Twist Springback Research Articles

Modelling and prediction of twist springback for UHSS thin-walled component with asymmetric complex section in roll forming process

Modelling and prediction of twist springback for UHSS thin-walled component with asymmetric complex section in roll forming process

Influence of local features on twist springback of high-strength steel long channels

With the wide use of high-strength steel (HSS) in structural body parts, the twist springback of high-strength steel parts has received extensive attention. Unlike automotive panels, structural body parts are arranged with many local features to meet functional requirements. The aim of this study is to investigate the influence of local features on twist springback to optimize the design of local features to reduce twist springback. In this paper, a typical long channel part (A-pillar upper inner plate) is taken as the object of study. A suitable location division method for this type of part is proposed to investigate the changes in twist springback and cross-sectional stresses in the part before and after the addition of local features at different locations through finite element simulations. The results show that the local features affect the stiffness and stress distribution of the parts and significantly affect the twist springback of the parts. Finally, the research results guided the optimization of the local feature design of an A-pillar upper inner plate, resulting in a remarkable 37% and 61% decrease in twist springback at the left and right ends of the optimized part, respectively. In addition, stamping molds were developed for optimized parts, and experiments were carried out to verify the effectiveness of the law and the reliability of the finite element model.

Numerical Study of Predicting Forming Process Based on Different Hardening Models in Advanced High Strength Steel Sheets

Sheet metal shaping for advanced high strength (AHS) steel sheets is commonly utilized in the manufacturing of automobile components. This helps to decrease the weight of new structures and increase the crashworthiness performance of these structures. The phenomenon known as springback deviation plays a significant role in creating such components via deformation and fracture. This study investigated the production of an S-rail from components made of steel grade 780 with a thickness of 1 millimeter by employing appropriate simulations using finite elements (FE) and generation. The materials were initially tested in order to collect the necessary parameter sets for the models being employed. The Barlat89 yield function, the Y-U kinematic hardening model, and a model combining the Y-U kinematic hardening model with the Barlat89 yield function were all used in the simulations. In addition, the forming limit curves (FLCs were utilized to assess the computed formabilities and served as the failure criteria. The deformation, springback effect, deviations, and twist springback of the components developed after the S-rail forming were subsequently studied, measured, and the findings compared. It was discovered that the proposed yield criteria and kinematic hardening models could accurately predict the formability of the material without causing any damage. The strain distributions acquired from the Y-U kinematic hardening indicated that the sidewall curl area was slightly larger than what was predicted by previous models. The model combining the Y-U kinematic hardening model with the Barlat89 yield function produced the most accurate predictions for overall springback effect, deviations, and twist springback of the AHS steel sheets.

Study of the Influence of part features on springback and its robustness

The influence of part geometry on twist springback was studied by a A-pillar inner plate. The part structural parameters was divided into cross-section and longitudinal axis, and the response surface model was established to analyze the influences of various structural parameters on the twist springback. The results show that the straight line 1, straight line 3, angle 2 and angle 4 of the cross section have a significant effect on the twist springback. In addition, the twist springback increases continuously with increasing of total length and ratio of arc to straight line and the decreasing of radius in the longitudinal axis. After adding features through the angular edges along the longitudinal direction, the maximum springback at the part end drops from -10.92mm to -2.934mm. The springback robustness analysis of this part were also analyzed, the results show that the maximum springback is strongly related to material yield strength, and the robustness is improved greatly after adding part features.

Influence of process and material parameters on the twist springback prediction of a panel

Both advanced high strength steels and aluminum alloys gained increasing popularity because of the constant effort to meet the social pressure of reducing the vehicle weight while keeping their safety. The ratio between material strength and weight is much higher when compared to other materials but, the high springback after forming is one of the disadvantages of these materials, particularly when exhibiting twisting and side wall curl, which are the two most difficult types of springback to control and compensate in die engineering. This study analysis the influence of several material and numerical parameters on the prediction of the twist springback, using the Twist Die. Two processing conditions were considered: (i) blank-holder force that constrains the metal flow and (ii) a stake bead, which changes the forming conditions from draw to stretch forming, at the end of the process. The modelling of the elastoplastic behavior of the sheet materials uses a wide range of experimental data, for a DP980 steel and a 6xxx aluminum alloy. In addition to the effect of the sheet material on springback, the effect of the following parameters is also analyzed numerically: (i) friction coefficient; (ii) beads; (iii) modulus of elasticity; (iv) work hardening law and (v) yield criterion. All numerical simulations were performed with the finite element in-house code DD3IMP. The process parameter that most affects the twist springback is the presence of the stake bead, reducing significantly the springback. In addition, the reduction of the friction coefficient and of the elastic modulus also leads to an increase in springback. On the other hand, the yield criterion has little influence on springback of this component. The twist springback shows a different trend for the steel and the aluminum alloy that seems to be related with the different yield strength but also with the distinct gap between the punch and the die.

Design on progressive corners of dies and macro textures of blank holders for S stamped parts

The shape dimensions of die corners and surface textures of blank holders are important in the effective control of twist springback. For predicting springback accurately, a mixed hardening model is presented for a thin-walled S beam made from TRIP780. Based on a proposed evaluation index for twist springback, the experiments of stamping and twist springback for TRIP780 are carried out. The twist springback angle is gauged by a three-coordinate measure instrument. A Response Surface Model (RSM) between the parameters of the mixed hardening model and the twist springback angles is established, and the parameters are inversed. The progressive die corners are designed for the twist springback compensation based on the stress distribution of the thin-walled S beam after stamping, and the die corner radius is optimized by the RSM and an Ant Colony Algorithm (ACA). Meanwhile, the macro textures of blank holders including longitudinal texture and transverse texture are designed. Based on the compensation analysis, a comprehensive compensation method which combined the progressive die corners with the longitudinal texture of the blank holder is proposed. The results show that the springback angle is reduced by 33.6%, proving the proposed comprehensive compensation method is effective.

Forming Technology for Reduction of Twist Springback in Curved Structural Part by Controlling of Stress at Flange

Forming Technology for Reduction of Twist Springback in Curved Structural Part by Controlling of Stress at Flange

On twist springback of a curved channel with pre-strain effect

In the field of automotive lightweight manufacturing, the advanced high-strength steel (AHSS) sheet gets a pivotal position owing to a good match between the plasticity and superior strength. However, in the complex multi-step loadings, the twist springback phenomenon generated by irregular and curved stampings has arisen great concerns. In this article, the material DP500 is adopted for the twist springback analysis in a two-step loading experiment. First, the large bone-shaped specimen is deformed to 4% strain along the rolling direction. Subsequently, the forming blank, cut from the large specimen at different directions, is stamped in a die to form a 3D curved channel. Meanwhile, the simulation analysis of the two-step loading procedure is built for twist springback prediction. An advanced distortional hardening model incorporated with an attenuated modulus model is applied for exactly capturing the deformation features under mutative strain path. A deep analysis with regard to the residual stress and elastic modulus distribution is conducted to evaluate the pre-strain's influence on the twist springback of this curved part. The result shows that mutative strain path induced by the change of the pre-strain axis has a significant impact on the twist springback.

Pre-strain effect on twist springback of a 3D P-channel in deep drawing

Abstract With the widely use of high-strength steel sheets in the automotive industry, the twist springback phenomenon of the steel sheets under multi-step forming conditions has received extensive attention. In this work, the Dual Phase steel DP500 is taken as the research object to investigate the complex non-linear elastoplastic behaviors and twist springback under two-step loading paths. The large specimen with a pre-strain of 4% true strain in rolling direction is carried out on a large tensile testing machine, and several specific blanks are extracted from it at different directions for a subsequent P-channel forming. The influence of twist springback associated with the pre-strain is analyzed. The finite element model based on the non-linear elastic model and the homogeneous anisotropic hardening model (HAH) is also established for the springback prediction and stress analysis. The results indicate that the pre-strain has a considerable impact on the twist springback. The non-linear strain path changes resulted from pre-straining not only influence the residual stress but also affect the elastic modulus distribution.

Numerical optimization of variable blank holder force trajectory and blank shape for twist springback reduction using sequential approximate optimization

This paper proposes an approach for twist springback reduction using variable blank holder force (VBHF) trajectory that the blank holder force (BHF) varies through the stroke. In addition, the blank shape is optimized. Therefore, design optimization of VBHF trajectory and blank shape for twist springback reduction is performed. Springback of U-shaped product is a simple deformation, whereas the one of S-rail-shaped product shows more complicated behavior due to twisting. As the result, compared with the springback of U-shaped product, it is difficult to evaluate the twist springback. A novel evaluation method for the twist springback is proposed, and the optimal VBHF trajectory and blank shape for the twist springback reduction are determined under several design constraints. Numerical simulation of the S-rail-shaped product is so intensive that response surface approach is valid. In particular, a sequential approximate optimization that the response surface is repeatedly constructed and optimized is used to determine the optimal VBHF and blank shape. Through numerical result, the validation of the proposed approach is examined.

Compensation of Twist Springback in High-strength Steel Based on Gradient Die Radius

Compensation of Twist Springback in High-strength Steel Based on Gradient Die Radius

An Experimental and Numerical Investigation on the Twist Springback of Transformation Induced Plasticity 780 Steel Based on Different Hardening Models

Investigation on twist springback is important to improve the accuracy of forming parts. In this paper, a double C rail made of transformation induced plasticity 780 (TRIP 780) steel is designed, and the stamping and twist springback are simulated with ABAQUS based on three different hardening models (including Ziegler, Johnson-Cook and combined hardening models). A new index for calculating the twist springback is proposed, which is based on the angle between two end section lines of the double C rail. The experimental results of twist springback are compared with the calculation results from three different hardening models. The calculation results based on combined hardening model are the closest to the experiment data. In order to compensate twist springback, a curved surface die is designed based on the geometric shape of the double C rail after twist springback. The stamping and twist springback are simulated based on the curved surface die and combined hardening model, and the twist springback is decreased obviously after compensation, which shows that the compensation of twist springback is effective.

Control strategy of twist springback for aluminium alloy hybrid thin-walled tube under mandrel-rotary draw bending

The focus of this work is to investigate the control strategy of twist springback of an industrial aluminium alloy extruded tube after mandrel-rotary draw bending, which is a complex nonlinear physical process with coupling multi-factor interactive effects. A particularly pronounced twist springback characteristic of an AA6060-T4 hybrid thin-walled bent tube was observed. It leads to difficulty at the assembly stage due to the inaccurate geometry of product. For an accurate modelling of material behaviours, a non-quadratic anisotropic yield criterion integrated with combined isotropic and kinematic hardening model was adopted to describe the strain-stress behaviours including anisotropy, Bauschinger effects and permanent softening. The corresponding mechanical tests, e.g., enhanced forward-reverse simple shear tests, were performed to identify the material parameters. By using the improved and validated finite element model, two process control strategies related to the mandrel nose placement and the axial push assistant loading are proposed for the assessment of the control efficiency. The simulation results indicate that the mandrel nose placement mainly affects the longitudinal angular springback but not twist deformation in the circumferential sections. The angular springback angle firstly increases and then decreases after several tests of forward mandrel nose placement. The other control strategy, additional axial push assistant loading with high boost, is able to reduce twist deformation, but the compensation of angular springback is not attained and even a slight increase is observed. It also leads to the rise of the of wrinkle tendency in the intrados sidewall. Finally, the wipe die rake is put forward to reduce the wrinkle tendency due to the high boost applied for twist control.

Constitutive modeling for path-dependent behavior and its influence on twist springback

The aim of this study is to investigate the path-dependent elastic-plastic behavior of dual-phase steel and its influence on the prediction of twist springback in the channel forming process. The anisotropic hardening responses of the sheet material for non-proportional loading, as well as the degradation of the elastic modulus in uniaxial and biaxial tension are investigated. A recently proposed distortional plasticity model combined with a dislocation density-based hardening approach was adopted to describe the flow behavior of the material. The results indicate that the present model simultaneously reproduces all of the experimentally observed features for both load reversal and changes of the principal strain axis. This constitutive description is employed in the finite element analysis of the forming of two channels with obvious twist springback characteristics. The complex strain path changes during the forming process are then analyzed using a proposed indicator. Finally, the relevance of the load changes and the stress distribution in the channel regarding twist springback predictions are discussed. The influence of loading path-dependent elastic modulus degradation for the prediction of twist springback is also assessed based on two different application geometries.

Finite element simulation of twist forming process to study twist springback pattern

Springback is one of the most common defects found in the metal forming of automotive parts. There are three conditions which can be considered as springback i.e. flange angle change, sidewall curl and twist springback and among them, twist springback is the most complicated problem. This study will focuses on the development of finite element simulation model of the twist forming process. The main aim of this project is to investigate the parameters that may affect the twist springback. Few parameters including twist angle, hardening constant and thickness are explored using finite element (FE) software ANSYS Workbench (16.0). The rectangular mild strips are used to form the twist forming. The standard material properties and stress-strain curve of mild steel had been used to get the springback prediction. The results of springback were measured by the difference of the bending angles before and after unloading process. The results were then be validated with the research made of Dwivedi et al., (2002). The results show that the springback angle reduces as the thickness of strips are increased and also as the angle of twist increases.

Experimental validation of numerical model for asymmetric deep drawing of DP780 steel sheet using digital image correlation

A validated numerical model for in-plane stress/strain prediction is essential in understanding the deformation behaviour of sheet metal forming process, in particular, asymmetric deep drawing of advanced high strength steel sheet. In this work, the Yld2000-2d anisotropic yield criterion integrated with the initial homogeneous anisotropic hardening model was employed to describe the complex material behaviours of DP780 steel as well as the adoption of Yoshida chord model for elastic modulus degradation. Digital image correlation technique was utilized to measure the in-plane strain and shape deviation of the developed P- channel. The validity of the numerical model was assessed by comparing the predicted strain distribution and twist springback with the measured results. It indicates that the developed numerical model based on the selected constitutive models is acceptable for the deformation analysis, although the predicted discrepancies still exist.

Optimization of Parameters in Twist Springback Process for High-strength Sheets Based on Improved Particle Swarm Optimization Algorithm and Wavelet Neural Network

Optimization of Parameters in Twist Springback Process for High-strength Sheets Based on Improved Particle Swarm Optimization Algorithm and Wavelet Neural Network

Twist springback characteristics of dual-phase steel sheet after non-axisymmetric deep drawing

This paper aims to investigate the twist springback characteristics of advanced high strength steel sheet subjected to deep drawing. A C-rail benchmark, which leads to a particularly pronounced twist springback characteristics, was developed. For an accurate numerical modeling of the process, a non-quadratic anisotropic yield criterion integrated with combined isotropic and kinematic hardening model was used to describe the strain-stress behavior including anisotropy and Bauschinger effects. The corresponding mechanical experiments, namely uniaxial tension and forward-reverse simple shear tests were performed to determine the material parameters. The digital image correlation technique was applied for component tests as well as the deformation and stress-strain analysis. The experimental validation of the elastic-plastic finite element model was assessed by comparing maximum in-plane strain, thickness reduction distribution and twist springback of the drawn rail. To explore the source of twist springback, the deformation associated with in-plane stress and bending moment was analyzed. The results indicate that the bending moment before springback caused by non-symmetric stress states play an important role in twist springback and control. Certain regions of the die radius were varied in a numerical analysis to control the bending moment for the minimization of twist springback as well as the preliminary results of the relationship between the ratio of variable die radius and twist springback.

Modelling and sensitivity analysis of twist springback in deep drawing of dual-phase steel

Twist springback induced by unbalance elastic deformation and residual stresses in a sheet after a forming is of particular importance and complexity. The twist springback can be influenced by several factors, such as blank shape geometry, material anisotropy and sheet piercing. A sensitivity study of these parameters provides insight into the twist springback control of rail parts. In the present work, a more reasonable evaluation of twist springback of a long member with respect to the central principal inertia axes of the longitudinal cross-section was proposed. In order to explore the source of twist springback, the analysis of the relationship between torsion moment and twist angle was introduced. Mechanical tests including uniaxial tension, forward-reverse shear and hydraulic bulge tests were conducted to determine the material constitutive parameters of a DP500 steel. Several key modelling techniques including the friction coefficient identification and digital image correlation were performed for improving the robustness of twist springback prediction of a typical design benchmark of a curved rail channel formed by deep drawing. Finally, the sensitivity of the constitutive model, material direction and blank piercing on twist springback was analysed in-depth and discussed based on experimental and numerical results.

Measurement of Twist Springback on AA6061-T6 Aluminum Alloy Strip - A Preliminary Result

Twist forming is one of a critical process in a sheet metal forming process that has a complex profile. There are a few parameters that need to be taken into consideration, such as twist angle, workpiece geometries including length, width and thickness and material properties of the workpiece material. In this study, the preliminary result of the twist forming behavior of an aluminum alloy strip with uniform section will be studied. The experiment is conducted using torsion test machine. At this stage, the torque pattern was studied and compared with the published work to validate the experiment test rig. The result showed an agreement with the published work.