Deep Drawing Experiments Research Articles

Analysis of Thickness Variation in 2219 Aluminum Alloy Ellipsoid Shell with Differential Thickness by Hydroforming

The process of spinning and machining for heavy plates has the problems of a large amount of machining, large springback, and easy cracking. Aiming to address these issues, we proposed a deep drawing forming method for a plate with differential thickness to manufacture an integral ellipsoid component with a thin zone in the middle and a thick zone in the periphery. The plate with a differential thickness was initially produced through machining, followed by the execution of deep drawing deformation. During the deformation process of plates with differential thickness, the thin zone is prone to rupture defects. Therefore, a hydroforming method utilizing an elastic auxiliary plate was adopted to solve this problem. Through mechanical analysis and deep drawing experiments, the influences of hydraulic pressure and elastic auxiliary plate on the distributions of thickness and strain were studied, and the influence of friction on hydroforming was analyzed. The results indicate that increasing the hydraulic pressure and setting elastic auxiliary plates can increase the interfacial friction, reduce the thickness thinning rate, and improve the thickness distribution and deformation uniformity within the thin zone. When the hydraulic pressure is 5.2 MPa and the thickness of the elastic plate is 5 mm, the maximum thickness thinning rate of the ellipsoid shell is 8.8%, which is 34% lower than that of the ellipsoid shell obtained via conventional deep drawing.

Microstructure evolution and twinning behavior of AZ31 magnesium alloy sheets with bimodal texture during cold deep-drawing deformation

Cold deep drawing experiments were conducted on AZ31 magnesium (Mg) alloy sheets with bimodal texture, which were prepared by the newly developed equal channel angular rolling and continuous bending and subsequent annealing (ECAR-CB-A) process. The results showed that the sheet could be successfully deep-drawn at a limiting drawing ratio (LDR) of 1.6, and the forming performance was better than that of the as-rolled base-texture sheet at room temperature. The microstructure after deep-drawing deformation was investigated by X-ray diffraction (XRD), optical microstructure (OM), and electron backscatter diffraction (EBSD). A large number of {10−12} extension twins (ETs) are observed in the outer shoulder region. Due to the bimodal texture, the activated {10−12} ET variants and the basal slip within the matrix have a higher Schmid Factor (SF) value when the outer shoulder region is under radial tensile stress, this enables the shoulder of the drawn cup to maintain good deformability. In addition, some {10−11} contraction twins (CTs) and {10−11}-{10−12} double twins (DTs) can be observed in this region, which is activated by the local strain accommodation between the twins and the slip systems, and the multiaxial stress. Due to different stress conditions, the volume fractions of {10−12} ETs in the inner shoulder region are less than that in the outer region. The stress concentration caused by {10−11}-{10−12} DTs that occurred in the edge region is the reason for the fracture of the drawn cups at a drawing ratio(DR) of 1.7.

Analysis of deep drawing with electro-permanent magnet based on coupling of multi-physics

The electro-permanent magnet (EPM) blank holder (EPMBH) technology has been combined with forming technology. The method commonly used in previous related studies was to simulate and analyze the magnetic field of the EPMBH device and obtain the magnetic attraction under corresponding conditions. During the forming process, a blank holder force with the same magnitude as the magnetic attraction was loaded, and then the temperature field of the EPMBH device was analyzed separately. Due to the lack of consideration of the interaction between various physical fields, there is a significant deviation between the simulation and experiment with this method. To improve the accuracy of analysis results, this article introduces an analysis method that considers the mutual influence of various factors and simulates the coupling of magnetic field, structural field, and temperature field in deep drawing, which is compared with the deep drawing experiment with EPMBH. There is no obvious temperature rise issue during the experiment, and constant blank holder force loading can be achieved with EPMBH. The results show that for 08-Al thin plate with an initial thickness of 0.8 mm and a diameter of 100 mm, the optimal magnetization current is 13 A and the drawn part can be obtained without wrinkling and fracture defects.

Effect of Process Variables on Interface Friction Characteristics in Strip Drawing of AA 5182 Alloy and Its Formability in Warm Deep Drawing

Warm forming is widely used to enhance the formability of aluminum alloy sheets. In warm deep drawing, the process variables significantly affect frictional characteristics at the tool–blank interface. It has been a conventional approach to use a constant value of friction coefficients in the finite element (FE) simulations. However, this can occasionally result in suboptimal accuracy of the predictions. In the present work, strip drawing tests were carried out on AA5182 aluminum alloy sheets to investigate the effect of important process variables, namely, temperature, contact pressure, and drawing speed, on the friction coefficient in the warm forming temperature range (100–250 °C) under lubricated condition. The results obtained from the strip drawing tests were used for defining the friction conditions in the simulation of warm deep drawing of cylindrical cups incorporating the variation of the friction coefficient with contact pressure and speed at different temperatures. The Barlat89 yield criterion was used to define the effect of anisotropy in the material. The Voce hardening law and Cowper–Symonds model were used to incorporate the effect of strain hardening and strain rate, respectively, in the simulation. Drawability and peak force were compared with the predictions when a constant friction coefficient was assumed. Warm deep drawing experiments were conducted to validate the predicted drawability and load–displacement curves. It is clearly observed that the accuracy of prediction of the limiting drawing ratio and peak load through simulations is improved by incorporating the effect of pressure and speed on friction coefficient as it captures the local variations of friction during warm deep drawing precisely, rather than assuming a constant average friction coefficient at all the tool–blank contact areas.

Multi-scale numerical investigation of deep drawing of 6K21 aluminum alloy by crystal plasticity and a stress-invariant based anisotropic yield function under non-associated flow rule

In this research, the earing characteristics of 6K21 aluminum alloy in circular cup deep drawing are investigated by virtue of experiments and multi-scale simulations including anisotropic Drucker, Hill48, Yld91 yield functions and crystal plastic finite element model (CPFEM). First, the deep drawing experiments of AA 6K21 are carried out to explore the influences of blank holding force (BHF) and blank diameter (BD) on earing profile and mechanical response. The user-defined material model subroutine is written for LS-DYNA explicit code, including constitutive model and ductile fracture criterion under associated or non-associated flow rule (NAFR). The parameters of the crystal plasticity model are calibrated by means of an optimization algorithm. Three yield functions under NAFR and CPFEM are used to predict earing in deep drawing simulation. The effects of five textures on the earing profiles and thickness variables are studied by CPFEM. The results demonstrate that the earing rate decreases slightly as the BHF increases. However, the mechanical response changes insignificantly. Moreover, as the BD increases, both the earing rate and mechanical response increase significantly. Considering computation accuracy and efficiency, the anisotropic Drucker function can accurately character the plastic deformation behavior of deep drawing. For five textures in CPFEM, Cube and Goss textures produce four ears at 0o and 90o from the rolling direction. Brass and S textures form six ears at 0o and 55o. Copper texture fabricates eight ears at 40o and 70o. The influences of five textures on earing rate are Goss > Cube > Copper > Brass > S. Furthermore, there are obvious thickness gradient fluctuations at the corner of the cup in Cube, Goss and Copper textures. It is expected to reduce the earing rate and improve the formability through reasonable allocations of experimental parameters and texture proportions.

New small-scale hydromechanical deep-drawing process using die-integrated active high-pressure generation system

In this study, hydraulic pressure generation and small-scale cylindrical hydromechanical deep-drawing experiments were conducted using a novel die-integrated active high-pressure generation system. The most significant feature is the installation of a hydraulic pressure-generating piston structure inside the die, which enables a high-pressure generation process of 100 MPa or higher inside the die. In addition, by taking advantage of the size effect of a smaller die, a high hydraulic pressure is actively generated using the same equipment as in conventional drawing processes. It was discovered that a piston installed in the die can actively generate a hydraulic pressure of 100 MPa or higher based on the Pascal principle. By downsizing the die, a hydraulic pressure of 100 MPa or higher can be generated using only the power of a small press machine (50 kN). By actively applying high hydraulic pressure counter and radial pressures, small-scale drawability can be significantly improved. Furthermore, the application of the proposed system to single-action presses and progressive dies can enable hydromechanical deep drawing with optimized conditions for each process in a single motion.

Assessment of Conical Die Deep Drawing Ability of DP800 and MART1400 Ad-vanced High Strength Steels

Deep drawing is one of the most important and vastly conducted sheet metal forming method. Thus, even small improvements achieved on the deep drawability of sheet metals significantly increases the ability of sheet metal to be formed into more complex products. Advanced high strength steels (AHSSs) are one of the most popular steels in the automotive industry due to their high strengths. However, their low ductility causes considerable splitting problems on the shop floors. In this study, deep drawing experiments have been conducted in conical dies with four different angles (0⁰, 7.5⁰, 12.5⁰, and 20⁰) for DP800 and MART1400 steels to observe whether a higher deep drawing ratio (DDR) can be achieved by deep drawing in conical dies for AHSSs. In addition, finite element analysis (FEA) has been utilized to estimate the DDR for each types of steels in different conical die setups. It has been observed that the deep drawing ability of MART1400 steel has not improved in any of the conical die setups. However, DDR of DP800 has slightly increased by 2.46% by deep drawing with 20⁰ die angle. A good agreement with the numerical and experimental results has been achieved.

Laser Powder Bed Fusion of Inconel 718 Tools for Cold Deep Drawing Applications: Optimization of Printing and Post-Processing Parameters.

Inconel 718 (IN 718) powder is used for a laser powder bed fusion (LPBF) printer, but the mechanical properties of the as-built object are not suited to cold deep drawing applications. This study uses the Taguchi method to design experimental groups to determine the effect of various factors on the mechanical properties of as-built objects produced using an LPBF printer. The optimal printing parameters are defined using the result for the factor response to produce an as-built object with the greatest ultimate tensile strength (UTS), and this is used to produce a specimen for post-processing, including heat treatment (HT) and surface finishing. The HT parameter value that gives the maximum UTS is the optimal HT parameter. The optimal printing and HT parameter values are used to manufacture a die and a punch to verify the suitability of the manufactured tool for deep drawing applications. The experimental results show that the greatest UTS is 1091.33 MPa. The optimal printing parameters include a laser power of 190 W, a scanning speed of 600 mm/s, a hatch space of 0.105 mm and a layer thickness of 40 μm, which give a UTS of 1122.88 MPa. The UTS for the post-processed specimen increases to 1511.9 MPa. The optimal parameter values for HT are heating to 720 °C and maintaining this temperature for 8 h, decreasing the temperature to 620 °C and maintaining this temperature for 8 h, and cooling to room temperature in the furnace. Surface finishing increases the hardness to HRC 55. Tools, including a punch and a die, are manufactured using these optimized parameter values. The deep drawing experiment demonstrates that the manufactured tools that are produced using these values form a round cup of Aluminum alloy 6061. The parameter values that are defined can be used to manufacture IN 718 tools with a UTS of more than 1500 MPa and a hardness of more than 50 HRC, so these tools are suited to cold deep drawing specifications.

Influence of elevated surface temperature on the formability in cold forming of aluminum alloy sheets

In recent decades, deep drawing has been widely used in the automotive industry for producing lightweight car body components of 5xxx and 6xxx aluminum alloys. Although sheets of these alloys are usually deep-drawn at room temperature, heat generated by friction and plastic deformation may locally increase the surface temperature of the drawing tools during the serial production of components. Therefore, this work investigates the influence of elevated surface temperatures of the tool on the formability of commercial hotmelt-lubricated 1.5 mm-thick EN AW-5182 and EN AW-6016-T4 sheets. Deep drawing experiments were performed at different constant surface temperatures between room temperature (RT) and 80 °C using a cross-shaped tool with open die. With increasing surface temperature, the maximum drawing depth – that was considered as indicator for the formability – decreased by about 21 % and 28 % for EN AW-6016-T4 and EN AW-5182, respectively. Tribological experiments performed using a pin-on-plate tribometer confirmed this trend. The results clearly showed that the coefficient of friction (COF) between the sheet and the tool significantly increase at elevated surface temperature; the most notable increase of the COF occurred between 40 °C and 60 °C.

Simulation of deep drawing of dual phase steel sheets incorporating tribological behaviour predicted by advanced friction modelling

In a deep drawing process, friction at the sheet metal-die contact interface affects the material flow in the flange as well as at the die entry affecting product quality significantly. The accuracy of predicted drawing force and thinning in deep drawing simulation strongly depends on friction modelling. The Coulomb friction model with a constant coefficient of friction is generally assumed in simulations. In reality, the actual friction coefficient depends on process variables such as local contact pressure, relative sliding velocity, and strain in the sheet material. In this work, an approach is presented for deep drawing simulation of dual phase (DP600) steel sheets incorporating the effect of these variables on the friction coefficient. Strip drawing tests under conditions similar to that exist in the flange area during deep drawing have been carried out. Deep drawing simulations have been performed using two friction models taking into consideration the variation of friction coefficient with respect to pressure and velocity. The predicted punch force and thickness variation are validated using deep drawing experiments. A considerable improvement in the accuracy of predicted results has been observed when compared to a constant coefficient of friction.

Use of uncoupled ductile damage models for fracture forming limit prediction during two-stage forming of aluminum sheet material

In this paper, failure limits of aluminum AA5052 sheet material were experimentally investigated, and subsequently, these were predicted using various uncoupled ductile fracture models. In this context, three different sets of experiments, namely two-stage stretch forming, two-stage deep drawing, and single point incremental forming experiments, were performed to estimate the failure limits under several different strain paths. Both the isotropic von Mises and anisotropic Barlat Yld2000 yield criteria were used to calibrate eight different fracture models, and found that incorporating an anisotropic model enhanced the accuracy of prediction for most of the fracture models. Moreover, it was identified that the incorporation of anisotropic yield theory in the Bao-Wierzbicki (BW) fracture model predicted the experimental fracture surface strains precisely for as-received sheet materials. This BW model-based fracture forming limit diagram (BW-FFLD) was transposed into a path-independent polar effective plastic strain (PEPS) locus to estimate the onset of fracture during two-stage forming experiments. Furthermore, the BW model was incorporated as a fracture initiation model in the finite element (FE) software, LS-Dyna, using the generalized incremental stress state dependent damage model (GISSMO) platform to predict the fracture location and dome height through the element erosion technique. It was observed that the dome height and cup height were predicted within 7 % and 5 % error margins in the FE simulation of two-stage stretch forming and deep drawing experiments, respectively. Furthermore, the damage evolution contour indicated that the accumulation of the damage value was rapid, which was responsible for the massive drop in the dome and cup heights during two-stage stretch forming and deep drawing experiments.

Tribological behaviour of ultra-thin stainless steel in micro deep drawing with graphene nanosheets

In this study, the micro deep drawing (MDD) experiments of an austenitic stainless steel with 40 μm in thickness were conducted using the lubricants containing different mass fractions of graphene nanosheets (GNS) in ethanol. Prior to the MDD tests, the lubricants with GNS concentrations of 5, 10, and 15 mg/ml were synthesised by mixing different amounts of GNS with pure ethanol, and then sprayed uniformly on the blank surface. The friction-reduction mechanisms of the GNS in the MDD were discussed by analysing the profile and surface roughness of the microcups. The results indicated that the GNS could reduce the friction and improve the surface quality of the micro products during the MDD process. In particular, the lubricant with 10 mg/ml GNS enabled the lowest drawing force, wrinkling, and surface roughness of the drawn microcup. These findings contribute to a better understanding of the friction-reduction mechanisms of using GNS in the MDD of materials.

Research on hydroforming of 5A06 aluminum alloy semi-ellipsoid shell with differential thickness

For the purpose of eliminating the annular welding seams in welding structures with differential thickness, a hydroforming method using a circular 5A06 aluminum alloy plate with a radial differential thickness in coupling with a flexible polyurethane auxiliary plate was proposed to form an integrated semi-ellipsoid shell. The circular 5A06 aluminum alloy plate had a smaller in the middle and a larger thickness in the periphery. In the forming process of such aluminum alloy plates, concentrated deformation and fracture might have occurred in the thin zone. According to the size of the target specimen, the testing plates with two types of thickness ratios were obtained by mechanical processing. Furthermore, the thickness and strain of the drawn specimens with different thickness ratios were analyzed under different hydraulic pressure by means of deep drawing experiments. Compared to the conventional deep drawing, the formability of 5A06 aluminum alloy plates with differential thickness could be effectively improved by hydroforming. The integrated semi-ellipsoid shells with the thickness ratios of 2/3 and 1/2 were obtained under the hydraulic pressure of 10 MPa with maximum thinning ratios of 8.5% and 10.9%, respectively. In a word, the increase in hydraulic pressure could effectively reduce the maximum thinning ratio in the thin zone, and improve the thickness distribution uniformity.

Influence of alloy composition and lubrication on the formability of Al-Mg-Si alloy blanks

The formability of 1.0 mm-thick Al-Mg-Si alloy blanks with different Si and Mg contents was numerically and experimentally investigated using two deep drawing tools: (i) a cross-shaped tool with open die and (ii) a complex-shaped panel tool with closed die. For the cross-shaped tool, forming velocity and blankholder force were constant and the formability was characterized based on the maximum drawing depth at crack initiation. For the complex-shaped panel tool the forming velocity and the drawing depth was constant and the formability was characterized based on the maximum blankholder force at crack initiation. Two types of commercial lubricants were applied on the blank surfaces. In order to investigate critical forming conditions, numerical models of both deep drawing processes were built using the AutoForm finite element (FE) software. Parameters required as input for these models were experimentally determined. The flow curve and the anisotropy of each of the aluminum alloys were determined using uniaxial tensile tests. Based on the results of pin-on-plate tests an advanced friction model which considers different contact pressures and sliding velocities was created using the TriboForm software. Good agreement between deep drawing simulations and experiments was achieved in terms of forming force, local thinning and strains. Experiments and simulations confirmed that the maximum drawing depth or blankholder force, respectively, tended to increase with increasing Si and Mg contents. However, the influence of lubrication on the formability of the Al-Mg-Si alloy blanks was much more significant than the influence of the alloy composition.

Research on deep drawing with multi-ring blank holder technique

In this paper, a novel multi-ring blank holder technique is developed. The blank holding force (BHF) provided by each ring can be independently and effectively applied on all radial regions. The principles and advantages of the multi-ring technique are first explained and analyzed by theoretical derivation, stress analysis, and forming simulation. The results indicate that the distribution of the blank holder force per unit area (FUA) applied by the new blank holder technique is more reasonable than using the conventional single blank holder and can better suppress the wrinkles. Finally, the effectiveness of the multi-ring blank holder technique is proven by a deep drawing experiment of the 08Al plate. It was verified that due to the reasonable FUA distribution, the use of the blank holder technique can suppress the wrinkles on the flange very well.

Deep-Drawing of Commercially-Pure Niobium Sheet

Pure Niobium is a material of interest for high-energy-physics applications including superconducting accelerators. Cold-rolled sheets of Nb exhibit significant plastic anisotropy. Here we report on the mechanical and forming properties of 99.95% pure, 1.02 mm thin, cold-rolled sheet. Uniaxial tension, biaxial tension and disc compression experiments are performed, the first two at multiple angles to the rolling direction of the sheet. The material is very ductile (uniform elongation ~30%), and exhibits significant plastic anisotropy (e.g., the R-values range from 1.2 in 45o to 2.5 in 90o). The results are used to calibrate the Yld2000-2D anisotropic yield function, with an exponent of 6 as Nb is BCC. They are also used to extract the hardening curve beyond the limit load in uniaxial tension. Deep-drawing experiments are performed using a die of 27.6 mm dia. and a punch of 25.4 mm dia. Blanks of various diameters are used. The successfully drawn cups exhibit significant earing. The experiments are simulated using Abaqus/Standard and shell elements. It is shown that a properly calibrated material model enables the numerical simulations to match the experiments.

A Materials Science-Based Approach to Finite Element Simulation of Warm-Forming of Al-Mg-Zn Alloys

Warm deep-drawing of pre-aged (under-aged) blanks of 7xxx series aluminum alloys (Al-Zn-Mg) at moderate temperatures of roughly 120–230°C is a promising route for producing parts with considerable geometrical complexity, good paint bake hardening response, and, thus, excellent final mechanical properties. Furthermore, oil-based lubricants can be used, eliminating the need for elaborate cleaning routines. However, finite element (FE) simulation of the process is challenging: time-temperature regimes during coupon testing for material cards should closely follow the real conditions in the press because the material undergoes significant changes at warm-forming temperatures, such as recovery and precipitation/coarsening/reversion of hardening phases. When convective heating is used for Nakajima or tensile testing, heating rates are usually too low to adequately represent real process conditions (where inductive or contact heating may be used). Here we present a method for establishing FE material cards and calibrating the GISSMO damage model using miniaturized tensile specimens for a dilatometer with inductive heating. The simulations are compared with warm deep-drawing experiments of pre-aged 7xxx and good agreement of minimum draw temperature for two alloys is achieved. The findings are discussed with regards to transmission electron microscopy investigations and final mechanical properties published earlier. It was found that warm-forming is suitable to produce complex 7xxx parts with high final strength. Conditions in the press can be represented by using miniaturized tensile specimens and inductive heating for calibration of material cards/damage models.

Flange Wrinkling in Deep-Drawing: Experiments, Simulations and a Reduced-Order Model

Flange wrinkling is often seen in deep-drawing process when the applied blankholding force is too small. This paper investigates the plastic wrinkling of flange under a constant blankholding force. A series of deep-drawing experiments of AA1100-O blanks are conducted with different blankholding forces. The critical cup height and wrinkling wave numbers for each case is established. A reduced-order model of flange wrinkling is developed using the energy method, which is implemented to predict the flange wrinkling of AA1100-O sheet by incrementally updating the flange geometry and material hardening parameters during the drawing process. A deep-drawing finite element model is developed in ABAQUS/standard to simulate the flange wrinkling of AA1100-O blanks under constant blankholding force. The predicted cup height and wave numbers from the finite element model and reduced-order model are compared with the experimental results, which demonstrates the accuracy of the reduced-order model, and its potential application in fast prediction of wrinkling in deep-drawing process.

Mechanical behavior and forming of commercially-pure niobium sheet

This work investigates the mechanical and forming behavior of pure niobium sheet, which has broad applications in low-temperature physics including the proposed International Linear Collider. An extensive suite of mechanical tests is performed on commercially-pure niobium (CP-Nb), including uniaxial tension, strain-rate-jump, biaxial tension and disc compression, which are used to characterize the plastic behavior of the CP-Nb sheet. The material is found to have significant plastic anisotropy, high R-values, significant ductility, and non-negligible rate-dependent behavior. Subsequently, two types of forming experiments, deep-drawing and stretch-forming, are conducted with CP-Nb blanks of different diameters. These two experiments subject the CP-Nb sheet to different modes of deformation and stress states, and are meant to highlight the strengths and deficiencies of constitutive models. To model the forming behavior of the CP-Nb sheet, the material hardening at large strains is extracted from the uniaxial tension test, including the strain-rate effect. The plastic anisotropy of the CP-Nb sheet is modeled with the Yld2000-2D and Yld2004-3D non-quadratic yield functions. The friction coefficient of 0.25 is inversely identified from the deep-drawing experiments, by matching the predicted and measured punch force–displacement responses. While the features of the deep-drawing experiment are captured well using the constitutive framework described above, those of the stretch-forming experiment are not. Agreement with the latter is accomplished only after a targeted recalibration of the anisotropic yield function. This underscores the general conclusion that successful modeling of plastic deformation processes requires an accurately calibrated yield function which captures the dominant, process-specific stress states.

Investigation of earing defect and thickness distribution in stamp forming of continuous glass fiber reinforced polypropylene composite laminates

When lightweighting studies are examined, thermoplastic matrix composites come to the fore as they have a high specific strength, are recyclable, and can be formed by thermoforming. Some obscurity needs to be overcome for the rapid forming of three-dimensional parts from laminated thermoplastic composites. In this study, deep drawing experiments were carried out to investigate the forming capabilities of continuous glass fiber reinforced polypropylene composite laminates. The parameters of drawing depth, laminate temperature, holding pressure, and punch speed were examined at each three different levels. The effects of these parameters were evaluated on the earing defect and the thickness distribution. It was concluded that the laminate temperature affected both deformations the most. It was determined that all parameters caused a change in flange diameter, but the amount of earing increased with the increase of drawing depth. It was established that inhomogeneous thickness distributions occurred in the part and the highest thickening took place in the curve region.