Bending Part Research Articles

Towards an integrated robust and loop tooling design for tube bending

Bent tubular parts have attracted extensive applications in various industries due to high strength and light weight. However, tube bending (TB) is a strong knowledge-based tri-nonlinear physical process with multi-tool constrains, and minor inappropriate tooling design may induce several failures such as wrinkling, over thinning (even fracture), section distortion, and springback. In response to the urgent requirements of the tubular products with mass quantities and diverse specifications, we proposed an integrated methodology for robust and loop tooling design for TB by combining several technologies such as knowledge-based engineering, parametric CAD modeling, and parametric finite element modeling. Via the spreadsheet formatted rules extracted from different sources of knowledge, several sequences are automatically conducted to preliminarily avoid the wrinkling and section distortion, including the selection of tooling sets (bend die, clamp die, pressure die, wiper die, or mandrel die with flexible balls), the determination of die dimensions, 3D modeling of both external and internal tools, die assemble, and the selection of material type for each die. Then, by importing the feature parameters of tools into 3D-finite elements models, the bendability of tube under previously designed multi-tool constraints is quantitatively evaluated in terms of multi-defect, and the springback can be calculated to redesign the bending die by radius reduction. The design variables are only tube diameter, wall thickness, bending radius, bending angle, and material types. The tool design system is then implemented, and the reliability and efficiency of the system are experimentally verified in the aviation industries regarding several practical bending cases with different specifications and tubular materials.

Rotating Moderately Thick Annular Disks via an Extension to Classical Theory

AbstractThe problem of rotating annular disk subjected to a uniformly distributed load is treated in two ways. Stress is divided into a rotating part because of the angular velocity and a bending part due to force loading. New set of equilibrium equations with small deflections is developed. Solutions for radial displacement, deflection, forces and moment resultants, and the rotating and bending stresses of the first-order theory are presented in terms of corresponding quantities of annular disks based on the classical theory. The boundary conditions at the edges of the annular disk are roller supported, clamped or free. Several examples are presented to illustrate the use and accuracy of these relationships. The effects of several parameters on the radial and vertical displacements and rotating and bending stresses are studied. It is observed that the classical theory is sufficient to study the problem of rotating annular disks. However, the inclusion of the effect of shear deformation is necessary to study precisely the curvature of moderately thick annular disks.

G040022 バルーン型ダイアプラムポンプの耐久性評価

This study focused the effect of anisotropy of balloon type diaphragm on it's endurance. The balloon type diaphragm was fabricated from the fiber reinforced rubber (FRR). In this study, 3 type of balloon in which reinforcement was different from each other were prepared to investigate the endurance time. The deformation of balloon was calculated by 3-dimensional FE model considering the anisotropy of the FRR. The numerical back analysis was performed to determine the material constant of the FRR. Test results showed that the endurance time of balloon was improved when the balloon with weak anisotropy was used. On the other hand the balloon with high anisotropy was used, the crack was initiated at the bending part of the balloon. The calculated distribution of principal strain shows good agreement with failure location of actual balloon. The calculated results also suggested that the strain energy density is effective parameter to predict the endurance time of balloon.

Collapsing Pressure of Casing Located at the Bend Part of Casing-Exit Sidetracking Well

Depending on the mechanical characteristics of casing located at the bending part of sidetrack horizontal well, the calculation model of casing collapsing strength under the effect of bending load is established, and corresponding theoretical formulae is derived. During the process of deducing formulas, the influence of bending load on the casing section out of roundness is ignored, which made the calculation formula benefits intuition and practicality comparing to the T.Tamano formula. The result of this paper is verified through the simulation value and laboratory test of casing used in the Jilin oilfield. It shows that the formula of this paper can meet the engineering commands; the axial load is significant to affect casing collapsing strength, and in the actual production process should be strictly controlled.

Research on Process Planning Method of NC Tube Bending

In order to improve efficiency and quality of tube process, a new process planning method for NC tub bending is proposed. Factors affecting NC tube bending process is firstly discussed, and NC bending process planning is also achieved by theoretical process set calculation, occurrence of interference processes set analysis, clamping difficult process analysis and optimal set of processes selection. The method above is effective and useful for planning process of the complex tube bending parts.

Microstructural effects in corrosion of aluminium tube alloys

Fine gauge extruded aluminium alloy tubes can experience preferential corrosion and early failure when they are formed into “u-bend” via cold deformation. The relationship between the electrochemical reactivity and the microstructure of the bent vs straight parts of the tube was established. Investigations were carried out on two alloys containing 0.08% and 0.22% (mass fraction) of manganese. The corrosion morphology of bent tubes after immersion in salt water acetic acid test (SWAAT) solution showed the highest attack at the bent region of the high-Mn alloy. SEM characterisation of the alloys showed that each alloy has one main type of coarse intermetallic particle. However, TEM observation showed that there is a distinct difference in particle morphology between the bent and straight regions of the high-Mn tubes, the bent region revealed an additional population of 10-50 nm Mn-rich intermetallic particles, which increased both the anodic and cathodic reactivity. For the low-Mn alloy, no such effects were observed. The results suggested that cold deformation of the high-Mn tube allowed room temperature precipitation of fine Mn-rich particles, which increased the cathodic reactivity of that region by providing more cathodic sites, and increased the susceptibility to pitting by removing noble Mn from solid solution. Such an effect was not observed for the low-Mn alloy.

Process parameter design of spring-back and spring-go in V-bending process using Taguchi technique

Bent parts of complex shapes with high precision are increasingly required. To achieve a high precision of parts, especially the required bending angle, a suitable design of process parameters is strictly considered. In this study, process parameters of bending angle, material thickness and punch radius were investigated. The finite element method (FEM), in association with the Taguchi and the analysis of variance (ANOVA) techniques, was carried out to investigate the degree of importance of process parameters in V-bending process. The results revealed that the degree of importance of process parameters in V-bending process depended on the spring-back and spring-go. The material thickness has a major influence on the spring-back. In contrast, in the case of spring-go, the bending angle has a major influence and closely followed by the material thickness. In addition to predicting the degree of importance of process parameters by the combination of the FEM simulation, the Taguchi technique, and the ANOVA technique, by facilitating an improvement in the quality of the required bending angle was strictly considered by optimization of these process parameters corresponding with the spring-back and spring-go.

A Predictive Model for Tolerance Verification of Bent Sheet Metal Parts

This paper presents a complete model including method and result for tolerance verification of bent sheet metal parts. The method uses a mathematical model to take into account aspects influencing the dimensional accuracy of linear and angular dimensions of bent parts. The model was implemented using a set of experimental data to estimate the dimensional accuracy for dimensions of interest of a specific part. Comparing the prediction data with the measured results allowed validation of the model.

Influence of Friction on Springback of Quadrangle Parts Bending

Springback is the prominent problem in bending forming of sheet metal, which is difficult to control accurately, especially for the complex shaped bending parts. The change of friction conditions will cause significant changes of bending springback amount. The theoretical analytical model of quadrangle parts bending, which takes into account of the harden ability, anisotropy and elastic deformation of material, is proposed in this paper based on the plane deformation assumption and the bending theory of sheet metal, the quadrangle parts bending of wide sheet is analyzed theoretically, the approximate calculation relational expression is derived between friction coefficient and springback angle, and the influence of friction on springback is discussed. In the same conditions, the springback result deduced from theoretical formula is basically consistent with numerical simulation and experiment result.

Powder injection moulding of premixed ferritic and austenitic stainless steel powders

In this experimental work, powder injection moulding (PIM) of premixed 316L and 430L gas-atomized powders was developed to obtain duplex stainless steels. A multicomponent binder constituted of high density polyethylene (HDPE) and paraffin wax (PW) in a volume ratio 50/50 was selected for the process. Feedstocks with powder loadings of 50, 65, 68 and 70vol.% were prepared. Mixing experiments were carried out at 170°C according to differential scanning calorimetry (DSC) results. The rheological characterization of feedstocks allowed establishing different rheological parameters as power flow index (n) and activation energy (Ea) in order to know their suitability for injection moulding. Critical powder volume concentration (CPVC) was determined by means of oil absorption method and a rheological model. The feedstock was injected at 170°C and three-point bending and tensile parts were obtained. Thermogravimetrical analysis (TGA) of binder allowed us to design the thermal debinding cycle and sintering was carried out in low vacuum at different temperatures. Finally, mechanical properties such as hardness and tensile strength were evaluated.

Forming Analysis and Die Design for the Bending Die for U Type Parts

In order to design the typical U-bending die, based on analysis the bending process, the die structure for the parts of the arm plate, and consider the factors of springback of bending, tensile, and impact of the clearance between Stamping and female die mould, detailed calculations the key parameters of the expanded length of the bending part, bending force, etc. It can determine the size of the rough and parameters of punch size and press tonnage, and the entire mold were installed and commissioned. The study results showed: The design of the mold has the advantages of simple structure, easy to use, and higher life, and achieve the design goals.

A new adaptive bending method using closed loop feedback control

As the competition from companies in low cost countries increases, the need for more automated production which reduces labour cost while improving product quality is required. A new rotary compression bending set-up with automated closed-loop feedback control is thus being developed. By transferring in-process measurement data into an algorithm for predicting springback and bend angle prior to the unloading sequence, the dimensional accuracy is improved. This work focuses on the development of this steering model. Since the method used does not increase cycle time, it is attractive for high-volume industrial applications. More than 150 bending tests of AA6060 extrusions were conducted to determine the capability of the technology. The results show that by activating the automated closed-loop feedback system, the dimensional accuracy of the bent parts is more than three times better than that obtained by traditional compression bending. Since the steering model permits the direct use of additional process data, such as instant wall thickness and cross sectional distortions, it is believed that extension of the measurement capabilities would improve the accuracy of the methodology even further.

The Design of Bending Parts Compound Die

Through analyzing U type bending parts that has bottom-holes, a suitable Compound die that can complete 4 procedures - lancing, bending , punching and be cut off at in the same forming-position was synchronously designed. The die working process and the main points of the design are introduced here. Production testing confirmed that there were different levels of improvements in the product quality, production efficiency and economic efficiency. In order to meet the design and development requirement of the die, the proportion of the compound and progressive dies in the dies production has been increased in consideration of the structure and production costs of the die.

Simulate Measure for Spring Back of Autobody Panel's Edge

With the higher quality requirement of automotive assembly, the demand for forming precision of the stamping part gets higher. The simulation of resilience around the edge of drawn parts of autobody panels has become a hot spot of automotive field. Currently, the study on resilience mainly focused on the principle of resilience of bent parts and its relative control whereas the investigation on resilience of drawing process is quite less. This paper has studied the object of automobile cover panel through comparison of captured contour to calculate the resilience of edges of part, resolve the resilience problems of drawn part, for which the traditional calculation method and CAE software, focusing on bending resilience issues, couldn’t provide their solution.

Determining Curvature of Air Bent Parts by Digital Image Processing

The dimensional accuracy of formed components is an important issue for stamping applications. The flexibility of the air bending process involve that for different bent angles, different final bent radius are obtained. For air bending parts, springback analysis and final angle measurement have usually been considered whereas final bent radius or curvature determination is pushed into the background. Even though this parameter is a non constant geometrical feature when punch bending radius is very small and there are few mechanical methods for measuring these non constant curvatures. This paper describes the measurement procedure of final bent radius through analysis and manipulation of scanned images of bent parts. The method fits different polynomial functions on bent profiles. Once the best adjustment is chosen, a zone curvature in an air bent part is defined and the radius on punch-sheet contact is quantified. For air bending conditions of small punch radius, this technique has given good results in order to determine the main geometrical features of an air bent part: final bent angle, final bent radius and curvature zone.

First-principles prediction and partial characterization of the vibrational states of water up to dissociation

A new, accurate, global, mass-independent, first-principles potential energy surface (PES) is presented for the ground electronic state of the water molecule. The PES is based on 2200 energy points computed at the all-electron aug-cc-pCV6Z IC-MRCI(8,2) level of electronic structure theory and includes the relativistic one-electron mass-velocity and Darwin corrections. For H 2 16O, the PES has a dissociation energy of D 0 = 41 109 cm −1 and supports 1150 vibrational energy levels up to 41 083 cm −1. The deviation between the computed and the experimentally measured energy levels is below 15 cm −1 for all the states with energies less than 39 000 cm −1. Characterization of approximate vibrational quantum numbers is performed using several techniques: energy decomposition, wave function plots, normal mode distribution, expectation values of the squares of internal coordinates, and perturbing the bending part of the PES. Vibrational normal mode labels, though often not physically meaningful, have been assigned to all the states below 26 500 cm −1 and to many more above it, including some highly excited stretching states all the way to dissociation. Issues to do with calculating vibrational band intensities for the higher-lying states are discussed.

Transformation optical design of a bending waveguide by use of isotropic materials

Based on the effective medium theory, we designed a simplified transformation media bending waveguide by use of only three kinds of isotropic material in an alternating layered structure. The design can be used to guide incoming waves smoothly along the bending part of a waveguide with slight distortions. Numerical simulations are performed to illustrate its functionality.

Experiments and Numerical Simulation of Hot Bending and Die Quenching for Ultra-High Strength Boron Steel

Hot bending and die quenching for U-shaped parts with ultra-high strength boron steel were experimented and simulated to study its quenching effect and accuracy. The results indicate that through the hot contact bending and die quenching, bending parts with higher strength and forming precision than that of cold stamping can be achieved. And the hot contact bending improves the quenching effect at the bottom of the bending part. The springback of hot contact bending decreases gradually when the blank holder force (BHF) increases, which is mainly negative for the impact of the thermal shrinkage moments. The numerical simulation results are consistent with the experiments’. Therefore, it verifies the reliability of finite element model and lays the foundation for the numerical simulation of the hot stamping process applied in complicated shape parts’ production.

New incremental methods for springback compensation by stress superposition

The paper deals with two new process variants invented by the authors. Both use the principle of stress superposition to reach an additional plastification of the material for a controlled influencing of the forming zone. By the superposition of an additional load on a forming process it is possible to compensate the springback effect e.g. of bending angles or bending radii to extend the forming limits of the material and to reduce the forming forces. The first process is the new process of incremental tube forming. This process is based on the combination of a spinning process with the free forming of tubular semi-finished products. This process is suitable to bend tubes two- and threedimensionally to an arbitrary contour and to manufacture tailored tubes. The process is useful to bend tubes without a die with full springback compensation. The second process is an advanced sheet metal air bending process using a roll which is pushed against the bending part after the loading operation and before unloading. This results in an incremental superposition of stresses along the bent part leading to a springback reduction and improvement of the crash properties. The paper shows the principles of both procedures and presents the results of the experimental investigations.

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.