Metal-forming Problems Research Articles

Multi-point forming springback compensation control oftwo-dimensional hull plate

Springback is always a technical problem in sheet metal forming. In this article, the rapid springback compensation control of two-dimensional hull plate is realized by theoretical calculation and numerical simulation. For the cylindrical shell, according to the bending forming theory of medium and thick plates, the total elastic-plastic bending moment is established, and the curvature change before and after springback is deduced. The curvature correction coefficient is determined by the precise numerical simulation technology. At the same time, the validity of the method is verified by cold bending experiment. For the shell with variable curvature, it is divided into several cylindrical surfaces according to the curvature gradient of its geometric section line. The compensation curvature array is obtained by the correction compensation algorithm of springback curvature of cylindrical plate, and the algorithm is verified by numerical simulation. The results show that the method is very close to the expected results. Thus, the efficiency and precision of forming will be improved, and the foundation of digitization of sheet metal forming is established.

The establishment of a newly modified numerical global springback compensation method

Part shape deviation caused by spring back is a quality problem in sheet metal forming. There are two major approaches, adjusting tooling shapes and adopting process control. This paper focused on tooling contour design. A new die design approach, called global compensation method (GC), has been proposed and it possesses following advantages. Compensation factor in displacement adjustment method (DA) is extended to a compensation matrix, thus every node has its own compensation magnitude and compensation direction, which are related to the global forming error.

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.

Effect of lubrication and friction coefficient on temperature distribution for combined backward forward extrusion process for alloy steel

During extrusion process ,the effects of friction between die and workpiece are important and it is one of the most serious problems in metal forming. Friction factor has different effects depending on the size of workpiece. In this study the effect of friction factor and lubrication effects on temperature distribution , power , and load for combined backward forward extrusion process was demonstrated . A numerical analysis based on finite element method by using Q form program was used to study the effect of friction factor through two type of condition , first for lubrication three values for friction factor were used ( 0.1, 0.2 ,0.3 ) .The second condition was un lubrication , the friction factors values were (0.25 , 0.5 ,0.75) . The material of specimen was steel C45.The parts to be manufactured was wrench socket and the lubrication was done by using water and graphite .The results showed that for lubricated and un lubricated conditions , the temperatures power and load were increased when the friction factor increased .

Implementation of anisotropic yield functions into the subroutine library “UMMDp”

To implement new yield functions into the user subroutines of advanced FE codes, professional skills and knowledge are required. The Japan Association for Nonlinear Computer Aided Engineering (JANCAE) has been acting as an organization that provides information and knowledge on finite element analysis (FEA) to the researchers and engineers in various positions involved in CAE. Since 2009, as one of the subcommittee activities for applying FEA to practical metal-forming problems, we have not only studied elastoplastic theory, but have also developed the Unified Material Model Driver for Plasticity (UMMDp), a user subroutine library. Basic yield functions, such as the von Mises and Hill’s quadratic yield functions, which almost all advanced FE code already has, were implemented in the UMMDp as a basic study at its beginning of the development. Up to now, many anisotropic yield functions, including Yoshida’s 6th-order polynomial, Barlat’s Yld2000 and Yld2004, Comsa and Banabic’s BBC2008, Cazacu’s CPB2006, and Vegter’s spline yield functions, have been implemented in the UMMDp, and it is possible to add a new yield function. In this presentation, the techniques for implementing yield functions in the UMMDp are explained. Moreover, the problem of BM1 in NUMISHEET 2016 is discussed as an example applying selected yield functions to the implementation procedure.

Heuristic Optimization for Skid Lines in Automobile Covering Parts

The skid line on the automobile covering parts is a critical problem in sheet metal forming, which will impact significantly the appearance of automobile products. A heuristic optimization method is presented to control the affected region of skids lines incorporating finite element analysis. In this method, the simulation analysis and optimization are repeated by adjusting drawbead restraining forces and the affected region of skids lines decreases until skids lines are restricted to the local features that cause skid lines. Finally, a typical automobile covering part is employed to verify the effectiveness of the proposed method and the results show a favorable effectiveness and practicability in drawbead optimization concerning skids lines.

Effect of Computational Parameters on Springback Prediction by Numerical Simulation

Elastic recovery of the material, called springback, is one of the problems in sheet metal forming of drawpieces, especially with a complex shape. The springback can be influenced by various technological, geometrical, and material parameters. In this paper the results of experimental testing and numerical study are presented. The experiments are conducted on DC04 steel sheets, commonly used in the automotive industry. The numerical analysis of V-die air bending tests is carried out with the finite element method (FEM)-based ABAQUS/Standard 2016 program. A quadratic Hill anisotropic yield criterion is compared with an isotropic material described by the von Mises yield criterion. The effect of a number of integration points and integration rules on the springback amount and computation time is also considered. Two integration rules available in ABAQUS: the Gauss’ integration rule and Simpson’s integration rule are considered. The effect of sample orientation according to the sheet rolling direction and friction contact behaviour on the prediction of springback is also analysed. It is observed that the width of the sample bend in the V-bending test influences the stress-state in the cross-section of the sample. Different stress-states in the sample bend of the V-shaped die cause that the sheet undergoes springback in different planes. Friction contact phenomena slightly influences the springback behaviour.

On gradient‐based optimization strategies for inverse problems in metal forming

AbstractIn the context of metal forming, optimization issues typically lead to inverse problems with a least‐squares minimization as the objective. Due to the nonlinearities in forming simulations, iterative optimization approaches have to be considered. Gradient‐based solution strategies for two inverse problems are proposed and compared to each other. Firstly, the identification of elasto‐plastic material parameters is regarded. Secondly, a recently developed approach for the determination of an optimal workpiece design is investigated. As a special feature, both approaches can be coupled in a non‐invasive fashion to arbitrary external finite element software via subroutines.

Prediction of springback in V-die air bending process by using finite element method

Springback phenomenon affects the dimensional and geometrical accuracy of the bent parts. The prediction of springback is a key problem in sheet metal forming. The aim of this paper is the numerical analysis of the possibility to predict the springback of anisotropic steel sheets. The experiments are conducted on 40 x 100 mm steel sheets. The mechanical properties of the sheet metals have been determined through uniaxial tensile tests of samples cut along three directions with respect to the rolling direction. The numerical model of air V-bending is built in finite element method (FEM) based ABAQUS/Standard 2016.HF2 (Dassault Systemes Simulia Corp., USA) program. The FEM results were verified by experimental investigations. The simulation model has taken into consideration material anisotropy and strain hardening phenomenon. The results of FEM simulations confirmed the ability of numerical prediction of springback amount. It was also found that the directional microstructure of the sheet metal resulted from rolling process affects the elastic-plastic deformation of the sheets through the sample width.

Modelling and solvability of a class steady-state metal-forming problems

Abstract For a class of steady-state metal-forming problems, with rigid-plastic, incompressible, strain-rate dependent material model and with unilateral contact and nonlocal Coulomb’s frictional boundary conditions, a variational inequality formulation is derived and by proving the convergence of a modified secant-modulus method, existence and uniqueness results are obtained. A finite element - modified secant-modulus computational algorithm is developed and applied for solving illustrative problems.

Rigid-Plastic Finite Element Simulation of Cold Forging and Sheet Metal Forming by Eulerian Meshing Method

A computational technique of rigid-plastic finite element method by using the Eulerian meshing method was developed to deal with large deformation problem in metal forming by replacing the conventional way of applying complicated remeshing schemes when using the Lagrange’s elements. During metal forming process, a workpiece normally undergoes large deformation and causes severe distortion of elements in finite element analysis. The distorted element may lead to instability in numerical calculation and divergence of non-linear solution in finite element analysis. With Eulerian elements, the initial elements are generated to fix into a specified analytical region with particles implanted as markers to form the body of a workpiece. The particles are allowed to flow between the elements after each deformation step to show the deforming pattern of material. Four types of cold forging and sheet metal clinching were conducted to investigate the effectiveness of the presented method. The proposed method is found to be effective by comparing the results on dimension of the final product, material flow behaviour and punch load versus stroke obtained from simulation and experiment.

A multi-objective optimization method based on Gaussian process simultaneous modeling for quality control in sheet metal forming

A new modeling method, related to multiple inputs and multiple outputs (MIMO), simultaneously based on Gaussian process (GP), is proposed to optimize the combinations of process parameters and improve the quality control for multi-objective optimization problems in sheet metal forming. In the MIMO surrogate model, for the use of the system information in processing and the accuracy of the model, quantitative and categorical input variables are both taken into account in GP simultaneously. Firstly, a general method is proposed for constructing covariance functions for GP simultaneous MIMO surrogate model based on correlation matrices. These covariance functions must be able to incorporate the valid definitions of both the spatial correlation based on quantitative input variables and the cross-correlation based on categorical input variables. Secondly, the unrestrictive correlation matrices are constructed by the hypersphere decomposition parameterization, thus directly solving optimization problems with positive definite constraints is needless, and the computational complexity is simplified. Compared with independent modeling method, the proposed GP simultaneous MIMO model has higher accuracy and needs less number of estimated parameters. Moreover, the cross-correlation between the outputs (quality indexes) obtained by proposed model provides some reference to further develop quality intelligent control strategies. Finally, a drawing-forming process of auto rear axle housing is taken as an example to validate the proposed method. The results show that the proposed method can effectively decrease the crack and wrinkle in sheet metal forming.

Sustainable and green manufacturing and materials design through computations

The main aim of the review is to address the importance of computations in the analyses of manufacturing processes during efficient materials design, tool design, and process design. Initially, the evolution of computations in manufacturing industries is highlighted. The applications of different computational approaches like numerical simulations, analytical modeling, soft computing, etc. in solving metal forming and joining problems are presented. Though there are several manufacturing processes, metal forming and joining applications are included in the present work. The later part of the review is about green manufacturing and sustainability, their relation with computations and manufacturing education. The green manufacturing and sustainability practices in different industries/fields (like automotive, machining, steel, food processing, computers, electronics) are tabulated. The significance of computations in green manufacturing and sustainability issues are described with a few examples from available literature. The last part of the work is about improving the awareness of green and sustainability concepts through manufacturing education. In this, the possible ways of modifying the present course content of ‘manufacturing technology’ in under-graduate education are suggested, by giving importance to green and sustainability concepts. The role of computations in manufacturing education is summarized finally.

Springback Prediction Compensation and Optimization for Front Side Member in Sheet Metal Forming Using FEM Simulation

Numerical simulation by finite element method has become a powerful tool in predicting and preventing the unwanted effects of sheet metals technological processing. One of the most important problems in sheet metal forming is the compensation of springback. To improve the accuracy of the formed parts, the die surfaces are required to be optimized so that after springback the geometry falls at the expected shape. This paper presents and discusses numerical simulation procedure of die compensation by using the methods of Simplified Displacement Adjustment (SDA). This analysis use Benchmark 3 models of Numisheet 2011. Sensitively analysis was done by using finite element method (FEM) show that the springback values are influenced by element size, integration points and material properties.

Influence of tool steel surface topography on adhesion and material transfer in stainless steel/tool steel sliding contact

Transfer of work material to the tool surface is a common problem in many metal forming and metal working operations, especially in the case of work materials with a high adhesion tendency e.g. stainless steel, aluminum and titanium. In many operations, material transfer occurs already during the initial contact and with time it may result in degradation and roughening of the tool surface which will affect the surface quality of the formed or machined work material surface, e.g. problems related to galling in sheet metal forming. In the present study, the mechanisms behind the initial stages of material transfer between stainless steel and tool steel have been investigated under well controlled laboratory conditions and analyzed using optical surface profilometry and scanning electron microscopy.The results show that, independent of tool surface topography, transfer of stainless steel occurs already after a very short sliding distance. Depending on the tool steel surface topography, initial transfer occurs on two different scales. For a fine polished tool steel surface, fine scale transfer occurs in connection to protruding hard phase particles (carbides and carbonitrides) while for a ground rough surface large scale transfer occurs in connection to grinding scratches, where these act to mechanically scrape off material resulting in lumps off stainless steel on the tool steel surface. Also, sliding perpendicular to the grinding scratches results in more severe material transfer as compared with sliding parallel to the grinding scratches. Finally, the present paper illuminates the usefulness of combining optical surface profilometry and scanning electron microscopy as a powerful analytical tool when it comes to understanding the mechanisms controlling material transfer in a sliding contact on a μm-scale level.

Goal Oriented Error Control for Frictional Contact Problems in Metal Forming

In this note, techniques for goal oriented error control of finite element discretizations are proposed for frictional contact problems. The finite element discretization is based on a mixed method, where Lagrange multipliers are introduced to capture the geometrical and frictional contact conditions. A posteriori error estimates for user-defined, probably non-linear quantities of interest are derived using the dual weighted residual method (DWR). Numerical results substantiate the applicability of the presented techniques to the simulation of metal forming processes.

Metal-forming problems with combined hardening

A class of quasi-steady metal-forming problems under nonlocal contact and Coulomb’s friction boundary conditions is considered with an incompressible, rigidplastic, strain-rate dependent, isotropic, and kinematic hardening material model. A coupled variational formulation is derived, the convergence of a variable stiffness parameter method with time retardation is proved, and the existence and uniqueness results are obtained.

The effect of non-linear recovery on springback prediction

Numerical prediction of springback remains one of the major problems in sheet metal forming. The quality of springback prediction for a sheet metal forming process depends on a precise estimation of the stress distribution all over the metal sheet. In particular, the decrease of the unloading elastic modulus (non-linear recovery) with increasing plastic prestrain during stress reversals, observed by several authors, was commonly not taken into account in FE analysis. A model is proposed which takes the elastic modulus evolution with plastic prestrain and the unloading stress into account. Numerical simulations show that this model coupled with a non-linear kinematic hardening model can accurately predict the springback amount.

Modelling and numerical approach to a class of metal-forming problems-Quasi-steady case

A class of quasi-steady metal-forming problems, with rigid-plastic, incompressible, strain and strain-rate dependent material model and with unilateral frictionless and nonlinear, nonlocal Coulomb's frictional contact conditions is considered. A coupled variational formulation, constituted of a variational inequality, with nonlinear and nondifferentiable terms, and a strain evolution equation, is derived and under a restriction on the material characteristics and using a variable stiffness parameters method with time retardation, existence, uniqueness and convergence results are obtained and presented. An algorithm, combining this method and the finite element method, is proposed and applied for solving an example strip drawing problem. Copyright © 2011 John Wiley & Sons, Ltd.

Micro deep drawing of micro cups by using DLC film coated blank holders and dies

Lubrication is one of the key problems in metal forming, and this is even more important in micro forming because of size effect on friction. Diamond like carbon (DLC) film coated blank holders and dies were used in forming micro cups with drawing blank diameters of 2 mm. A plasma immersion ion implantation and deposition (PIIID) process was proposed to treat the blank holders and drawing dies. Raman spectrum, scratch test, and ball-on-disc test were used to investigate the structure, adhesion strength, and tribological property of the DLC films. The micro deep drawing experiments were carried out at room temperature on a universal testing machine at a drawing velocity of 0.1 mm/s without lubrication, and under the lubrication of castor oil and DLC film. The results showed that the micro cups were well formed with a minimum inner diameter of 0.95 mm under the lubrication of DLC film. The DLC film which dramatically decreased the drawing force and increased the limit drawing ratio (LDR) was better than other lubrication conditions and can be chosen as a proper lubricant in micro forming for mass production.