Springback In Process Research Articles

Elastic-Plastic Numerical Simulation of Cold Rotary Forging for Hypoid Gear and the Springback Error

To achieve the effect of anti-fatigue manufacturing for hypoid gear, the author put forward a new type cold rotary forging technology, the method simplifies the die structure and adopts the local line contact continuous plastic forming. Based on the basic theory of elastic-plastic finite element method (FEM),the author uses ABAQUS to carry out numerical simulation of cold rotary forging and discuss how to build finite element geometric model and grid it in detail, and analyse the definition of workpiece material model in ABAQUS and the merger technology of Abaqus / Explicit and Abaqus / Standard. In order to measure springback error accurately, the alveolar surface shap after springback was got through the technology of surface reconstruction, it was put into Geomagic Qualify software and compare with target CAD model,then the springback error can befully assessed through comparing results.The examles proof that ABAQUS can simulate the deformation and springback process accurately, springback error of cold rotary forging can not be ignored,so springback error must be compensated.

Research on Assembly Variation Modeling of Aircraft Weakly-Rigid Structures

A large number of weakly rigid parts are used in the progress of aircraft assembly, while it’s deviation will affect the quality of the product finally. The assembly variation model of aircraft weakly rigid parts based on influence coefficient method are constructed for controlling assembly accuracy effectively. Based on the linear elastic hypothesis of small deformation, the model carry out the mechanical analysis of aircraft weakly rigid parts in the typical process of positioning, clamping, jointing and spring-back. Influence coefficient matrix of the key features affected by parts manufacturing variation and fixture variation is calculated through the Finite Element method and Monte Carlo simulation, then the assembly variation model is constructed. Finally, based on the above model, an engineering example of assembly variation prediction of aircraft panels was given.

Research on Spring-Back Simulation and Die Surface Optimization of Automotive Panel Stamping Process

The spring-back phenomenon in automotive panel forming is one of the main quality problems, which may affect the tolerance and final shape of panel products. The stamping and spring-back process simulation for the automotive panel were realized by using the Auto form software, emphasizing on the possibly spring-back quantity forecasted and the die surface was optimized to control spring-back. The reasonability of optimization scheme was proved by comparing the simulation result with the actual part.

Process metallurgy analyses to design a high-bendability and high-springback property sheet by using two-scale finite element method

In this study, we develop bendability and springback prediction analysis code for an optimum crystal texture design to generate an ideal aluminum alloy sheet through the sheet rolling and heat treatment processes. To elucidate the relationships between the sheet metal formability and the crystal texture, we applied our two-scale finite element (FE) procedure based on the crystallographic homogenization method to analyze the bending and springback process. Our code employed two-scale FE model, such as the microscopic polycrystal structure and the macroscopic elastic plastic continuum by introducing the crystal orientation distribution, such as the texture characteristics. It means that our code can predict the plastic deformation of sheet metal in the macro-scale, and the crystal texture and hardening evolutions in the micro-scale. The macro-FE model consisted of the die, the punch and the sheet metal. The die and the punch were modelled as the rigid bodies in “V-bend” test problem. The crystal orientation distribution was employed in the microscopic polycrystal FE model, which was assigned by a three-dimensional representative volume element (RVE). This FE model was used as the initial textures for “V-bend” process analyses. The RVE model was featured as 3×3×3 equi-divided iso-parametric solid elements, totally 27 FEs with 216 crystal orientations. Bendability was evaluated by the coefficient of shear strain concentration index using two-scale FE results. On the other hand, the springback characteristics were evaluated by springback angle defined by the angular difference between before and after springback, which occurred in the punch and die removing process. We studied two relationships between (1) the bendability and (2) the springback. Furthermore, we designed the polycrystal texture through the asymmetric rolling and annealing heat treatment process to generate a high-bendability and high-springback property polycrystal material. Annealing heat treatment was modeled as the growth of Cube {0 0 1}〈1 0 0〉 orientation by using the Johnson–Mehl–Avrami׳s equation. In the process optimization, we adopted the asymmetric rolling ratio and the annealing heat treatment time for the design parameters, and the bendability factor and the springback angle as the objective functions. The response surface algorithm was used to optimize the design parameter for maximizing the bendability and minimizing the springback angle. As an optimized result, the asymmetric ratio 1.13 and the annealing heat treatment time 13.5 min were obtained.

Modeling and simulation for multiple-step incremental air-bending forming of sheet metal

Based on Hill’s yielding criterion and plane strain condition, the explicit expressions of elastoplastic constitutive model are derived in this paper which takes into account the effects of transverse stress, neutral surface shifting, and sheet thickness thinning on the sheet springback of air-bending. Then, this model is embedded into ABAQUS software platform by means of programming. Finally, 3D ABAQUS finite-element models (FEM), used to form the semiellipse-shaped workpiece with super length and large opening of sheet metal, are established, and the multiple-step incremental air-bending forming and springback processes are simulated. The simulation and experiment results show that the data predicted with the new constructed constitutive model under the plane strain condition are in much better agreement with experimental data than those predicted with the constitutive model built-in ABAQUS. It can be taken as a valuable mathematical tool used for multiple-step incremental air-bending forming simulation of large area sheet metal.

Simulation and Analysis of Speed Accessory Based on DYNAFORM

This paper study the object of the speed accessory and give the forming numerical simulation of its bending process based on software DYNAFORM. The simulation analysis the effects to its bending springback produced by four factors such as thickness of plate, die fillet, texture of material and the friction coefficient, and research on the factors affect the springback through the orthogonal experiment method, determine the impact factor of the four factors to the bending springback process and find the optimum technological parameters combination.

A Numerical Study of the Spring-Back Phenomenon in Bending with a Rebar Bending Machine

Recently, the rebar bending methodology started to change from field processing to utilizing rebar bending machines at plant sites prior to transport to the construction locations. Computerized control of rebar plant bending machines provides more accurate and faster bending of rebars than the low quality inefficient field processing alternative. The bending process involves plastic deformation of rebars, where bending stress beyond the yield point of the material is applied. When the bending stress is removed, spring back is caused by the elastic restoring stress. Therefore, an accurate numerical analysis of the spring-back process is required to reduce the bending process errors. The most sensitive factors affecting the spring-back process are the bending radius, the bending angle, the diameter of the rebar, the friction coefficient, and the yielding strength of material. In this paper, we suggest a numerical modeling method using these factors. The finite element modeling of the dynamic mechanical behavior of the material during bending is performed using a commercial dynamic analysis program “DAFUL.” We use the least squares approach to derive the spring-back deflection as a function of the rebar bending parameters.

Quantitative prediction of reduction in large pipe setting round process

The control manner during the process to ensure the quality of pipe products mainly relies on the operator’s experience, so it is very necessary to study the setting round process and obtain its spring-back law. The setting round process is shaping an oval section pipe into circular section, so it is difficult to provide a quantificational analysis for its spring-back process because of the curvature inequality of pipe section neutral layer. However, the spring-back law of the circle-oval process can be easily predicted. The experimental method is firstly used to establish the equivalent effect between the setting round process and the circle-oval process. The setting round process can be converted into the circle-oval process. There are two difficulties in the theoretical analysis for the circle-oval process: elastic-plastic bending problem of curved beam; statically indeterminate problem. A quantitative analytic method for the circle-oval process is presented on the basis of combination of the spring-back law of plane curved beam with the element dividing idea in finite element method. The ovality after unloading versus the relative reduction is plotted with analytical and experimental results respectively, which shows a fair agreement. Finally, the method of quantitative prediction of reduction for large pipe setting round is given based on the equivalent effect and the analytical results. Five pipes, which are needed to be set round, are used to carry out experiment so as to verify this method. The results of verification experiment indicates that, in the experimental range, the residual ovality are all under 0.35% after the once only setting round with the theoretical prediction reductions. It is much less than the 1% requirement of pipe standard. Applying the established theoretical analysis is able to correct the pipe ovality with sufficient accuracy, which provides theoretical direction to plant use.

Numerical Simulation and Experimental Investigation of Springback in U-Channel Forming of Tailor Rolled Blank

In order to grasp the springback rule of TRB (tailor rolled blank) parts after forming, the springback behavior of TRB was investigated by integrating such three means as theoretical research, numerical simulation and stamping experiments. Fundamental theories of springback were analyzed. The stamping and springback processes of annealed 1.2/2.0 mm TRB, 1.2 mm and 2.0 mm plates for U-channel were simulated, and the simulation results were compared with the experiments. The results indicate that the springback of TRB falls in between those of the 1.2 mm and 2.0 mm plates. It is desirable for the TRB U-channel to have die clearance of 1.1 times maximum blank thickness and friction coefficient of about 0.12, and longer thickness transition zone is preferable. The simulation data demonstrate reasonably good agreement with the experiments.

Springback Analysis of TC4 Titanium Alloy Complex Part with Double Curvature under Single Point Incremental Forming Process

To make the structure of aircraft meet the aerodynamic requirements, complex lightweight structures such as double curvature shape and high-strength lightweight materials such as titanium alloy are generally used in design and forming of aircraft skin parts. But the forming processes and problems aimed to this kind of parts remain to be investigated further now. In this paper, based on single point incremental forming process, the TC4 titanium alloy aircraft parts with a complex double curvature was studied. In order to reduce the springback during the forming process an appropriate addendum surface was added to the part surface, and then ABAQUS software was applied to carry out numerical simulation of the forming and springback process. The results show that springback of complex titanium part with double curvature is small at both ends of part while large in the middle and the distribution of springback orientation depends on the curvature. For that the part is difficult to form by single point incremental forming process without springback compensation, so the tool path needs to be improved firstly. The simulation results can play a role for guiding the parameters selection and the compensated surface design of single point incremental forming process which can achieve the cold forming of parts with complex structure for poor formability materials.

The Influence of Compressive Pressure in the Thickness Direction on Spring-Back for Aluminum Alloy

This study evaluates the effect of the compression between the punch and the die on spring-back after the punch reaches the dead point. Utilizing the elastic-plastic FEM, the forming and spring-back process of aluminum alloy V-shape sheet is simulated. The investigation is also carried out through experiment. It is shown that spring-back decreases as the ratio of the average pressure and tensile strength increases when the ratio is small; Spring-back increases slightly as the radius of the punch increases from 8mm to 16mm. The results of the 2D plain strain element are in good agreement with the experiment results.

Optimization of Process Parameters of U-Shape Sheet Metal Based on Compensation of Geometric Springback Value

Taking example for U-shape sheet metal, the paper studies the forming and springback process with Dynaform, how much the springback influenced by several factors is studied, including die figure, stamping velocity, the stroke, the blank holder force and friction. Then a useful conclusion can be reached: Using die figure to optimize the technological parameters remarkably reduce the springback value, it provides a new method to control and solve the springback issue.

Simulation of Shape Distortions during Flat Bottom Raising Process with Titanium Alloy Sheet Based on ADINA

Raising processes of titanium alloy sheets TC1Mδ1.45 were simulated based on ADINA FEA software. The shape distortions induced by plastic anisotropy during forming and springback processes were described. A series of forming tests were conducted for the comparison of simulation prediction and test measurements. Reasonable agreement was obtained between the predicted and measured profiles of formed parts，It shows that the ADINA software is suitable for the analysis of the forming and springback processes of anisotropic titanium alloy sheets. Two sorts of shape distortion phenomena exhibit in the raised workpieces fabricated in room temperature after springback or elastic recovery process: Firstly, the bottom of the flange in the specimen distorts to be a wavy surface and not a plane. There two high points and two low points, and the high points locate in the flange periphery along the transverse direction (TD), and the low points locate in the periphery along the rolling direction (RD); Secondly, the top surface of the raising specimen distorts to be a wavy surface too, and the distortion shape is similar to that in the flange. During thermoforming at 600°C, the elastic recovery can be suppressed effectively and the shape distortion resulted from springback processes can be eliminated, but the anisotropy characteristics of the titanium alloy sheets can not be changed, so forming at high temperature can not solve all the shape distortion problems except the distortion occurred for the reason of springback, unhomogeneous deformation in thickness still exists. Keywords: Titanium Alloy Sheet; Raising; Springback; Shape Distortion; Adina

A new anisotropic elasto-plastic model with degradation of elastic modulus for accurate springback simulations

Springback, a phenomenon that is governed by elastic strain recovery after the removal of forming loads, is of great concern in sheet metal forming. There is no doubt that in this regard, physically reliable numerical modelling of the forming process and predictions of springback obtained by respective computer simulations are crucial for controlling this problem. Unfortunately, by currently available approaches, springback still cannot be adequately predicted in general. In this paper, a new constitutive model is proposed which considers simultaneously sheet anisotropy, damage evolution and strain path-dependent stiffness degradation during sheet metal forming. For parameter identification of the built constitutive model, a particular experimental procedure is developed and an optimization procedure is employed to solve the inverse problem that arises. The proposed approach to constitutive modelling is validated in the end by a simulation of the springback in the formed HSS steel sheet. The simulation results, which prove to be in good agreement with the experimental ones, lead to the conclusion that accurate modelling only of anisotropic yielding is not enough to accurately predict the springback phenomenon; the constitutive model should also include the strain path-dependent change of the elastic moduli.

Multi-step incremental air-bending forming simulation for U-shaped workpiece with super length and large opening of sheet metal

The sheet metal multiple-step air-bending forming is a common and effective manufacturing process. It is suitable for forming large workpiece without requiring time-consuming setup operations. Most researches on incremental air-bending forming are mainly based on experiments, and on trial and error basis, the forming processes are described through macroscopic metal deformation. ABAQUS finite element model based on Hill’s anisotropic yield criterion under plane strain conditions is proposed in this paper for studying multi-step incremental air-bending forming process. The numerical simulation for workpiece forming of sheet metal is performed by ABAQUS/Explicit and Standard solvers. ABAQUS/Explicit module is used to simulate the sheet metal forming process, and ABAQUS/Standard module is utilised to simulate the springback process. The researches show that the results predicted with simulation are very close to the experimental data. It can be taken as a valuable tool for process design of multi-step incremental air-bending forming of sheet metal.

Research on Stamping Forming and Spring-Back of Automotive Panel

In order to solve spring-back problem of the stamping forming process, A method for stamping forming and spring-back process simulation of automotive panel by finite element technologies was proposed. The solid model of automobile right side strengthening panel was created in UG software and transmitted to Dynaform. The stamping forming and spring-back process simulation were realized by using Dynaform. The distribution of strain, the variety of the sheet thickness and the spring-back were analyzed. The maximum stress or strain, the minimum thickness and the maximum spring-back were obtained. The simulation results can reflect the real stamping forming of the strengthening panel, and forecast the possibly spring-back value in stamping process. This research can optimize the stamping process and provide strong references for the design of the automotive panel die.

The Shape Distortions Formed in Flat Bottom Punch Raising Process with TC2Mδ1.53 Titanium Alloy Sheet

Raising processes of titanium alloy sheets TC2M were simulated by using ADINA FEM software. The shape distortions induced by plastic anisotropy during forming and springback processes were described. A series of forming tests were conducted for the comparison of simulation predictions and test measurements. Reasonable agreement was obtained between the predicted and measured profiles of formed parts. Two sorts of shape distortion phenomena exhibited in the raised workpieces fabricated in room temperature after springback or elastic recovery process: Firstly, the bottom of the flange in the specimen was distorted to be a wavy surface and not a plane. There are two highest points and two lowest points, and the highest points located in the flange periphery along the transverse direction (TD), and the lowest points located in the periphery along the rolling direction (RD); Secondly, the top surface of the raising specimen was distorted to be a wavy surface too, and the distortion shape is similar to that in the flange.

Investigation on the TRIP Steel Sheet Forming Processes with Respect to Punch Speed Loading-Paths

Loading path is one of importance factors that influence the formability of sheet forming process. In this study, the effect of punching speed loading paths (PSLP) on forming and spring-back processes of TRIP (transformation induced plasticity) steel has been investigated. Four kinds of loading paths with three punch speeds are introduced to verify the cup drawing and U-channel spring-back processes based on a constitutive model accompanying the strain-induced martensite transformation. The results show that higher punch speed results in the thickness uniformity of drawing cup and the spring-back angle of stamping U-channel increased with the same loading path. Furthermore, a given loading path (C4) not only increases the minimum thickness of cup but also decreases the spring-back angle of U-channel.

Spring-Back Prediction of U-Channel Stamping with Martensite Transformation

As an advanced high strength steels, transformation-induced plasticity (TRIP) steel has obtained more and more attentions in automotive body components forming. The TRIP effect of this steel can improve the strength of the material, which results in the spring-back angle is different with that without TRIP effect. In this paper, the spring-back process of U-channel stamping with TRIP effect is studied by deformation energy method, which is based on a constitutive model accompanying strain-induced transformation in strain rate condition. The results have shown that martensite volume fraction distribution in key parts is related to the deformation energy of material, which induces the spring-back angle higher than those without TRIP.

Springback Prediction of Axial Symmetry Sheet Part Drawing

Springback in drawing of an axial symmetry sheet metal part was studied. First of all, according to a springback formula of simple bending, the moment was modified by concerning of axial symmetry shape of part to construct a formula for predicting the springback. Then, springback process was analyzed with FE software Dynaform. Finally, drawing experiment was carried out. Use the reverse engineering and software Geomagic to obtain the shape and springback of the part. Excluding errors of measurement and simulation, the results of experiment and finite element simulation and predictive model were compared, and it shows that the predictive model works well.