Precision Bending Research Articles

Research on Precision Bending Forming Technology of Aluminum Alloy Outer Frame

In this paper, the 6063 aluminum alloy outer frame is prone to cracking during bending forming. We analyze the strength and plasticity of the material through tensile experiments (in situ stretching, high-temperature stretching), and establish constitutive models based on component material parameter equations. Using COMSOL Multiphysics software, numerical simulation was conducted on the bending forming of 6063 aluminum alloy profiles, analyzing the stress and deformation of the material during the extrusion process. By utilizing simulation results to design and improve the process and mold, the aluminum alloy outer frame will not produce cracks during the bending forming process, thereby improving the product qualification rate.

Cold-hot Integrated Precision Bending of Ultra-high Strength Steel Welded Tube without Springback Compensation

Cold-hot Integrated Precision Bending of Ultra-high Strength Steel Welded Tube without Springback Compensation

Wall thinning characteristics and prediction in numerical control bending of high strength Ti-3Al-2.5V tube

Owing to the unique properties of high strength Ti-3Al-2.5V tube, wall thinning is prone to happen in tube bending. To accomplish tube precision bending forming, the wall thinning needs to be precisely predicted and effectively controlled. A theoretical model considering circumferential deformation was presented to reveal the inherent relationship for wall thickness distribution versus tube geometrical parameters, and its reliability was validated by published experimental results. Using finite element (FE) simulation combined with orthogonal test, the effect rules and significances of process parameters on wall thinning in numerical control (NC) bending for high strength Ti-3Al-2.5V tube were investigated. The results show that the significant factors sort from the largest to the smallest for wall thinning in tube bending as the clearance of tube versus mandrel C m, axial feed of mandrel e, friction of tube versus mandrel f m, clearance of tube versus bending die C b, clearance of tube versus wiper die C w and push assistant speed of pressure die v p; the wall thinning decreases for the larger C m and v p, while increases for the larger C b, C w, f m, and e. Furthermore, the prediction model of maximum wall thinning ratio was established based on the significant process parameters by multiple linear regression method. Compared with the results of orthogonal test, the relative error of that is less than 6.5%, which can be employed for rapidly predicting the wall thinning in tube bending.

Springback law of high-strength 21-6-9 stainless steel tube in numerical control bending under different process parameters

In order to achieve the precision bending deformation, the effects of process parameters on springback behaviors should be clarified preliminarily. Taking the 21-6-9 high-strength stainless steel tube of 15.88 mm × 0.84 mm (outer diameter × wall thickness) as the objective, the multi-parameter sensitivity analysis and three-dimensional finite element numerical simulation are conducted to address the effects of process parameters on the springback behaviors in 21-6-9 high-strength stainless steel tube numerical control bending. The results show that (1) springback increases with the increasing of the clearance between tube and mandrel Cm, the friction coefficient between tube and mandrel fm, the friction coefficient between tube and bending die fb, or with the decreasing of the mandrel extension length e, while the springback first increases and then remains unchanged with the increasing of the clearance between tube and bending die Cb. (2) The sensitivity of springback radius to process parameters is larger than that of springback angle. And the sensitivity of springback to process parameters from high to low are e, Cb, Cm, fb and fm. (3) The variation rules of the cross section deformation after springback with different Cm, Cb, fm, fb and e are similar to that before springback. But under same process parameters, the relative difference of the most measurement section is more than 20% and some even more than 70% before and after springback, and a platform deforming characteristics of the cross section deformation is shown after springback.

Deformation behaviors of 21-6-9 stainless steel tube numerical control bending under different friction conditions

For contact dominated numerical control (NC) bending process of tube, the effect of friction on bending deformation behaviors should be focused on to achieve precision bending forming. A three dimensional (3D) elastic-plastic finite element (FE) model of NC bending process was established under ABAQUS/Explicit platform, and its reliability was validated by the experiment. Then, numerical study on bending deformation behaviors under different frictions between tube and various dies was explored from multiple aspects such as wrinkling, wall thickness change and cross section deformation. The results show that the large friction of wiper die–tube reduces the wrinkling wave ratio η and cross section deformation degree ΔD and increases the wall thinning degree Δt. The large friction of mandrel–tube causes large η, Δt and ΔD, and the onset of wrinkling near clamp die. The large friction of pressure die–tube reduces Δt and ΔD, and the friction on this interface has little effect on η. The large friction of bending die–tube reduces η and ΔD, and the friction on this interface has little effect on Δt. The reasonable friction coefficients on wiper die–tube, mandrel–tube, pressure die–tube and bending die–tube of 21-6-9 (0Cr21Ni6Mn9N) stainless steel tube in NC bending are 0.05–0.15, 0.05–0.15, 0.25–0.35 and 0.25–0.35, respectively. The results can provide a guideline for applying the friction conditions to establish the robust bending environment for stable and precise bending deformation of tube bending.

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.

Finite element simulation of laser assisted bending with moving mechanical load

Laser bending is an advanced technique to bend the sheet metal worksheet by means of thermal stresses instead of mechanical forces. It is a non-contact type process in which a concentrated high power laser beam works as a processing tool. In the present work, three-dimensional sequential thermo-mechanical non-linear elasto-plastic numerical model of laser-assisted bending has been developed by using finite element method. The developed numerical model is used to analyse laser bending of magnesium alloy AZ31B worksheet with a moving mechanical load. The effects of transient load on stress-strain distribution and bend angle distribution in the sheet metal worksheet are investigated. The results showed that the bending of worksheet depends on the laser beam parameters as well as magnitude of mechanical load applied. These results will be useful in the precision bending of difficult-to-form materials using laser bending process.

Springback law of thin-walled 6061-T4 Al-alloy tube upon bending

To achieve the precision bending deformation, the springback behaviors under various forming conditions should be clarified preliminarily. Taking the thin-walled 6061-T4 Al-alloy tube of 50.8 mm×0.889 mm (outer diameter×wall thickness) as the objective, the single-factor experimental analysis and the 3D-FE based numerical orthogonal test are conducted to address the effects of forming parameters on the springback behaviors in 6061-T4 Al-alloy tube bending. The results show that: 1) The springback angle increases linearly with increasing of the bending angle. 2) The significant factors from high to low are the clearance between tube and mandrel, the bending radius, the friction between tube and pressure die, the clearance between tube and wiper die, the clearance between tube and pressure die, the coefficient of boost velocity, the friction between tube and mandrel, the number of mandrel balls. 3) The effect rules of significant parameters on springback of 6061-T4 Al-alloy tube are similar to those of stainless steel and Ti-alloy tubes. Springback becomes larger with increasing of the bending velocity, the tube-die clearance, the relative bending radius, the tube-pressure die friction and relative push assistant speed. While the springback decreases with increasing of the mandrel extension length, the number of mandrel balls and tube-mandrel friction.

Springback characterization and behaviors of high-strength Ti–3Al–2.5V tube in cold rotary draw bending

Stress-relieved Ti–3Al–2.5V bent tube in hydraulic bleeding systems improves the overall performance of advanced aircraft and spacecraft due to its unique high specific strength. However, the high ratio of yield strength to Young's modulus may induce significant elastic recovery after unloading. The precision bending of the high strength Ti-tube (HSTT) depends on the understanding of the springback features and mechanisms. Using the plasticity deformation theory, the explicit/implicit 3D-FE and the physical experiments, the springback behaviors of the HSTT under multi-die constrained cold rotary draw bending (RDB) are addressed. The results show that: 1) The elastic recovery of the HSTT should be characterized by the significant angular springback, the radius growth and the sectional springback; Both the angular and radius springback should be compensated, while the sectional one decreases the cross-section flattening; 2) Among multiple parameters, both the material properties (Young's modulus, strength coefficient and anisotropy exponent) and the geometrical dimensions (bending angle and bending radius) dominate the unloading; Both the angular and radius springback values decrease with the smaller bending radii; The angular springback increases linearly with the larger bending angles, while the radius growth fluctuates little with the increasing of the bending angles at the later bending stages; Both the springback values of the HSTT are far larger than the ones of the 5052O Al-alloy tube and the 1Cr18Ni9Ti tube; The maximum variations of the angular and radius springback with changing of the processing parameters are 78% and 62.5% less than the maximum ones under different material properties and geometrical ones, respectively. 3) A two level springback compensation methodology is proposed to achieve the precision bending in terms of both springback angle and radius.

Precision bending of high-quality components for volume applications

Recent new technology developments were presented in the field of industrial bending operations, including flexible stretch forming and 3D rotary stretch forming. Attempts were made to give an overview of different mechanisms that influence dimensional accuracy, including local cross-sectional deformations such as suck-in and volume conservation effects, along with global deformations such as springback. An analytical model was developed to determine the particular influence of different material, geometry and process parameters on dimensional variability of bent components. The results were discussed in terms of overall process capability ( C p) and associated process windows. The results show that different governing mechanisms prevail in various bending operations, meaning that attention has to be placed on controlling those process parameters that really are important to part quality in each specific case. Several strategies may be defined for reducing variability. One alternative may be to design more robust process and tool technology that reduce the effect of upstream parameters on dimensional variability of the formed part. The results show that optimal tool design and technology may in specific cases improve the dimensional accuracy of a formed part. Based on the findings discussed herein, it is concluded that advances in industrial bending operations require focus on improving the understanding of mechanical mechanisms, including models and parameter development, new technology developments, including process, tool, measurement and control capabilities, and process discipline at the shop floor, combined with a basic philosophy of controlling process parameters rather than part attributes.

Friction role in bending behaviors of thin-walled tube in rotary-draw-bending under small bending radii

For contact dominated rotary-draw-bending (RDB) of thin-walled tube, friction role should be focused to achieve precision bending under small bending radii ratio ( R d / D < 2.0, R d -bending radius, D-tube diameter). By using explicit FE simulation combined with physical experiment, underlying effects of the friction on bending behaviors are explored from multiple aspects such as wrinkling, wall thickness variation and cross-section deformation. The results show that: (1) By using a simulative twist compression test (TCT), the dynamic contact conditions of RDB with large slipping are reproduced, and the coefficients of the friction (CoFs) under various tribological conditions in RDB are estimated, which provides physical basis for understanding friction role and boundary conditions for FE simulation. (2) Both positive and negative effects of friction role are observed since the friction on each interface affects the multi-defect with different or even contrary tendencies. The effect sensitivity on wrinkling is less obvious than that on wall thinning and cross-section deformation. Under smaller R d / D, the bending becomes more sensitive to the friction conditions. (3) Considering the knowledge about friction role on individual interface of RDB, by changing two decisive parameters affecting the CoFs such as lubricant types and tube/tool materials, an optimal strategy is proposed to apply the tribological conditions and thus the stable and accurate bending conditions are established for precision forming of RDB under smaller R d / D.

Manufacture of a Seal Flange with E-Cross-Section

A new technology for manufacturing large sealing flange is presented. It involves bending combined with welding and finishing machining at the construction site. The innovation in this method is that the preliminary machining of the section, using a heavy-duty vertical lathe, is replaced by precision bending. Therefore large diameter flange can be manufactured at very low cost. Bending of a specimen with an E-cross-section was investigated by numerical simulation and experiment. The mechanism of lateral deformation was analyzed and the method to overcome it was given. This technology was successfully used for manufacturing a large flange which used in a large wind tunnel.

Role of mandrel in NC precision bending process of thin-walled tube

The thin-walled tube NC bending process is a much complex physical process with multi-factors coupling interactive effects. The mandrel is the key to improve bending limit and to achieve high quality. In this study, one analytical model of the mandrel (including mandrel shank and balls) has been established and some reference formulas have been deduced in order to select the mandrel parameters preliminarily, i.e. mandrel diameter d, mandrel extension e, number of balls n, thickness of balls k, space length between balls p and nose radius r. The experiment has been carried out to verify the analytical model. Based on the above analysis, a 3D elastic–plastic FEM model of the NC bending process is established using the dynamic explicit FEM code ABAQUS/Explicit. Thus, the influences of mandrel on stress distribution during the bending process have been investigated, and then the role of the mandrel in the NC precision bending process such as wrinkling prevention has been revealed. The results show the following: (1) Wrinkling in the tube NC bending process is conditional on membrane biaxial compressive stress state; the smaller the difference between the biaxial membrane stresses is, the more possibility of wrinkling occurs. (2) If the mandrels of larger sizes are used, it will cause the neutral axial to move outward and the difference between the in-plane compressive stresses to become more obvious, which may increase minimum wrinkling energy and anti-wrinkling ability. But the larger mandrel sizes make outside tube over-thinning. (3) When the mandrel extension length increases, the neutral axial will move outward and the difference between the biaxial compressive stresses becomes larger, but the significance is less than that of the mandrel diameter. The excessive extension will cause tube to over thin or even crack. (4) The significance of ball number's effect on the neutral axial position and difference between biaxial compressive stresses is between ones of mandrel diameter and mandrel extension. Increasing the ball number will enhance the thinning degree and manufacturing cost. The results may help to better understanding of mandrel role on the improvement of forming limit and forming quality in the process.

Springback of thin-walled tube NC precision bending and its numerical simulation

The springback is one of the key factors which affect the forming quality of thin-walled tube NC precision bending. The elastic-plastic finite element method was proposed to study the springback process of thin-walled tube NC precision bending and the combination of dynamic explicit algorithm and the static implicit algorithm was proposed to solve the whole process of thin-walled tube NC precision bending. Then, the 3D elastic-plastic finite element model was established based on the DYNAFORM platform, and the model was verified to be reasonable. At last, the springback rule of thin-walled tube NC precision bending and the effect of geometry and material parameters on the springback rule of thin-walled tube NC precision bending were studied, which is useful to controlling the springback of thin-walled tube NC precision bending, and the numerical simulation method can be used to study other effect of parameters on the forming quality of thin-walled tube NC precision bending.

New forming technologies used in manufacturing large vessels

In this paper, some new forming technologies such as the forming of curved shell using reconfigurable discrete die, the precision bending of large flange with a complicated shape of the cross section, the integrated hydro-bulge forming (IHBF) method for manufacturing LPG spherical tank and the method of machining seal surface of large flange using a multifunction machine tool is introduced. The practical applications of the above-mentioned method in manufacturing different vessels are also given.

Research on the precision bending of a workpiece with a complicated cross-section for manufacturing a large flange

A new technology used for manufacturing large flanges with a complicated cross-section is presented in this paper. It consists of precision bending combined with finish machining. First, the rules of the bending process were determined by experiment. A large flange, 8.5m diameter, is manufactured by using this technology. The results show that it is feasible to manufacture large flanges by this method.

Research on the precision bending of a workpiece with a complicated cross-section for manufacturing a large flange

A new technology used for manufacturing large flanges with a complicated cross-section is presented in this paper. It consists of precision bending combined with finish machining. First, the rules of the bending process were determined by experiment. A large flange, 8.5 m diameter, is manufactured by using this technology. The results show that it is feasible to manufacture large flanges by this method.

Numerical simulation of the influence of air bending tool geometry on product quality

The quality of a bend is determined by the accuracy and consistency of the angle along the length of the part. This accuracy is directly related to the penetration of the tool in the die. Small variations in tool penetration can cause relatively large changes in bend angle. Such variations are caused by changes in the repeatability of the tool stopping point, by deflections of the press brake beams and by distortions of the tooling. Earlier studies [Int. J. Mech. Sci. 22 (1980) 583; J. Mater. Process. Technol. 35 (1992) 129; Precision bending of sheet metal, Master’s Thesis, University of Twente, 1992; A finite element simulation of free bending, in: Proceedings of the Second International Sheet Metal Conference, SheMet’94, University of Ulster, 1994, pp. 201–211] on finite element modelling of the air bending process assume that the tooling is perfectly rigid. The present 3D finite element model of press brake air bending tools allows calculation of elastic distortions in typical tools and relates the distortion to the accuracy of the formed part. The finite element model has been validated by experiments conducted on a commercial press brake. Some suggestions are made for improvements to the direct and cross stiffness of the tools which should lead to improved alignment of the tool and die and, in turn, to improved product accuracy.

On the working accuracy of laser bending

Bending of sheet metal by laser-induced thermal stresses (laser bending) can be used for rapid prototyping and other bending tasks that demand a high flexibility of the process. Experimental investigations on laser bending in the range of the temperature gradient mechanism showed an acceptable reproducibility of the bending angle and the bending radius for a wide range of bending actions. A comparison of different irradiation strategies enabled an analysis of the efficiency of the process. In order to realise a specific bending angle a closed loop system was built, making precision bending to within an accuracy of ± 0.2° possible. The basis of the system consists of different strategies for the calculation of the single irradiation steps which are based on theoretical considerations concerning the working accuracy.

Considerations on High Precision Bending using Hydraulic Servo Valve with High Response LDM.

Considerations on High Precision Bending using Hydraulic Servo Valve with High Response LDM.