Blank Holder Pressure Research Articles

A Study on the Design of Compound Die with Constant Blank Holder Pressure

This paper introduces blanking, drawing and compound die of the cylindrical parts. The compound die applies the special structure to maintain a constant blank holder pressure, which is not increased by drawing. It reduces the processes and improves the efficiency of production.

Prediction of wrinkling and fracturing in viscous pressure forming (VPF) by using the coupled deformation sectional finite element method

Viscous pressure forming (VPF), which uses a kind of semisolid, flowable and viscous material as pressure-carrying medium (PCM), is a new flexible-die forming (FDF) process of sheet metals. In VPF, wrinkling and fracturing are two major failure modes. It is more difficult to predict the occurrence of wrinkling and fracturing in VPF than the conventional sheet metal forming processes due to the coupled deformation of sheet metal and viscous medium. In this paper, a sectional finite element method (SFEM) for analysis of the coupled deformation of sheet metal and viscous medium is developed. The C-B wrinkling criterion based on the energy method and a ductile fracture criterion on the basis of Lemaitre damage theory are proposed to analyze the VPF process of aluminum ladder part via combining with SFEM. The wrinkling and fracturing defects occurred in VPF are thus predicted. The effects of blank holder pressure and the interface condition between sheet metal and viscous medium on the wrinkling and fracturing formation in VPF are investigated. Based on the simulation results of SFEM, the comparison with the experimental data is conducted and the efficiency of the developed approach is thus validated.

English

The hydroforming deep drawing process is one of the sheet metal forming process. The pressurized fluid is used as a medium in this process. Hydro forming technology provides an attractive alternative to conventional matched die forming, especially for cost sensitive, lower volume production and for parts with irregular contours. The performance of deep drawing process can be enhanced by using the liquids. The process performance can be improved through improvement of parameters like draw ratio, thickness ratio, ratio of volume to surface area of product, no scratches developed on outer side of cup and formability index. In this process, the pressurized liquid is utilized for many purposes as the sheet metal blank is supported in entire forming process, elimination of fracture in deformation of cup and formation of wrinkles on the wall and edges of the cup are minimized. The liquid pressure effects on radial, hoop and drawing stresses of blanks in during the process. The liquid pressure is obtained from ANSYS Flotran CFD analysis software for using three oils such as castor oils, olive oil and heavy machine oil. The evaluation of oil pressures through change in the punch speed at constant punch radius. The pressure of oil is acting radially on surface of blank during the process. The radial pressure of oil is controlled by the blank holder pressure. As these two pressures are equal, the deformation of blank is uniform to get a required shape and also it prevents the blank failure during deformation. The pressure of oil depends on punch speed. The oil pressure increases with increase in the punch speed. The oil pressure is the dominant parameter for failure and success of forming of cups from the cylindrical blanks. This pressure of oil is used to evaluate the blank holding pressure. In this paper the numerical studies are carried on the effect of punch speed on oil pressure in hydroforming deep drawing process.

Finite element analysis of stiffness and static dent resistance of aluminum alloy double-curved panel in viscous pressure forming

The static dent resistance performance of the aluminum alloy double-curved panel formed using viscous pressure forming (VPF) was studied by finite element analysis, which mainly considers the forming process conditions. The whole simulation consisting of three stages, i.e., forming, spring-back and static dent resistance, was carried out continuously using the finite element code ANSYS. The influence of blank holder pressure (BHP) and the drawbead on the stiffness and the static dent resistance of the panels formed using VPF was analyzed. The results show that the adequate setting of the drawbead can increase the plastic deformation of the double-curved panel, which is beneficial to the initial stiffness and the static dent resistance. There is an optimum BHP range for the stiffness and the static dent resistance.

Optimizing the deepdrawing of multilayered woven fabric composites

Deepdrawing experiments are performed on double-layered laminates consisting of glass/PP woven fabrics. The forming of woven composites is often accompanied by unwanted wrinkles and springback. By using a fractional factorial experimental design, the influence of preheating temperature, deepdrawing velocity, blankholder pressure, mould temperature and interlayer thickness on wrinkling and springback are assessed. The parameter values that result in an optimal quality of shape are determined. The effects are explained by linking them to the interply shear behaviour and the change in temperature during deepdrawing. It can be concluded that a high preheat temperature, a high deepdrawing speed, a medium blank holder pressure, a low tool temperature and the addition of extra polypropylene between the layers leads to a wrinkle free and fully formed composite.

Experimental Investigation of Springback Variation in Forming of High Strength Steels

Abstract The use of high strength steels (HSSs) in automotive body structures is a prominent method of reducing vehicle weight as an alternative to use of aluminum and magnesium alloys. However, parts made of HSSs demonstrate more springback than parts made of mild steels do. Moreover, variations in the incoming material, friction, and other process conditions cause variations in the springback characteristics, which prevent the practical applicability of the springback prediction and compensation techniques. Consequently, it leads to amplified variations and quality issues during assembly of the stamped components. The objective of this study is to investigate and gain an understanding of the variation of springback in the forming of HSSs. Two sets of experiments were conducted to analyze the influence of the material property (dual-phase steels from different suppliers), lubrication, and blank holder pressure on the springback variation. The experimental results showed that the variation in the incoming blank material is the most important factor. In summary, the thicker the blank is, the less the springback variation. On the other hand, blanks without a coating show less springback variation. The application of lubricant helps us to reduce springback variation, although it actually increases the springback itself. The more uniform the friction condition, the less the springback variation. The influence of blank holder pressure on the springback variation is not distinguishable from the system-level noise in our experiment.

Intelligent control scheme of divided blank holder for square-cup deep-drawing process

To extend the potentially applicable process of the database- and Finite-Element-Method (FEM)-assisted system for the intelligent control (DFMASIC) of press systems for circular-cup deep-drawing, previously developed by the authors, the control system concept was applied to the divided and variable Blank-Holding-Pressure (BHP) control in the process. The basic idea proposed is that each divided controllable part, the straight part and corner part of the blank holder, may be considered and controlled individually as a circular-cup-drawing portion. For the divided and variable BHP control in the square-cup drawing, the results of the DFMASIC system show an enhancement of more than 40% for the maximum drawn cup height, compared with experimental results. Consequently, it is verified that the DFMASIC system is applicable to the square-cup drawing process as well as for circular-cup drawing.

Effect of Punch Geometry in the Deep Drawing Process of Aluminium

The effect of different punches head profile on deep drawing of 5005 H34 Aluminium circular blanks to manufacture a cup-shape product were studied. Experiments were conducted by a 150 ton hydraulic press with using different punches geometry and lubricants viscosity. The drawing force, blank holder pressure, and movement of the punch were measured during experiments to monitor effects of various manufacturing parameters during the drawing process. The surface finish and dimensions of all cups were determined after drawing processes. The geometry of the punch influences the friction force between the blank and punch, and consequently the stretching bottom surface of the cup. The Flat punch geometry produced cups with better surface finish, higher drawing force, and thinner cup wall thickness in comparison to other punches geometry. The Bore punch geometry enhances the stretching of the bottom part of the cup. The presence of lubricant in the process improves the stretching of bottom part of a cup for all punches profile.

Development of an analytical model for warm deep drawing of aluminum alloys

In this study, an analytical model was developed to investigate the effects of material, process, and geometric parameters in the warm forming of aluminum alloys under simple cylindrical deep drawing conditions. The model was validated with both existing experimental findings in the literature and FEA results. The effects of the main process parameters (i.e., temperature, forming rate, blank holder pressure (BHP), and friction between a blank and a tooling element) on formability were studied under a variety of warm forming conditions. The developed model offers rapid, useful, and reasonably accurate results for the design of warm forming process by predicting the deformation mechanism of the material and the relationships between limiting drawing ratio (LDR) and process parameters in isothermal and non-isothermal heating conditions. It was demonstrated that significant formability improvement could be achieved when a large temperature gradient was realized between die and punch, while a slight decrease of LDR was observed when tooling elements and a blank were heated up to same temperature levels.

One-step FEM based control of weld line movement for tailor-welded blanks forming

One-step finite element method (also called inverse approach) is widely used recently in the automobile industry. In order to speed up and ensure the convergence of Newton–Raphson iterations, energy based 3D mesh mapping algorithm is used to obtain the initial solution. The action of punch and die, effect of restraining forces under the blankholder due to drawbeads and blankholder pressure with friction are considered as well. Hydraulic controlled pads used to clamp the weld line during deep drawing process are simplified as static external force to reduce the movement of weld line. The above-mentioned methods have been implemented in authors’ in-house one-step code InverStamp. The initial weld line can be well predicted by one-step finite element analysis from the desired weld line in a formed workpiece which is demonstrated by a rectangular cup drawing study.

One-step FEM-based evaluation of weld line movement and development of blank in sheet metal stamping with tailor-welded blanks

Currently, more and more tailor-welded blanks (TWBs) are used in the automobile industry. It is very important to locate the weld line and predict its movement during the forming process. The initial weld line can be predicted by one-step finite-element analysis according to the desired weld line in the final workpiece. Meanwhile, weld line movement during the deformation process can be evaluated in advance. In this paper, the procedures of finite-element analysis of one-step FEM with TWBs are established. The contact between tool and blank and the effect of restraining forces under the blankholder due to drawbead and blankholder pressure are considered as well. Forming limit diagram (FLD) is used to show not only the tendency of reduction in thickness and fracture but also of increase in thickness and wrinkle. Hydraulic controlled pads used to clamp the weld line during the deep drawing process are simplified as static external force to eliminate the movement of the weld line. In order to speed up and ensure the convergence of Newton-Raphson iterations, energy-based 3D mesh mapping algorithm is introduced to obtain the initial solution. The above-mentioned methods have been implemented in the authors’ in-house one-step FEM code InverStamp. A rectangular cup drawing case demonstrates that this approach can be easily implemented to evaluate weld line movement and develop initial blank in sheet metal stamping with tailor-welded blanks.

Hydromechanical Deep Drawing of Tailor Welded Blanks

This paper investigates the conventional and hydromechanical deep drawing of circular tailor welded blanks (TWBs) with a linear weld line. TWBs offer the possibility to combine different materials, different thicknesses and different coatings within one part, as to optimally fit the applied loads with the lowest possible weight. By combining the hydromechanical deep drawing process with TWBs, a new range of applications can be offered. For the investigations experimental trials are carried out, as well as finite-element simulations. The material parameters of the parent materials and of the weld line are determined and included in the modelling of the TWB. A tool die is designed allowing the hydromechanical deep drawing of TWBs while taking into account the sealing of the TWB and the gap in thickness created by blanks of different thickness. In this way a different blank holder pressure can be applied on each side of the TWB, using a segmented blank holder and a multi-point cushion system. The goal of this study is to investigate the influence of the counter pressure on the deep drawing process of TWBs with particular interest given to the weld line movement during the forming process. It is found that the deep drawing process can be simulated accurately by the finite-element analysis and that the weld line movement plays a crucial role in the deep drawing of a sound part.

Determination of Proper Temperature Distribution for Warm Forming of Aluminum Sheet Materials

In warm forming of aluminum sheet materials, determination, realization, and maintenance of optimal temperature gradient is a key process parameter for increased formability. In this study, a two-phase procedure for efficient and accurate determination of proper temperature condition for warm forming of aluminum sheet metal blanks is presented using a hybrid 3D isothermal/non-isothermal finite element analysis (FEA) and design of experiments (DOE) approach. First, the relative trend, priority and overall temperature ranges of aluminum sheet metal blank regions are obtained using isothermal FE modeling and DOE techniques to reduce the analysis time significantly. In this phase, different temperature levels were assigned onto different regions of the deforming blank material (i.e., holding region, corner region, etc.). Heat transfer with the tooling and environment during the deformation process is ignored in order to achieve rapid predictions. Second, few additional non-isothermal FEAs, taking heat transfer into account, are conducted to validate and to refine the warm forming conditions based on the results from the isothermal FEA/DOE analysis. The proposed hybrid methodology offers rapid and relatively accurate design of warm forming process, especially for large parts that require 3D FE analysis. In addition, effects of forming speed (v), friction (μ), and blank holder pressure on formability are investigated. Increasing part formability is observed with decreasing punch speed and blank holder pressure while an optimal process window is found in case of varying friction coefficients.

Finite Element Modeling and Analysis of Warm Forming of Aluminum Alloys—Validation Through Comparisons With Experiments and Determination of a Failure Criterion

In this study, thermomechanically coupled finite element analysis (FEA) was performed for forming aluminum rectangular cups at elevated temperatures. In order to identify the onset of a failure during FEA, applicability, accuracy, and repeatability of three different failure criteria (maximum load, minimum thickness, and thickness ratio) were investigated. The thickness ratio criterion was selected since it resulted in accurate prediction of necking-type failure when compared with experimental measurements obtained under a variety of warm forming conditions. Predicted part depth values from FEA at various die-punch temperature combinations and blank holder pressures conditions were also compared with experiments, and showed good agreement. Forming limit diagrams were established at three different warm forming temperature levels (250°C, 300°C, and 350°C). An increasing limiting strain was observed with increasing forming temperature both in FEA and experiments. In addition, strain distributions on the formed part obtained under different die-punch temperature combinations were also compared to further validate the accuracy of FEA. A high temperature gradient between die and punch (Tdie>Tpunch) was found to result in increased formability; i.e., high part depths.

Influence of resin dies and resin auxiliary sheets on deep drawability of metal foil

The loading paths of blankholding pressure strongly influenced the limiting drawing ratio in deep drawing of metal foils. The limiting drawing ratio decreased as blank thickness decreased and it decreased rapidly below a certain value of blank thickness. The blankholding pressure required for the elimination of wrinkling increased rapidly as the sheet thickness decreased. As the blank thickness decreased, the area of the permissible loading zone of blankholding pressure decreased considerably. In the deep drawing of pure copper foils, the use of a PTFE die and a Nylon 66 auxiliary sheet was effective in the prevention of wrinkling. In this case, the clearance between the punch and die was set to be approximately 84.4% of the total thickness of the auxiliary sheet and foil blank. The Nylon 66 auxiliary sheet was subjected to ironing during deep drawing and the foil blank was subjected to strong compression in the thickness direction in the wall of the foil cup as well as at the flanges of the die shoulder, due to the action of the punch, Nylon 66 auxiliary sheet and PTFE die. Thus, the wrinkling could be prevented effectively. Meanwhile, in spite of this strong compression in the thickness direction, the significant decrease in the limiting drawing ratio was avoided due to the good lubrication that the PTFE die possesses in itself.

Intelligent sheet stamping process using segment blankholder modules

A sheet forming simulator with a finely segmented blank holder for stamping process of non-circular parts was developed to confirm the effect of variable distributed blank holding pressure (BHP). The BHP was controlled through an intelligent press control system. The same evaluation functions for fracture and wrinkling as ones in the previous work were adopted for fuzzy inference of incremental BHP. In this study, the simulator was applied to square-cup deep-drawing process, using 36 blank holder modules with 3 embedded hydraulic cylinders, that is, a total of 108 segment blank holding actuators were employed for controlling the material flow of blank into the die cavity. The blank holder unit can be flexibly constructed for forming process of an arbitrary shape because of a segment module structure. To facilitate the implementation of the simulator, the concept of virtual processing system was utilized. The BHP trajectories for each blank holder were obtained by the virtual database and finite element method (FEM)-assisted intelligent press control system based on the concept. Through the implementation of sequential BHP control according to the trajectory, the potential application of the simulator to non-circular parts was verified and discussed.

Optimisation of magnesium alloy stamping with local heating and cooling using the finite element method

A new deep-drawing process with a localised heating and cooling technique was verified to improve sheet forming of a magnesium alloy which is impossible to form by conventional methods at room temperature. Deep-drawing experiments were conducted at a temperature of about 400°C for the blank and deep-drawing tool (holder and die) and at a punch speed of 200mm/min. In the deep-drawing experiment, a drawn-cup of height 90mm (drawing ratio (DR=R0/Rp)=3.6) was achieved using both the local heating and cooling technique and the variable blank holder pressure (BHP) technique. However, the optimal experimental condition of temperature distribution was not estimated for the heating at the flange location and the cooling at the punch shoulder location. The objective of this study is to simply simulate the deep-drawing process with temperature dependency using finite element (FE) simulation and the ANSYS/LS-DYNA FE simulation code to confirm the effective factors. The finite element models were validated against the experimental findings and, subsequently, were used to optimise the temperature distribution in the process in order to produce increased formability.

613 弾塑性有限要素法による対向液圧成形解析プログラムの開発(OS 塑性加工(3))

Sheet hydroforming is known as one of effective methods of improving formability. However, determination of optimal control of hydraulic pressure, blankholding pressure, and punch travel is necessary to achieve better formability than that in conventional stamping. This paper presents the development of sheet hydroforming simulation program by static-explicit finite element method. The simulated results of the cylinder deep-drawing were compared with experimental results and showed good agreements. This confirmed the validity of the developed code.

Formability enhancement in magnesium alloy deep drawing by local heating and cooling technique

A new deep drawing process with a local heating and cooling technique was developed because sheet forming of a magnesium alloy is very difficult by the conventional method at room temperature. The objective of this study is to clarify how much the formability of a magnesium alloy sheet can be enhanced by using the new technique. A magnesium alloy sheet of 0.5 mm thickness was used. Deep drawing experiments were conducted at a temperature of about 400 °C for the blank and deep drawing tool (holder and die) and at a punch speed of 200 mm/min. As a result, the drawn cup height of 115 mm was achieved by using both the local heating and cooling technique and the variable blank holder pressure (BHP) technique. It is confirmed that the deep drawing performance of the magnesium alloy can be considerably enhanced under the appropriate temperature distribution for the local heating and cooling technique and with variable BHP control.

Formability enhancement in magnesium alloy stamping using a local heating and cooling technique: circular cup deep drawing process

A new deep drawing process with a localized heating and cooling technique was developed to improve sheet forming of a magnesium alloy which is very difficult by conventional methods at room temperature. The objective of this study is to clarify how much the formability of a magnesium alloy sheet can be enhanced by using the new technique. A magnesium alloy sheet of 0.5 mm thickness was used. Deep drawing experiments were conducted at a temperature of about 400 °C for the blank and deep drawing tool (holder and die) and at a punch speed of 200 mm/min. As a result, the drawn cup height of 115 mm was achieved by using both the local heating and cooling technique and the variable blank holder pressure (BHP) technique. It was confirmed that the deep drawing performance of the magnesium alloy can be considerably enhanced using the appropriate temperature distribution for the local heating and cooling technique and with variable BHP control.