Springback Of Sheet Metal Research Articles

Finite element simulation of the complete sheet metal blanking cycle: Effect of blanking clearance on force curve and cut edge quality

Sheet metal blanking process is a manufacturing process that is widely used in sheet metal forming and particularly in the electronics and automotive industries. The outcome and quality of the blanked parts are affected by various parameters such as the blanking clearance, the sheet metal mechanical properties and the wear of tools. However, experimental campaigns to assess the effects of these parameters on the process outcome can be prohibitively expensive for the industry. As a result, numerical simulation of the blanking process is becoming increasingly important to gain insight into the process and study these effects.The present paper provides a novel finite element (FE) simulation procedure to predict the complete blanking cycle including sheet metal cutting, sheet metal springback, punch penetration in die, and stripping phases. A blanking force curve showing the punch force at all phases can thus be obtained. The commercial finite element code ABAQUS® has been chosen to develop this procedure using ABAQUS/Explicit® code for the cutting phase and ABAQUS/Standard® code for the remaining phases. Based on this procedure, the influence of the blanking clearance on the punch force-displacement curve and on the cut edge quality has been studied. The obtained results have been compared to previous literature results and experimental findings.

Springback Behavior of Aluminum/Polypropylene/Aluminum Sandwich Laminates

The springback of sheet metals after forming has been widely studied for decades using numerical and experimental methods. Many of these springback studies involve aluminum alloys. This study aims to understand the springback behavior of aluminum-polypropylene-aluminum laminates as they are being used increasingly in automotive and other applications because of their weight saving potential. A finite element model of the draw bending of a U-channel based on Numisheet’93 benchmark study is built using LS-DYNA. First, the model is validated and studied for springback prediction of single AA5182-O aluminum alloy sheets, and then it is extended to the study of the springback behaviors of AA5182-O/polypropylene/AA5182-O laminates with various combinations of core and skin thicknesses. The numerical model is also validated by experiment. Effects of various tool design and process parameters, such die radius, punch radius and blank holder force, on the springback of the sandwich laminates are studied. The effect of numerical modeling parameters is also considered.

Numerical Simulation and Experimental Research on Multi-Point Forming of Aluminum Alloy Sheets Based on Ultrasonic Vibration

In this study, the multi-point plastic forming of 2024-O aluminum alloy sheets is the research object, ultrasonic vibration-assisted forming is applied in the stamping process, a combination of ABAQUS/EXPLICITE numerical simulation and theory is used, and multi-point forming experiments are performed to verify the research. In the process of multi-point forming, the influence of ultrasonic vibration on the plastic deformation and springback of sheet metal has inspired a new idea and method for multi-point forming of sheet metal. This paper presents the following: the basic theory of multi-point stamping and ultrasonic vibration-assisted metal sheet plastic forming; a comparison of the material parameters of the multi-point stamping method with and without ultrasonic vibration; the influence of different times on the results; the changes in parameters such as stress and strain at different frequencies; and the effect of its springback.

A novel method for the spring-back analysis of a hot stamping steel

Spring-back of sheet metal affects the dimensional accuracy of the components after stamping and has to be eliminated or corrected. Advanced high strength steels (AHSS) are prone to spring-back while forming at ambient temperatures. Hot stamping process is an effective technique to reduce the spring-back upon forming. The forming temperatures and the phase transformations associated with quenching are known to influence the spring-back. However, the detailed experimental analysis on spring-back behaviour is limited due to the difficulty in physically simulating the thermal-mechanical conditions prevailing in a typical hot forming process. In the present work, a novel V-bending technique is presented for effectively measuring the spring-back using a thermal-mechanical simulator, Gleeble™. V-bending is carried out by applying a compressive force along the longitudinal plane of AHSS steel strips at forming temperatures. Upon V-bending, samples were cooled at different cooling rates while maintaining the forming loads to simulate die quenching. Results indicate that the spring-back decreases and becomes close to zero (at a cooling rate of 20 K s−1) with an increase in cooling rate for a hot stamping steel. Further, an increase in cooling rate results in spring-forward owing to the formation of an increased volume fraction of martensite.

Effect of the Pre-Strain on the Elastic Behavior of a Dual-Phase Steel with Different Martensite Contents

The modulus of elasticity is an important parameter for an accurate prediction of the springback in sheet metal forming processes. With increasing plastic deformation, this modulus behaves nonlinearly and declines, which leads to an unpredictable springback behavior. The most cited reason for this nonlinearity is the dislocation movement during plastic deformation that especially occurs with multiphase steels. The present contribution investigates the nonlinear unloading behavior and the resulting decrease of the elastic modulus from a differently heat treated DP980 steel. The heat treatments set five different microstructures with martensite volume fractions in the range of 42 to 95 %. By means of the tensile test, a decline of the elastic modulus according to pre-strain was examined by evaluating the chord-modulus during unloading at different strain levels. In addition, a nano-hardness test was performed. It turned out that in all heat treatment conditions, a pronounced decrease in the modulus of elasticity up to 25% from the initial value occurred. With decreasing annealing temperature and lower martensite volume fraction, respectively, the martensite hardness increased, leading to higher hardness differences between the ferrite and the martensite phase in the microstructure. This led to an increase of strain hardening, i.e. to an increased formation of fresh mobile dislocations in the vicinity of the harder martensite phase during plastic deformation. As a result, the modulus of elasticity decreased more sharply. Thus, in the present contribution, an interplay between the martensite volume fraction and its hardness on the decrease of elastic modulus could be clearly manifested.

Development of springback tester and the effect of forming speed on the springback of four sheet metal bending processes

With the current increasing emphasis on issues of energy saving, emission reduction, driver and passenger safety in automotive industry, lightweight bodywork is an effective measure to reduce vehicle energy consumption. And also, high-strength bodywork structure can improve automobile safety performance because of its high impact absorption energy, and high fatigue resistance. In sheet metal forming, springback is a main defect with using high strength steel. Aiming to investigate sheet metal springback phenomenon for high-strength steel, a multi-funtional springback test machine is built. The testing machine can perform four types of springback tests: V-bend, U-bend, stretchbend and drawbend, and all these tests have been carried out to investgate the effect of springback factor in sheet metal forming processes for example forming speed. The research found that the springback angle of U-bend and drawbend increase with enlarging speed, however, V-bend and stretchbend show the opposite trend.

Improving Prediction of Springback in Sheet Metal Forming Using Multilayer Perceptron-Based Genetic Algorithm.

This paper presents the results of predictions of springback of cold-rolled anisotropic steel sheets using an approach based on a multilayer perceptron-based artificial neural network (ANN) coupled with a genetic algorithm (GA). A GA was used to optimise the number of input parameters of the multilayer perceptron that was trained using different algorithms. In the investigations, the mechanical parameters of sheet material determined in uniaxial tensile tests were used as input parameters to train the ANN. The springback coefficient, determined experimentally in the V-die air bending test, was used as an output variable. It was found that specimens cut along the rolling direction exhibit higher values of springback coefficient than specimens cut transverse to the rolling direction. An increase in the bending angle leads to an increase in the springback coefficient. A GA-based analysis has shown that Young’s modulus and ultimate tensile stress are variables having no significant effect on the coefficient of springback. Multilayer perceptrons trained by back propagation, conjugate gradients and Lavenberg–Marquardt algorithms definitely favour punch bend depth under load as the most important variables affecting the springback coefficient.

Springback Prediction in Sheet Metal Forming, Based on Finite Element Analysis and Artificial Neural Network Approach

Sheet metal forming is one of the most important manufacturing processes applied in many industrial sectors, with the most prevalent being the automotive and aerospace industries. The main purpose of that operation is to produce a desired formed shape blank, without any material failures, which should lie well within the acceptable tolerance limits. Springback is affected by factors such as material properties, sheet thickness, forming tools geometry, contact and friction, etc. The present paper proposes a novel neural network system for the prediction of springback in sheet metal forming processes. It is based on Bayesian regularized backpropagation networks, which have not been tested in the literature, according to the authors’ best knowledge. For the creation of training examples a carefully prepared Finite Element model has been created and validated for a test case used in similar industrial studies.

An Iterative Compensation Algorithm for Springback Control in Plane Deformation and Its Application

In order to solve the springback problem in sheet metal forming, the trial and error method is a widely used method in the factory, which is time-consuming and costly for its non-direction and non-quantitative. Finite element simulation is an effective method to predict the springback of complex shape parts, but its precision is sensitive to the simulation model, particularly material model and boundary conditions. In this paper, the simple iterative method is introduced to establish the iterative compensation algorithm, and the convergence criterion of iterative parameters is put forward. In addition, the new algorithm is applied to the V-free bending and stretch-bending processes, and the convergence of curvature and bending angle is proved theoretically and verified experimentally. At the same time, the iterative compensation experiments for plane bending show that, the new method can predict the next compensation value based on the springback of each test, so that the target bending angle with the error of less than ± 0.1% and the target curvature with the error of less than 0.5% are obtained after 2‒3 iterations. This research proposes a new iterative compensation algorithm to predict springback in sheet metal forming process, where each compensation value depends only on the iteration parameter difference before and after springback for the same forming process of same material.

Evaluation of surface asperity based contact friction models under different conditions

Finite element (FE) simulation has been often used to optimize sheet metal forming process. In order to increase predictive capability for the formability and springback of sheet metals in the FE simulations, advanced numerical techniques and constitutive models have been regarded as critical issues and thus investigated by numerous researchers. However, most of the sheet metal forming simulations employed the Coulomb friction law with a constant value, which in fact is known to be a function of contract pressure, surface quality and sliding velocity. In this study, the asperity based friction model proposed by Westeneng [1], as one of most promising microscale models, was investigated and evaluated by introducing different contact assumptions. Modified friction model was evaluated for estimating the friction coefficient under different variables influencing the frictional condition.

Characterization of mechanical properties and formability of a superplastic Al-Mg alloy

In order to develop a reliable constitutive model for predicting formability and springback of sheet metals during superplastic forming (SPF) and quick plastic forming (QPF), characterization of elastic-plastic behavior, as well as formability of the material is essential. In the present study, the module of elasticity, uniaxial flow behavior and anisotropy, as well as the forming limit curve (FLC) of one of an SPF/QPF grade AA5083 was investigated. The variation of Young’s modulus with temperature was measured from the uniaxial tensile tests for four temperatures ranging from 25 to 500 °C. The impact of temperature and strain rate on the flow behavior of the material was investigated via uniaxial tensile tests for three temperatures (420, 450, and 480 °C) and at three strain rates (0.001, 0.01, and 0.1 s−1). The dependency of the flow stress on the material orientation with respect to the rolling direction (0, 45, and 90°) was assessed using uniaxial tensile tests at a constant temperature. In addition, the evolution of plastic anisotropy with plastic strain and strain rate was assessed by measuring the Lankford coefficient (r-value). Finally, the FLC of the material at 450 °C was characterized according to Nakazima tests procedure for three strain paths (i.e. uniaxial tension, plane strain, and biaxial tension).

The influence of warm forming in natural aging and springback of Al-Mg-Si alloys

Warm forming is a very interesting solution to improve formability and reduce springback. Natural aging is an open issue for heat treatable aluminum alloys, since it causes variability in sheet metal forming operations, namely in the parts shape, as well as in-service behavior. Therefore, this work aims to study the contribution of warm forming to minimize the variability caused by natural aging and reduce the springback in sheet metal forming operations. The thermo-mechanical behavior of two Al-Mg-Si alloys, EN AW 6016-T4 and EN AW 6061-T6, is studied in function of temperature (from 22 to 300 °C) using uniaxial tensile tests, cylindrical cup tests and split ring (springback) tests. Moreover, for the EN AW 6016-T4, the study was also performed in function of the storage time (from 1 to 18 months). At 22 °C, the increase of the storage time leads to a clear increase of the yield stress and of the work hardening and, consequently, of the springback. Warm forming at temperatures between 200 and 250 °C, using a short exposure time, reduces the yield stress and the work hardening and, consequently, springback for both alloys. Moreover, the effect of natural aging is minimized. Thus, warm conditions can be used as an effective solution to minimize the variability caused by the natural aging and reduce the springback in forming operations of heat treatable aluminum alloys.

An Investigation and Prediction of Springback of Sheet Metals under Cold Forming Condition

Low formability and springback especially at room temperature are known to be major obstacles to advancements in sheet metal forming industries. The integration of numerical simulation within the R&D activities of the automotive industries provides a significant development in overcoming these drawbacks. The aim of the present work is to model and predict the springback of a Galvanized low carbon steel automotive panel part. This part suffers from both positive and negative springback which physically measured using CMM. The objective is to determine the suitable forming process parameters that minimize and compensate the springback through robust FE model. The analysis of the springback was carried out following (Isotropic model and Yoshida – Uemori model) which are calibrated through cyclic stress strain curve. The material data of the Galvanized low carbon steel was implemented via lookup tables in the commercial finite element software Pam-Stamp(TM). Firstly, the FE model was validated using the deformed part which suffers from springback problem at the same forming condition. The FE results were compared with the measured experimental trails providing very good agreement. Secondly, the validated FE model was used to determine the suitable forming parameters which could minimise the springback of the deformed part.

Effects of temperature, forming speed and stress relaxation on springback in warm forming of high strength steel sheet

Abstract Springback of sheet metals in warm forming is strongly influenced by temperature, forming speed and the stress relaxation. In the present work, springback of a high strength steel sheet of 980 MPa grade in V- and U-bending was experimentally investigated at temperatures ranging from room temperature to 973 K. In both V- and U-bending, amount of springback decreased with temperature rise especially at temperatures above 573K. Springback was much reduced by lower forming speed. These phenomena directly correspond to the material’s viscoplastic behavior at elevated temperature. The effect of stress relaxation on the springback was discussed by performing a V-bending springback experiment and the visco-plasticity stress analysis.

Effect of Stress Relaxation on Springback of Steel Sheet in Warm Forming

Springback of a high strength steel (HSS) sheet of 980 MPa grade was investigated at elevated temperatures ranging from room temperature to 973 K. From U-and V-bending experiments it was found that springback was decreased with increasing temperature at temperatures of above 573 K. Furthermore, springback was decreased with punch-holding time because of stress relaxation. In this work, the stress relaxation behavior of the steel was experimentally measured. By using an elasto-vicoplasticity model, the stress relaxation was described, and its effect on the springback of sheet metals in warm forming was discussed theoretically.

Numerical Investigation on Springback of 22MnB5 Steel in Hot Stamping

The springback of 22MnB5 steel in hot forming was investigated using simulation of AUTO-FORM, and a mechanics model is presented to analysis spring-back. The results show that temperature is key parameter to affect the springback of 22MnB5 steel in hot forming. Raising temperature is effective method controlled the springback in hot forming of 22MnB5 steel. When temperature is below 300℃, the thickness of sheet has influence on the springback. While temperature is over 500℃, the effect of the thickness of the sheet on springback is not significant. Blank holder force, friction coefficient, punch radius, strain rate have little effect on the springback in sheet metal forming for 22MnB5 steel.

Energy Efficient Servo Controlled Roll Levelling Machines

The roll levelling and coil straightening facilities are becoming one of the most important process steps when forming Ultra High Strength Steels. The correct levelling and straightening of these materials are the main responsible for the stabilization of the residual stresses through the thickness and post forming springback of sheet metal formed components.Due to the arrangement of the rolls in roll levellers, micro-sliding occurs between the rolls and the sheet and the first rolls are subjected to high torques and high forces since they are responsible for the plastification of the material to a high extent. In order to reduce these drawbacks and optimize the energy consumption avoiding energy loses due to friction, the use of servo technology in levelling processes is studied in this paper.A wide range of materials are levelled using the conventional and the new servo controlled strategy that uses two servo motors and the process improvements are quantified.

A novel 3D optical method for measuring and evaluating springback in sheet metal forming process

Abstract A novel 3D optical method for measuring and evaluating the springback in sheet metal forming is presented and its principle, program and steps are studied. The optical method includes a measuring method and evaluation indexes. The point cloud, obtained using photogrammetry and surface scanning systems, is used as the workpiece shape after springback. The original mould is regarded as the CAD model before springback. The point cloud and CAD model are aligned in Geomagic Qualify. A cutting line for the point cloud or CAD model can be obtained at any point in any direction of their cross sections. The springback is calculated as the difference between any two corresponding key points on the two cutting lines. The evaluation index S consists of a 3D springback value w and its vectors along x, y and z directions. Feasibility of the optical method is verified by using a refrigerator door shell.

DESIGN PARAMETERS SELECTION OF SPRINGBACK EFFECT IN AIR-V BENDING USING TAGUCHI APPROACH ON ADVANCE HIGH STRENGTH STEEL-DP590

Advanced High Strength Steels (AHSS) are increasingly utilized especially in automotive industry. However, forming of AHSS is challenging particularly in prediction of springback effect caused by material properties, tools and dies parameters, work material and bending technique factors. An air V-bending process was chosen as an evaluation problem because it showed larger springback effect. This paper presents an optimization to predict the influence of various parameters on springback of sheet metal in air V-bending process using Taguchi method (TM). The experimental study was conducted on DP590 sheets with plate thickness of 1 and 2 mm under different process parameters such as punch radius, die radius, die gap and punch travel. A significant level of springback parameters was further described by using the analysis of variance (ANOVA). It showed that the contribution percentage of each factor to springback was calculated to optimum level and the significant levels of entire factor were observed. The thickness of material, die width, punch travel and punch radius were found to be the most significant factor affecting springback while die radius is insignificant.

VBHF System Research Basing on the Technology of Fuzzy PID Control

High precision forming of sheet metal stamping parts are required to control springback in sheet metal process, how to accurately predict and control the springback is a scientific problem for high-performance precision manufacturing. VBHF (Variable blank holder force) technology is an effective measure to control the springback of sheet metal, and the realization of the variable blank-holder force system is a difficulty. VBHF system mostly control the flow of servo valve to control the pressure of ejection cylinder so as to control the blank-holder force. The stability and real- time were influenced greatly by the precision of the valve and the control current instantaneous changes. This paper quotes PID control module based on the technology of fuzzy to control the VBHF. Its principle is based on PID controller to add a fuzzy control module. Application of virtual instrument LabVIEW software is to build the operating system and real-time data acquisition system. Through parameter, adjustment can meet the system's rapid, stable and robust requirements.