Tube Hydroforming Process Research Articles

Loading path prediction for tube hydroforming process using a fuzzy control strategy

Tube hydroforming has recently drawn the attention of the automotive industries due to its several advantages over conventional forming methods. For a given blank tube and part design, the success of tube hydroforming process is highly dependent on the loading paths (axial feeding versus internal pressure). To obtain a part with the required shape and minimize the tube wall thickness variation during Tee extrusion tube hydroforming process, an adaptive simulation approach integrated with a fuzzy logic control algorithm is used in this paper. A necking indicator and a wrinkling indicator obtained from simulation results are used as the input of the fuzzy logic control, and the output sets of the fuzzy logic control are used for adjusting the loading path. In this way, a reasonable loading path for producing an acceptable Tee extrusion tube can be obtained, and its validity is verified by experiments.

Fourier series based finite element analysis of tube hydroforming—Generalized plane strain model

Abstract In previous paper [Fourier series based finite element analysis of tube hydroforming—An axisymmetric model, Eng. Comput. 23 (7) (2006) 697–728], an axisymmetric analysis of tube hydroforming process was discussed. In the present paper, a generalized plane strain implicit formulation of the cross-sectional expansion of an extruded aluminum tube with pressurized fluid to fill a hydroforming die is presented. The cross-section of the tube is modeled with thin straight and circular segments with constant thickness, and Fourier series are used to approximate nodal displacements. The material of the tube is assumed to obey a rate-independent, elastoplastic model that takes into account work hardening and normal anisotropy. At the tube-die interface, frictional stress is assumed, based on Coulomb friction, to be proportional to the contact pressure whenever relative sliding occurs. The kinematics relationships are derived based on thin shell theory, and the equilibrium equation is derived based on virtual work principle. The axial feed is implemented by imposing either a compressive force or strain in the tube length direction. Frictional boundary condition is introduced into the formulation in the form of a penalty function, which imposes the constraints directly into the tangent stiffness matrix. The Newton-Raphson iterative method is used to incrementally solve the resulting nonlinear equations. Two examples of tube hydroforming problems are solved and numerical predictions of the deformed shape, hydroforming pressure, and deformation strains are compared with experimental and ABAQUS results.

Automatic Approach on Derivation of Loading Path Using Adaptive Finite Element Analysis Simulation Method

Loading path is one of the most influential parameter in tube hydroforming(THF) process. Load history has a major effect on failures such as buckling, necking, bursting, and so on. Because loading conditions that consist of axial feeding and internal pressure are imposed simultaneously. Therefore suitable loading path should be determined to prevent onset of failures i.e. bursting on final products. This paper deals with the procedure on determination of the loading path in order to ensure the robustness of the final products after the THF. In order to verify the availability and feasibility of the proposed methodology a subframe model of engine cradle module in automotive is implemented. In this study, thinning ratio and forming limit stress diagram is used to demonstrate the improvement of the finished product. The result shows that the developed algorithm has successfully promoted the effectiveness and feasibility in the THF. Consequently, it is shown that the automatic approach on the determination of loading condition which is proposed in this paper will provide a valuable method to satisfy the increasing practical demands for designing process condition in THF.

내구성을 고려한 토션빔형 후륜 현가장치의 튜브 하이드로포밍 공정 설계

Generally, the forming process of suspension system parts have been considered only considered with the formability and have not been considered with the durability of suspension system. But the durability of suspension system is very important characteristic for the dynamic performance of vehicle. Therefore, the suspension system should be manufactured to consider the durability as well as the formability. This paper is about an optimum forming process design with the effect of section properties to consider the roll durability of torsion beam type suspension. In order to determine the tube hydroforming process for the satisfaction the roll durability, the stamping and hydroforming simulation by finite element method were performed. And the results from finite element analysis and roll durability examination showed the tube hydroforming process of torsion beam is optimized as satisfying the durability performance.

A study of forming pressure in the tube-hydroforming process

Abstract The forming pressure required to produce a desired part using the tube-hydroforming process was investigated in the present study. The relationship between hydraulic pressure, outer corner radius of the deformed tube, tube thickness and tube yield stress was established based on a proposed theoretical model. In the theoretical model, the material hardening property was taken into consideration. Since the friction in the tube-hydroforming is smaller than that in the conventional stamping process, the die-closing force was also calculated according to the forming pressure predicted by the proposed theoretical model under frictionless condition. The finite element analysis was performed to validate the proposed theoretical model. In order to confirm the accuracy of the finite element simulations, two different finite element codes were employed to conduct the analysis and the simulation results were compared. The predicted values calculated by the proposed theoretical model were found to agree well with those obtained from the finite element simulation results.

Analytical modeling of wall thinning during corner filling in structural tube hydroforming

In a tube hydroforming process, an internal pressure is used to expand a circular tube into one with non-circular sections. Friction at the material/die interface plays an important role in determining the distribution of the thickness during deformation. In this paper, an analytical model is developed to determine the variation in the stresses and strains along the tube wall as the internal pressure increases to expand the circular tube into a square cross-section. Based on the analytical model, a parametric study is conducted on the effects of the coefficient of friction and the material properties on the distribution of cross-section thickness in the hydroformed tubes. Such parametric study is useful in establishing guidelines for designing the structural tube hydroforming process. It also helps in the search for limits of the process capabilities. One of the strengths of analytical modeling is that it gives more insights into the mechanism through which friction affects the deformation during tube hydroforming.

Experimental and analytical evaluation on flow stress of tubular material for tube hydroforming simulation

Abstract For the finite element simulation in tube hydroforming process, the flow stress must express the bi-axial state of stresses similar to that of the actual hydroforming operation. In this work, experimental and analytical methods to acquire the flow stress of tubular materials for hydroforming application were performed. Conventional tensile tests on specimens extracted from both a flat sheet and a roll-formed tubular material were conducted. And then, in order to consider the bi-axial state of stress, free bulge test of a simple tubular material was carried out and analysis results using flow stresses obtained from both test methods were compared and evaluated with the free bulge test. Therefore, it is concluded that the flow stress obtained from the free bulge test should be used for input material property for the numerical analysis of the tube hydroforming process to enhance the accuracy of those.

The effect of prebending on the formability in the tube hydroforming process of an aluminum rear subframe

The effects of 2D and 3D prebending on the forming limit in the tube hydroforming process of an automotive rear subframe are evaluated and compared through finite element analyses and experimental tryouts. The influence of the strain path corresponding to each prebending method is discussed in terms of a forming limit diagram (FLD) and a forming limit stress diagram (FLSD). An incremental strain-to-stress transformation scheme to plot the FLSD from the FLD along an arbitrary strain path is proposed. A tube hydroformability testing system designed and manufactured to provide an arbitrary combination of internal pressure and axial feed is introduced. A forming limit diagram of the A6063 aluminum tube material is obtained from free bulging, T-shape forming and cross-shape forming tests using this system.

Friction coefficient estimation of tube in hydroforming with radial crushing in square die

Friction plays an important role in tube hydroforming (THF)process, and then accurate determination of the coefficient of friction (COF) becomes a paramount task to promote the application of the process. After a detail discussion of the method in existence, a new measuring model of determining COF in expansion zone of THF is proposed on the basis of the principle of tube hydroforming with radial crushing. The measuring model features a round tube hydro-formed into a square part under both a constant internal hydraulic pressure and a radial compression, with the difference of the two diagonal lengths in the square section of deformed part as a friction force or COF indicator. The COF can be determined through matching experimental and FEM simulation results by comparison of the variation of the indicator. The finite element method simulation results of low carbon steel and stainless steel tubes show that the indicator is conveniently measurable and extremely sensitive to the friction force or the COF, therefore can be used as a index to evaluate lubricant performance under realistic friction conditions occurring in the expansion zones of THF process. The results also indicate the measuring model is simple and feasible.

Fourier series based finite element analysis of tube hydroforming

PurposeThe purpose of this paper is to provide an axisymmetric model of tube hydroforming using a Fourier Series based finite element method.Design/methodology/approachFourier series interpolation function, which considerably reduces the size of the global stiffness matrix and the number of variables, is employed to approximate displacements. The material of the tube is assumed to be elastic‐plastic and to satisfy the plasticity model that takes into account the rate independent work hardening and normal anisotropy. Numerical solution obtained from an updated Lagrangian formulation of the general shell theory is employed. The axial displacement stroke (a.k.a. axial feed) during tube hydroforming is incorporated using Lagrange multipliers. Contact constraints and boundary friction condition are introduced into the formulation based on the penalty function, which imposes the constraints directly into the tangent stiffness matrix. A forming limit curve based on shear instability and experimental measurements are used as fracture criteria.FindingsThe results obtained from this new formulation are compared against the nonlinear finite element code ABAQUS and experimental measurements for isotropic and transversely anisotropic tube materials. The hoop and axial strains predicted with AXHD code compared excellently with those from ABAQUS FEM code using plane stress axisymmetric (SAX1) and four‐node shell (S4R) elements. However, in the case of aluminum, the numerically predicted maximum hoop strain underestimated the actual hoop strain measured from the tube bulging experiment.Practical implicationsThe axisymmetric hydroforming program (AXHD) developed in this work is very efficient in simulating the free‐forming stage of the tube hydroforming process under simultaneous action of internal pressurization and displacement stroke.Originality/valueAlthough Fourier Series based finite element method has been used in metal forming, the extended application presented in this paper is novel in the finite element analysis of tube hydroforming.

Mechanism of improvement of formability in pulsating hydroforming of tubes

The mechanism of improvement of formability by the oscillation of internal pressure in a pulsating hydroforming process of tubes was examined. Free bulging hydroforming experiments of mild steel tubes under oscillating and constant inner pressures were performed. For a high constant pressure, a round bulge with local thinning was observed, whereas wrinkling occurred for a low constant pressure. The occurrence of these defects was prevented by oscillating the internal pressure in the pulsating hydroforming. In the pulsating hydroforming, a uniform expansion in the bulging region was obtained, and thus the formability was improved by preventing the local thinning. It was found from an observation of deformation behaviour, using a video camera, that the tube is uniformly expanded by repeating the appearance and disappearance of small wrinkling. The cause of the uniform expansion for the pulsating hydroforming was also interpreted from the variation of stress components. In addition, a similar deference in deformation behaviour between the oscillating and constant inner pressures was also obtained in finite element simulation.

Finite element modeling of tube hydroforming of polycrystalline aluminum alloy extrusions

Finite element modeling of tube hydroforming requires information about the anisotropy of the extruded aluminum tube. Unlike sheet metals, the complex geometry of extruded tubes makes it difficult, except in extrusion direction, to directly measure material properties. Therefore, polycrystalline models provide a good alternative for calculating the anisotropy of the tube in all directions and under various loading conditions. Using a rate-independent single crystal yield surface and rigid plasticity, a Taylor-type polycrystalline model was developed and implemented into ABAQUS/Explicit finite element (FE) code using VUMAT. The constitutive model was then used to calculate the crystallographic texture evolution during the hydroforming of an extruded aluminum tube. Initial crystallographic texture measured using orientation imaging microscopy (OIM) and uniaxial tensile test data obtained along the extrusion direction were input to this FEA model. In order to efficiently and practically simulate the tube hydroforming process using the polycrystalline model, sensitivity to the number of grain orientation, total simulation time, and number of finite elements were studied. Predicted results agreed very well with experimentally measured strain obtained from tube hydroforming process.

A simple experimental tooling with internal pressure source used for evaluation of material formability in tube hydroforming

Material properties have powerful impact on the tube hydroforming (THF) process and the quality of the deformed tube, so it is important to select proper materials and evaluate the material formability prior to conducting the process. A simplified and applied tooling, which has no use for any external hydraulic pressure source but internal one, was designed for charactering the material formability in THF. A pressurized-fluid supplier is automatically established to provide the internal pressure and axial load synchronously required for THF, and the ratio of the two loads is achieved by proper design of the supplier. As a stand-alone hydraulic bulging fixture, the tooling can be worked on a conventional press, even on a single action press. Free bulge forming (FBF), bulge forming with axial loading (BFAL), free and restrained bulge forming (free and fixed ends) can be fulfilled by the tooling, and furthermore, bulge forming with proportional loading to some extend can be realized. Comparative bulge forming experiments under various forming conditions were carried out with the tooling to validate this project and the results suggest that restrained conditions on the tube ends highly affect the FBF, while the ratio of the two loads dominates the BFAL.

Investigation on determination of loading path to enhance formability in tube hydroforming process using APDL

During tube hydroforming (THF) process, failure modes such as buckling, necking and bursting may occur because axial feeding and internal pressure are imposed simultaneously. Therefore, the suitable loading condition in THF with regard to internal pressure and axial feeding should be designed to improve formability and to avoid failure modes on the final hydroformed product. This study deals with the procedure for the determination of the loading path in THF for improving the formability of the final product after the THF. The suitable loading path is based on the adaptive method using ANSYS parametric design language (APDL). This proposed procedure is demonstrated via a sub-frame model of an engine cradle module in an automobile to be able to satisfy the specifications required after hydroforming, such as excessive thickness thinning phenomena, and the results have been proved to be successful on its effectiveness and feasibility. Consequently, it is shown that the approach proposed in this study will provide a valuable method to satisfy the increasing practical demands for designing the process conditions in THF.

Investigation on preformed shape design to improve formability in tube hydroforming process using FEM

A selection of proper tubular blank and a suitable preformed tube shape as well as a reasonable combination of the internal pressure and the axial feeding are essential parameters for successful tube hydroforming processes (THF). A carefully selected preformed shape can be considered as a key factor for successful THF, since thinned sections may not be able to endure internal pressure during expansion, and consequently burst, whereas excessive thickening may lead to wrinkles. This paper introduces a novel numerical approach as an effective tool to design the preformed shape in order to improve the formability based on the deformation history during forward numerical simulation about THF. This numerical approach is implemented in a simple free bulge case in order to be able to enhance the formability. The results proved to be successful on its effectiveness and feasibility. Consequently, it is shown that the novel numerical approach, proposed in this paper, with which to design the preformed shape will provide a feasible method to satisfy the increasing practical demands for enhancement of the formability in THF.

Formability of tube hydroforming under various loading paths

Finite-element simulations of the tube hydroforming process with rectangular dies are carried out for various loading paths, and the reasons why the loading paths of the so-called pressure advanced type, in which the hydraulic pressure is raised to a certain magnitude in advance of the axial pushing, are effective to obtain good formability are investigated in detail. It is clarified that, in the early stage of the deformation process by the pressure advanced type, the growth of local wrinkling is prevented and the effect of axial pushing from the tube ends is attained at the whole part in the axial direction. Consequently the desirable biaxial stress condition of the circumferential tensile and longitudinal compressive stresses is obtained in the subsequent stages, thus achieving large expansion without the occurrence of local wrinkling and local thinning.

Improving the Reliability of the Tube-Hydroforming Process by the Taguchi Method

The tube-hydroforming process has undergone extremely rapid development. To ensure a reliable hydroforming process at the design stage, applying robust design methodologies becomes crucial to the success of the resulting process. The reliability of the tube-hydroforming process based on the tube wall thickness thinning ratio is studied in this paper. In order to improve the reliability of the process, the Taguchi method, which is capable of evaluating the effects of process variables on both the mean and variance of process output, is used to determine the optimal forming parameters for minimizing the variation and average value of the thinning ratio. Finite element simulation is used to analyze the virtual experiments according to the experimental arrays. A cross-extrusion hydroformed tube is employed as an example to illustrate the effectiveness of this approach.

Hydroforming process optimization of aluminum alloy tube using intelligent control technique

In this study, to determine the optimal loading path of tube hydroforming process, a database-assisted fuzzy process control algorithm proposed previously by the authors was applied to T-branch forming with a counterpunch. The tubular material used is aluminum alloy (A6063-T1) and has an outer diameter of 42.7 mm and wall thickness of 1.2 mm. Control variables is axial feed, counterpunch displacement, and internal pressure. The first two variables are dependent on the last one, which is an independent variable. In the control algorithm, new evaluation functions are adopted for buckling at the shoulder part of the branch and for contact fitting with a counterpunch. For a “virtual control system” including fuzzy algorithm with the evaluation functions, an explicit dynamic finite element code is used in the simulation. The experiments are carried out using a fuzzy controlled path obtained by the virtual control system, compared with the conventional manual control path that is attained by a trial-and-error approach. As a result, a T-branch product is successfully hydroformed. This result shows that the fuzzy control algorithm and virtual control system can provide an adequate loading path in the hydroforming process for an aluminum alloy tube.

Applications of hydroforming processes to automobile parts

Hydroforming process recently draws attention of automotive industries due to its advantages like the increased strength, weight reduction, improved quality and reduced tooling cost. This paper summarizes some of our experiences of tube and sheet hydroforming process design by simulation technique through actual tryout. Parts included in this paper are tie bar, subframe and engine mount bracket. The simulations for the entire hydroforming processes were performed and their results were used to predict and fix the forming failures like the wrinkling and the fracture. Based on this experience, we also suggested necessary improvements in the design procedure.

알루미늄 튜브 하이드로포밍 성형 해석 및 성형성 평가

A tube hydroformability testing system was designed and manufactured to observe the forming steps and to provide arbitrary combination of internal pressure and axial fred. The forming limit diagram of an aluminum tube was obtained from the free bulge test and the T-shape forming test using this system, giving the criteria for predicting failure in the hydroforming process. The hydroformability of aluminum tube according to different conditions of a prebending process was discussed, based on the finite element analysis and the forming limit test. The effects of 2D and 3D pretending on the tube hydroforming process of an automotive trailing arm were evaluated and compared with each other.