Drawbead Restraining Force Research Articles

Bridging the gap between engineering and tryout of sheet metal forming parts by a smart solution

When a good simulation solution is found by an engineering department the challenge is to transfer this knowledge properly to the tryout process, because in an ideal process, the tryout would reproduce engineered results in a minimum time. But very often this knowledge transfer exists only of handing over printed simulation reports to the tryout team and then it depends on the interpretation of such a document to reproduce all important information to get similar results in reality. A solution to improve this situation would be to connect engineering and tryout with a smart digital solution, which supports tryout to reproduce the results from simulation fast and easy. The draw-in from simulation solution can be used as target to reproduce the same draw-in at tryout, because if draw-in is matching, then also the material flow is matching and the strain distribution too. To do so a sensitivity analysis based on the found simulation solution should be calculated by variation of the drawbead restraining and binder force and then exported to a smart digital tryout solution. Finally this smart digital tryout solution would provide all required information to tryout that they are able to reproduce the draw-in like engineered as fast as possible to speed up the process by avoiding unnecessary tool modifications. Based on this the gap between engineering and tryout can be bridged in a more efficient way.

Finite Element Simulation of Deep Drawing Processes for Shell Bar RR Impact RH/LH

Finite Element Method (FEM) is one of the most useful techniques to analyze problems in metal forming process because of this technique can reduce cost and time in die design and trial step [1]. This research is aimed to predict the optimal parameters in order to eliminate cracks and wrinkles on automotive deep drawing product “Shell Bar RR Impact RH/LH”. The material was made from high strength steel JSC440W sheet with thickness 1.8 mm. The parameters that had been investigated were blank holder force (BHF) and drawbead restraining force (DBRF). In order to simplify the process, punch and die in the simulation were assumed to be a rigid body, which neglected the small effect of elastic deformation. The material properties assumed to be anisotropic, behaved according to the constitutive equation of power law and deformed elastic-viscoplastic, which followed Barlat 3 components yield function. Most of the defects such as cracks and wrinkles were found during the processes on the parts. In the past, the practical productions were performed by trial and error, which involved high production cost, long lead time and wasted materials. From the results, when decreased blank holder force to 30 tons, cracks on the part were removed but wrinkles had a tendency to increase in part area because of this part is the asymmetrical shape. Finally, applying about drawbead restraining force at 154.49 and 99.75 N/mm could improve product quality. In conclusion, by using the simulation technique, the production quality and performance had been improved.

A new optimization method for sheet metal forming processes based on an iterative learning control model

Aiming at improving the efficiency of process optimization for industrial application, a new intelligent optimization method for sheet metal forming processes is proposed based on an iterative learning control model, which is constructed to imitate the die trial process in production. In this model, process parameters are adjusted according to a learning updating law, in which the deviations between the practical forming quality and the desired forming quality are used to determine input parameters in the next cycle, in combination with experience learned from preceding trials. Each learning process leads to a forming quality deviation smaller than the latest one, and the desired forming quality is obtained when the forming quality deviation becomes small enough to be neglected after several times of learning. To apply this model to actual processes, the forming quality is quantified firstly by accumulating the forming quality of the related elements with their contributions considered. Afterwards, the learning updating law is designed by multiplying the forming quality deviation with a varied learning gain. In the end, the intelligent updating strategy of the learning gain is proposed, which guarantees the proper parameter variation in each trial and gives rise to a fast convergence speed. By using this method, a new optimization algorithm of the drawbead restraining force (DBRF) is proposed, in which the scheme of drawbead segmentation can be decided automatically. The rapidity and practicability of the algorithm are verified by numerical experiments of automobile covering panels.

Analysis of Drawbead Behaviour for Sandwich Sheets in Sheet Forming Simulation

Lightweight sandwich sheets represent an alternative in the framework of body lightweight construction. They are made of metal face sheets which form a shear-resistant bond with the thermoplastic core layer. The present work describes the drawbead behavior of sandwich sheets and how it can be modelled in a numerical simulation. Drawbeads are used to control the rate of material flow into the die cavity and are located in the binder area. In the numerical simulation they are either modelled as physical drawbeads or replaced by an equivalent drawbead in which a certain drawbead restraining force (DBRF) is specified as a boundary condition. The values of DBRF can be obtained in a strip test, via numerical simulation or predicted with the aid of a drawbead model. In the current study, strip tensile tests through different physical drawbeads are conducted for sandwich materials. With the obtained variables, restraining forces and thinning values, the results from numerical simulations can be evaluated. Once an optimal simulation approach is found, a parameter study can be conducted to analyze the main influencing factors on drawbead behavior. The results from this study can be leveraged to create a semi-empirical drawbead model.

Optimization of the structural and process parameters in the sheet metal forming process

The quality of the sheet metal forming product is determined by defects such as wrinkling, springback, etc. Optimization techniques can avoid such defects while the desired final shape is obtained. The design variables of the optimization process consist of the structural parameters and process parameters. The structural parameters are the initial blank shape, geometry, etc. and the process parameters are the blank holding force (BHF), the drawbead restraining force (DBRF), etc. In this paper, the two groups of parameters are separately optimized. The structural parameters are optimized by the equivalent static loads method for non linear static response structural optimization (ESLSO) and the process parameters are optimized by the response surface method (RSM). A couple of examples are solved by the iterative use of ESLSO and RSM, and the solutions are discussed.

Experimental Study and Analysis of the Influence of Drawbead against Restriction and Deep Drawing Force of Rectangular Cup-Cans with Tin Plate Material

Drawbead are often used to control the flow of material, stress and deep drawing force in the flange area. This paper discussed the drawbead (fully, not fully and without drawbead) that combined with variations in the blank holder force against restriction of material flow and drawbead restriction force of deep drawing with palm oil lubrication. In this paper, analytical and experiments are used to predict the drawbead restraining and deep drawing force. The tin steel sheet with a thickness of 0.2 mm is used as speciment. The results obtained, that the application fully drawbead be very effective in controlling the flow of materials in the flange, as compared to not fully and without drawbead. In the beginning of the process (punch stroke < 4 mm), the magnitude of restraining force and deep drawing force can be increased. And, the magnitude of Radial Stress increases, conversely the magnitude of tangential stress decreased. This can prevent the occurrence optimum blank holder force is recommended in range 4394-8788 N. Comparisons of results between the analysis and experiments show the phenomenon is similar.

Evaluation of Draw Bead Geometry on Deep Drawing of Complex Rectangular Shape Part

The control of blank-holder force (BHF), is one of the main parameters in deep drawing. Fracture, wrinkling and inappropriate draw-in of sheet edges on certain locations are the main defects that occur due to insufficient and not well distributed restraining force of sheet flow into die cavity by BHF. It was demonstrated that appropriate utilization of draw beads with appropriate geometry and location in die could reduce or even eliminate these defects. Achieving an optimum geometry and location of draw beads are main issues in tooling stage that would cause high cost due to trial and error. In this paper, 2D FE analyses to reach draw bead restraining Force (DBRF) for several usual draw beads geometries were performed. 3D FE analyses of deep drawing process of a rectangular automotive panel with complex and parametric geometry with the presence of draw beads were simulated by the use of ABAQUS6.9 commercial FEM package to reach an optimization of best location and also best geometry. Response surface method with full factorial case was employed for optimization. Simulation results were validated by experimental data of deep drawing.

Evaluation of Draw Bead Geometry on Deep Drawing of Complex Rectangular Shape Part

The control of blank-holder force (BHF), is one of the main parameters in deep drawing. Fracture, wrinkling and inappropriate draw-in of sheet edges on certain locations are the main defects that occur due to insufficient and not well distributed restraining force of sheet flow into die cavity by BHF. It was demonstrated that appropriate utilization of draw beads with appropriate geometry and location in die could reduce or even eliminate these defects. Achieving an optimum geometry and location of draw beads are main issues in tooling stage that would cause high cost due to trial and error. In this paper, 2D FE analyses to reach draw bead restraining Force (DBRF) for several usual draw beads geometries were performed. 3D FE analyses of deep drawing process of a rectangular automotive panel with complex and parametric geometry with the presence of draw beads were simulated by the use of ABAQUS6.9 commercial FEM package to reach an optimization of best location and also best geometry. Response surface method with full factorial case was employed for optimization. Simulation results were validated by experimental data of deep drawing.

A hybrid approach for estimating the drawbead restraining force in sheet metal forming

In order to achieve better part quality in sheet metal forming the rate of the material flow into the die cavity must be efficiently controlled. This control is obtained using a restraining force supplied either by the blankholder tool, drawbeads or both. When the restraining force required is too high, the use of drawbeads is necessary, although excessive blank deformation may be produced. Some other disadvantages such as adjustment difficulties during die try-outs to determine the actual Drawbead Restraining Force (DBRF) may also be encountered. One way to solve these problems and to reduce the number of die try-outs - which are very much time consuming - is to introduce/define accurate enough drawbead concepts. The present study will make use of a method that has been developed using the similitude approach in order to understand the influence of the most important parameters on DBRF and to establish a pre-estimate DBRF theory. Data bases have been developed throughout Explicit Dynamic Finite Element Method (EDFEM) based simulations. The results are compared with experimental data bases provided by Nine (1978) and with the analytical model of Stoughton (1988) results. The average of absolute error with respect to experimental data bases was around 6% and, for the studied cases, the maximum discrepancy was found to be below 11%. For the analytical and experimental cases, the average of absolute error was approximately 5% and, for the studied cases, the maximum error was below 7%. In terms of precision, the predictions derived from this approach are adequate when compared with analytical and experimental results. For this reason, the approach has been validated and accepted as a contribution to STAMPACK®, a commercial explicit dynamic finite element based system for forming processes numerical simulation.

Equivalent drawbead models for sheet forming simulation

Equivalent drawbead models associated with drawbead types, with which the geometrical modeling of drawbeads can be replaced in a numerical simulation of the stamping process, are introduced. The accuracy of the equivalent drawbead models rapidly computing the drawbead restraining and opening forces, based on the hybrid membrane/bending method accommodating Barlat’s anisotropic yield function for the plane stress state and the modified Chaboche model considering the Bauschinger effect and transient behavior under the plane strain condition, is verified by comparing the equivalent drawbead forces with those obtained from the finite element simulation. Moreover, the drawbead forces computed by equivalent drawbead models are employed in a finite element simulation of the automotive fender stamping process, from which the effectiveness and applicability of equivalent drawbead models are observed by comparing strains and draw-ins with those measured in the tryout panel.

Drawbead Restraining Force Modeling with Anisotropic Hardening

Drawbead Restraining Force Modeling with Anisotropic Hardening

Multiobjective robust optimization method for drawbead design in sheet metal forming

It is recognized that fracture and wrinkling in sheet metal forming can be eliminated via an appropriate drawbead design. Although deterministic multiobjective optimization algorithms and finite element analysis (FEA) have been applied in this respect to improve formability and shorten design cycle, the design could become less meaningful or even unacceptable when considering practical variation in design variables and noises of system parameters. To tackle this problem, we present a multiobjective robust optimization methodology to address the effects of parametric uncertainties on drawbead design, where the six sigma principle is adopted to measure the variations, a dual response surface method is used to construct surrogate model and a multiobjective particle swarm optimization is developed to generate robust Pareto solutions. In this paper, the procedure of drawbead design is divided into two stages: firstly, equivalent drawbead restraining forces (DBRF) are obtained by developing a multiobjective robust particle swarm optimization, and secondly the DBRF model is integrated into a single-objective particle swarm optimization (PSO) to optimize geometric parameters of drawbead. The optimal design showed a good agreement with the physical drawbead geometry and remarkably improve the formability and robust. Thus, the presented method provides an effective solution to geometric design of drawbead for improving product quality.

등가 드로비드 모델의 실험적 검증 및 차체 스탬핑 해석에 적용

An equivalent drawbead model(EDM) for sheet metal forming analysis, which replaces complex drawbead geometries with drawbead forces in modeling the stamping dies with finite elements, is experimentally verified and applied to the numerical simulation of auto-panel stamping process. The drawbead restraining and opening forces of elliptical drawbead, circular drawbead, square drawbead, and step drawbead are obtained by performing the drawbead pulling test and compared with those of EDM and commercial code models(CCM). Better agreement with experimental measurements is found in EDM than CCM. Furthermore, the excellence of EDM is demonstrated in its application to the auto-body stamping analysis.

Drawbead Restraining Force Modeling: Nonlinear Friction

Drawbead Restraining Force Modeling: Nonlinear Friction

A numerical method for rapid estimation of drawbead restraining force based on non-linear, anisotropic constitutive equations

Numerical procedures to predict drawbead restraining forces (DBRF) were developed based on the semi-analytical (non-finite-element) hybrid membrane/bending method. The section forces were derived by equating the work to pull sheet material through the drawbead to the work required to bend and unbend the sheet along with frictional forces on drawbead radii. As a semi-analytical method, the new approach was especially useful to analyze the effects of various constitutive parameters with less computational cost. The present model could accommodate general non-quadratic anisotropic yield function and non-linear anisotropic hardening under the plane strain condition. Several numerical sensitivity analyses for examining the effects of process parameters and material properties including the Bauschinger effect and the shape of yield surface on DBRF were presented. Finally, the DBRFs of SPCC steel sheet passing a single circular drawbead were predicted and compared with the measurements.

자동차 스템핑 금형의 드로우비드력 특성에 관한 연구

The drawbeads, which are used for controlling the flow of the sheet into die cavity by imposing the tension and for preventing the forming defects like wrinkling, springback, etc. during the sheet forming process, affect the formability strongly because of the differences in the restraint and opening forces according to the drawbead shapes and dimensions. In this study, the experimental device enabling to measure the drawbead restraining and opening forces is manufactured and the drawing forces of circular, square, and step drawbeads are measured. The drawbead restraining and opening forces of a circular drawbead are increased as its drawbead height is increased. Similarly, those of a square drawbead are increased as its height is increased and shoulder radii decreased. The drawbead forces obtained from the experiment were compared with those calculated in the numerical simulation of stamping process of automotive fender. Good agreement was found so that the experimental measurements can be used in the simulation of auto-body stamping process.

Simulation-based prediction model of the draw-bead restraining force and its application to sheet metal forming process

Draw-bead is applied to control the material flow in a stamping process and improve the product quality by controlling the draw-bead restraining force (DBRF). Actual die design depends mostly on the trial-and-error method without calculating the optimum DBRF. Die design with the predicted value of DBRF can be utilized at the tryout stage effectively reducing the cost of the product development. For the prediction of DBRF, a simulation-based prediction model of the circular draw-bead is developed using the Box-Behnken design with selected shape parameters such as the bead height, the shoulder radius and the sheet thickness. The value of DBRF obtained from each design case by analysis is approximated by a second order regression equation. This equation can be utilized to the calculation of the restraining force and the determination of the draw-bead shape as a prediction model. For the evaluation of the prediction model, the optimum design of DBRF in sheet metal forming is carried out using response surface methodology. The suitable type of the draw-bead is suggested based on the optimum values of DBRF. The prediction model of the circular draw-bead proposes the design method of the draw-bead shape. The present procedure provides a guideline in the tool design stage for sheet metal forming to reduce the cost of the product development.

하이브리드 박막/굽힘 방법을 이용한 드로비드력의 예측

A simplified numerical procedure to predict drawbead restraining forces(DBRF) has been developed based on the hybrid membrane/bending method which superposes bending effects onto membrane solutions. As a semi-analytical method, the new approach is especially useful to analyze the effects of various constitutive parameters. The present model can accommodate general anisotropic yield functions along with non-linear isotropic-kinematic hardening under the plane strain condition. For the preliminary results, several sensitivity analyses for the process and material effects such as friction, drawbead depth, hardening behavior including the Bauschinger effect and yield surface shapes on the DBRF are carried out.

2D elasto-plastic FE simulation of the drawbead drawing process

The drawing process including the locking and pulling phase under a drawbead of circular and rectangular section shape is simulated by means of a static-implicit FE code developed by the authors for 2D elasto-plastic simulation of sheet metal forming. The influence of the main bead geometrical parameters on the binder hold down force (BHDF) and drawbead restraining force (DBRF) is analyzed. The deformation law and loading characteristics of the sheet around the drawbead are studied during the two sequential phases. The calculated results show a good agreement with the experimental data. The investigation lays a foundation for setting up an applied drawbead model in the future 3D simulation of drawbeads.