Thin-walled Tube Bending Research Articles

Experimental study on the effect of dies on wall thickness distribution in NC bending of thin-walled rectangular 3A21 aluminum alloy tube

To predict and control wall thickness distribution of thin-walled rectangular 3A21 aluminum alloy tube, the experiments of rotary draw bending process under multi-dies constraints are conducted. It is found that the thickness changing rates in middle bent zone are large, and the maximum values are obtained nearby the tube ridges. The effects of core die, pressure die, mandrel die, and bend die on thickness changing rate are significant. And the thinning rate increases with increase of core number, bend velocity, clearance between tube–pressure die interface and mandrel extension, but it decreases with increase of bend radius and boost velocity of pressure die. The thickening rate increases with increase of core number, boost velocity of pressure die and clearance between tube–wiper die interface, but it decreases with increase of bend radius and bend velocity.

Knowledge-based substep deterministic optimization of large diameter thin-walled Al-alloy tube bending

Regarding increasing applications with mass quantities, diverse specifications, and close quality tolerance, the precision bending of large diameter thin-walled (LDTW) Al-alloy tube should be efficiently achieved. However, bending of LDTW Al-alloy tube is a highly tri-nonlinear process with possible multi-defect, needing strict coordination of various bending tools and processing parameters. Considering the coupling effects of various forming parameters on multiple defects, this study developed a knowledge-based substep methodology to solve the deterministic optimization of LDTW Al-alloy tube bending with multi-objective and multi-variable under multiple factor constraints. Considering narrow forming window under small bending radii (Rb < 2D, Rb—bending radius, D—initial tube diameter), a finite element (FE)-based stepwise iterative search method is proposed to optimize key forming parameters of LDTW Al-alloy tube under small Rb, and the search direction is based on bending knowledge. While for large Rb bending with wide optional ranges of forming parameters, a hybrid optimization approach is used by combining virtual design of experiment, FE simulation, approximate response surface model, sequential quadratic programming algorithm, or genetic algorithm. Using orthogonal experimental method, three-dimensional (3D)-FE simulation, experiential data, and analytical formulae, knowledge on key forming parameters, coupling effects on multiple defects, effect significance, and design rules are obtained as well as initial values and design ranges. By several practical bending scenarios with D up to 100 mm, the proposed substep deterministic optimization methodology for LDTW Al-alloy tube bending is evaluated.

Relations between the stress components and cross-sectional distortion of thin-walled rectangular waveguide tube in rotary draw bending process

The significant cross-sectional distortion is one of the major problems in the bending of thin-walled rectangular waveguide tube. The cross-sectional distortion, which contains the flange distortion and the web distortion, depends on the stress components distribution. In this paper, the cross-sectional distortion characteristics are investigated using a three-dimensional finite element (FE) model. Results show that: the maximum flange distortion locates at the symmetric line; meanwhile, the maximum web distortion locates at the extrados ridge of the tube. The deformation zone of the tube can be divided into three sub-zones considering the loads and deformation, viz., the clamp die affect zone, the middle zone, and the mandrel/cores affect zone. Then the underlying relations between the cross-sectional distortion and the stress components are obtained. It is found that the flange distortion has a close relation with the circumferential stress. At the same time, the web distortion is relevant to both the tangential and the circumferential stress. The above relations are verified by FE models with different cores number. Moreover, some guidelines are introduced to help reduce the cross-sectional distortion.

The Effect of Normal Anisotropy on Thin-walled Tube Bending

Thin-walled tube bending has common applications in the automobile and aerospace industries. The rotary-draw-bending method is a complex physical process with multi-factor interactive effects and is one of the advanced tube forming processes with high efficiency, high forming precision, low consumption and good flexibility for bending angle changes. However, it may cause a wrinkling phenomenon, over thinning and cross-section distortion if the process parameters are inappropriate. Wrinkles propagate in thin-walled tube, but in some cases, localize in a finite zone and lead to failure. Wrinkling prediction in thin-walled tube bending processes has been an important and challenging subject in the related industry. In this paper, the plastic deforming behavior and wrinkling mechanism for a thin-walled tube is simulated and the results are compared with the available experimental ones. Next, the effect of anisotropy on ovalization, thickness and wrinkling of tube is investigated using FEM. Numerical results are presented showing the effects of the various kinds of materials and geometric parameters on wrinkling using anisotropic yield function.

FE-Based Analysis of Heat Bending of Thin-Walled Ti-Alloy Tube with Large Diameter and Small Bending Radius

The numerical control (NC) heat bending of thin-walled Ti-alloy tube with large diameter and small bending radius with Ф50×1×R75mm (diameter OD bending radius CLR) is explored by 3D-FE thermal-mechanical coupling simulation of heat conducting and NC bending. The results show that: (1) The heating of both pressure die and mandrel is proved to be appropriate to obtain the required temperature field. (2) In terms of wall thickness variation, wrinkling and cross-section deformation, the optimum span of the key parameters are obtained: the bending velocity of 0.4rad/s, the matched pressure die speed of 80%-110%, and temperature of 600-800°C.

Springback prediction for rotary-draw bending of rectangular H96 tube based on isotropic, mixed and Yoshida–Uemori two-surface hardening models

Based on the isotropic-hardening model, mixed-hardening model and Yoshida–Uemori two-surface model, the accuracy of springback prediction, such as section sag after springback, springback radius and springback angles, is researched for rotary-draw bending of thin-walled rectangular H96 tube to achieve a high precision of springback prediction. The material parameters of the three hardening models are obtained from the tensile and tension–compression tests of rectangular H96 tube specimen. The results show that, due to the tube undergoes reverse loading path in the bending process, and the Yoshida–Uemori model can well describe the transient Bauschinger effect and permanent softening of reverse loading, the Yoshida–Uemori model is more suitable for springback angle prediction than the other two hardening models, especially for the springback prediction with large deformation. Its average error is only 5.18%. The Yoshida–Uemori model also performs better on the prediction of section sag after springback, but the advantage is not obvious, and all of the three hardening models can accurately predict the springback radius with the average errors even smaller than 2.60%. It is also found the occurrence of tube reverse loading depends on the mandrel die, so if the tube is filled by the PVC mandrel, the three hardening models almost obtain the same prediction results; the filler of the tube determines whether the Yoshida–Uemori model should be considered.

Sensitivity of springback and section deformation to process parameters in rotary draw bending of thin-walled rectangular H96 brass tube

In order to study the effects of the process parameters on springback and section deformation, a sensitivity analysis model was established based on the combination use of the multi-parameter sensitivity analysis method and the springback/section deformation prediction finite element model, and by using this model the sensitivities of the springback and the section deformation to process parameters were analyzed and compared. The results show that the most sensitive process conditions for springback angle are the boost speed and the pressure of pressure die, and the most sensitive process condition for section deformation is the number of cores. When the clamp force, the boost speed and the pressure of pressure die are utilized to control section deformation, the effect of these process parameters on springback should be considered. When the process parameters are mainly used to control springback, the effect of these process parameters on the section deformation should be always considered.

Springback Angle and Plastic Elongation Prediction of Thin-Walled Tube Bending by FEM

Springback is an inevitable phenomenon while the load is released due to the elastic property after tube bending. This leads to an increase in the radius of curvature and elongation by plastic deformation, a reduction in the bending angle of the bent tube, a decrease in dimensional accuracy and fits with others difficulty. By elastic–plastic finite element methods (FEM), a reasonable simulation model for thin-walled tube bending is established to define the relationships between process parameters and springback angle, plastic deformation. With 210 kinds of models, the results show that: 1) Springback angle and plastic elongation of bending tube are related to bending angle, bending die diameter and tube thickness. 2) Controlling functions for plastic elongation and springback angle in bending tube process are given, which is verified by tube bending experiments.

Investigation on Corner Filling Process in Hydroforming of Thin-Walled Aluminum Alloy Tubular Part with Polygonal Sections

Bursting at the corner during calibration stage is a popular failure mode in hydroforming process of tubular part with polygonal sections. Bending of thin-walled tube is also a big obstacle for hydroforming process, especially for aluminum alloy tube. In this paper, a thin-walled aluminum alloy tubular part with polygonal sections was hydroformed with the step of hydro-bending, preforming and hydroforming. The influence of internal pressure during bending was discussed. Corner filling process of a symbol section was analyzed, such as filling sequence, corner shape changing and thickness distribution. The corner with less expansion ratio contacted the die first and thickness reduction is smaller. Bursting occurred in the corner with big expansion ratio. If the corner is located in the outer side of bending arc, danger of bursting is more severe. The key factor is to maintain a sound shape for the section before calibration to keep the expansion distribution evenly. [doi:10.2320/matertrans.MF201114]

Plastic Deformation Analysis of Thin-walled Tube Bending under Internal Pressure

The hydro-bending process of thin-walled tube provides several advantages:The section flattening is minimized by controlling the internal pressure,and the internal pressure delays the onset of wrinkling on the compression side and boosts the bending limit of the thin-walled tube.A new infinitesimal equilibrium equation for the hydro-bending process considering the effect of internal pressure is established.Then based on the plastic theory,the numerical solutions for the stress and strain components are obtained for a typical thin-walled tube.The finite element analysis is also conducted to verify the theoretical model.By comparing the theoretical result with the numerical results,it is found that the theoretical prediction and simulation results are in generally good agreement.The axial and circumferential stresses go up with the increasing of internal pressure.The circumferential strain increases linearly with pressure increasing,whereas the thickness strain decreases linearly as internal pressure increases.

Bending behaviors of large diameter thin-walled CP-Ti tube in rotary draw bending

AbstractThe rotary draw bending(RDB) of large diameter thin-walled (LDTW) tube needs the strict cooperation of multiple processing parameters to avoid possible multiple defects. Due to the specific properties, the bending behaviors of LDTW commercial pure titanium (CP-Ti) tube are much more complex to achieve precise deformation. With the CP-Ti tube of 50.8 mm (out diameter, D)×0.508 mm (wall thickness, t)×101.6 mm (bending radius, R) as a representative component, the bending behaviors of LDTW CP-Ti tube under different processing conditions were investigated. With experiments and analytical analysis, the bending characteristics of the CP-Ti tube were identified. Then, based on the orthogonal experimental design, a series of three-dimensional FE models of RDB for LDTW CP-Ti tube were established, and the effects of processing parameters on the bending behaviors were numerically investigated. The results show that: 1) Wrinkling is the primary behavior for the LDTW CP-Ti tube in RDB, and the larger the difference between the maximum wall thickening and the maximum wall thinning degrees of the bent tube, the larger the wrinkling tendency; 2) The bending behaviors of the LDTW CP-Ti tube are very sensitive to the some processing parameters, and the wrinkling is significantly affected by the mandrel shank diameter, while the wall thinning is remarkably affected by the clearance between wiper die and tube, mandrel shank diameter. The qualified bent tube with the wall thinning of 11.43%, the cross-section distortion of 2.69% and the wrinkling height less than 2% is then obtained.

Forming limits under multi-index constraints in NC bending of aluminum alloy thin-walled tubes with large diameters

With increasing diameters of aluminum alloy thin-walled tubes (AATTs), the tube forming limits, i.e. the minimum bending factors, and their predictions under multi-index constraints including wrinkling, thinning and flattening have been being a key problem to be urgently solved for improving tube forming potential in numerical control (NC) bending processes of AATTs with large diameters. Thus in this paper, a search algorithm of the forming limits is put forward based on a 3D elastic-plastic finite element (FE) model and a wrinkling energy prediction model for the bending processes under axial compression loading (ACL) or not. This algorithm enables to be considered the effects of process parameter combinations including die, friction parameters on the multi-indices. Based on this algorithm, the forming limits of the different size tubes are obtained, and the roles of the process parameter combinations in enabling the limit bending processes are also revealed. The followings are found: the first, within the appropriate ranges of friction and clearances between the different dies and the tubes enabling the bending processes with smaller bending factors, the ACL enables the tube limit bending processes after a decrease of the mandrel ball thickness and diameters; then, without considering the effects of the tube geometry sizes on the tube constitutive equations, the forming limits will be decided by the limit thinning values for the tubes with diameters smaller than 80 mm, while the wrinkling for the tubes with diameters no less than 80 mm. The forming limits obtained from this algorithm are smaller than the analytical results, and reduced by 57.39%; the last, the roles of the process parameter combinations in enabling the limit bending processes are verified by experimental results.

Theoretical, Numerical and Experimental Investigation of the Effects of Manufacturing Process Parameters on Thin-Walled Tube Bending Defects

The aim of this paper is to survey thin-walled tube bending process (without use of mandrel and booster). In tube bending process there are several effective parameters such as wall thickness, outer diameter-to-wall thickness ratio, and centerline bending radius-to-outer diameter ratio. Any mismatch in selecting these parameters would cause defects like wrinkling, variation in wall thickness, and cross section distortion. Firstly, the effects of these parameters on the initiation of the wrinkle, depth of wrinkling, change in wall thickness, and cross section distortion are studied. For this purpose, an FE commercial code has been used to simulate the process. Then, a series of experimental tests have been carried out to verify the results simulation. A comparison between analytical and experimental results shows a reasonable agreement with each other. Based on this comparison, it has been observed that there is a critical bending radius for any tube with a certain radius and thickness, in which the wrinkling begins to occur. For a certain bending angle and radius, it have been observed that the depth of wrinkling, change in wall thickness, and cross section distortion increase with reduction in wall thickness and outer diameter-to-wall thickness ratio

Deformation behaviors of thin-walled tube in rotary draw bending under push assistant loading conditions

In rotary draw bending (RDB) of thin-walled tube with small bending radii, by using pressure die or booster, the axial pushing force is applied to the tube to control the flow states of tube materials. While the roles of the push assistant loading (PAL) conditions are perplexing due to multiple defects inherent to tube bending. Based on an analytical description of the PAL functions, the deformation behaviors of thin-walled tube in RDB under three different PAL conditions are addressed with respect to wall thinning, cross-section deformation and wrinkling numerically combined with experiment considering PAL functions. The results show that: (1) besides the push assistant level fp and fb, the actual stretch amount Δ l of tube, the relative slip distances L 1 between tube and pressure die and L 2 between tube and clamp die can be used to evaluate the PAL roles. (2) The suitable boosting method is that the tube is boosted directly at the trailing end of tube; The synchronous mode is the optimal one to reduce the wall thinning degree I t and the cross-section deformation degree I d among sole pressure die, independent and synchronous modes between pressure die and booster; the role of pressure die is limited under sole pressure die mode due to dynamic friction conditions, and the suitable range of f ( fp & fb) for each matching mode is obtained. (3) the PAL function plays more significant effect on the extrados (reducing of I t and I d ) than that on the intrados (enlarging of wrinkling tendency I w ); The PAL conditions under synchronous mode play more significant effect on bending behaviors than sole pressure die mode; With smaller R d / D, the PAL can avoid L 2 and wrinkling near clamp die more effectively as well as reducing the I t and I d more effectively.

Roles of Surface Booster System on Bending of Thin-Walled Copper Tube

Thin-walled C12200 circular copper tube has been widely used in HVAC (heating, ventilation, air conditioning, and refrigeration) industry. Rotary draw bending is a versatile and precise method in forming of thin-walled copper tubes. Wall thinning and sectional fattening are the two main defects that affect tube quality in industrial applications. With traditional die settings, such as adjusting position or type of the mandrel, one factor usually decreases at the expense of increasing the other. An assistant equipment, surface booster system, has been recently developed to relieve both defects at the same time. In the present study, the role of the booster system in the bending process is investigated with finite element simulation. A basic model of copper tube rotary draw bending is established and validated by experiments. Then, cases of different sets of main parameters of the booster system are studied. The relationship between loading force, lower displacement, speed of the booster, and forming characteristics of tube is obtained based on which suggestions about process parameters settings are given. The results provide a better understanding of the role of the booster system in the improvement of forming quality.

A study on plastic wrinkling in thin-walled tube bending via an energy-based wrinkling prediction model

Thin-walled tube bending is an advanced technology for producing precision bent tube parts in aerospace, aviation and automobiles, etc. With increasing demands of bending tubes with a larger tube diameter and a smaller bending radius, wrinkling instability is a critical issue to be solved urgently for improving the bending limit and forming quality in this process. In this study, by using the energy principle, combined with analytical and finite element (FE) numerical methods, an energy-based wrinkling prediction model for thin-walled tube bending is developed. A segment shell model is proposed to consider the critical wrinkling region, which captures the deformation features of the tube bending process. The dissipation energy created by the reaction forces at the tube–dies interface for restraining the compressive instability is also included in the prediction model, which can be numerically calculated via FE simulation. The validation of the model is performed and its physical significance is evaluated from various aspects. Then the plastic wrinkling behaviors in thin-walled tube bending are addressed. From the energy viewpoint, the effect of the basic parameters including the geometrical and material parameters on the onset of wrinkling is identified. In particular, the influence of multi-tools constraints such as clearance and friction at various interfaces on the wrinkling instability is obtained. The study provides instructive understanding of the plastic wrinkling instability and the model may be suitable for the wrinkling prediction of a doubly-curved shell in the complex forming process with contact conditions.

3D numerical study on wrinkling characteristics in NC bending of aluminum alloy thin-walled tubes with large diameters under multi-die constraints

Abstract With an increase in the diameters of aluminum alloy thin-walled tubes (AATTs) and a decrease in their bending radii, wrinkling characteristics and its prediction under multi-die constraints have become a key problem urgently to be solved for improving the forming quality in numerical control (NC) bending of AATTs with large diameters. Thus in this paper, considering the characteristics of the bending processes, based on the ABAQUS software environment, a 3D elastic–plastic finite element model and a wrinkling energy prediction model under multi-die constraints are established and their reliabilities are validated, respectively, in which, the appropriate choosing of forming parameters is achieved to guarantee no excessive thinning and flattening in the processes even if wrinkling borders on occurring. By combining the two models, variation relationships of the maximum wrinkling factor with different compressed deformation zones and forming ratios, and effects of clearances and friction between different dies and tubes on the maximum wrinkling factor are obtained, and then an investigation into the wrinkling characteristics is carried out for the processes. It is found that the larger the diameters of AATTs, the larger the wrinkling sensitive zones (WSZs), and there is a larger possibility of wrinkling in the bending segments of WSZs than in the straight ones; the larger the effects of clearances and friction between different dies and tubes on wrinkling.

Three-dimensional finite-elements modeling and simulation of rotary-draw bending process for thin-walled rectangular tube

According to the characteristics of the rotary-draw bending process of a thin-walled rectangular tube, a three-dimensional finite-elements model of this process is built under the ABAQUS/explicit environment based on the solution of several key techniques, such as contact boundary condition treating, material properties definition, meshing technology, etc. The actions of pressure die, wiper die, clamp die and mandrel are considered in the modeling process. Then the reliability of the model is validated by comparison with experiments in the literature. Furthermore, numerical simulation and analysis of the thin-walled rectangular tube bending process of 3A21 aluminum alloy have been carried out by using the model. The distribution laws of tangential stress in the process have been analyzed. The results show that the maximum tangential stress increases sharply in the initial stage and then keeps nearly constant with the progress of the bending process. The circumferential compressive stress zone is basically unchanged when the bending process becomes stable.

Numerical Simulation on Influence of Clearance and Friction on Wrinkling in Bending of Aluminum Alloy Rectangular Tubes

The clearance and friction have large influence on wrinkling in rotary draw bending process of thin-walled rectangular tube. In this paper, a three-dimension Al FEM model of rotary draw bending of thin-walled rectangular tube is built under the ABAQUS/ Explicit environment. Based on the model, simulation and analysis of rotary draw bending for aluminum alloy 3A21 thin-walled rectangular tube have been carried out. The results show that the height of wrinkling wave decreases obviously with the decrease of the clearance between mandrel and tube or with the increase of the friction coefficient between wiper die and tube; however, the effect of friction coefficient on wrinkling becomes weaker while increasing the clearance between mandrel and tube. The achievements of this study provide a guideline for determining the process parameters for thin-walled rectangular tube in rotary draw bending process.

Springback analysis of numerical control bending of thin-walled tube using numerical-analytic method

Springback has an important influence on the forming quality of numerical control (NC) bending of thin-walled tube. In the paper, using the numerical-analytic method proposed by authors, the springback mechanism and laws of the tube bending have been analyzed. The results show the following: (1) there are two sources of springback, one is from the plastically curved part of the tube, which has an approximate bilinear relation to the bending angle; the other is from the straight portion, which varies like an exponent line with the bending angle. (2) Based on the above features of springback angle, reasonable regression equations between springback angle and bending angle under different conditions can be obtained. (3) The larger the strength factor, or the smaller the relative bending radius or the hardening exponent, the larger the springback angle. The research may serve as a significant guide to accurate prediction and control of springback.