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Springback is one of the factors that causes decreased product quality in tube bending; 2D and 3D stretch bending can be used to manufacture a complex geometry of a tube with springback reduction. For a nonlinear springback problem in tube bending, an artificial neural network (ANN) is an attractive data-driven approach to achieving springback prediction and control. The main objective of this paper is to control springback and improve geometrical quality with an ANN in 2D and 3D stretch bending of a rectangular tube. In general, an ANN is trained with collected data sets from a large number of experiments, causing expensive costs and time-consuming work. In the present work, the training data sets for the proposed ANN are obtained from both experiments and an analytical springback model. As the analytical model can adopt different bending angles, material properties, and geometries, supplementary data by the analytical model significantly reduced the number of experiments needed for ANN training. Contrary to the typical springback predictions, the proposed ANN synthesizes the machine settings based on the desired dimensions as the inputs. It is shown that springback can be controlled by specifying the bend angles provided by the ANN prediction. The proposed ANN method was validated in 2D and 3D stretch bending of a rectangular tube, and its prediction and control performance are favorably compared to an ANN trained with only experimental data sets. [ABSTRACT FROM AUTHOR]

In profile bending, the geometrical defect that reduces dimensional quality is mainly due to springback. While predicting dimensions after bending is important for quality control, many factors during bending cause difficulty in springback prediction. Furthermore, complex three-dimensional (3D) shapes in bending can make springback prediction significantly more difficult. This work presents a springback prediction method for varying curvature 3D profile/tube bending. An advanced five-axis bending machine, with rotary semi-dies opposing each other, has been developed. As the geometry of the bend die constrains the workpiece in the bending region, a model for 3D stretch bending is established from the rotational motion of the bend die. The discretized curvature of a bent profile geometry is described by using the Frenet-Serret frames, and a model for springback prediction is further developed based on the kinematics analysis of the bending process. This generalized analytic approach and numerical simulation are applied to evaluate springback in both 2D and 3D stretch bending of a thin-walled aluminum profile with a rectangular cross section. The analytical and numerical results for springback prediction are validated with experiments, showing good agreement. The developed model is able to evaluate 3D springback of a profile with arbitrary cross section efficiently for product design and development. [ABSTRACT FROM AUTHOR]

[Display omitted] • A classification model of the contact between the profile's flange and the roller die was established for the stretch-bending process. • The maximum theoretical interference value was calculated to predict the extent of local deformation after contact. • Finite element software was used to analyze the changes in equivalent plastic strain of the deformation results. This study aims to investigate the influence of the roller dies' characteristics of shapes on the forming results in the roller-based flexible multi-point three-dimensional stretch bending forming (FSBRD) process for thin-walled profiles, as well as the prediction of mold-induced impressions during the FSBRD process. Considering the specific contact mode, an L-shaped section profile's flange was selected as the research object to analyze the impact of the roller dies' slot's geometric parameters on the product. A classification model of the contact between the profile's flange and the roller die was established for the vertical bending process, and the maximum theoretical interference value (i max) was calculated to predict the extent of local deformation after contact. Subsequently, finite element software was used to model the process and analyze the changes in equivalent plastic strain (PEEQ) of the deformation results when using roller dies with slots of different parameters, including straight, inclined, and arc-shaped slots. The analysis results indicate that the width of the straight slot has a significant influence on the forming quality of the product, as a smaller slot width leads to larger local dimples on the product surface. Replacing the straight slot with an inclined or arc-shaped slot improves the abrupt changes in local PEEQ, resulting in reduced macroscopic local dimples. The simulation results align with the analytical model's variation of i max. This study defined the theoretical contact angle γ and introduced the concept of the contact area and the local theoretical interference zone, providing a reasonable explanation for the observed PEEQ variations. Furthermore, based on the conclusions of the research above, modified experiments were designed, resulting in favorable forming effects. The validation of the simulation results was performed by comparing the local dimples in the contact zone of the actual experimental results. [ABSTRACT FROM AUTHOR]

In the flexible stretch bending of multi-point roller dies process, the deformation of workpiece is mainly driven by clamps. Therefore, the movement track of clamp has a great influence on the forming effect of workpiece. Y-profile, T-profile, and L-profile are taken as the research objects. Simulation and experiments are carried out with two different movement tracks. The influence of the movement tracks on shape error, springback error, and thickness variation of different profiles is discussed. The experimental results of the three profiles processed by the double-sided forming method are consistent with the simulation results, which proves the accuracy of the numerical simulation. The results show that the movement track has a great influence on shape error. Compared with double-sided forming, one-sided forming can effectively reduce springback error. The two different movement tracks have no obvious influence on thickness change. [ABSTRACT FROM AUTHOR]

Stretch bending is a popular forming technique aiming at forming the long product's axis into a desired curvature with the cross-section remaining constant. The most efficient and convenient method to prevent the defects in stretch bending such as axial springback and cross-sectional distortion is the optimization of forming path. In this work, a function of stretch length and bending angle is utilized to represent the forming path, and two new variables, total stretch length and distribution ratio, are proposed to better describe the effect of forming path on forming quality. Based on the data obtained from finite element simulation, a machine learning model is established to rapidly predict forming quality of the rail with a hat-shaped section. The forming path is optimized by multi-objective optimization method based on NSGA-II algorithm. The results show that the stretch bending quality is mainly determined by the total stretch, while the stretch distribution in three forming steps (e.g., pre-stretch, bend stretch and post-stretch) is a minor factor in controlling stretch bending quality with a few exceptions. With total stretch's increment, the forming angle firstly increases dramatically and tends to a steady state at last, while the cross-sectional distortion increases constantly. The optimal forming path obtained indicates that the stretch of optimal forming process is an equal-ratio combination of the post-stretch and bending stretch. [ABSTRACT FROM AUTHOR]

Springback, fracture, and cross-section distortion are common defects in stretch bending process of profiles. The crease defect of profiles is not obvious in the traditional stretch bending process. However, in the 3D flexible stretch bending of multi-point roller die process, due to the multi-point roller dies instead of the whole die, the forming process is more complex. Therefore, the crease can no longer be ignored. In this paper, the finite element model is established, and the effect of different process parameters on crease defect is discussed, and experiments are carried out with the forming equipment. The validity of numerical simulation is verified by experimental results. The results show that the crease defect becomes more obvious with the increase of the pre-stretching length, the post-stretching length, and the friction coefficient. The number of roller dies has a significant effect on the change of crease defect. However, the change of roller die radius has little effect on the crease defect. [ABSTRACT FROM AUTHOR]

Tension-dominated stress state in the stretch bending process probably leads to localized tensile stress, especially in the manufacture of thin-walled, high-strength, or complex-shaped components. That results in nonuniform residual stress distribution and inferior shape accuracy. In this paper, a friction-assisted stretch bending (FASB) process is proposed to deal with this problem. A rubber sheet is attached with sheet metal to generate tangential friction at rubber/metal interface. The tangential friction assists in modifying stress distribution in the loading process. Finite element analysis was conducted to determine the effects of process parameters on deformation behaviors of the sheet metal. The results show that a rubber sheet with hardness ranging from Shore 57D to 70D and a rubber/metal thickness ratio (ξ) value around 1.0 can effectively reduce sheet metal thinning and decrease springback in the stretching and bending stress states. By taking the simulated process parameters as a reference, fuselage profiles with variable bending curvature and sections were successfully manufactured. Maximum thinning ratio of the formed part was 6.1%, and the section deviation after unloading was reduced by 52.9%, on average, compared with conventional stretch bending. The improved forming accuracy can be attributed to the relatively uniform distribution of longitudinal stress. That results in uniform elastic recovery in longitudinal direction. Further industrial application of the FASB process for the manufacture of large-sized and complex-shaped parts will be expectable. [ABSTRACT FROM AUTHOR]

This paper proposes a new stretch bending approach for aluminum alloy extrusion profiles based on a novel pre-hardening forming (PHF) process. Tensile tests were carried out to examine the flow behavior and mechanical responses of a 7A09 extrusion profile in PHF process. Microstructure evolution was investigated through X-ray diffraction (XRD), transmission electron microscopy (TEM), scanning electron microscope (SEM), electron backscatter diffraction (EBSD), and small angle X-ray scattering (SAXS). It is interesting to find that the yield stress at 200 °C was higher than that at 185 °C. The quantitative analysis revealed that the higher volume fraction of precipitates (200 °C) played a greater role than the refinement of precipitate sizes (185 °C) in precipitation strengthening mechanism, thereby causing an enhanced hardening effect. This phenomenon indicated that there was a preferred temperature zone for the precipitation behavior in PHF process, and it also explained the lower yield stress at 185 °C than that at 200 °C. Additionally, similar results were also observed in strength of the warm-deformed alloys. The optimal strength (σ / σ 0.2 =589/517 MPa) can be achieved at 200 °C without subsequent heat treatment, which exceeded the typical strength of 7A09-T6 extrusion. The primary strengthening mechanisms in PHF process were strain hardening and precipitation strengthening, and the warm forming procedure caused a hardening effect, rather than a softening impact as in traditional warm/hot forming procedures. [Display omitted] • The yield stress and warm-deformed strength initially increased and then dropped with the increasing forming temperature. • An optimal warm-deformed strength superior to typical 7A09-T6 was obtained at 200 °C without subsequent heat treatment. • The higher volume fraction played a greater role than refinement of precipitate sizes in precipitation strengthening. • The warm forming procedure caused a hardening effect, rather than a softening effect during traditional warm/hot forming. [ABSTRACT FROM AUTHOR]

2024 aluminum alloy L section extrusion profile stretch bending structure parts are key components in aircraft panels floor and joint. Aiming at the stretch bending springback problems of this kind of structure part，a stretch bending and springback finite element model was established based on the displacement controlled clamp trajectory modeling method，and the influences of pre stretching, post stretching and friction coefficient on springback were analyzed. The significance of pre stretching, post stretching and friction coefficient to springback was studied by orthogonal experiments. The results show that increasing pre stretching or post stretching can reduce the radius springback ratio，the lubricant between extrusions with die reduces the radius springback ratio. The variance analysis of the orthogonal experiment shows that the post stretching and friction coefficient have significant influence on the experimental indexes at the levels of Fo. 2s (2,2). [ABSTRACT FROM AUTHOR]

Copyright of Journal of Harbin Institute of Technology. Social Sciences Edition / Haerbin Gongye Daxue Xuebao. Shehui Kexue Ban is the property of Harbin Institute of Technology and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Copyright of Journal of Harbin Institute of Technology. Social Sciences Edition / Haerbin Gongye Daxue Xuebao. Shehui Kexue Ban is the property of Harbin Institute of Technology and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

With the increasing demand of the parts with multi-segment curvature, long length, and complex section shape, the required target shape is more and more difficult to meet. In this article, a flexible three-dimensional (3D) multi-point stretch bending processing method for a roller die is proposed, and a flexible 3D stretch bending equipment of a roller die is developed. With the application of flexible 3D stretch bending technology of roller dies, the complex 3D parts can be formed at one time with only two degrees of freedom. In order to better evaluate the springback deformation of 3D parts, the total springback process of the flexible 3D stretch bending parts of a roller die is divided into two parts: horizontal bending springback distance and vertical bending springback distance. The springback law of different length profiles is studied by numerical simulation and compared with the experiment. From the perspective of springback, this study analyzes the parts produced by the 3D FSBRD process and studies the influence of different process parameters on springback. [ABSTRACT FROM AUTHOR]

Based on the application of snake-spine-like structures, this paper proposes a roller-type multi-point flexible 3D profile bending process with snake-spine-like structures (Flexible stretch-bending with roller dies - driven by snake-like mechanism, FSBRD-S), and establishes a finite element model. Taking the L-shaped cross-section profile as the research object, different working modes and contact modes are defined to study their impact on crease defects during the vertical bending step, and the new structure is designed to improve the forming quality of the products' surface. The research results show that changing the contact mode leads to a change in the relative angle between the die and the billet. In the process of larger angle vertical bending, the FSBRD-S process can effectively reduce the crease defects generated by the traditional FSBRD process, especially in the area near the clamp. Furthermore, this article proposes the FSBRD-S shape-adjusting technology, which allows for adjustments to the FSBRD-S process based on actual needs, to obtain products with different surface qualities. [Display omitted] • Adaptive multi-point flexible-bending technology driven by snake-spine-like motion mechanism has been proposed. • The dispersed molds with multi-degrees of freedom changes the contact mode between the profile and the molds. • Finite element simulation combines with microscopic analysis and forming experiments to verify the accuracy of the shape adjustment mechanism. [ABSTRACT FROM AUTHOR]

Springback is a common defect caused by elastic recovery in the plastic forming process, which can cause the formed workpiece to deviate from the target shape. The purpose of this paper is to grasp the influence law of process parameters on springback deviation so as to optimize process parameters to reduce springback. Taking the Y-profile as the research object, the influence of process parameters such as horizontal bending radius, vertical bending radius, transition zone length, radius of roller dies, and wall thickness of the profile on springback deviation is discussed by numerical simulation. Additionally, the validity of the numerical simulation is verified through experiments. The springback law obtained by numerical simulation is applied to practical production, and the large-scale production of the Y-profile is realized.

High precision stretch bending of aluminum alloy profile is the key technology for making car’s frame body. A numerical simulation study on the displacement-controlled process for a typical kind of L-section aluminum alloy profile used in high-speed rail with finite element analysis software is presented. The effect of different friction coefficients, with or without baffle and cover plate on the equivalent stress, strain and cross-sectional distortion are investigated. It is shown that the increase of the friction coefficient can increase the cross-sectional distortion, equivalent stress and strain. The installation of baffle and cover plate can significantly reduce the cross-sectional distortion in the middle section of the profile, and increase the equivalent stress and strain to some extent.

In view of the stretch bending process of the profile, an expanded study is carried out for the forming and springback of the profile with any cross-section in the loading method of prebending and tension (prebending-tension). Base on the analysis of stress and strain in cross section, the stretch bending is divided into twelve cases, then the corresponding determination conditions and general springback analysis step are established. According to the analytical model, the deformation types and springback of rectangular and U-section profiles are predicted and verified by numerical simulations and experiments. The comparative study of the results by three methods clearly demonstrates that the prediction of springback is reliable. Moreover, the springback analysis of stretch bending in the loading methods of prebending-tension show that, when the bending radius is constant, the bigger the tension is, the smaller the springback is; under the condition of equal tension, the smaller the bending radius is, the smaller the springback is; the springback laws of both profiles consistent The accurately predicted springback values can provide a theoretical basis for flexible manufacturing and intelligent control of the stretch bending of profiles. [ABSTRACT FROM AUTHOR]

• Characterizing uniaxial tension, plane strain tension, and shear stress states of martensitic steel. • Adjusting yield function exponent and size of finite element model for calibration of fracture models. • Predicting hole expansion fracture of martensitic steel accurately with GTN-shear fracture model. • Predicting bending fracture of martensitic steel accurately with Hosford-Coulomb fracture model. In this study, fracture of martensitic steel in hole expansion and stretch bending was predicted by finite element analysis with shell elements. Various mechanical experiments were conducted to characterize mechanical properties related to fracture as well as plasticity. Then, Swift-modified Voce and Yld2000-2d well-described plasticity properties of martensitic steel. For fracture modeling, Hosford-Coulomb (HC) and shear-modified Gurson-Tvergaard-Needleman (GTN-shear) models were selected and calibrated with load–displacement curves of three fracture tests. The hybrid numerical-experimental method was used for the HC model and inverse identification with finite element model updating was used for the GTN-shear model. In calibration, an exponent of yield function and mesh size were adjusted to match the strength of plane strain state and to maintain consistency of mesh size. After calibration, both fracture models were applied to numerical simulations of conical hole expansion and stretch bending tests. The GTN-shear model predicted well fracture in the conical hole expansion test but not in the stretch bending. The prediction results of HC model were vice versa. Through triaxiality analysis, these differences between the two models may result from a non-linear loading path and description of localized necking. [ABSTRACT FROM AUTHOR]

In this investigation, the attention is focused on the minimum bending radii of 2196-T8511 and 2099-T83 Al-Li alloy extrusions. To predict the failure of Al-Li alloys, sheet and extrusion stretch bending tests are developed, carried out and simulated using finite element model. The theoretical minimum bending radius is introduced to derive a safe lower limit for the bending radius which can serve as a guideline for tool and product design. Stretch bending tests of Al-Li alloys are performed using the three-point bending test and displacement-controlled stretch bending test at room temperature. The finite element model incorporates three-dimensional solid elements and ductile damage modeling. The experimental results show that Al-Li alloy extrusions in stretch bending show three types of failures, occurring at the unbent region near the entrance of the jaws, at the region below the exit of the die and within the region in contact with the die, respectively. Comparison between predicted values and experimental results has been made, a consistent agreement being achieved, reflecting the reliability of the present model. The three types of failure mechanisms which compete with each other are tensile localization failure, die-corner failure and shear failure, respectively. Based on the analytical models, experiments and simulations, it appears that the three distinct failures need to be applied to predict the minimum bending radius and range of failures that can occur with 2196-T8511 and 2099-T83 Al-Li alloy extrusions in stretch bending. [ABSTRACT FROM AUTHOR]

For the last two decades, strong demands for the light weighted structures of automobiles have been increasing in all over the world. In order to satisfy the demands, the high strength steel sheets (hereafter HSSs) have been widely utilized in the various automobile related companies. However, for the companies, it is still one of the hard tasks to apply HSSs for the automobile parts with complex shapes, due to low ductility and large springback of the HSSs. In the present research, we assumed fracture limits in stretch bending are theoretically obtained with the assumption that fracture occurs when stretching force reaches its maximum value. The authors proposed an explicitly theoretical analysis method based on the maximum load criterion that can easily and rapidly allow us to predict the fracture and springback of HSSs by using two no dimensional parameters (limited wall stretch L / L 0 ( L : limit wall length of a sheet, L 0 : initial wall length) and bending radius t / R (t: sheet thickness, R : bending radius)). For the evaluations of this method, the comparisons between stretching bending experiments of HSSs and the corresponding theoretical calculations were conducted. From the comparisons, the calculated results by our proposed method have good agreements with the experimental observations. [ABSTRACT FROM AUTHOR]

In this paper, the springback of the aluminium alloy AA5754 under hot stamping conditions was characterised under stretch and pure bending conditions. It was found that elevated temperature stamping was beneficial for springback reduction, particularly when using hot dies. Using cold dies, the flange springback angle decreased by 9.7 % when the blank temperature was increased from 20 to 450 °C, compared to the 44.1 % springback reduction when hot dies were used. Various other forming conditions were also tested, the results of which were used to verify finite element (FE) simulations of the processes in order to consolidate the knowledge of springback. By analysing the tangential stress distributions along the formed part in the FE models, it was found that the springback angle is a linear function of the average through-thickness stress gradient, regardless of the forming conditions used. [ABSTRACT FROM AUTHOR]

To achieve high-precision bent components for rail vehicles, the stretch bending properties of the common L-section aluminum extrusions with variable contour curvatures were investigated by simulation. The causes of the defects, such as bad die fittingness, cross-section distortion of horizontal plate sagging and low contour accuracy, were analyzed, and the corresponding control methods were proposed. The simulation results demonstrate that die fittingness could be significantly improved by increasing the die elongation. The horizontal plate sagging distortion of L-section aluminum components could be eliminated by modifying the die supporting surface curve, i.e., to reduce the depth from the die's outer surface according to the shrinkage of the profile's vertical wall. By applying suitable springback compensation to the bending die geometry, the contour accuracy could be enhanced exponentially. Using the optimal process parameters and defect controlling methods, the stretch bending tests were then carried out, and results indicate that the proposed controlling methods were quite effective and the scale production of high-precision bent parts has been achieved. [ABSTRACT FROM AUTHOR]

Post-stretching elongation is a crucial process parameter in stretch bending process because of its significant influence on the forming effects. In this paper, the displacement loading method was presented to control the movement of the jaw in order to avoid the instability of tensile force in mechanical loading method. Typical aluminum hollow profile used in high-speed trains was selected as the research object. Stretch bending process with five levels of post-stretching elongations was carried out by finite element (FE) simulation. The simulation results reveal that an increment of the post-stretching elongation leads to smaller shape error and springback but larger cross-sectional distortion and spatial twist. The forming defects index, which is based on normalizing and weighting four forming defects, was put forward to evaluate comprehensive forming effects. Furthermore, the backtracking method was used to obtain the optimal post-stretching elongation. Experimental validation was conducted on stretch-wrap bending machine. The experiment part meets the processing requirements, thereby validating the reasonability of the optimization method. Measured results showed consistency with numerical analysis which verifies the feasibility of using FE simulation to guide the experiment. [ABSTRACT FROM AUTHOR]

The aluminum–lithium (Al–Li) bent extrusion products offer opportunities for significant improvements in structural performance due to its lightweight material and component. However, the high ratio of strength to Young's modulus may induce significant elastic recovery after unloading. The precise bending of the Al–Li alloys extrusion depends on the understanding of the springback features and mechanisms of the profile stretch bending process, which is a much complex physical process with multi-factors coupling interactive effects. For this purpose, the springback behaviors of the age-hardened 2196-T8511 and 2099-T83 Al–Li alloys extrusions with Z-section and T-section under displacement controlled cold stretch bending (DCSB) are investigated. Firstly, an analytical model is developed based on the radius of strain neutral layer and verified experiments are carried out. Secondly, the connector element in FEM is used to simulate DCSB. Furthermore, the roles of material, radius, process parameters and friction condition are revealed. Finally, springback control method is proposed to ensure the stabilization and precision of bending parts. The results show that: (1) The analytical model and finite element method can be used to evaluate effectively the effects of material and process parameters on springback of Al–Li alloys extrusions in DCSB. (2) 2196-T8511 and 2099-T83 Al–Li alloys extrusions show significant springback at room temperature because of its higher strength to Young's modulus. (3) Increasing pre-stretching or post-stretching strain can significantly reduce the radius springback and time-dependent springback of 2196-T8511 and 2099-T83 Al–Li alloys extrusions, but it is limited by the lower fracture strain. (4) The lubricant between extrusions with die reduces the stable radius springback ratio greatly for Al–Li alloys in the T8 temper. [ABSTRACT FROM AUTHOR]

Copyright of Journal of Harbin Institute of Technology. Social Sciences Edition / Haerbin Gongye Daxue Xuebao. Shehui Kexue Ban is the property of Harbin Institute of Technology and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Al-Li alloys extrusions improve the performance of advanced aircraft due to their low density and high stiffness. In order to determine whether 2196-T8511 and 2099-T83 Al-Li alloys extrusions with high ultimate tensile strength/Young's modulus ratios, also exhibit significant elastic recovery, the springback behaviors of the two Al-Li alloys extrusions under displacement controlled cold stretch bending are addressed, using the simple plasticity deformation theory, the explicit/implicit FEM and the physical experiments. The results show that applied post-stretch strain affects springback of extrusions. The two Al-Li alloys extrusions show time-dependent springback at room temperature. The analytical solution and finite element simulation are effective means to assess the impact of material and process parameters on springback in stretch bending. [ABSTRACT FROM AUTHOR]

The main objective of this work is to quantify the impact of the most important parameters on dimensional accuracy in stretch forming, combining analytical models and experiments conducted in industry-like stretch forming operations. Using the deformation theory of plasticity, an analytical moment-curvature model for prediction of deformations of a curved flange under the action of longitudinal stretching and transversal (local) bending was established. By combining suitable equilibrium and compatibility equations, the model was used for prediction of cross-sectional distortions. The overall results formed the basis for the development of a closed-form relationship for prediction of cross-sectional distortions. This model explicitly expresses the most important influential parameters and their impact on cross-sectional distortions. The results show that anisotropy, as represented by a Hill (1948) relationship, is the most important material characteristic with regard to suck-in of individual cross-sectional members. The strain hardening characteristic and the initial yield stress level of the material have very limited impact on local distortions. Moreover, geometrical parameters such as flange width, flange thickness, cross sectional height and web depth, play an important role with regard to dimensional accuracy. The analytical model also shows that the flange width is the single most important design parameter with regard to the nominal value of the flange’s suck-in, whereas the flange thickness is the main source to variability, i.e. noise parameter. The analytical results show remarkably good correlation with experimental results obtained in a full-scale rotary stretch forming setup. [ABSTRACT FROM AUTHOR]

Abstract: Fracture limits in sheet stretch bending were theoretically obtained on the assumption that the fracture occurs when the stretching force reaches its maximum value. From the calculated results, a fracture criterion has been presented where limit wall stretch, L max/L 0 (L max: limit wall length of a sheet, L 0: initial wall length), is explicitly given as a function of the non-dimensional bending curvature, (t 0: sheet thickness, R: bending radius) and the material''s work hardening exponent (n-value). To verify this criterion, three-point stretch bending tests with various punch-radii were performed on three types of aluminum sheets (A5182-O, JIS6061-T4 and JIS6N01-T5). The predicted limit wall stretch, as well as limit forming height, were in good agreement with the experimental results. [Copyright &y& Elsevier]

Local deformation of individual cross-sectional members is of great interest in bending of aluminium alloy extrusions for tight tolerance production such as automotive components. The primary concern is the impact of such distortions on manufacturability as well as the dimensional tolerances of the component. This paper presents analytical models for the determination of local post-buckling and suck-in deformations in stretch bending. The models are based on the deformation theory of plasticity combined with an energy method using appropriate shape functions. The analytical predictions are being verified with experimental results. Based on the present findings, a simplified design method for evaluation of bendability of sections in industrial forming operations is being proposed. The results show that the slenderness (b/t) and the width of the flange are the main parameters related to the bending radius at the onset of plastic buckling and the magnitude of local deformations, respectively. Material parameters have proven to be relatively more important to the former than to the latter. Although there is some discrepancy at tight nominal bend radii, the overall correlation between the experimental and theoretical results is surprisingly good. It is therefore concluded that the present method provides to be an efficient means to the evaluation of bendability of rectangular hollow sections. [Copyright &y& Elsevier]

Springback is a common defect caused by elastic recovery in the plastic forming process, which can cause the formed workpiece to deviate from the target shape. The purpose of this paper is to grasp the influence law of process parameters on springback deviation so as to optimize process parameters to reduce springback. Taking the Y-profile as the research object, the influence of process parameters such as horizontal bending radius, vertical bending radius, transition zone length, radius of roller dies, and wall thickness of the profile on springback deviation is discussed by numerical simulation. Additionally, the validity of the numerical simulation is verified through experiments. The springback law obtained by numerical simulation is applied to practical production, and the large-scale production of the Y-profile is realized. [ABSTRACT FROM AUTHOR]