Springback In Process Research Articles

Analysis of TRIP Steel HCT690 Deformation Behaviour for Prediction of the Deformation Process and Spring-Back of the Material via Numerical Simulation.

This paper deals with the analysis of TRIP steel HCT690 deformation behaviour. The mechanical properties and deformation characteristics of the tested material are determined using selected material tests and tests that consider the required stress states used to define the yield criterion boundary condition and subsequent deformation behaviour in the region of severe plastic deformation. The measured data are subsequently implemented in the numerical simulation of sheet metal forming, where they are used as input data for the computational process in the form of a selected material model defining the yield criterion boundary and, furthermore, the material hardening law during deformation of the material. The chosen numerical simulation process corresponds to the sheet metal forming process, including the subsequent spring-back of the material, when the force does not affect the material. Furthermore, the influence of the chosen computational model and selected process parameters on the deformation and spring-back process of the material is evaluated. In addition to that, at the end of the paper, the results from the numerical simulation are compared with experimentally produced sheet stamping.

Research on springback compensation for multi-point forming of corrosion-resistant aluminum alloy hyperbolic component

Springback is the reverse elastic deformation produced by the unloading process, which is a common phenomenon in the sheet metal stamping and forming process and affects the final forming accuracy of the part. Aiming at the problem of springback error in the multi-point forming process of hyperbolic component for ships, the springback phenomenon of hyperbolic component was studied by combining theoretical analysis, numerical simulation and forming test. The mechanical property parameters and stress-strain curves were obtained by tensile tests using a new corrosion-resistant aluminum alloy as the sheet material. The springback compensation method is introduced, the springback compensation formula based on surface curvature is derived, and the compensated mold surface is further corrected and fitted using the cubic B-sample method. The multi-point punch tooling was generated and modeled by the multi-point 3D modeling software MPFCAD and finite element software to simulate the multi-point forming and unloading springback process of the hyperbolic member. Multi-point forming tests were conducted on a multi-point forming press for corrosion-resistant aluminum alloy hyperbolic component, and the formed parts were checked for accuracy and error analysis by 3D scanning and GOM Inspect software. The results show that the springback compensation method used in this paper can effectively reduce the springback error in the multi-point forming process of corrosion-resistant aluminum alloy hyperbolic component, and the effect is very good.

Influence of auxiliary mold stretch-bend forming on the forming quality for L-section aluminum alloy profile

To improve the stretch-bend forming precision of aluminum alloy profiles with complex open sections, the relationship stress–strain distribution and the spring-back radius variation were analyzed under different stretch-bend stages. Numerical simulation was performed on the auxiliary mold stretch-bend and spring-back process for the L-section aluminum alloy profile with variable curvature. The effects of cover plate pressure and baffle gap on residual stress, section deformation and spring-back value after forming were investigated. The results show that the stretch-bend warpage can be avoided by setting the cover plate on the straight section of the profile web plate. With the increase of the cover plate pressure, the section distortion of the vertical plate increases by 82%, and the maximum spring-back increases by 71%. A baffle plate was added to the outside of the vertical plate, and the baffle gap is proportional to the amount of section distortion and inversely proportional to the spring-back value. The critical cover force (1 kN) and the critical baffle gap (1 mm) obtained by numerical analysis are used in the stretch-bend forming experiment, and the maximum error between the two results is 2.39%. The numerical simulation has a certain reference value for the rational design of the auxiliary mold stretch-bend process parameters.

A new predicting model study on U-shaped stamping springback behavior subjected to steady-state temperature field

Springback is the main defect in the U-shaped stamping process, which affects the forming accuracy and shape of parts, and one of the main reasons is that the temperature of materials affects the stress distribution during deformation. This paper establishes a U-shaped predicting model considering one-dimensional temperature field, deformation of bending and anti-bending as well as anisotropy of material to study the influence of temperature field on stress distribution. This theoretical model studies thermodynamic behavior of aluminum material during sheet formability and springback process, such as the variation of sheet thickness, the relative offset of neutral layer and so on. The theoretical calculating model and finite element analysis model of U-shaped stamping parts are established by using Mathematica software and ABAQUS software, and the calculating results are compared by the case 1 so as to verify the accuracy of present work.

Time-dependent springback of high strength titanium tubular materials: Experiment and modeling

• Residual stress and dislocation evolution of HSTT during bending and springback comprehensively obtained. • Compression-tension uneven axial residual stress-driven creep mechanism of time-dependent springback for HSTT revealed. • Viscoelasticity-Kelvin constitutive model considering stress attenuation developed for modeling time-dependent springback. • Combining Viscoelasticity-Kelvin with SIM and Chord modulus models for accurate prediction of time-dependent springback. • Deformation-history dependent effects of time-dependent springback for spatial multi-bending tubes clarified. Although time-dependent springback is minor compared with instantaneous springback, its deformation-history dependent effects may deteriorates the compactness of parts assembly and poses potential hazards to the safety and stability of the equipment systems especially under harsh service conditions. However, time-dependent springback still has not been paid enough attention, and how to accurately predict this phenomenon is still a challenge needed to be solved urgently. In this work, taking high-strength Ti-3Al-2.5V titanium tubular materials (HSTT) upon bending as a case, the experimental exploration of the physical mechanisms and the prediction modeling for time-dependent springback of the HSTT were conducted. First, the residual stress and dislocation evolution of HSTT during bending, instantaneous springback and time-dependent springback are comprehensively experimentally obtained, and the compression-tension uneven residual stress-driven creep deformation mechanism of time-dependent springback for HSTT was revealed. Then, considering stress attenuation, a Viscoelastic-Kelvin constitutive model for time-dependent springback was developed and combined with the stress invariant-based model (SIM) and Chord modulus model to accurately predict the whole process of bending, instantaneous springback and time-dependent springback of the HSTT. Finally, the verified model is employed to explore the evolution rules of time-dependent springback and residual stress of HSTT upon bending, and the deformation-history dependent effects of time-dependent springback for spatial multi-bending component are clarified. The findings and methods of this study could aid in achieving higher precision manufacturing of high performance tubular components.

Springback prediction of 7075 aluminum alloy V-shaped parts in cold and hot stamping

In this paper, the springback behavior of high strength aluminum alloy 7075 is studied by experiments and finite element (FE) simulation. Firstly, an analytical model is established to predict the springback angles and analyze the springback trend. The springback experimental tests are conducted by using the V-shaped stamping dies. The influence of deformation temperature, punch radius, and blank holder force on the springback angles is studied. Finally, an FE simulation model is performed to investigate the deformation characteristics and springback process of the aluminum alloy sheet. The results show that the change of springback angles is direct proportional to the punch radius. The springback angles increase with the decreasing deformation temperature and the increasing blank holder force. The stress relaxation that occurs during the die holding stage is the primary reason of reducing the springback compared with cold stamping. Low blank holder force will cause side wall curl, which results in the deviation of forming size. The FE simulation model considering stress relaxation is capable of precisely predicting the change of springback angles, and the simulation results exhibit good consistency with the experimental results.

Numerical simulation and analysis of JCOE pre-bending of submarine pipeline

In this paper, the chemical composition and mechanical properties of L360M pipeline steel are analyzed, and the formulation method of JCOE prebending process for submarine pipeline steel pipe is introduced. Based on the Augmented Lagrange, Ansys software was used to simulate the prebending process numerically with the whole process from model establishment to boundary condition and parameter setting is introduced in detail. The process of bending, yielding and springback of steel plate was analyzed to obtain the general rule of elastic-plastic change of steel plate during JCOE prebending forming. Comparing the theoretical and simulated values of the springback, the ultimate stress and the residual stress after springback in the JCOE pre-bending process, the relative errors are 7.8%, 6.6% and 15.2%, which are within the allowable error range. The results show that the JCOE finite element analysis model is effective and feasible.

Analysis of eleven cross-roll straightening process of steel tube based on cubic spline function and continuous bending elastic-plastic theory

Taking the eleven cross-roll tube straightening process as the research object, the process of single bending, springback deformation, and residual deformation of the steel tube is deduced. For the micro-beam segment, the bending times of the tube during the whole straightening process are calculated according to bending two times for one rotating circle. By means of the cubic spline function, taking the characteristic points of contact between the tube and the straightening roller as the parameters, the displacement function of the tube bending state is obtained. Based on the obtained function, the reverse bending curvatures at any position are obtained. Taking the residual curvature of the previous bending as the initial curvature of the next bending, the repeating bending process and springback process for the micro-beam segment are iteratively calculated, and the final residual curvature of the micro-beam segment is calculated. Then, the final straightening precision is obtained. By comparing with the field data, the straightening precision model is proved to be effective. Finally, by comparing with the six cross-roll straightening process, it is proved that the eleven cross-roll straightening has higher straightening precision.

Influences of thermal effects on residual stress fields of an aluminium-lithium alloy induced by shot peening

In this paper, the thermal effects and the corresponding influences on the residual stress fields of a 2060-T8 aluminium-lithium alloy induced by shot peening are investigated both theoretically and numerically. Based on the Hertz contact theory, a theoretical analysis is conducted by considering energy transformation during the shot peening process. Moreover, in the numerical simulation, explicit methods for the coupled thermomechanical problem and the purely mechanical case are employed to compute the dynamic process. The static method is adopted for the spring-back process to acquire the residual stress fields. Then, the numerical model is verified by comparing the predicted temperature with the theoretical results and comparing the residual stress fields with the experimental results. The results indicate that shots with a higher velocity or a larger radius possess greater kinetic energy so that more frictional heat can be obtained from the energy transformation, and the temperature on the contact surface is definitely higher. The compressive residual stresses in the surface layers will decrease after considering the thermal effects. This can be ascribed to the comprehensive influences of thermal relaxation and the decrease in yield strength at high temperatures. As a result, a modified empirical equation is established to describe the distributions of residual stresses considering and neglecting the thermal effects. The proposed models considering the thermal effects can help predict the residual stress distributions under different processing parameters and provide a better understanding of the shot peening process.

Springback prediction of AL6061 pipe in free bending process based on finite element and analytic methods

The free bending process is a promising process for forming metal pipes. It can be achieved without the frequent replacement of mould. This process has attracted considerable attention of researchers. However, its springback after unloading is a key issue that influences the final formed shapes of the pipe. In this study, finite element (FE) and analytic methods are used to predict the springback phenomena of the AL6061 pipe. The analytic model is enhanced by considering the neutral layer offset. Furthermore, to better investigate the springback process, the FE model of the free bending process is established. The influence of process parameters (e.g. friction, clearance, and mobile die section shape) on bending springback is investigated after the free bending process. The springback angle generally varies in the range of 2–2.5°, and the influence of process parameters on the final springback of the pipe in the free bending process is also discussed. Results showed that the neutral layer offset has a tendency to move towards the material tensile direction in the free bending process, which is different from the traditional rotary bending. Thus, the analytic model of pipe bending springback is optimised with the addition of the neutral layer offset. This study contributes to reinforcing the understanding of the springback mechanism and has a guiding significance for free bending process quality.

Effect of roller dies on springback law of profile for flexible 3D multi-point stretch bending

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

Study of Spring Back Process in Sheet Metal: A Review

Study of Spring Back Process in Sheet Metal: A Review

Springback simulation analysis of angle shape forming of springs based on orthogonal experiment method

The springback phenomenon in the angle shape forming process of spring affects the efficiency and accuracy of spring machine adjustment. In this paper, the angle shape forming process and springback process of SWOSC-V material are simulated by finite element analysis software ABAQUS, and orthogonal experiments are designed. According to the simulation results, the importance order and changing trend of each parameter are determined, and the parameters of minimum springback angle and springback law are obtained. It provides a reference for practical application. It is proved that the combination of finite element method and orthogonal experiment can improve the efficiency of finding the springback law.

Compensation of springback error based on comprehensive displacement method in cold rotary forging for hypoid gear

Special cold rotary forging method for the fabrication of the big wheels of hypoid gears is proposed. The proposed method is established on the basis of the requirements of antifatigue manufacturing processes and the tooth profile characteristics of hypoid gears combined with the movement and forming methods of cold rotary forging. The geometric grid model is constructed on the basis of the basic theory of elastic-plastic thermo-mechanical coupling finite element for metal. Reasonable process parameters and boundary conditions are established. Thus, the cold rotary forging finite element model is built. The springback tooth surface is reconstructed through the results of finite element numerical simulation. The size and distribution of the springback error is the detected. In the springback process, a large displacement and large rotation can occur, so a comprehensive displacement compensation algorithm is adopted to modify the rotary forging die, and a springback error compensation iteration system is constructed based on the modified algorithm. In the case of a camion driving axle gear, the correction of the rotary forging die is analyzed. Results show that the error is already within the allowed range through only three iterations, which proves the efficiency of the system. The modified die is used for machining experiments. The measurement results of the experiment gear are consistent with the simulation results, which proves the reliability of the system. The LTCA of the gear further proves its reliability in compensating for springback error using numerical simulation technique.

Mechanical Behavior of Hinge Lozenge Grid Structure

There are two phenomena in the inflation process of the existing stent, dogboning and axial expansion, which will shorten the life of the stent and lead to the failure of stenting. Firstly, The hinge lozenge grid structure with negative Possion’s ratio was reported. Secondly, the process of inflation and springback of stent were simulated based on finite element method in order to analyse its expansion, axial expansion ratio and resilience rate. It is demonstrated that hinge lozenge grid structure with symmetrical deformation exhibits “full-scale expansion” structural properties. Besides, the diameter of inflated stent is twice as much as initial after expansion. Also, it shows axial elongation as well as increasing axial expansion ratio. The displacement changes obviously with the increase of pressure with other conditions unchanged. This new structure not only improves the radial support performance of intravascular stents significantly, but also overcomes the shortage of traditional stents, which provides a new idea for the design and optimization of intravascular stents.

Behavior of Piles Subjected to Surcharge Loading in Deep Soft Soils: Field Tests

A series of field tests were conducted to examine the behavior of pile foundation subjected to adjacent surcharge loading in deep soft soils. The emphasis was on the pile deflection, bending moment, soil horizontal displacement and lateral earth pressure acting on the piles under different surcharge loading conditions. It was found that among the surcharge loading distance, intensity and width, the surcharge loading distance was the most significant factor affecting the adjacent piles in deep soft soils. The springback process of piles subjected to adjacent surcharge loading after unloading was a slow process changing with time. The mean lateral earth pressure on the pile facing the surcharge loading is slightly larger than that opposite to the surcharge loading. The pile bending moment and mean lateral earth pressure acting on the pile decrease with time due to the consolidation process of soft soil. 3D finite element model in ABAQUS is established to study the influence of consolidation process of soft soil on piles subject to adjacent surcharge loading.

Theoretical Analysis of Five‐Point Bending and Springback for Preforming Process of ERW Pipe FFX Forming

Flexible forming excellent (FFX) forming of electric resistance welding (ERW) pipe is an advanced roll forming method. In order to understand FFX forming mechanism and set reasonable roll parameters, five‐point bending process and springback process for preforming section of ERW pipe FFX forming are analyzed. Under various assumptions, the bending process of sheet metal is divided into full elastic bending stage and elastic‐plastic bending stage by analyzing the forming law and simplifying the contact state model of roll bending process. Based on the theory of plane bending theory, the five‐point bending springback model is established. Mathematical expressions of bending curvature and rotation angle of arbitrary particle on plate under arbitrary state are derived. The curvature calculation formulas of each particle on plate after springback are obtained, and then the calculation formulas of bending angle and rebound angle after springback are obtained. The theoretical analysis results are verified by the wide plate five‐point bending experiment. The theoretical value of springback angle agrees well with the experimental results. The maximum deviation of springback angle is 0.42 degrees. The results show that the five‐point bending model is reasonable. It provides theoretical support for the preforming model of flexible roll forming.

Research on the Springback of Square TA18 Titanium Alloy Tube on the Numerical Simulation

This paper focuses on how bending and springback process of the titanium tubes with different bending radius and bending angle affect the springback rate after unloading and analyses tube distributions and variations of stress and strain by establishing a three-dimensional elastic-plastic finite element model of square TA18 titanium alloy tube based on ABAQUS/explicit and ABAQUS/standard. It is shown that under the same process parameters, the sprignback rate obtained by numerical simulation is in good agreement with that measured in the experiments. The springback rate after unloading increases with the increase of the bending radius linearly, and it increases nonlinearly with the decrease of bending angle. The distribution of the tube-roundness and the relationship between its roundness and springback rate under different process parameters could be obtained by comparing the variation of the absolute value of its outer wall unit at the maximum principal strain before and after unloading.

Evolution of Young’s Modulus of Cold-Deformed Pure Aluminium in a Tension Test

Young’s modulus varies with crystallographic orientation, temperature and alloying, but also with cold working and heat treatment. In this work, the evolution of Young’s modulus in polycrystalline pure aluminium (99.5%) with different cold-working levels determined at room temperature is presented. The deformation process was carried out in a universal tension machine and measurements were performed by ultrasounds. The Young’s modulus diminished from 70 to 65 GPa for 0-5% of deformation (elongation) and then increased with successive cold-working (68 GPa for 8.5% of elongation). These values were obtained 8 hours after plastic deformation was applied. This behaviour is compared with the Young’s modulus determined by extensometry in the same material. In this case, the modulus decreased from 70 to 63 GPa (3.5% of elongation) and then increased until 68 GPa for 10% of elongation. Results obtained on pure iron (Armco) deformed in the same conditions are included for comparative purposes. Values of Young’s modulus measured during the springback process after plastic deformation at different level are also included. Values obtained are between 10-15% lower than those measured 8 hours after plastic deformation.

The Out-of-Plane Compression Behavior of Cross-Ply AS4/PEEK Thermoplastic Composite Laminates at High Strain Rates.

The dynamic mechanical behavior of thermoplastic composites over a wide range of strain rates has become an important research topic for extreme environmental survivability in the fields of military protection, aircraft safety, and aerospace engineering. However, the dynamic compression response in the out-of-plane direction, which is one of the most important loading conditions resulting in the damage of composite materials, has not been investigated thoroughly when compared to in-plane compression and tensile behavior under high strain rates. Thus, we used split Hopkinson pressure bar (SHPB) tests to conduct the out-of-plane compression test of cross-ply carbon fiber-reinforced polyetheretherketone (AS4/PEEK) composite laminates. Afterward, the damage mechanism under different strain rates was characterized by the macrostructure morphologies and scanning electron microscope micrographs. Two major cases of the incomplete failure condition and complete failure condition were discussed. Dynamic stress-strain curves expound the strain rates dependencies of elastic modulus, failure strength, and failure strain. An obvious spring-back process could be observed under incomplete failure tests. For the complete failure tests, secondary loading could be observed by reconstructing and comparing the dynamic response history. Lastly, various failure modes that occurred in different loading strain rates illustrate that the damage mechanism also shows obvious strain rate sensitivity.