like feed rate and magnetic flux density are varied to get information about the behaviour of the tested fluid. The achievable cavity pressure is perhaps the most important parameter, because it determines the geometry of the part at the end of the forming step, especially at the small radii of the component. Another result of these tests is the fundamental potential of magnetorheological fluids for the process of hydroforming of blanks.

Modern automotive bodies are made of high and ultra high strength steel up to 90 mass percent of the body in white. These steels do not only possess a high light weight potential but also increase crash performance of the passenger cabin. The described benefits are facing the problems of forming these steels. With a low formability at room temperature and high flow stresses the complexity of parts out of these materials is limited. In a warm forming process with temperatures up to 600°C the formability could be increased and the process forces could be decreased. Especially high complex parts are produced by hydroforming a technology allowing undercuts and uniform strain distributions in the part. For temperatures up to 600°C there is a need of an appropriate medium for hydroforming. Fluids normally used at room temperature are only temperature stable up to about 350°C and tend like gases to leakage. Using a granular material like small ceramic beads allow high temperatures and reduce the risk of leakage. The Drucker-Prager-Cap material model allows to describe this medium for the numerical simulation. The accuracy of the numerical simulation with the gained material model is compared with different experiments in which the parameters were identified and a real part geometry of a cup formed with granular material as medium.

The majority of the materials used in modern lightweight frame structures are aluminium alloys. But some aluminium alloys, e.g. EN-AW6060, are not or hardly joinable using conventional joining techniques. In this case innovative joining methods like friction stir welding; joining by dieless hydroforming or by electromagnetic compression lead to good joint’s quality. Friction stir welding has been widely investigated for joining sheet metal, but joining tubular workpieces creates new challenges in handling and processing, which will be described here. Joining by Dieless Hydroforming has been introduced in both plant and automotive engineering in the 1970ies. This joining method was used to join heat exchangers or camshafts made of steel. Recently, joining of aluminium has been targeted and is addressed below. Joining by Electromagnetic Compression offers the opportunity to manufacture high strength joints by e.g. form-fit. Groove’s design has been adopted targeting failure of the basic tube material, which is described here.

Tubular components, such as stepped tubes, conical tubes and box shape tubes, are mainly produced in tube hydroforming process. Obtaining a sharp corner is a main goal in some of these components. In this paper, the corner filling in stepped tubes is studied by a multistage new die. The proposed die was simulated and the filling of die cavity was investigated. In this respect, the finite element software, ABAQUS 6.4, has been used for simulation. In order to verify the simulation results, the new die of stepped tube was manufactured and some experiments have been performed. The results obtained from the experiments verified the simulation results. It is shown that by using the new die parts with sharp corners could be produced. The simplicity of the die and low internal pressure are another advantages of this die. The thickness distribution was also examined by both the FE simulation and experiments and it is shown that a better distribution could be obtained by the proposed die set.

This research examines the effect of the tube bending and hydroforming processes on the characteristics of aluminium alloy s-rail structures used in crash applications. Tube bending and hydroforming experiments are conducted using a fully instrumented mandrel-rotary draw tube bender and a 1,000 tonne hydroforming press to investigate the effect of bend severity on the thickness and strain distributions within the tube. Finite element simulations of the tube bending and hydroforming process, that consider previous deformation history, are developed to serve as a predictive tool that provides additional insight into the manufacturing of the s-rail. The bending of the s-rail results in thinning on the outside and thickening on the inside of the bend, due to axial strains in those regions. The most significant variable affecting the degree of thickness change and strain in the bend is the bend severity. “Boost” in bending, refers to the technique whereby a compressive axial load is applied to the portion of the tube being bent, and can also increase the overall thickness and work hardening in the bend regions of the s-rail, which has been shown to increase the overall resistance to deformation of the hinge during collapse (Oliveira 1). The low-pressure hydroforming operation induces circumferential strain at the corners of the s-rail cross-section, despite undergoing near zero circumferential expansion.

International audience; This paper presents a numerical methodology which aims to improve 3D thin sheet hydroforming processes. This methodology is based on elastoplastic constitutive equations accounting for non-linear anisotropic hardening. The experimental study is dedicated to the identification of material parameters from the global measure of sheet displacement, thickness evolution and internal pressure expansion. Applications are made to study the effect of die shape, anisotropic flow and hardening law on the hydro-formability of sheets.

International audience; The hydroforming process of a T-tube is simulated with the finite element code ABAQUS. The influence of the internal pressure and the axial displacement levels on the final tube quality is evaluated through a "process diagram". Due to the strain rate range observed during the process, the strain rate sensitivity of the material is considered for the determination of the forming limit curves and for simulation of the process. Theoretical and numerical evaluation of the forming limit curves shows that formability increase with the strain rate sensitivity coefficient m. The determination of the process diagram for a higher value of m emphasizes that the forming zone (tube with zero defect) significantly grows. The optimization of hydroforming process is very sensitive to forming limit curves identification and the effects of strain rate on formability must be accurately quantified.

For three dimensional tube hydroforming operations (i.e. T or Y shaped tubes) the calibration of both material feeding history and internal pressure path during the process is crucial and many approaches to such optimization were presented; the authors developed some procedures to optimize pressure paths and punch velocity histories with the application of an integrated method FEM - Gradient based optimization tools. In this paper, an experimental validation campaign of the utilized optimization strategies is presented with the aim to assess the effectiveness of the developed procedures. An optimization procedure (gradient based techniques) was applied on the process parameters leading to the determination of an optimal pressure path. Finally, a testing machine was set up to carry out hydroforming operations on T-shaped tubes. The developed equipment allows a computer assisted control of both the internal fluid pressure paths and the punches actions (material feeding paths). The experimental evidences validated the results obtained by the optimization strategies utilized to design the process parameters.

Joints which are solely produced by forming processes are capable of transmitting e.g. axial loads by means of dominating force- (alternatively named interference) or form-fit. Furthermore, a transmission of load could be directed by a combination of both and with supporting adhesives. Joining by forming has been done by compressing tubes using external rolling and electromagnetic forming; joining by expansion has been performed by dieless hydroforming and rolling. Moreover, a problematic constraint for joining by expansion or compression, namely joining of identical materials, which is a topic of a current research project within the scope of SFB/Transregio 10, has to be taken into account. Consequently, the article focuses on the feasibility of combining joining by forming processes and adhesives for joining of tubular workpieces made of identical material (EN-AW6060F22). Resisting loads of form- and force-fit joints have been taken as a reference.

This work aims to assess the influence of different finite element formulations in the performance and quality of solution obtained by numerical simulation in the analysis of tailor-welded hydroformed tubular parts. Tube hydroforming represents a cost effective forming process for high-strength, low weight products on, as an example, automotive and airspace applications. On the other side, the use of tailor-welding in order to obtain custom-made combinations of thicknesses and materials - leading to a wide variety of user-defined products - can be introduced into conventional tubular hydroforming processes in order to further improve the applicability range of the later process. The main goal of the present work is to describe the state-of-the-art in the field, focusing on distinct finite element formulations and providing guidelines for the simulation of tubular hydroforming process combined with tailor-welded joining techniques. Hexahedral solid and solid-shell enhanced assumed strain elements, either with reduced and full numerical integration procedures, are analyzed in order to infer about the potentialities of the combined forming technology. Material characterization of the heat affected zone is included and the influence of finite element modeling on defects onset and prediction during forming is considered.