Die Radius Research Articles

Semi-analytical models for flexure deformation in one-step simulation of sheet metal forming

This paper presents the application of multi scale techniques to the simulation of sheet metal forming using the one-step method. When a blank flows over the die radius, it undergoes a complex cycle of bending and unbending. First, we describe an original model for the prediction of residual plastic deformation and stresses in the blank section. This model, working on a scale about one hundred times smaller than the element size, has been implemented in SIMEX, one-step sheet metal forming simulation code. The utilisation of this multi-scale modeling technique improves greatly the accuracy of the solution. Finally, we discuss the implications of this analysis on the prediction of springback in metal forming.

An improved two-arcs deformational theoretical model of the expansion tubes

In this study, the theoretical model of the expansion metal tubes reported in [1] is improved by considering the die radius rdie. After the critical die radius rdie* decided by the tube radius-thickness ratio and the conical angle of die is introduced, the tube expansions are classified into three different deformation modes, according to the relation between actual die radius rdie and the critical die radius rdie*. The detailed theoretical studies of these models are given in order to extend the applicability of the proposed theoretical model.Compared with the relevant experimental and finite element results, it is validated that the current model gives a more accurate steady compressional force, within a wide range of parameters, i.e., the tube radius-thickness ratio ≥ 20, and the die conical angle α ≤ 40° Besides, the expanded tube radius could be accurately predicted, which is important in the metal tube forming. The energy absorption abilities of the expansion tubes are then optimized by taking the tube material properties and friction into consideration.

FE modeling of warm flanging process of large T-pipe from thick-wall cylinder

The large T-branch pipe made from the thick-wall cylinder is an important part in power, petroleum, and chemical equipment. The warm flanging process is used to manufacture the high-performance large T-branch pipe from thick-wall cylinder. The warm flanging process has a bulk-forming characteristic with heterogeneous temperature field and represents very different from the sheet flanging process. The finite element method is adopted to study the warm flanging process of large T-branch pipe due to complex local heating and local deformation. A viscoplastic FE model was built to simulate the whole process in the same process, including heating, forming, cooling, and relevant elastic springback. Only one set of mesh was used to ensure the connection of heating and forming, which was never proposed in the warm flanging process before. The experiment was conducted to verify the proposed model by comparing the geometry and defects. Accordingly, two kinds of typical defects, buckling and wrinkling, were found in both of the simulation and experiment results. And, the reasons of defects were investigated with the stress and metal flow analysis. The short lower die leads to the buckling. Due to the ellipse outer edge, the uneven rebound makes wrinkling at the ends of the process. Three relevant improved methods, lengthening the lower die, increasing the fillet of the upper die, and increasing the radius of the upper die, were proposed and studied to decline the defects.

Numerical parameters for deep drawing simulation of a double bowl sink

Abstract Numerical parameters have significant impact on the results of finite element simulations. Wrong selection of these parameters causes erroneous results and too long computation time in the analyses. Therefore, numerical parameters should be selected properly in order to obtain accurate results in the finite element simulations. In this study, the effects of the numerical parameters used in finite element simulations are investigated. Deep drawing of a double bowl sink is modeled and simulations are done with different parameters. Influences of element size and refinement level on the blank, the effect of the number of elements on the die radius and dynamic effects are investigated and optimum parameters are determined. The results obtained are compared with experimental data, and a good agreement is observed.

Optimal shape design of functionally graded thickness inversion tubes subjected to oblique loading

This paper aims to understand and optimize the crush response of Functionally Graded Thickness (FGT) tubes with various thickness distributions subjected to oblique loading using multi-objective optimization method. Hence, finite element (FE) models are established and their results are validated by experimental tests. Two objective functions (specific energy absorption and peak load) are approximated by four different multi-objective optimization models: the weighted average, multi-design optimization (MDO) technique, constrained single-objective optimization, and geometrical average methods. The optimum design results demonstrate that the selection of appropriate inversion tube parameters such as the die radius, the coefficient of friction between the die and tube, and thickness distribution function have significant roles in the crashworthiness design. The results give new ideas to improve the crashworthiness performance of inversion tubes under oblique loading conditions.

Galling mechanism in metal forming process with TRD coated die against advanced high strength steel sheet

Abstract Galling behavior in sheet metal forming of advanced high strength steel (AHSS) is of great concern in automobile industry. To examine the galling mechanism in sheet metal forming, Finite element analysis and U-bending test with VC coating die coated by thermo-reactive diffusion process (TRD) against DP780 sheet were carried out. The results show that scratches are firstly observed on the die radius surface, mainly distributed at 0-10°and 30-50°. As the forming number increases, the galling mechanism changes from adhesive wear to abrasive wear, accompanied by adhesive tumors and debris. The Ry increases from 0.481μm to 3.44μm for TRD coated die surface and from 0.718μm to 6.82μm for workpiece, respectively. The wear depth predicted by finite element analysis agrees with the experimental result.

Multi-objective optimization of functionally graded thickness tubes under external inversion over circular dies

This paper optimizes the crushing response and energy absorption of functionally graded thickness (FGT) inversion tubes using the multi-objective optimization method. The numerical results, which are validated by the experimental tests, confirm that optimizing geometry of FGT inversion tube improves energy absorption capacity with respect to ordinary uniform tube UT with the same weight. Our study shows that the die radius r, coefficient of friction μ d between the die and tube, and thickness distribution function have great influence on the responses of FGT inversion tubes. The specific energy absorption (SEA), peak crushing force $$ {P}_{max} $$ , and dynamic amplification factor (DAF) are selected as the objectives of crashworthiness optimal design. Finally, the weighted average method, multi design optimization (MDO) technique, constrained single-objective optimization, and geometrical average method were employed to find the optimal configuration of the proposed inversion tube. The results give new design ideas to improve crashworthiness performance of inversion tubes.

Drawing of Hexagonal Cup

The main aim of this work is to produce hexagonal cup drawn from flat sheet (blank Ø80) and effect of wall corner radii of die on drawing process. The dimension of diagonal and side hexagonal cup are (41,36mm) and (36 mm) respectively, and (0.7mm) thickness made from low carbon steel (1006–AISI), has been produced. A commercially available finite element program code (ANSYS11.0), was used to perform the numerical simulation of drawing operation. Two types of wall corner radii of die ( =0.7, 4 mm) with constant punch profile radius equal to ( =4) mm and die profile radius equal to ( =8 mm (were used to investigate the effect of die corner radius on punch force, variation of cup wall thickness and the strain distribution over the cup wall. The numerical results of this model were compared with experimental results and the results show that, the greatest thinning occurs when used wall corner radius of die equal to ( = 0.7mm) due to great stretching of the metal over the corner radius. The best strain and thickness distribution over all zones in produced cup obtained when using wall corner radius of die is equal to = 4 mm).

Research on the Effects of Hot Stamping Process Parameters on Mechanical Property for U-Shape Part

For the sake of research on the hot stamping property of high strength steel, the stamping forming of USIBOR1500P is simulated by the nonlinear finite element software Dynaform and Ansys/ls-dyna. The initial data simulated on USIBOR1500P is obtained by the hot tensile test. The simulation results show that the martensite weight percentage and Vickers hardness are in inverse proportion to stamping speed and initial die temperature. Otherwise, they are increased when the heat conduction coefficient is rising. Thus they affect the final properties of machinery of U-shape part. The maximum stress appears in the die and punch radius, and the minimum stress appears in the flange and the bottom of the blank. The minimum temperature value appears in the flange and the maximum temperature value appears in the die and punch radius.

Verification the Numerical Simulation of the Strip Drawing Test by its Physical Model

When numerically simulate the stamping processes, it is important to define the friction coefficients in different regions. These depend on the deformation processes due to various stress-strain states in each area. In the deep drawing process, the friction conditions in the blankholder-blank-die area and blank-die radius area differ. The analytical models for the friction coefficients determination by strip drawing test are presented in the paper. The equations have been used to calculate the friction coefficients based on a physical model of the strip drawing test and its numerical simulation. The physical and numerical experiments have been performed on Zn coated IF steel DX54D with thickness 0.78 mm. Hill48 yield law and Hollomon's hardening curve have been used as material characteristics when numerically simulated. The blank-holding forces 4 and 9 kN have been set during the experiment and numerical simulation. Good conformity of numerical simulation and the physical model have been found when friction coefficients were calculated from analytical models including the ratio of drawing forces measured with fixed and rotated cylinder. Additionally, the normal contact pressure under the blankholder and on the die radius was evaluated from the numerical simulations. The highest value has been found at the die radius start.

Theoretical model of a metal tube under inversion over circular dies

The inversion of a metal tube over a circular die is an important energy absorption device. Taking into consideration the curvature change during inversion process, this study proposes a two-dimensional theoretical model. Using rigid-perfectly plastic (R-PP) material idealization, its steady inversion load, curling radius after the tube׳s separation from the die, and the optimization of the die radius are analytically obtained based on energy conservation.Compared with the FE simulations, the current model greatly improves the prediction accuracy of the steady inversion force, with the deviation smaller than 10%. The prediction of the tube radius after inversion agrees well with the FE simulation and experimental data. Out of our expectation, the optimized die radius is found to be different from that of free inversion radius of the same tube. In this study, a simple formula of the optimized die radius is given.

Multi Scale Models for Flexure Deformation in Sheet Metal Forming

This paper presents the application of multi scale techniques to the simulation of sheet metal forming using the one-step method. When a blank flows over the die radius, it undergoes a complex cycle of bending and unbending. First, we describe an original model for the prediction of residual plastic deformation and stresses in the blank section. This model, working on a scale about one hundred times smaller than the element size, has been implemented in SIMEX, one-step sheet metal forming simulation code. The utilisation of this multi-scale modeling technique improves greatly the accuracy of the solution. Finally, we discuss the implications of this analysis on the prediction of springback in metal forming.

The Upper Beam Tryout Process Combined with Finite Element Simulation and Experiment

An upper beam is investigated by combination of finite element simulation and tryout methods. The results of deformation simulation and grid experiment were studied. The results show that the direction of principal and side strain in the crack area simulated by CAE software are same as the results received by grid experiment. The result gives a direction for solving the crack problems. It is important that the blank size in both ends is reduced to decrease the bending stress in the die radius. But the effect is very limited for the end region is far from crack area. Combined with the method of reducing the blank size, decreasing the height of the drawbead, enlarging the die radius, improving the smoothness the tension stress is decreased effectively. And the qualified drawing panel is produced finally.

Twist springback characteristics of dual-phase steel sheet after non-axisymmetric deep drawing

This paper aims to investigate the twist springback characteristics of advanced high strength steel sheet subjected to deep drawing. A C-rail benchmark, which leads to a particularly pronounced twist springback characteristics, was developed. For an accurate numerical modeling of the process, a non-quadratic anisotropic yield criterion integrated with combined isotropic and kinematic hardening model was used to describe the strain-stress behavior including anisotropy and Bauschinger effects. The corresponding mechanical experiments, namely uniaxial tension and forward-reverse simple shear tests were performed to determine the material parameters. The digital image correlation technique was applied for component tests as well as the deformation and stress-strain analysis. The experimental validation of the elastic-plastic finite element model was assessed by comparing maximum in-plane strain, thickness reduction distribution and twist springback of the drawn rail. To explore the source of twist springback, the deformation associated with in-plane stress and bending moment was analyzed. The results indicate that the bending moment before springback caused by non-symmetric stress states play an important role in twist springback and control. Certain regions of the die radius were varied in a numerical analysis to control the bending moment for the minimization of twist springback as well as the preliminary results of the relationship between the ratio of variable die radius and twist springback.

Development of anew spring-back factor for a wiping die bending process

In the present study, anew spring-back factor for a wiping die bending process was proposed and characterized to achieve a more accurate predicted bend angle. The analysis was performed on aluminum A1050-H14 using the two-dimensional plane strain modeling of an elasto-plastic, finite element model. The simulated results were validated by comparison with experimental results. It was revealed that, in contrast to previously suggested theories, the spring-back factor depended not only on the ratio of the die radius to workpiece thickness but also on the bend angle. The application of the new spring-back factor, which considers the effects of the bend angle on the bending characteristics in the bending allowance zone and the reversed bending characteristics in the unclamped leg of the workpiece, resulted in better accuracy of the bend angle prediction compared with that obtained using the conventional spring-back factor.

Investigation and numerical analysis of impulsive hydroforming of aluminum 6061-T6 tube

Nowadays impulsive forming processes have become popular among scientists and industrial companies due to their unique capability at increasing formability in various materials and reduction in production time and cost. In this research, finite element analysis of impulsive hydroforming on the sheet and tube was carried out using an explicit scheme and the interaction between the fluid and the shell elements representing the workpiece was approximated through the use of the surface based acoustic-structural interaction. This allowed transferring the pressure from the electrical discharge in the fluid medium, determined by the Geers and Hunter model, to the nodes representing the workpiece. The behavior of the sheet and tube was assumed to follow the Johnson–Cook structural model and the physical constants for the model were taken from other research papers. The proposed finite element model was verified by comparing the results of the model to the experiments published by another researcher and were found to be in good agreement. The FE model was applied to the impulsive forming of the tube so that the effect of discharge energy, die radius and friction coefficient could be studied in the tube electrohydraulic forming process. It is observed that the discharge energy value has major effect on the process and the friction coefficient has minor effect relative to the others. Results showed that Al6061-T6 tube did not sustain any damage even by experiencing stresses near the ultimate strength stress due to the high strain rate of the process. Elastic spring back of the tube decreased with increasing in the energy level, die radius and friction coefficient, due to the impact with the die and the lower induced stresses. Material flow into the die cavity improved by increasing in the die radius, resulting in formability improvement.

Effect of tool geometry variations on the punch force in micro deep drawing of rectangular components

In this study, the impact of tool geometry variations on the punch force in micro deep drawing of rectangular parts was investigated. In contrast to deep drawing of rotationally symmetrical components in deep drawing of rectangular parts further tool geometry parameters, such as the corner radii of the die and punch influence the process and the process result. However, their impact on a micro deep drawing process is not known. Experimental micro deep drawing tests, as well as FEM simulations were carried out to determine the punch forces for a variation of the corner radius and the die radius. It could be demonstrated that an increasing corner radius size leads to an increasing punch force in deep drawing. Enlarging the corner radius from 147 to 250 µm resulted in a 36 % higher punch force. In contrast, an increase of the die radius size results in a decreasing punch force. Here, enlarging the die radius from 76 to 143 µm led to a decrease of the punch force of 26 %.

Magnetic pulse forming of AZ31 magnesium alloy shell by uniform pressure coil at room temperature

The magnetic pulse forming process of AZ31 magnesium alloy shell using uniform pressure coil at room temperature was investigated. ANSYS FEA software was used to analyze the distribution of magnetic flux density of the uniform pressure coil and magnetic pressure for loading on the AZ31 sheet. The characteristic of forming process of AZ31 shell was revealed, and magnetic pulse forming process of AZ31 shell and effect of Al alloy sheet with different thickness were presented by experiments. Due to impact between sheet and die, the rebound profiles on the bottom of deformed sheets were observed. In order to remove the rebound profile, AA5052 sheets were employed to drive the deformed AZ31 sheets. The section contour of R = 30 mm (R means bottom radius of die) shell deformed by 0.5-mm thickness of driver sheet driving once and R = 15 mm shell deformed by 1-mm thickness of driver sheet driving twice are good agreement with die, not only width direction (AB direction) but also length direction (CD direction). However, there was a big obstacle to deform the AZ31 shell with R = 2 mm, because the die had small bottom radius and sidewall section. Variation of effective strain and velocity with width direction and length direction during magnetic pulse forming without driver sheet and with Al driver sheet were analyzed by simulation.

Numerical Modeling to Determine Test Conditions of Shear Blanking Test for a Hybrid Material

A dedicated blanking test (DBT) was designed to measure the bonding shear strength of a metallic hybrid sample. To identify the required design parameters of the rig, a macro numerical model was developed using Abaqus Finite element (FE) package. Copper clad aluminum hybrid samples fabricated by an axi symmetric forward spiral composite extrusion (AFSCE) process were analyzed using the developed numerical model. The effect of the design parameters including sample thickness, blanking clearance and the die and punch fillet radii were determined to ensure a pure shear blanking along the interface. The numerical results showed that the sample thickness, clearance and fillet radii have a significant effect on the measured bond shear strength and the location of the failure. The required rig was designed and composite copper clad aluminum bonding shear strength was experimentally determined based on the numerical findings.

Influence of the plastic anisotropy modelling in the reverse deep drawing process simulation

This study deals with the description of the anisotropic behaviour of the mild steel sheet used in the reverse deep drawing process of a cylindrical cup, which was proposed as benchmark at the Numisheet’99 conference. The effect of the yield criterion on the numerical results is analysed using three yield functions, von Mises, Hill’48 and Barlat Yld’91, combined with the Swift hardening law. The anisotropy parameters of the Hill’48 model are identified using either the yield stresses or r-values, obtained from the uniaxial tensile test at three different directions. On the other hand, the anisotropy parameters of the Yld’91 are determined taking into account both the yield stresses and r-values, minimizing an objective function. The comparison between experimental and numerical results is presented, being the punch force evolution and the thickness distribution along the cup wall the principal variables under study. In both forming stages, the predicted punch force evolution is close to the experimental one, whatever the yield criterion adopted. Nevertheless, the cup wall thickness distribution is strongly influenced by the yield criteria, being clearly overestimated by the von Mises yield criterion. On the other hand, the Yld’91 yield criterion provides a thickness distribution closer to the experimental one, for both forming stages. The strain paths during both forming stages ranges from uniaxial compression, when the material flows between the die and blank-holder, to plane strain in the cup wall, whereas the important strain path changes occurs in the die radius.