Conventional Deep Drawing Process Research Articles

Efficient net shape forming of high-strength sheet metal parts by Transversal Compression Drawing

In this contribution, a new forming method is presented for high-strength steel sheet metal materials called Transversal Compression Drawing (TCD). For TCD, the blankholder of the conventional deep drawing process is replaced by sliders introducing a vertical force along the blank edge. Compared to conventional deep drawing, compressive stresses are thereby superimposed in the flange area of the sheet metal material, reducing the springback of formed components and the forces required during the process. Proof of this is provided here on the basis of numerical investigations in which conventional deep drawing and TCD are compared using the example of an “S-Rail” component made from DP980. Results of these investigations reveal that with TCD a maximum reduction in springback by more than 5 mm is achieved, leading to an improvement in the component´s overall shape accuracy of more than 55%. Furthermore, frictional work is decreased by − 6.92 kJ/kg, resulting in an overall reduction of maximum forming forces by 67.4%. Besides, TCD enables a trim-free net shape forming of the final part contour in a single operation and an increased material utilization of 4.5% from coil to part. Not least, no sheet thinning occurs with TCD, whereas a maximum thinning of 12% is observed with the conventional deep drawing process.

A novel approach to the conventional deep drawing process

In this study, the mechanical formability of Al6061-T6 sheet material using a pre-bulging process was experimentally investigated. Therefore, an innovative die entrance design was applied to conventional deep drawing dies. In addition to the formability of the Al6061-T6 material, the effects of the innovative design on the energy consumption and thickness distribution were also investigated. For the experimental studies, deep drawing dies capable of mechanically pre-bulging at 0°, 15°, and 30° angles were designed and experimental studies were carried out at a 10 mm/sec forming speed with constant blank holder force. It was observed that the Al6061-T6 material, which was drawn at the highest ratio of ß = 2.0 in a single operation with the conventional deep drawing method, can be deep drawn at a drawing ratio of ß = 2.2 in a single operation with this new method, and the forming force was reduced by 24.45%. It was found that the deep-drawn Al6061-T6 sample, which was drawn at the highest ß = 2.2 drawing ratio, exhibited a maximum sheet thinning of 15%, and it could be formed with a single die in a single operation without forming defects such as cracking and wrinkling.

Effect of Hydroforming Drawing Cups on Thickness Variation and Surface Roughness

Recently, hydroforming was developed to address the emerging problems encountered by the conventional rigid tool-based deep drawing process. Hydroforming is a specialized type of die forming process, that uses a rigid die while the pressure provided by the liquid acts as a punch to shape the sheet metal. The current paper is directed to study the hydroforming process numerically and experimentally as a means for shaping aluminum alloy sheets based on the quality of product thickness variation and surface roughness. Moreover, it offered a comparative investigation of the experimental and numerical findings of this process. Therefore, thickness variation has been calculated numerically by designing a numerical model using Marc software which fits in large deformation simulation. On the other hand, thickness variation and surface roughness were measured experimentally along drawn cups and compared with the numerical results. The numerical results of thickness variation are matched with the experimental results. Furthermore, surface roughness was measured and compared before and after drawing at five regions. Since there is no contact between the upper side of a cup and any metallic parts, surface roughness depends only on the effect of plastic strain and was found to be increased in all regions.

A novel hydrodynamic deep drawing utilizing a combined floating and static die cavity

A novel method named hydrodynamic deep drawing process utilizing a combined floating and static die cavity (HDDC) was proposed in this research, in order to depress wrinkling during hydrodynamic deep drawing process to form a conical cup with higher height. A special experimental setup of a combined die cavity, which a static chamber inlaid with an inner floating die cavity, was designed to implement the modified hydrodynamic deep drawing experiments. At first, the feasibility of the modified method was evaluated in detail by numerical analyses and experimental tests. Then, the effects of the liquid counter pressure in die cavity on the forming process were also studied. It was found that the proposed method HDDC was feasible and the suppressing wrinkling effect dramatically came into being by using a floating die cavity during the hydrodynamic deep drawing process for conical cups of higher height. The rigid contact between the crater corner of the floating cavity and the blank contributes to the suppressing wrinkle effect during the hydrodynamic deep drawing process utilizing a combined floating and static die cavity. The hydrodynamic deep drawing process of conical cups utilizing a combined die cavity becomes more robust compared with the conventional hydromechanical deep drawing process.

Evolutionary optimization of deep-drawing processes on servo screw presses with freely programmable force and motion functions

Servo screw presses with freely programmable force and motion functions lead to innovative forming technologies for deep drawing of sheet metals. The advanced application potential of the machine type is mainly based on the accuracy and flexibility. Due to the increase of process parameters in deep-drawing processes with variable force and motion functions, the standards for method planning (consideration of machine properties, parameterization of the movement functions) in comparison to conventional deep-drawing processes increase. The high number of parameters motivates the aim: A systematic design of deep-drawing processes with free force and motion functions on servo presses based on computational science methods. In the context of this publication, the determination of optimal parameters (force and motion functions) for a deep-drawing process with superimposed vibrations on servo screw presses will be investigated. With the help of evolutionary optimization approaches a process-design for a deep-drawing process with superposition of low-frequency oscillations will be carry out. The results of the evolutionary optimization approaches are validated by experiments with cross die part.

Mathematical Modeling and Analysis of Hoop Stress in Hydroforming Deepdrawing of n-sided Polygonal Cup

The main objective of this paper presents the analytical evaluation and mathematical modelling of hoop stresses of aluminium 7075 alloys in hydro forming deep drawing of n-sided polygonal cup. It is very important to find the magnitude of these stresses generated within the flange region during the deep drawing process for various n-sided polygonal cups. In the flange region two types of stresses will be generated. When is radial tensile stress, it is taking place radially outward direction from the side of the cup to outer side of the blank material. and other is hoop stress it is compressive. It is perpendicular to the radial lines drawn from the job axis to the side of the blank. It is also parallel or tangential to the blank circumference. These two stresses will be generated within the blank material by the application of punch force.. As compared to the conventional deepdrawing process, hydroforming is very convenient. uniform deformation of the blank taking place throughout out the process.

Comparative study of conventional and hydromechanical deep drawing processes based on finite element analysis

A two-dimensional finite element analysis has been performed to investigate hydromechanical and conventional deep drawing processes. The effects of the fluid structure interaction on the material formability, the strain and the thickness distributions are investigated. Large plastic deformation is observed in the plank at the bottom and the corner of the punch. Plastic deformation distribution results show a difference between the hydromechanical deep drawing process and the conventional deep drawing which is due to the friction effect. This latter represents one of the major features of the hydromechanical deep drawing process. Concerning the formability of the blank, the obtained results show that the hydromechanical deep drawing process gives a better formability than the conventional deep drawing process.

Energetic evaluation of press hardening processes

The awareness and commitment to carefully use energy and other resources is increasing, in view of climate change and the shortage of resources. Sustainable practice starts with sustainable production. The press hardening of sheet and tube metal components offers a range of optimization approaches. It becomes clear that a holistic view of the life cycle of components and products is essential. On the one hand, press hardening manufacturing process is significantly more energy demanding than conventional deep drawing process. On the other hand, they are also associated with significant energy and life cycle savings in the utilization phase of the manufactured product. The main focus of this work was on the visualization of energy consumption as well as the development of innovative energy-efficient process chains for press hardening. Based on a technological analysis, the investigated process chains were energetically evaluated and approaches to improve the energy balance were deduced.

Experimental investigation of tool-sided surface modifications for dry deep drawing processes at the tool radii area

Abstract In conventional deep drawing processes lubricants are applied to reduce friction and wear. Demands for increased sustainability, environmental protection and resource efficiency motivate the realization of lubricant-free forming processes. The direct tool-workpiece contact during dry deep drawing leads to changed tribological conditions. Especially in the areas of increased normal and shear stresses, such as the die radius, the dry contact causes an increased risk of wear and damage to the sheet surface. A well-known approach to face the challenges of dry deep drawing of steel sheets and aluminum alloys is the application of amorphous carbon based coatings on the tool surfaces. Within this study the tribological behavior of conventional and modified tool surfaces at the critical radii area is investigated with a strip bending rotation test. In this test, the friction coefficient is determined based on the relative movement between a rotating test cylinder and a sheet-metal strip bent in a die. For the tribological tests the sheet materials AA6014, AA5182 and zinc coated DC04 are applied. The modification of the tool sided surface was achieved by applying ta-C and a-C:H coatings to the test cylinder. In addition to tests with coated surfaces, tests with uncoated tools are carried out for reference. By analyzing the resulting friction coefficients for the different sheet materials, the suitability of ta-C and a-C:H coatings for dry deep drawing processes is evaluated comparatively. In order to investigate cause-effect relations as well as wear mechanisms, the tool and workpiece surfaces are characterized before and after testing.

Improving the springback behavior of deep drawn parts by macro-structured tools

Many automotive parts are manufactured by means of sheet metal forming technology. The process limits in sheet metal forming are highly dependent on the material flow and friction forces. In most cases, it is beneficial to reduce the friction between tool and workpiece to expand the process limits and increase the lifetime of tools. Macro structuring of tools is a novel approach to reduce the amount of friction forces in the deep drawing process [1]. The induced alternating bending in sheet metal during the deep drawing with macro-structured tools leads to an increase of its geometrical moment of inertia and consequently stabilizes the sheet against wrinkling. An increase in the peak-to-valley height difference, which is directly associated with a greater restraining force in flange area, leads directly to improved dimensional accuracy in terms of springback behavior of workpiece. This positive effect of the increased restraining force is known from the literature [2], but in lubricant free deep drawing process it is not applied by means of conventional blankholder force but also geometrically through macro structuring of tools. Within the scope of this paper, the influence of alternating bending on the springback behavior of parts in deep drawing process with macro-structured tools is studied. Since the springback in a workpiece depends on its material, two industry relevant materials DC04 and Al5182 are chosen for numerical and experimental tests. For this purpose conventional deep drawing process is compared with lubricant free deep drawing process. To investigate the effect of alternating bending on springback behavior of the components in lubricant free deep drawing with macro-structured tools, the ring splitting method is used. In this test, a ring from each cylindrical deep drawn cups formed by standard and macro-structured tools will be cut out and subsequently split to open. The opening gap of split ring indicate the amount of tangential residual stresses in rotationally symmetric deep drawing parts which is an indicator for springback behavior. The results of this paper show that springback behavior of sheet metal parts can be reduced by increasing the peak-to-valley height difference during lubricant free forming process with macro-structured tools.

Theoretical, numerical and experimental investigation of hydro-mechanical deep drawing of steel/polymer/steel sandwich sheets

Fabricating flat sandwich sheets into components with a required shape and dimensions is a challenging job in the metal forming field. In this article, hydro-mechanical deep drawing was used for sandwich sheet forming. The aim of the work is to achieve higher drawing ratio of these sheets. Theoretical, numerical and experimental analysis of the hydro-mechanical deep drawing of sandwich sheets was carried out. Separated layers theory method is used for theoretical analysis of the process. Then, the numerical simulation of the process was developed by finite element method. The effect of core layer thickness on the forming force of the sandwich sheet and effective parameters of the process such as strain and forming force was investigated. Experimental works were conducted on the steel/polymer/steel sandwich sheets by a hydro-mechanical deep drawing die. A good agreement was observed between theoretical, numerical and experimental results. The safe zone of fluid pressure for achieving a part without rupture was obtained. It was shown that the limit drawing ratio is increased by increasing the pressure but after a particular point, the limit drawing ratio is decreased by increasing the chamber pressure. It was also observed that maximum drawing ratio for achieving a part without rupture in the hydro-mechanical deep drawing process is higher than conventional deep drawing process.

Enhancement on deformation uniformity of double curvature shell by hydroforming process and curved blank-holder surface

To manufacture a component with uniform deformation as well as homogeneous properties to fulfill the need of good consistency in service, both tool geometry and forming method were taken into account on the forming of double curvature shell. Experimental setups with planed and curved blank-holder surfaces combined with hydroforming process were performed on the evaluation of stain and thickness distribution compared with conventional deep drawing process. The average strain and its standard deviation on the formed shell were calculated as the indicators of whole strain level and strain uniformity. The results show that the most homogeneous strain, tensile strength, and micro-hardness can be achieved by the combination of hydroforming process and curved blank-holder surface.

Experimental and Finite Element Studies of Redrawing for ASS 316 at Elevated Temperatures

In this study, experimental and Finite Element (FE) analysis has been investigated for conventional circular deep drawing and redrawing process for ASS 316 at room temperature and 200°C. Initially, uni-axial tensile tests experiments have been performed to analyze the deformation behavior and material properties. Furthermore, circular blanks are deep drawn using conventional deep drawing process and then redrawn to a lower diameter. The various quantitative parameters such as Limiting Draw Ratio (LDR), thickness distribution have been evaluated. The overall LDR obtained is 2.667 at room temperature and 2.933 at 200⁰C, which is significantly higher than the single stage draw. Additionally, these processes have been simulated using DYNAFORM software with LSDYNA server. The results of the simulations were compared with the experimental results. The FE results are shows close agreement with experimental data.

Assessment of anisotropic hardening models for conventional deep drawing processes

Assessing the predictive capabilities of recent advanced constitutive modelling approaches for processes with industrial complexity is a challenging task. Real process conditions such as blankholder pressure distribution, friction and tool elasticity sensitively affect experimental observations, making the isolation of constitutive effects difficult. A systematic approach is proposed in this work to assess the performance of anisotropic hardening models with the least possible disturbance from process conditions. Two deep drawing examples were used for these purpose (“cross die” and “lackfrosch”) in conjunction with a mild steel (DC05). Optically measured strain distributions have been compared to corresponding simulations, which have been calibrated to accurately match the measured blank draw-in. The effect of initial yield locus shape as well as anisotropic hardening effects have been discussed.

Study on micro hydro-mechanical deep drawing using finite element method

A numerical model was established to investigate the micro hydro-mechanical deep drawing process of austenitic stainless steel 304 foil (0.05 mm thickness). Due to the miniaturisation of the specimen size, the effect of grain size, gap distance and radial pressure during drawing process could be prominent. The results indicate that the appropriate radial pressure and gap distance could improve the limit drawing ratio (LDR) of manufactured cylindrical cups by reducing the friction resistance. The maximum LDR obtained in the present work reaches 3.2, which is much higher than that obtained by conventional deep drawing process.

Deep Drawing with Local Hardening on Digital Multi-axis Servo Press

The paper discusses a new drawing technology, based on a synchronized movement of ram and cushion with multiple bending operations in alternating directions called “bi-directional deep drawing (BDD).” The goal is to avoid local thinning by strengthening the weak point using local hardening. BDD operations are realized before the conventional deep drawing process. This results in a local strain hardening at the weak point of the workpiece, which is usually located at the bottom punch radius. Two major aspects have to be given attention due to the high number of process parameters. On the one hand, for process design, it is helpful to have a tool by means of which it is possible to simultaneously create both the machine program for the servo press and the initial configuration for the process simulation. From the authors’ point of view, this complexity can only be represented by a numerical analysis method, on the other hand. Consequently, both aspects are given attention in this paper.

Evaluation of the quality for sheet deep drawing using a magnetorheological fluid (MRF)

Sealing problems, subsequent cleaning processes and poor force transmission effect etc. series of problems which strongly restrict the development and application of traditional medium pressure-based sheet forming technology. To overcome these problems, the magnetorheological fluid (MRF) can be used as the alternative force transmission medium. In this study, the deep drawing process of a 304 stainless steel sheet using MRF was investigated. The die cavity was filled with MRF and electric current was used to quantitatively adjust the magnetic fields distribution, which then controls the deformation behavior of the forming sheet. As compared to the conventional deep drawing process, experimental results clearly show that significant improvement in the produced sample quality was obtained when using the MRF with the electric current of 2 A. These improvements include: the height of the boundary circle reduces by 20%, the wall thickness distribution is more uniform, the rebound ratio correspondingly reduces from 9.6% to 0.67%, and the degree of sticking mode and the size precision are significantly increased. The results of this study provide scientific guidance to solve the bottleneck in the traditional deep drawing forming technology. The potential applications of the MRF-based new deep drawing technology to improve the product quality were explored.

Electromagnetic Pulse Assisted Progressive Deep Drawing

Cracks frequently occur in conventional cylindrical deep drawing process due to the lower formability of aluminum alloy sheet at room temperature. Therefore, a new approach named electromagnetic pulse assisted progressive deep drawing is proposed in this paper. This method gains the radial electromagnetic force which helps to push the sheet metal in radial direction by placing the circular thrust coil upon and underneath the flange, while gaining the axial electromagnetic force by placing drawing coil in the bottom of the punch. The results shows that the placement of the radial thrust coil has significant effect on the sheet metal's state and distribution of stress-strain; In addition, the interaction of the axial drawing force and the radial thrusting force has great effect on the depth of the deep drawing cylindrical parts.

Effects of sheet thickness and anisotropy on forming limit curves of AA2024-T4

In this study, the effects of sheet thickness and anisotropy of AA2024-T4 on forming limit curve (FLC) are experimentally investigated according to ISO 12004-2 standard. A new limit strain measurement method is proposed by using the grid analysis method so as to determine limit strains conveniently and reliably. In addition to the regular test specimens, various widths are added to enhance the FLC’s accuracy at the plane strain condition (PSC). The accuracy and reliability of the proposed method are verified for different materials. Results illustrate that an increase in the sheet thickness increases the FLC level. The additional experiments for additional widths improve the accuracy of the FLC at the PSC, and the position of the lowest major strain value differs from the literature. However, the effect of anisotropy on the FLC is found to be insignificant. Finally, experimental and numerical case studies are carried out for conventional deep drawing, stretch drawing, and hydraulic bulge processes. Results reveal that different FLCs are necessary for different thicknesses for accurate predictions.

Numerical analysis of the potential of deep drawing processes with hydrostatic pressure lubrication

Deep drawing is one of the most important forming procedures for the economic production of sheet metal components. Especially for high-volume parts, deep drawing is a very efficient method of fabrication with high utilization of semi-finished parts. Certainly, conventional deep drawing processes are restricted by forming limits due to part failure during the drawing process. The process force is one of the most important factors for this restriction. The narrow process window, especially for deep drawing of light-weight materials, can be extended by reducing the friction forces at the die radius, using hydrostatic pressure lubrication. After the numerical analysis of the appearing loads of deep drawing processes, the optimal position for the insertion of pressurized lubricant was identified and the potential of the hydrostatic pressure lubrication was predicted. With experimental tests, the results of the simulations were approved. Both, the simulations and the experimental tests showed a significant reduction of the process forces.