Deep Drawing Parts Research Articles

Re-manufacturing of Pre-deformed Automotive Sheet Metal Stamping Scrap Without Melting

Abstract The recycling of aluminium sheet metal typically involves shredding and re-melting, processes which are both energy-intensive and challenged by the presence of metallic contaminants. To mitigate these issues, this study explores an alternative approach: the re-manufacturing of deep-drawn parts directly from scrap aluminium sheets, thus bypassing the melting step. We used 2 mm thick Al-Mg sheet metal in H111 temper to produce simulated stamping scrap (miniaturized bonnets). Blanks were cut from these bonnets and secondary parts in a cross-cup geometry were deep-drawn using two different forming processes: warm-forming at 200 °C and O-temper forming at room temperature. The resulting maximum draw depths were 20-22 mm for warm-forming and 25-30 mm for O-temper forming. While warm-forming resulted in lower draw depths, O-temper forming led to coarse recrystallized grain formation in some regions. Our approach could significantly reduce the energy consumption associated with aluminium recycling.

Investigation on the Effect of Blank Holder Force and Initial Blank Size on the Thinning Problem of the Fuel Tank Part Made from Aluminum Alloy Sheet 5754-O under Deep Drawing Process

Deep drawing process is a common sheet metal forming technique in motor vehicle manufacturing. There are three primary defects that could be occur in deep-drawn parts: tearing, wrinkling, and thinning. When the thinning is difficulty detected by visual inspection. As a result, this study aims to address the thinning issue in a fuel tank part made from an aluminum alloy sheet AA5754-O 1.5 mm thick under cold working deep drawing process, while the manufacturer's desired upper limit for thinning is 20%. Two influential parameters viz. blank holder force and initial size of blank, were investigated and optimized by using Finite Element Analysis (FEA) through PAM-STAMP simulation software with the validated material model was based on Hill’s 1948 anisotropic yield criterion with Swift hardening law. The mechanical parameters in the mentioned model were derived from the results of uniaxial tensile tests. In conclusion, both the hydraulic cushion's blank holder pressure and the initial size of the blank were found to influence the thinning of the part, either individually or in combination. Despite optimizing both parameters, they were unable to consistently achieve the desired limit.

Improving the Quality of Tantalum Cylindrical Deep-Drawn Part Formation Using Different Lubricating Media-Coated Dies

Lubrication is one of the key factors to improve metal-forming quality. In the process of deep drawing, seizing tumors easily occur on the contact surfaces between the tantalum metal and the mold, which greatly affects the forming quality of the deep-drawn parts. Quality-forming quality problems that occur during the deep drawing of tantalum metal are studied from the perspective of lubrication in this paper. Three lubrication media, caster oil, PE (polyethylene) film, and DLC (Diamond Like Carbon) film, were adopted in the deep drawing of tantalum cylindrical cups. A universal testing machine and microscope were used to investigate the effect of lubrication media on the limit-drawing ratio, maximum forming force, and surface topography quality during the deep drawing process of the tantalum sheet. The results reveal that the lubrication of the PE film and DLC film can greatly improve the forming quality of the tantalum metal sheet, in which the DLC film has higher wear resistance and lower friction coefficient and can be used as the lubricating medium in the industrial forming process of tantalum deep-drawn parts.

Experimental investigation and numerical optimization of sheet metal forming limits during deep drawing process of DD14 steel

This work aims to experimentally study the deep drawability of DD14 hot-rolled steel sheets and to optimize numerically the material formability. The material anisotropy was confirmed by metallographic analysis of the material and tensile tests on specimens taken in three orientations with respect to the sheet rolling direction. Where the stress-strain curves show a sensitivity of material to the Piobert-Lüders phenomenon. The die pressure and the blank holder were considered as controlling factors on plastic instability and the success of the deep drawing operation. The forming limit curves (FLC) were plotted to highlight the different deformation modes that the sheet metal underwent during the deep drawing process. The collected deep-drawn parts observation shows severe plastic instability, until fracture. The initial plastic anisotropy is determined by the Hill48 quadratic criterion and the work hardening by the Hollomon power law. It results, during the experimental tests, that the front bottom corners of the deep drawn part are the areas at high risk of damage. The various numerical simulation scenarios followed by comparisons with the experimental results, allowed us to confirm the optimum conditions that minimize the material's plastic instability risks, forming operation “Step” and BHP “Amplitude”.

A Novel Method for Friction Coefficient Calculation in Metal Sheet Forming of Axis-Symmetric Deep Drawing Parts

Friction is one of the important factors in sheet metal forming. It greatly affects dynamic behaviors of metal sheets and stress and strain distributions in the metal sheets. In this study, deformation characteristics, stress–strain distribution, and change law of symmetrical parts in the process of deep drawing are analyzed using a new theoretical model based on the plastic flow law and partitioning the forming area. In the model, the least-square method is used to linearize the friction coefficient in nonlinear problems and reverse the calculation of friction coefficients to interpret the friction coefficient. To evaluate the model, the friction coefficient in sheet metal drawing of axis-symmetric deep drawing parts under various friction conditions was measured using a self-developed measuring system. The comparison between the experimental results and the calculation using the model shows a good agreement. The results show that the drawing force increases with the increase in punch depth; the friction coefficient decreases with the rise in punch depth. The friction coefficient obtained by fitting is relatively stable, and the average error is less than 3%. Using the friction coefficient model in finite element simulation analysis, it shows that the thickness and blank shape errors are less than 5%. The novel method studied in this paper shows great significance in support for theoretical research, numerical simulation research, and sheet metal stamping performance evaluation.

A novel process of sheet metal inverse bulging pre-deformation for deep drawing forming using magnetorheological fluid as flexible media

At the Magnetic field condition, the surface quality of formed parts can be improved significantly. To investigate the technical advantages of Magnetorheological (MR) fluid as a soft media, eliminate the defects of the parts because of the complex deformation, such as wrinkling, cracking, and over thinning. A new method of sheet deep drawing forming with MR fluid through inverse bulging pre-forming was proposed, which has made the wall thickness distribution more uniform and changed the stress distribution of sheet by changing the rheological property of MR fluid. The theoretical pressure transfer model of MR fluid as media and the configuration model of inverse bulging pre-forming are established. It can be concluded that the relationship between bulge height and load time have been shown consistency compared with experimental results and agree well with the theoretical analysis. And the configuration model have shown good agreement from the experiments results and the numerical results espectively with theoretical results. The uniformity of the wall thickness and the surface quality of the deep-drawn parts are improved significantly with the increase of the inverse bulging height. When the inverse bulging height is about 9 mm, the pre-forming effect is optimal, which provides theoretical guidance and is of much potential to the forming of the and thin-walled complex parts in industry fields.

Crystal plasticity as complementary modelling technique for improved simulations results of anisotropic sheet metal behaviour in forming processes

The accuracy of the simulation results in terms of metal sheet forming strongly depends on the capability of modelling the anisotropic material behaviour. In addition, predictive capabilities of the models are strongly influenced by the way how the constitutive model parameters are calibrated. Macroscopic models lean towards to become more complex in order to map the material behaviour more precisely. As consequence the amount and complexity of the experiments is increasing as well. In addition, it is well known that, some of the experiments, for example the equibiaxial compression test, are difficult to perform and therefore, a reasonable coupling of crystal plasticity (CP) modelling and macroscopic models is proposed. It is worth to mention that, in the domain of CP, arbitrary load cases are possible and therefore, any stress ratio of the yield criterion can be used for calibration. Prediction of anisotropic material behaviour of AA6016-T4 and DC05 sheets based on CP simulations were previously presented and compared with the macroscopic Yld2000-2d model. Their data set is now used for the calibration of the parameters of the macroscopic model, where in contrast to the classical procedure, the exponent of the yield locus is defined as a fitting parameter. The strain distributions predicted by the models have been compared with DIC-measurements of Nakajima samples. The predictive capabilities of the CP-based fitting procedure, compared to the classical fitting, are highlighted. Additionally, a comparison of the strain distribution prediction between all model variants is performed on a cruciform shaped deep drawing part. It underlines the importance of the correct prediction of the yield normal, as it is given by the crystal plasticity computation.

Epilamization of surface as a way to plasticize cold-rolled low carbon steel

Abstract. About 60 % of automobile and 40 % of tractor parts of various shapes and sizes are made from cold-rolled thin-sheet low-carbon steel by cold stamping. Automatic cutting lines for rolled sheet steel into blanks for stamping and automatic presses for the manufacture of deep-drawn parts of complex geometric shapes from a sheet result in increased demands on the quality of the metal: high technological ductility in order to improve stampability and obtain the required degree of deformation without fracture and ensuring sufficient strength after stamping to reduce weight, fuel economy and vehicle safety. In this regard, the search for new technological solutions relevant to ensure these conflicting requirements for the consumer properties of steel sheets is relevant. According to modern concepts, an approach that determines the influence of a thin surface layer on the deformation behavior and formation of product properties is promising for solving this problem. In this paper, we propose a method for significant improving of formability while maintaining the strength of low-carbon cold-rolled sheet steel by changing the state of the surface by epilating (EP). It is established that EP significantly reduces surface roughness, heals surface defects and significantly plasticizes the product, which greatly improves the stampability of 08кп steel blanks. Estimated by the Ereksen method, the ability of a sheet of 08kp steel to be drawn varies from the high-temperature group to values exceeding the requirements of WWTP, which according to GOST 9045-93 are regulated only for the best quality steel 08Yu. At the same time, sheet strength and resistance to brittle fracture increased. This effect has been obtained for the first time and is fixed by a patent for the invention.

Wrinkling Prediction of Rectangular Cup Deep Drawing Process for Aluminum Alloy Sheets by Using the Modified Yoshida Buckling Test

Nowadays, the industry has been growing interest in lightweight material for automotive and cookware manufacturing. The formability of sheet material is an important issue in these industries. The wrinkling behavior is one of the most failure in sheet metal forming and is often occurred in deep drawing process in cookware manufacturing. In this work, the developed wrinkling limit curves (WLCs) using experimental and numerical simulation of a modified Yoshida buckling test were precisely used to predict the wrinkling behavior of rectangular cup deep drawing for aluminum alloy sheets grade AA5054-O and AA5052-H32. The Industrial parts, the rectangular cup deep drawing was firstly performed for both investigated aluminum sheets for obtaining the wrinkling initiation on the side wall area of deep drawing parts. Subsequently, the experimental formed parts were carefully measured the draw-in of deformed blank sheets and drawing depth to validate the finite element (FE) model. Then, the FE simulation of the corresponding drawing tests were calculated, by which were implemented with the Hill’48 yield criterion and Swift hardening law to descript anisotropic plastic deformation. As a result, the local principle Major and Minor principle strains of observed wrinkle areas were gathered in the side wall area of the rectangular cup deep drawing test. Finally, the developed WLCs of aluminum alloy sheets were applied to predict the wrinkling formation of the formed deep drawing parts. Comparatively, the influence of different aluminum alloy grades on the WLCs and wrinkling behavior were explicitly investigated.

Influence of process parameters on deep drawing of 2060 Al–Li alloy under hot stamping process

In this paper, the hot stamping formability of 2060 Al–Li alloy was studied by numerical simulation and experimental tests. The thickness of 2060 Al–Li alloy parts was analyzed when the deformation temperature is 400 °C, 450 °C and 480 °C, stamping speed is 15 mm/s, 25 mm/s and 35 mm/s. Simultaneously, the influence of lubrication on the thinning of 2060 Al–Li alloy cup-shaped parts is also analyzed. And Vickers hardness of the forming parts was tested after hot stamping tests. The results show that the deep drawing parts have good thickness uniformity at the deformation temperature ranging from 400 °C to 450 °C. However, the thickness of the cup parts is thinning seriously when the deformation temperature is 480 °C. With the increase of stamping speed, the thinning rate of cup-shaped parts decreases gradually. In this study, the thinning rate of the drawing parts is smaller when stamping speed is 35 mm/s. Compared with stamping parts without lubrication, cup parts with deeper depth can be obtained under better lubrication. With the improvement of lubrication conditions, the crack position of the formed part gradually shifts to the center of the cup. The simulation results and experimental results have good consistence.

Effect of reverse pre-bulging on magnetic medium deep drawing formability of aluminum spherical bottom cylindrical parts

The fairing represented by the structural characteristics, nowadays, of spherical bottom cylindrical parts is mostly utilized to protect the shell of space launch vehicle. However, such components have a pre-bulging behavior in the flexible medium-assisted deep drawing. If not properly controlled, excessive thinning of wall thickness will result in cracking defects. In this paper, the effect of reverse pre-bulging on magnetic medium-assisted deep drawing of aluminum spherical bottom cylindrical parts is studied and contrasted. The results show that the pre-bulging can improve the formability and quality of the components of the magnetic media–assisted deep drawing. When the pre-bulging height increases from 0 to 6 mm, the maximum thinning rate of the wall thickness of deep drawing parts decreases by about 28%, and the coordinated deformation and uniformity of the wall thickness of each part are significantly improved. At the same time, the ultimate forming height of spherical bottom cylindrical parts is increased by about 10%, the springback is obviously reduced, and the accuracy of the shape and size is improved. It provides scientific guidance for a precise forming process and quality control of typical thin-walled deep cavity components with geometric characteristics such as spherical bottom or cone.

Planar Anisotropy, Tension–Compression Asymmetry, and Deep Drawing Behavior of Commercially Pure Titanium at Room Temperature

The planar anisotropy (PA) and tension–compression asymmetry (TCA) of the CP-Ti were investigated via uniaxial tension and compression tests at room temperature. The formability and the earing behavior of the CP-Ti sheet were studied via deep drawing experiment. The deep drawing simulations using the uniaxial tensile and the compressive curves as the hardening rules were compared with each other and with the experimental results. The CP-Ti sheet showed PA and TCA in yielding and strain hardening. The PA was characterized by the plastic strain ratio r0, r45, and r90 of 1.47, 2.06, and 2.05. The TCA showed PA, which showed tension–compression yield strength ratios of 1.12, 1.08, and 1.04 in 0°, 45°, and 90° in the rolling direction, and tensile and compressive hardening exponent ratios of 0.86, 0.8, and 0.62. The orientation distribution functions (ODFs) analysis demonstrated that the tensile and the compressive deformation textures were different and showed PA. The simulative results, including the simulated forming force and the earing profiles using the uniaxial tensile and compressive curves as the hardening rules, were not in agreement with each other. The results were not in good agreement with the experimental results, implying that the TCA had an important effect on the formability of the sheet. The TCA tended to reduce the thickness of the deep drawing parts, increase the earing ratio, and affect the drawing force.

Spatial multiplexing and autofocus in holographic contouring for inspection of micro-parts.

We present a method for fast geometrical inspection of micro deep drawing parts. It is based on single-shot two-wavelength contouring digital holographic microscopy (DHM). Within the capturing process, spatial multiplexing is utilized in order to record the two required holograms in a single-shot. For fast evaluation, determining the locations where the object is in focus and stitching all focus object's areas together is achieved digitally without the need for any external intervention using an autofocus algorithm. Thus, the limited depth of focus of the microscope objective is improved. The autofocus algorithm is based on minimizing the total variation (TV) of phase difference residuals of the two-wavelength measurements. In contrast to standard DHM, an object side telecentric microscope objective is used for overcoming the image scaling distortions caused by a conventional microscope objective. The method is used to reconstruct the 3D geometrical shape of a cold drawing micro cup. Experimental results verify the improvement of DHM's depth of focus.

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.

Effect on Blank Holding Force on Blank Deformation at Direct and Indirect Hot Deep Drawings of Boron Steel Sheets

This study involves performing direct and indirect hot press forming on ultra-high-strength steel (UHSS) boron steel sheets to determine formability. The indirect hot press process is performed as a cold deep drawing process, while the direct hot press process is performed as a hot deep drawing process. The initial blank temperature and the blank holding force are set as parameters to evaluate the performance of the direct and indirect deep drawing processes. The values of punch load and forming depth curve were obtained in the experiment. In addition, the hardness and microstructure of the boron steel sheets are examined to evaluate the mechanical properties of the material. The forming depth, maximum punch load, thickness, and thinning rate according to blank holding force were examined. The result shows that a larger blank holding force has a more significant effect on the variation of the thickness and thinning rate of the samples during the drawing process. Furthermore, the thinning rate of the deep drawing part in with and without fracture boundary was respectively examined.

Effect of Planar Anisotropy and Tension-Compression Asymmetry of CP-Ti on its Deep Drawing Behavior at Room Temperature

The planar anisotropy (PA) and tension-compression asymmetry (TCA) of the commercially pure titanium (CP-Ti) were investigated through uniaxial tension and compression experiments at room temperature. By deep drawing experiment, the formability and the earing profile for the CP-Ti were studied at room temperature. The deep drawing simulations using the hardening rules of uniaxial tensile or compression curves were compared with experimental results. The results show that the CP-Ti has obvious PA, and the plastic strain ratiosr0,r45andr90are 1.47, 1.64 and 2.05, respectively. The CP-Ti sheet shows the tension-compression asymmetry of yielding and hardening. The TCA also shows obvious PA. The tension-compression yield strength ratio of 0°, 45° and 90° to the rolling direction are 1.12, 1.08, 1.04, and the tension-compression hardening exponent ratio are 0.86, 0.8 and 0.62, respectively. The simulative results without considering TCA indicate that the forming force, the wall thickness and earing profile are not in good agreement with the experimental ones. Therefore, the earing appeared in 45° is contribution of the PA and TCA. The TCA will reduce the thickness of the deep drawing parts, increase the earing ratio and affect the drawing force.

Micro deep drawing of T2 copper foil using proportional decreased tools

Cooper foils are widely used in micro electronic industry, and they are suitable to be deep drawn to form cup-like parts. In this study, micro deep drawing experiments were conducted by using T2 copper foils after an annealing process, and three scale factors (λ = 0.5, 1, and 2) were set to indicate effects of proportional decreased tool dimensions and processing parameters on the forming result. The experimental results show that micro deep drawing parts with internal diameters of 0.5, 1.0, and 2.0 mm can be formed successfully. And the 0.5-mm cup drawing part has achieved the minimum dimension in recent reports. The standardized punch travel-deep drawing force curves are similar, and the maximum deep drawing force is decreased with smaller scale factor. The thickness distributions of different processing parameters are all decreased firstly and then show the trend to increase from bottom to upper regions. We find that the size effect influences the maximum deep drawing force during the forming process and the quality of forming part. And the maximum limit drawing ratio (LDR) is 2.2 for the experiment with scale factor of 0.5. Forming regularities of the proportional decreased micro deep drawing process can be presented clearly by changing the scale factor.

Superplasticity and Micro-arrayed Deep-Drawing Behavior of Ni-Co/GO Nanocomposite

In this article, Ni-Co/GO nanocomposite was fabricated by AC pulse electrodeposition method. The room temperature strength tests and the superplasticity of the nanocomposite were investigated by the tensile tests. A 5 × 5 micro-arrayed deep-drawing die was designed to explore the feasibility of micro-forming. The as-deposited material has a narrow grain size distribution with a mean grain size of 50 nm. The addition of GO as a reinforcing phase can effectively enhance the room temperature tensile strength of the nanocomposite, but reduce the plasticity. When adding GO to the plating bath, a maximum elongation of 467% was observed for the specimen with a GO content of 0.01 g/L at 773 K and a strain rate of 1.67 × 10−3 s−1 by tensile tests. Micro-arrayed deep-drawing tests were subsequently performed with male die diameter of 0.58 mm and female die diameter of 0.8 mm. The experimental relative drawing height values were measured and compared with the deep-drawing parts without GO additive. It is found that the micro-arrayed deep-drawing with rigid male die at high temperature was feasible and forming parts with good shape could be got. The thickness distribution analysis of the deep-drawing parts showed that wall thickness changed ranging from 53 to 95 μm, and the thickness reduction at the punch fillet is the most obvious.

Feedback control in deep drawing based on experimental datasets

In large-scale production of deep drawing parts, like in automotive industry, the effects of scattering material properties as well as warming of the tools have a significant impact on the drawing result. In the scope of the work, an approach is presented to minimize the influence of these effects on part quality by optically measuring the draw-in of each part and adjusting the settings of the press to keep the strain distribution, which is represented by the draw-in, inside a certain limit. For the design of the control algorithm, a design of experiments for in-line tests is used to quantify the influence of the blank holder force as well as the force distribution on the draw-in. The results of this experimental dataset are used to model the process behavior. Based on this model, a feedback control loop is designed. Finally, the performance of the control algorithm is validated in the production line.

Improved process robustness by using closed loop control in deep drawing applications

The production of irregular shaped deep-drawing parts with high quality requirements, which are common in today’s automotive production, permanently challenges production processes. High requirements on lightweight construction of passenger car bodies following European regulations until 2020 have been massively increasing the use of high strength steels substantially for years and are also leading to bigger challenges in sheet metal part production. Of course, the more and more complex shapes of today’s car body shells also intensify the issue due to modern and future design criteria. The metal forming technology tries to meet these challenges by developing a highly sophisticated layout of deep drawing dies that consider part quality requirements, process robustness and controlled material flow during the deep or stretch drawing process phase. A new method for controlling material flow using a closed loop system was developed at the IFU Stuttgart. In contrast to previous approaches, this new method allows a control intervention during the deep-drawing stroke. The blank holder force around the outline of the drawn part is used as control variable. The closed loop is designed as trajectory follow up with feed forward control. The used command variable is the part-wall stress that is measured with a piezo-electric measuring pin. In this paper the used control loop will be described in detail. The experimental tool that was built for testing the new control approach is explained here with its features. A method for gaining the follow up trajectories from simulation will also be presented. Furthermore, experimental results considering the robustness of the deep drawing process and the gain in process performance with developed control loop will be shown. Finally, a new procedure for the industrial application of the new control method of deep drawing will be presented by using a new kind of active element to influence the local blank holder pressure onto part flange.