T-shape Hydroforming Research Articles

Application of an efficient anisotropic damage model to the prediction of the failure of metal forming processes

The main objective of this study is the numerical implementation of an advanced elastic–plastic model fully coupled with anisotropic ductile damage. The implemented formulation has been defined in the framework of thermodynamics of irreversible processes and a symmetric second-order tensor is adopted to describe the anisotropic damage state variable. After a summary of the main constitutive equations is given, the numerical integration of constitutive equations is performed using implicit and asymptotic integration schemes. Finite element simulation is performed using ABAQUS/Explicit software and the developed VUMAT subroutine. Next, the application of the developed model to T-shaped hydroforming of tubes and square-cup deep drawing metal forming processes is thoroughly discussed and failure onset zones due to anisotropic ductile damage growth are predicted and the results were consistent with the literature. Finally, by making an assumption that kinematic hardening can be ignored, an elastic predictor/plastic corrector algorithm requiring the solution of one equation is introduced. The assessment of the developed one-equation return-mapping algorithm is carried out by applying it to the simulation of the tensile test of a pre-notched bar. The Central Prossessing Unit time decreases noticeably using one-equation return mapping algorithm compared to the conventional return mapping algorithm and the numerical results are in good agreement with previous numerical simulations and experiments.

Factors influencing the forming characteristics in micro tube hydroforming by ultra high-forming pressure

Abstract The focus of this study is micro tube hydroforming (MTHF) for fabricating complex shaped tubular or three-dimensional hollow micro components, which is a scaled down technology of tube hydroforming. In our previous study, a new MTHF system with ultra-high pressure generator was developed and a T- and cross-shaped micro tube hydroforming of phosphorous-deoxidized copper tube with diameter of 500 µm and thickness of 100 µm was successful. In this study, a micro T-shaped hydroforming as well as a micro cross-shaped hydroforming are carried out to confirm influential factors on micro forming characteristics of MTHF. Lubrication condition, material property, formed shape and grain size are mainly considered as influential factors, and discussed.

Microstructure evolution in TRIP-aided seamless steel tube during T-shape hydroforming process

Transformation-induced plasticity aided seamless steel tube comprising of ferrite, bainite, and metastable austenite was processed through forging, piercing, cold-drawing, and two-stage heat treatment. T-shape hydroforming is a classic forming method for experimental research and practical production. The current work studied austenite-to-martensite transformation and microcrack initiation and propagation of the tube during T-shape hydroforming using electron backscattering diffraction, scanning electron microscopy, and transmission electron microscopy. The strain distribution in the bcc-phase and fcc-phase was studied by evaluating changes in the average local misorientation. Compared to the compressive stress, metastable austenite with similar strain surrounding or inside the grains transformed easier under tensile loading conditions. The inclusions were responsible for microcrack initiation. The propagation of the cracks is hindered by martensite/austenite constituent due to transformation induced plasticity effect. The volume fraction of untransformed retained austenite decreased with increase in strain implying transformation-induced plasticity effect.

Effect of Initial Position of the Counterpunch on T-Shape Hydroforming

The loading path is crucial to the quality of forming parts in the process of tube hydroforming. The counterpunch is usually used to control the protrusion height and also to control the evolution of thickness and avoid over thinning in T-shape hydroforming. In this study, the experiments of T-shape hydroforming are conducted, in which tubular material used is stainless steel and has an outer diameter of 103mm. A fuzzy logic-based load control algorithm is developed for optimizing the loading path, and four different initial positions of the counterpunch are designed to investigate its influence on wall-thinning and the corner radius at protrusion end. The results show that the minimum thinning can be obtained with an initial position of 12.5mm, while a smaller corner radius is obtained with an initial position of 37.5mm.

Plastic damage of T-shape hydroforming

The Gurson-Tvergaard-Needleman model (GTN model) was employed to analyze bursting behavior in the hydroforming of stainless steel T-shape. A free-bulging test combined with simulation was conducted to determine the critical porosity and the failure porosity in GTN model. The effects of the forming pressure and the axial feeding on damage development were investigated and the influences of stress triaxiality and the plastic strain on porosity variation were also studied. The results show that a higher forming pressure or a less axial feeding will lead to bursting failure. The stresses of the top of protrusion are in bi-axial tension state, while the stresses of the side wall of main tube are in hoop tension state and axial compression state, respectively. The plastic strain has a more significant influence on the porosity than the stress triaxiality under the lower internal pressure; however, the stress triaxiality will govern the growth of porosity under the higher internal pressure. The simulation results give a good agreement with the experimentally determined thickness, and the maximum thickness-thinning rate is about 36%.

A Comparison between Three Meta-Modeling Optimization Approaches to Design a Tube Hydroforming Process

Computer aided procedures to design and optimize forming processes have become crucial research topics as the industrial interest in cost and time reduction has been increasing. A standalone numerical simulation approach could make the design too time consuming while meta-modeling techniques enables faster approximation of the investigated phenomena, reducing the simulation time. Many researchers are, nowadays, facing such research challenge by using various approaches. Response surface method (RSM) is probably the most known one, since its effectiveness was demonstrated in the past years. The effectiveness of RSM depends both on the definition of the Design of Experiments (DoE) and the accuracy of the function approximation. The number of numerical simulations can be strongly reduced if a proper optimization approach is implemented: one of the main issues about optimization techniques is related to the design necessity of performing either global or local approximation. This paper aims to test the efficacy of some meta-modeling techniques in the optimization of a T-shaped hydroforming process. In this paper three optimization approaches based on different meta-modeling techniques are implemented. In particular, classical Polynomial Regression approach (PR), Moving Least Squares approximation (MLS) and Kriging method are applied. The results showed that, thanks to the peculiarities of MLS and Kriging methods, it is possible to strongly reduce the computational effort in sheet metal forming optimization, particularly in comparison with a classical PR approach. Differences were highlighted and quantified.

Improvement of formability in T-shape hydroforming of tubes by pulsating pressure

The effect of oscillations in the internal pressure on tube wall thickness and die corner filling in the pulsating hydroforming of T-shape tubes is examined using finite element simulation and experiments. The thinning behaviour of the tube during the pulsating hydroforming is studied for different coefficients of friction to investigate the mechanism of the improvement in formability. It is shown that the thinning behaviour is similar for different friction conditions. It is also illustrated that the pulsating pressure improves the formability, even for frictionless tube hydroforming. Thus, the reason for the improvement in the formability may not be due to a reduction in the friction level. In addition, the effects of the amplitude and frequency of the pulsating pressure on the thinning behaviour of tubes and die corner filling are examined. It is shown that, while a small number of cycles and a large amplitude of the pulsating pressure decrease the filling ratio of the die corner, they are more effective in improving the formability.

Thermoelastoplasticity applied to T-shaped tube hydroforming optimization

Hydroforming simulation of T-shaped tube is performed using an thermoelastoplastic model implemented in Forge-2005©(fully implicit FEM code). A thick cylindrical AA-6060-T4 aluminium alloy tube is inflated in a T-shaped die. A third tool limits the material flow in the central branch during loading. An iterative scheme is used to obtain the load path. A three dimensional case of T-shaped hydroforming is proposed. This work studies the sensitivity of the process regarding to crucial parameters like, die/tube friction, tools kinematic, die radius, inner pressure law and material hardening. Impact on thickness repartition and plastic strain in the finale part is studied. An improved load path is proposed regarding to those aspects. In the same time the position and size of potentially dangerous zones regarding to plastic instability or damage are checked. Looking to the gradients of plastic strain and triaxiality $${{\sigma _{hydro} } \mathord{\left/ {\vphantom {{\sigma _{hydro} } {\sigma _{mises} }}} \right. \kern-\nulldelimiterspace} {\sigma _{mises} }}$$ through the thickness, the interest of a 3D continuum damage tool to predict formability is enlightened.

3-D Finite Element Simulation of Pulsating T-Shape Hydroforming of Tubes

The effect of oscillation of internal pressure on the formability and shape accuracy of the products in a pulsating hydroforming process of T-shaped parts was examined by finite element simulation. The local thinning was prevented by oscillating the internal pressure. The filling ratio of the die cavity and the symmetrical degree of the filling was increased by the oscillation of pressure. The calculated deforming shape and the wall thickness are in good agreement with the experimental ones. It was found that pulsating hydroforming is useful in improving the formability and shape accuracy in the T-shape hydroforming operation.

Adaptive Simulations of T-Shape Tube Hydroforming Processes

A successful THF process depends largely on the loading paths for controlling the relationship between the internal pressure, axial feeding and the counter punch. In this study, an adaptive algorithm combined with a finite element code LS-DYNA 3D is proposed to control the simulation of T-shape hydroforming with a counter punch. The effects of the friction coefficients at the interface between the tube and die on the loading path and thickness distribution of the formed product are discussed. Experiments of protrusion hydroforming are also conducted. The final shape and thickness distribution of the formed product are compared with the simulation results to verify the validity of this modeling.

Experiments on T-shape hydroforming with counter punch

In this study, a hydroforming test machine is designed and developed for tube hydroforming processes. This hydroforming test machine features four independent controls of two axial feeding punches, an internal pressure, and a counter punch. Using annealed AA6063-T5 and 6011A aluminum tubes, experiments of bulge forming and T-shape hydroforming are conducted. Loading paths and thickness distribution of the formed product are discussed. The branch heights of the formed products with and without the counter punch are compared to manifest the merit of using a counter punch during tube hydroforming.