Cup Drawing Research Articles

Optimum design of formable CFRP sheets by generic algorithm and FE analysis by homogenization of multilayered structure with macroscopic anisotropy

A new method for designing carbon-fiber-reinforced plastic (CFRP) sheets with a suitable ply structure for stamping is proposed. This method combines a generic algorithm with a three-dimensional finite element method (FEM) to reproduce a layered structure by homogenizing the fiber structure with elastic-plastic anisotropy of each layer. The maximum strain is used as a fracture index to evaluate the severity of sheet deformation under stamping. The ply structure of the CFRP is optimized for elliptic cup drawing, and the optimized ply structure is validated experimentally. Through the experimental validation, it is proven that the proposed method gives acceptable results for the optimization of the ply structure of thermosetting CFRP sheets for cold/warm stamping.

Square-Cup Deep Drawing of Relatively Thick Sheet Metals through a Conical Die without Blankholder

The present study introduces a finite element analysis and experimental verification of the square cup drawing. Experimental results are presented for deep drawing using two different sheet metal; an annealed aluminum (AL99.5w) and brass alloy (CuZn37) having nominal thickness to of 2, 2.5 and 3 mm. The experiments were conducted using a conical die of 18o half cone angle with square aperture at the die exit of 44×44mm and different relative punch/die clearances 1.5, 1.0, 0.9, and 0.8to. The last three values for relative punch/die clearance give nominal simultaneous corrective ironing ratios 0, 10, and 20% respectively. Flat-bottomed square punches with nose radius of 4mm and different sizes of side wall lengths were used. The corner radii for the punch and die aperture were 8 and 10 mm respectively. The experimental and finite element results showed a very good agreement between results of the deep drawing loads, limiting drawing ratios and modes of failures.

Numerical Simulation and Experimental Analysis on the Deep Drawing of Cylindrical Cups

In the deep drawing process, material of blank is transformed into the desired complicated shape by a punch. In this paper, a technique for increasing the drawability of AA1200 aluminium alloy cylindrical cups has been developed. Effects of die and punch geometry including die and punch fillet radius, on limiting drawing ratio (LDR), drawing load with respect to punch stroke and strain of the cup wall have been investigated numerically for optimal process design. A commercial finite element simulation package, ANSYS 14.0, is used in order to determine the optimum limiting drawing ratio. An experimental setup is built accordingly with a half cone angle of 18°. In the experimental and finite element analysis, AA 1200 alloy sheets are used. The effects of the original blank thickness (t = 2 mm) on the various LDR and punch load are numerically investigated. The present process successfully produces cylindrical cups with drawing ratio of 2.64.

Experimental characterization and numerical prediction of ductile damage in forming of AA1050-O sheets

In this paper, a modeling of the deformation behavior of AA1050-O sheets is presented. The modeling of this kind of material is based on various mechanical tests such as tensile, hydraulic bulge, Marciniak and Nakazima deep drawing, as well as cup drawing tests. These tests are performed on planar sheets of 0.5mm thickness. The experimental database obtained from planar specimens is used to identify and validate the material parameters of a large strains elastoplastic model based on Hill׳s anisotropic plasticity criteria and coupled with damage. The identified elastoplastic model is then, implemented as a user subroutine – VUMAT- into the finite elements code ABAQUS, and validated by numerical simulations of the deep drawing tests. The Forming Limit Curves (FLC) are also determined numerically and compared to the experimental data.

Wrinkling during Cup Drawing with NUMISHEET2014 Benchmark Test

Wrinkling occurs when a blank is subjected to compressive stresses during the forming process as in the flange of a cup during drawing. Although the failure limit due to plastic flow localization can be simply defined by the FLC at each point of a continuum, the wrinkling limit cannot be defined with simple variables such as strain, stress, and thickness. Wrinkling is strongly affected by the mechanical properties of the sheet material, the geometry of the tools and blank, and contact conditions. The analysis of wrinkling initiation and growth is, therefore, difficult to perform due to the complex synergistic effects of the controlling parameters. Because of these difficulties, the study of wrinkling has generally been conducted case by case. A unique wrinkling criterion, which could be used effectively for various sheet forming processes, has not yet been proposed. There were many investigations on the effect of process parameters (BHF and friction) and geometry on wrinkling. However, there are few reported results on the influence of the material model on wrinkling. This paper shows how strain hardening and r‐values affect wrinkle formation in its magnitude, initiation, and direction through the NUMISHEET2014 benchmark test for wrinkling during cup drawing.

알루미늄 판재의 다단계 드로잉에 있어서 원통컵의 치수 정밀도 비교

Deep drawing of cylindrical cups is one of the most fundamental and important processes in sheet metal forming. Circular cups are widely used in industrial fields such as automobile and electronic appliances. Some of these cups are formed by a one-stage process, others such as battery cases and beverage cans are made by a multi-stage process. In the current study the multi-stage deep drawing of aluminum sheet metal is examined. The process consists of two deep drawing operations followed by two ironing operations. The press die, which can be used for the four-stage forming process, was manufactured allowing punch and die components to be easily changed for various experiments. The rolling direction of both the sheet and the drawn cups was always positioned toward the horizontal x-direction on the die face to minimize experimental errors during the progressive forming. The dimensional accuracy of the cylindrical cups formed at each stage and the earing defect due to the anisotropy of sheet were investigated. The influence of anisotropy on the thickness distribution was also examined. Both the thickness and the outer diameter of the cups were measured and compared for each set of experimental conditions. It was found that the dimensional accuracy of cups rapidly improves by employing the ironing process and also by increasing the amount of ironing.

Influence of process parameters on deep drawing of AA6111 aluminum alloy at elevated temperatures

To gain a deep insight into the hot drawing process of aluminum alloy sheet, simulations of cylindrical cup drawing at elevated temperatures were carried out with experimental validation. The influence of four important process parameters, namely, punch velocity, blank holder force (BHF), friction coefficient and initial forming temperature of blank on drawing characteristics (i.e. minimum thickness and thickness deviation) was investigated with the help of design of experiments (DOE), analysis of variance (ANOVA) and analysis of mean (ANOM). Based on the results of ANOVA, it is shown that the blank holder force has the greatest influence on minimum thickness. The importance of punch velocity for thickness deviation is 44.35% followed by BHF of 24.88%, friction coefficient of 15.77% and initial forming temperature of blank of 14.995%. After determining the significance of each factor on forming characteristics, how the individual parameter affects characteristics was further analyzed by ANOM.

Study on Yield Function and Plastic Potential Under Non‐Associated Flow for Accurate Earing Prediction in Cup Drawing

Prediction of more than four ears in a cup drawing process can be successfully achieved by considering r‐value and stress directionalities. Yld2004‐18p based on associated flow rule and Yld2000‐2D based on non‐associated flow rule are the examples. The former, however, is more costly in terms of computational efficiency than the latter. In this work, an anisotropic constitutive model based on non‐associated flow rule which combines two different functions, Hill (1948) and Yld2000‐2d, is implemented to a user defined material model. The accuracy of the anisotropic directionalities (yield stresses and plastic strain ratios) is evaluated. Simulation of a mini‐die cup drawing with a body stock alloy predicted eight ears, in good agreement with the experimental results. The use of Hill (1948) model for the yield function and Yld2000‐2d for plastic potential under the framework of non‐associated flow rule led to accurate prediction of up to eight ears at the lower computational cost.

An evolving plane stress yield criterion based on crystal plasticity virtual experiments

This paper presents a new hierarchical multi-scale framework that allows taking into account evolution of the plastic anisotropy during sheet forming processes. The evolution of crystallographic texture, which is identified as the main source of the plastic anisotropy, is predicted by the ALAMEL crystal plasticity model. An extension to the phenomenological anisotropic plane-stress yield criterion BBC2008 is proposed, which provides adaptive updates of the local anisotropy in the integration points of the macroscopic finite element model. To this end, the BBC2008 is systematically recalibrated to data provided by the crystal plasticity virtual experiment framework (VEF). An enhanced identification algorithm is proposed. The new algorithm exploits comprehensive material characterization delivered by the VEF.The deep drawing of cylindrical cups is used as a benchmark case. An industrial-grade aluminium alloy AA6016 is chosen for the test case. The experimental part of the study includes X-ray diffraction measurements of the texture as well as mechanical testing, which comprises uniaxial tensile tests, a bulge test and the deep drawing of cylindrical cups. A noticeable through-thickness gradient in terms of both the texture and the plastic anisotropy is identified in the initial material. This issue is taken into consideration in the study.Three groups of simulations have been performed, in which (i) the BBC2008 was calibrated by means of the mechanical tests, (ii) the BBC2008 was calibrated by means of the VEF based on the initial texture, but kept constant throughout the simulation, and (iii) the BBC2008 was systematically recalibrated by means of the VEF to reflect the effects of texture evolution. The earing profiles measured in the experimentally drawn cups are compared to the ones predicted by the simulations. It is found that the cup profile predictions by (i) are clearly inferior compared to both (ii) and (iii). However, in the considered process (iii) provides only a moderate improvement over the results of (ii). The explanation of this limited impact of the anisotropy evolution is based on the analysis of the evolved texture and associated plastic anisotropy.

Study of Earing Defect during Deep Drawing Process with Finite Element Simulation

Deep drawing is one of widely used sheet metal working process in industries to produce cup shaped components at a very high rate. In deep drawing process, a sheet metal blank form cylindrical components by process in which central portion of sheet is pressed into die opening to draw the metal into desired shape without folding the corners. Earing is one of the major defects observed during deep drawing process due to anisotropic nature of sheet metal. Earing is defined as formation of waviness on uppermost portion of deep drawn cup. Knowledge about ear formation in deep drawing process allows a prior modification of process which can result in defect free final product with financial saving and time. The initial blank shape used in present study is circular in nature.The objective of present study aims to produce parts which are earing defect free. Earing can be reduced by modifying the initial blank shape such as use of non circular blank as in present study. Efforts have been made to study the earing problem in deep drawing of cylindrical cups by finite element modeling software HYPERWORK-12 and Incremental RADIOSS as solver. The blank material selected for study is EN10130FeP06 mild steel sheet of 1mm thickness as it has wide application in fabricating automobile parts. Mechanical parameters of mild steel are incorporated in finite element simulation of deep drawing process. Significant earing was observed at rolling and transverse direction on deformed cup form circular blank. Modification of initial blank is done to reduce the earing defect. The results show significant reduction of % earing height and drawing load as well as improvement in maximum thickness variations.

Experimental and Numerical Investigation on a Pressure Dependent Friction Model

The objective of this paper is the investigation of the implemented pressure dependent friction model in the FE simulation program AutoForm. Since the values for the required parameters of this approach are not defined in the actual FE simulation program, this paper contributes to a first definition of these parameters. Therefore, experimental investigations with the cup drawing tests are carried out. With the support of the experimental results regarding the maximum stamping force, the model is calibrated and subsequently validated by the comparison of the sheet thicknesses of the experimental and numerical investigations. The results of this validation reveal a good accordance of simulation and reality in nearly all areas. However there are also areas in which the prediction accuracy decreases in comparison to the basic simulation. Therefore, additional investigations have to be carried out which concentrate on the modification of this pressure dependent approach towards a better universal prediction accuracy of the simulation.

Characterization of mechanical property of magnesium AZ31 alloy sheets for warm temperature forming

A method based on the numerical inverse approach to characterize the mechanical property of the Magnesium AZ31 alloy sheet for warm temperature forming was discussed in this work. In particular, temperature-dependent hardening and strain rate sensitivity were characterized based on uniaxial tensile test data measured at between 100°C and 300°C with the interval of 50°C. Hardening deterioration associated with micro-void development as well as dynamic recovery and dynamic re-crystallization, observed beyond the uniform deformation limit, was also accounted for. Importance of the proper characterization of the hardening deterioration was confirmed by validating the failure by strain localization in the circular cup drawing test under the warm forming condition. With mechanical behavior properly described, failure with strain localization was predictable without referring to forming limit diagram but directly evaluating strain localization for material elements in this work. Uniaxial compression tests were also performed at various temperatures below 200°C to assess asymmetric behavior in tension and compression.

Local Reversion of Cold Formed AISI 301LN

This study demonstrates applying laser heat treatment for reversion treatments of cold-formed AISI 301LN. Sheets were cold- rolled to final thicknesses of 1.5 and 3mm (65pct reduction), having martensite fraction of 70-95%. Sheets were heated locally by a laser beam to various peak temperatures to obtain different degrees of martensite reversion to austenite. Mechanical properties and formability of grain-refined and coarse-grained structures were measured by tensile, bending and Erichsen cup tests. In addition to standard Erichsen cup test, additional interrupted tests were carried out, where cups were first stretched close to the critical strain. Drawn cups were then heated locally by a laser beam to revitalize the structure and thereby enhance the formability in the following cupping test until failure.Various structures were produced: completely reverted microstructures (T > 700°C) with grain sizes 0.9 - 2μm in addition to partially reverted structure (T < 700°C) containing nano- and ultrafine-grained austenite (0.6μm) with some martensite. Results showed that local laser heat treatment is suitable for the reversion treatment to refine the austenite grain size. Refinement of the austenitic structures increased strength properties and the formability was better than with coarse grained structures having the same strength. Especially the yield strength was significantly enhanced, being around 900MPa in the strongest reverted structure compared to the 300-400MPa of the coarse grained austenitic structure. It was demonstrated that the local laser treatment restored formability of the drawn cups, allowing stretching to be continued.

An experimental and numerical study of micro deep drawing of SUS304 circular cups

Micro deep drawing is a promising technology for mass production of complex 3D micro metal products. Significant size effects at a micro scale, however, obstruct application of this technology and block utilisation of traditional finite element method (FEM). Therefore, a micro tensile test system was developed to obtain accurate material properties considering size effects. Subsequently, a Voronoi blank model was developed for the micro scale simulation. Moreover, micro deep drawing experiments were conducted and their results were compared with the simulation results. The simulation results have a good agreement with the experimental data. Furthermore, the wrinkling at the cup mouth increases with the growth of grain sizes on the SUS304 sheets.

Investigation of Hot Formability of AZ61 Mg Alloy

High temperature mechanical properties and formability of the AZ61 magnesium alloy are evalu-ated in this paper. Tensile tests were conducted to obtain the formability parameters at elevated temperatures of up to 400℃. The results showed that at higher temperature, yield strength and ultimate tensile strength of the material decrease significantly, while the material experiences an increase in ductility (maximum elongation before break). A model has been created in finite ele-ment software Abaqus to further study the deep drawability of the AZ61 Mg alloy. Effects of dif-ferent process parameters such as punch and die geometry, forming speed and temperature as well as blank-holder force on square cup drawing of the AZ61 alloy were investigated and optimum process parameters are obtained which can be used as a design guide in sheet metal forming industry.

407 凹凸形状肩部のダイを用いた深絞り容器の波面形成

407 凹凸形状肩部のダイを用いた深絞り容器の波面形成

Earing and Anisotropy Indices of Texture Components in the Hot-Rolled 3104 Alloy

The paper describes an experimental verification of a previously proposed formula establishing the relationship between the crystallographic parameters of a rolled sheet and the anisotropy index in a hot-rolled aluminum alloy. The main texture components were identified in the hot-rolled 3104 alloy using the X-ray structure analysis. The crystallographic parameters and anisotropy indices were then calculated both for the entire workpiece and for each individual texture component. The earing level of the hot-rolled workpiece was determined using the process of cylindrical cup drawing. Cup formation was also simulated using the finite element software package PAM STAMP. The earing data obtained through t simulation were compared with experimental results. For the validation of the calculations the hot-rolled workpiece anisotropy indices were also experimentally determined.

Mechanical property of magnesium alloy sheet with hardening deterioration at warm temperatures and its application for failure analysis: Part II – failure analysis

The mechanical properties of a thin AZ31B Mg alloy sheet (with the thickness of 0.5 mm) were characterized for its anisotropy, temperature-dependent hardening (including its deterioration) and strain rate sensitivity based on simple tension test data measured at 100 °C, 150 °C, 200 °C, 250 °C, respectively, in Part I. As for anisotropy, simple tension tests were performed along three (rolling, transverse and in-between) directions to calibrate the Hill1948 yield function. As for temperature-dependent hardening, hardening as well as its deterioration (or softening) behavior observed beyond the uniform elongation limit was numerically characterized based on the inverse calibration method, in which strain rate sensitivity was also considered. The mechanical properties were confirmed to properly predict failure by strain localization for all the simple tension tests involved in the characterization procedure. Ultimately, the mechanical properties characterized in Part I were applied in Part II to analyze the failure by strain localization in the cross-shaped cup drawing tests developed as the benchmark problem for the NUMISHEET2011 conference [1]. The results showed that the mechanical properties with hardening deterioration properly predicted failure, while hardening without deterioration (obtained following the common practice) did not, confirming the importance of including the hardening deterioration in tensile property characterization, especially to predict forming failure by strain localization.

Mechanical property of magnesium alloy sheet with hardening deterioration at warm temperatures and its application for failure analysis: Part I - property characterization

The mechanical property of a thin AZ31B Mg alloy sheet (with the thickness of 0.5 mm) was characterized for its anisotropy, temperature-dependent hardening (including its deterioration) and strain rate sensitivity based on simple tension test data measured at 100 °C, 150 °C, 200 °C, 250 °C, respectively, in Part I. As for anisotropy, simple tension tests were performed along three (rolling, transverse and in-between) directions to calibrate the Hill1948 yield function. As for temperature-dependent hardening, the common practice is to characterize hardening only up to the uniform elongation limit and to extrapolate the data to cover the range beyond its limit. In this work, hardening as well as its deterioration (or softening) behavior observed beyond the uniform elongation limit was numerically characterized based on the inverse calibration method, in which strain rate sensitivity was also considered. The mechanical properties were confirmed to properly predict failure by strain localization for all the simple tension tests involved in the characterization procedure. Ultimately, the mechanical properties characterized in Part I were applied in Part II to analyze the failure by strain localization in the cross-shaped cup drawing tests developed as the benchmark problem for the NUMISHEET2011 conference [1].

초음파 진동 딥 드로잉 공정에서의 마찰감소효과 분석을 위한 유한요소해석 및 실험

The current study presents experimental and numerical results on the effect of ultrasonic vibrations on a cylindrical cup drawing of a cold rolled steel sheet(SPCC). An experimental apparatus, which can superimpose high frequency oscillations during deep drawing, was constructed by installing on the tooling ultrasonic vibration generators consisting of a piezoelectric transducer and a resonator. Conventional and vibration-assisted cylindrical deep drawing tests were conducted for various drawing ratios, and the limiting drawing ratios(LDR) for both methods were compared. To evaluate quantitatively the contribution from the ultrasonic vibrations to the reduction of friction between tools and material finite element analyses were conducted. Through a series of parametric analyses, the friction coefficients, which minimized the differences of punch load data between the experiments and simulations, were determined. The results show that the application of ultrasonic vibration effectively improves the LDR by reducing the friction between the tools and the material.