Deep Drawing Tests Research Articles

Thermal-mechanical behaviors of dual-phase steel sheet under warm-forming conditions

This paper examined the thermal-mechanical behaviors of the given dual-phase (DP) steel sheet at warm-forming temperatures (20–190°C). The dynamic strain aging effect of the given material was observed via thermal-uniaxial tensile tests and the temperature-dependent flow stress function was then established. Moreover, the biaxial tensile tests at series of elevated temperatures were also carried out and the corresponding experimental yield loci were then determined by utilizing the concept of plastic work contour. For the convenience of characterizing the thermal-mechanical yielding behaviors of the given material, a temperature-dependent Yld2000-2d yield criterion was proposed in this work, of which the exponent and anisotropic parameters were replaced by the nonlinear fitting functions expressed in terms of temperature. Afterwards, the proposed model, together with other existed constitutive models, were programmed as user subroutines VUMAT in ABAQUS with ‘NICE’ explicit integration algorithms. The cylindrical deep drawing tests under warm forming conditions and corresponding FEM simulations were then conducted to assess the precision of the proposed model.

Comparative study on drawability of CR340/CFRP composites by using theoretical and experimental methods

In this study, a hybrid composite material was fabricated by stacking carbon fiber-reinforced plastic on CR340 plates to increase the specific strength and specific stiffness, compared to thick boron steel plates or dual-phase steels. A deep drawing test was conducted for this hybrid composite material, using various blank holding force, to assess its formability and potential use in vehicle parts. After experiment, the results of formability were compared with analysis data by using ABAQUS explicit. The formability was then assessed according to the blank holding force and friction coefficient. The friction coefficient decreased with increasing Bf. After deep drawing, the epoxy flow behavior was examined. Problems with the metal/CFRP hybrid composites were investigated through macroscopic and microscopic observations.

テキスタイルグリーンコンポジットの熱成形解析における有限要素モデリングとその実験的検証

A new finite element model of textile green composites is proposed to simulate thermoforming process in this study. The model is assembled with actual configuration of the green composites and the interface between yarn and matrix has certain GAP. The mechanical behavior of yarn was considered by using truss element. To verify these models, deep drawing tests were performed with experiment. As a result, orientation of yarn and thickness of drawn cup agreed with experiment well. After this process, strength of drawn cup was evaluated with compression test in both finite element method (FEM) and experiment. In FEM, to remove GAP between yarn and matrix, tied contact method that adjust the unconformity of mesh was used. The deformation behavior of the drawn cup agreed with experiment. The effectiveness of thermoforming process to design products with FEM was verified.

Evaluation of deep drawing force under different friction conditions

The purpose of this study is to investigate the variation of the required punch load during the deep drawing process under different friction conditions. In this regards, several deep-drawing tests of cylindrical cups were conducted under four friction conditions at the tool–blank interface. The first case was the dry deep-drawing, considered as a reference friction condition, while in the other three cases hydraulic oil, lithium-based grease and animal fat were used as lubricants. For each friction case, three levels of blank holding force were adopted, namely 10, 20 and 25 kN. The finite element simulation of the deep-drawing process was used to generate a set of calibration curves. By overlapping the experimental load-stroke curves on the calibration curves, the friction coefficient was estimated for each friction case.

Improvement in Material Flow During Nonisothermal Warm Deep Drawing of Nonheat Treatable Aluminum Alloy Sheets

Automotive industries are very much interested in implementing warm forming technology for fabrication of light weight auto-body panels using aluminum alloys without localized thinning or splitting. A nonheat treatable and low formable AA5754-H22 aluminum alloy sheet was selected in the present work, and a laboratory scale warm deep drawing test set-up and process sequences were designed to improve material flow through independent heating of punch and dies. Significant enhancement in cup depth was observed when the temperature of punch and dies were set to 30 °C and 200 °C, respectively. Thermo-mechanical finite-element (FE) model of the nonisothermal deep drawing test was developed successfully to study the improvement in material flow incorporating Barlat-89 yield theory using temperature dependent anisotropy coefficients and Cowper–Symonds hardening model. It was found that a nonisothermal temperature gradient of approximately 93 °C was established within the blank from the center to flange at the start of deformation, and subsequent evolution of temperature gradient helped in improving material flow into the die cavity. The effect of temperature gradient on forming behavior in terms of cup height, ear profile, and thinning development across flange, cup wall, and blank center were predicted and validated with experimental results.

Measurement of Coefficient of Friction in Hot Stamping by Hot Deep Drawing Test

Hot stamping process has been developed to produce the steel automobile parts with an ultra-high-strength of 1500 MPa. The effect of scale thickness on the formability in hot stamping was investigated by a hot deep drawing test in our previous research. The draw-in lengths of flange increased with decreasing the scale thickness. It is supposed that thin scale thickness resulted in low coefficient of friction at the flange area. The other reason is the temperature of wall zone would become low according to decreasing the scale thickness or increasing of the thermal transfer coefficient and it slightly inhibits local deformation at the wall area. It is difficult to separate these phenomena. To quantify the effect of scale thickness on the friction at the flange area during hot deep drawing, the coefficient of friction was directly measured. The coefficient of friction decreases with decreasing scale thickness.

Characterisation and full-scale production testing of multifunctional surfaces for deep drawing applications

Full-scale deep drawing tests using tools featuring multifunctional surfaces are carried out in a production environment. Multifunctional tools display regularly spaced, transversal grooves for lubricant retention obtained by hard-turning, separated by smooth bearing plateaus realized by robot assisted polishing. Advanced methods are employed to characterise the tools’ surface topographies, detecting the surface features and analysing them separately according to their specific function. Four different multifunctional dies as well as two un-textured references are selected for testing. The tests are run using a non-hazardous, environmentally friendly lubricant, and the forming forces are constantly recorded. Multifunctional dies exhibit very good performances, with no galling occurrence and punch forces generally lower than the two references.

Analysis of Square Cup Deep-Drawing Test of Pure Titanium

The prediction of formability of titunium is more difficult than steels since its strong anisotropy. If computer simulation can estimate the formability of titanium, we can select the optimal forming conditions. The purpose of this study was to acquire knowledge for the formability prediction by the computer simulation of the square cup deep-drawing of pure titanium. In this paper, the results of FEM analsis of pure titanium were compared with the experimental results to examine the analysis validity. We analyzed the formability of deepdrawing square cup of titanium by the FEM using solid elements. Compared the analysis results with the experimental results such as the forming shape, the punch load, and the thickness, the validity was confirmed. Further, through analyzing the change of the thickness around the forming corner, it was confirmed that the thickness increased to its maximum value during forming process at the stroke of 35mm more than the maximum stroke.

Effect of cycloaliphatic structure of polyester on the formability and stone-chip resistance for automotive pre-coated metals

Abstract Four types of cycloaliphatic structure of polyester were synthesized, using 1,4-cyclohexanedicarboxylic acid (1,4-CHDA). Those resins were formulated to make polyester/melamine coatings to control the formability, and to have good stone-chip resistance. The characteristics, viscoelastic behavior and flexibility of those resins were measured by DMA and tensile test. Cycloaliphatic structure of polyester coatings were coated on the cold roll steel sheets to verify formability, using a deep drawing test and stone-chip resistance was measured by the chipping resistance test at the −20 °C. Results showed that storage modulus decreased, and glass transition temperatures shifted to lower temperatures with increasing contents of cycloaliphatic structure. So, cycloaliphatic structure of 1,4-CHDA provides lower stiffness and higher softness to the polyester coating and has better elasticity than aromatic structure of IPA. To analyze the formability, we calculated F U (the forming coefficient based on strain energy) and F e (the forming coefficient based on strain). When F U and F e are both larger than 1, the polyester coatings have good formability. Also, BCHDA-20 had 0.44% of removed area by the chipping resistance test and it means that cyclic structure of 1,4-CHDA has better elasticity than aromatic structure, and can give better impact resistance From those tests, BCHDA-20 which had 20 mol of 1,4-CHDA had good formability and also showed good stone-chip resistance. So, cycloaliphatic structure provides lower stiffness and higher softness to the polyester coating for automotive pre-coated metals.

Effect of plastic anisotropy of ZK60 magnesium alloy sheet on its forming characteristics during deep drawing process

The plastic anisotropy of a ZK60 magnesium alloy sheet was investigated using uniaxial tensile tests and deep drawing tests. The earing behavior of the sheet during deep drawing was studied by both experimental and finite element analyses. The ZK60 alloy sheet exhibits higher plastic strain ratio (r) value in 45° than those in 0° and 90° to rolling direction, and the r value decreases with temperature increasing in various loading directions. A negative planar anisotropy (△r) value results in earing in 45° to rolling direction. Higher absolute value of △r leads to larger average earing ratios. With drawing ratio (DR) increasing, the average earing ratio first increases to a peak and then drops, showing a bell-shape curve. The average earing ratio of cylindrical drawn cup increases as the deep drawing proceeds. At the shoulder region of drawn cups, the most reduction in thickness strain occurs in 45° to rolling direction of the sheet. At the necking region, the minimum thickness strain in 0° is lower than those in 45° and 90° directions. At the thickening region, the minimum thickness strain in 45° is lower than those in 0° and 90° directions due to the large circumferential compression stress and the large negative value of planar anisotropy △r value.

Effect of through thickness strain distribution on shear fracture hazard and its mitigation by using multilayer aluminum sheets

The formability of sheet metal is generally accepted to be limited by the so-called Forming Limit Curve (FLC). This is valid for a majority of operations, given that localization immediately precedes fracture. For the characterization of the latter, a microscopy based new method is applied on Nakazima specimens. Furthermore a simple cup deep drawing test is employed to investigate the shear failure phenomenon and extend the fracture limit in the left hand side of the principal strain space. In addition, fracture phenomenon in aluminum alloy AA6016 sheet sample is investigated by using different fracture criteria. The measured principal fracture strains ɛ11f and ɛ22f are then implemented in the FE-code to predict rupture. Moreover, initiation and propagation of cracks in monolithic and multilayer aluminum alloys, are studied. A newly designed triangle shape deep drawing part is used in the framework of this work to validate the constitutive and failure models as well as investigate the advantage of a multilayer material, compared to the monolithic one.

Constitutive modeling of evolving plasticity in high strength steel sheets

In this paper, biaxial tensile tests with cruciform specimens were conducted to obtain the experimental plastic work contours of DP590, DP780 and DP980 sheets. It was found that for high strength dual phase steel sheets, the outlines of the experimental work contours in the first quadrant evolve evidently with the increase of plastic dissipation. In order to calibrate the evolving isotropic and anisotropic plastic behaviors simultaneously, the Yld2000-2d yield criterion with variable exponent and coefficients (Yld2000-2d-Var) was introduced. In this model, the exponent m and coefficients αi of the Yld2000-2d was assumed as the function of the equivalent plastic strain. The identification procedures of the introduced parameters were then proposed based on minimizing the difference between the experimental and the model predicted yield points, using Levenberg–Marquardt optimization method. Afterwards, the proposed model was implemented into ABAQUS as user subroutine VUMAT with semi-implicit back-Euler integration algorithm. The numerical simulations of hydro-bulging and cylindrical deep drawing tests were then carried out to verify the validity of the proposed model. The results showed that the proposed model could enhance the predicting accuracy in both tests due to its flexibility.

Experimental investigation on electrically assisted cylindrical deep drawing of AZ31B magnesium alloy sheet

The effect of the electric pulses on the ductility of AZ31B magnesium alloy sheet was studied through cylindrical deep drawing test. In order to show the advantages of the electric pulses during this test, deep drawing tests both at room temperature and at elevated temperatures induced by the electric pulses were carried out using the self-designed device which only allows the electric pulses flow through the flange and die corner regions. The result shows that as temperature rises, the limit of the deep drawing depth increases. The limit of the deep drawing depth increases even faster when the temperature is more than 373 K. Moreover, to find out whether the athermal effect exists or not in this process, experiments with only varying the current frequency and peak current at the same temperature were conducted. The result confirms the existence of the athermal effect. Microstructure evolution analysis shows that the dynamic recrystallization induced by the electric pulses at a relatively lower temperature facilitates the ductility improvement.

Influence of temper on the performance of a high-strength Al–Zn–Mg alloy sheet in the warm forming processing chain

Al–Zn–Mg aluminium alloys have greater strength than conventional aluminium alloys used in the automotive industry, but little has been reported on their formability and paint bake response. In this paper the strength and formability of age-hardenable AW-7921 alloy sheet across a range of tempers from the under-aged to peak-aged condition is investigated by warm tensile tests at temperatures between room temperature and 230°C, and cross-die deep-drawing tests at 230°C. Differential scanning calorimetry (DSC) was used to study the precipitation states of the AW-7921 sheet in the as-received and warm cross-die deep-drawn conditions. Formability was found to improve at 230°C and was sensitive to the initial temper of the sheet. Light aging for 10min at 100°C resulted in only GP Zones present in the sheet, while both GP Zones and η’ precipitates formed after a subsequent moderate aging at 120°C for 50min. Dynamic recovery and the partial dissolution of precipitates were found to contribute to the increase in formability at elevated temperatures. Across the tempers investigated, the T4 temper has shown the best combination of warm formability and high post-paint baking strength.

Microstructures and failure analyses of DP980 laser welded blanks in formability context

In the present study, Erichsen cup height and limiting drawing ratio of fiber laser welded DP980 blanks were compared with respect to that of parent metal to understand the role of deformation mode in formability context. The strain localization was observed consistently at the outer heat affected zone (HAZ) during both the tests in laser welded blanks with failure propagated in radial direction and parallel to the weld. The microstructure development in the outer HAZ was analyzed by SEM, TEM and instrumented nano-indentation. The SEM images of the necked region revealed void initiation at the interface of ferrite and martensite due to heterogeneity in properties between the phases. The TEM bright field images with SAD analysis confirmed tempering of martensite and carbide precipitation accompanied with reduction in hardness in the outer HAZ, referred as soft zone (SZ). FE simulation results considering local weld properties revealed strain localization and subsequent failure under plane strain deformation mode due to the presence of the SZ in both Erichsen cup and deep drawing tests. It was found that the reduction in formability due to the presence of SZ was not severe in deep drawing process as compared to the stretch forming test. This was due to the difference in thickness distribution and thinning development in the blanks deformed under different stress and strain states inherited from the tool geometry.

Development of new lubricants for hot stamping of Al-coated 22MnB5 steel

The use of lubricants is effective for decreasing the forming load in hot stamping of Al-coated 22MnB5 steel. It is desired that new lubricants for hot stamping are developed. In this study, first, the coefficients of friction were measured using commercial lubricants for hot forging with the hot flat drawing simulator. The coefficient of friction of a commercial lubricant that consisted of a hydrophilic polymer and a mineral salt was the lowest. Second, lubricants with added different solid lubricants were newly developed and their coefficients of friction were measured. The coefficient of friction of the lubricant with added swellable mica was the lowest. Third, the formability of Al-coated 22MnB5 steel using the newly developed lubricant was examined with the hot deep drawing test machine and its formability was superior. A new high-performance lubricant for hot stamping was developed.

Formability and strengthening mechanism of solution treated Al–Mg–Si alloy sheet under hot stamping conditions

Aluminum alloy hot stamping has been developed to improve formability and avoid thermal distortion by combining hot forming and quenching in one operation in recent years. In order to investigate the effects of heating temperature on formability and strengthening of a solution treated Al–Mg–Si alloy sheet, uniaxial tensile test, deep drawing test and free bulging test were carried out at temperatures ranging from 25 to 500°C. The corresponding strengthening behavior was reflected by Vickers hardness measurement and microstructure was observed to clarify the strengthening mechanism with electron backscattering diffraction and scanning electron microscope methods. It was found that the fracture strain and limiting bulging height increased significantly until the temperature was elevated to 400°C. The limiting drawing ratio increased as temperature rose to 200°C and decreased afterwards. The hardness changed with temperature increasing, two peak hardness appeared at 200 and 500°C. The maximum hardness could arrive at 115HV. Formation of coarse β′ precipitates resulted in the decrease in hardness at temperatures ranging from 250 to 450°C. Enhanced formability and strength were obtained simultaneously at 200 and 500°C, either of which can be chosen as appropriate forming temperatures for hot stamping.

Design, Fabrication, and Experimental Validation of a Warm Hydroforming Test System

In this study, a hydroforming system was designed, built, and experimentally validated to perform lab-scale warm hydromechanical deep drawing (WHDD) tests and small-scale industrial production with all necessary heating, cooling, control and sealing systems. This manuscript describes the detailed design and fabrication stages of a warm hydroforming test and production system for the first time. In addition, performance of each subsystem is validated through repeated production and/or test runs as well as through part quality measurements. The sealing at high temperatures, the proper insulation and isolation of the press frame from the tooling and synchronized control had to be overcome. Furthermore, in the designed system, the flange area can be heated up to 400 °C using induction heaters in the die and blank holders (BH), whereas the punch can be cooled down to temperatures of around 10 °C. Validation and performance tests were performed to characterize the capacity and limits of the system. As a result of these tests, the fluid pressure, the blank holder force (BHF), the punch position and speed were fine-tuned independent of each other and the desired temperature distribution on the sheet metal was obtained by the heating and cooling systems. Thus, an expanded optimal process window was obtained to enable all or either of increased production/test speed, reduced energy usage and time. Consequently, this study is expected to provide other researchers and manufacturers with a set of design and process guidelines to develop similar systems.

Characterization of Tensile Properties, Limiting Strains, and Deep Drawing Behavior of AA5754-H22 Sheet at Elevated Temperature

Automotive industries are very much interested in characterization of formability improvement of aluminum alloys at elevated temperatures before designing tools, heating systems, and processing sequences for fabrication of auto-body panels by warm forming technology. In this study, tensile tests of AA5754-H22 aluminum alloy were carried out at five different temperatures and three different strain rates to investigate the deformation behavior correlating with Cowper-Symonds constitutive equation. Laboratory scale warm forming facilities were designed and fabricated to perform limiting dome height and deep drawing tests to evaluate forming limit strains and drawability of sheet metal at different tool temperatures. The forming limit strain and dome height improved significantly when both the die and punch were heated to 200 °C. Remarkable improvement in deep drawn cup depth was observed when die and punch temperatures were maintained at 200 and 30 °C, respectively, producing a non-isothermal temperature gradient of approximately 93 °C across the blank from flange to center. The forming behavior at different isothermal and non-isothermal conditions were predicted successfully using a thermo-mechanical FE model incorporating temperature-dependent properties in Barlat-89 yield criterion coupled with Cowper-Symonds hardening model, and the thinning/failure location in deformed cups were validated implementing the experimental limiting strains as damage model.

Compound deep drawing and extrusion process for the manufacture of geared drum

A compound deep drawing and extrusion process was proposed in this study to produce the part like geared drum on a servo-controlled press. To improve the formability of the proposed process, the influences of various slide motions like speed motion, oscillation motion, and step motion, on the material performance were studied based on simple standard tensile test and deep drawing tests. And then, specific designed oscillation motion and step motion were adopted in compound deep drawing and extrusion process to evaluate their feasibility. The results showed that by setting a step motion at an early stage of the process, the part could not only achieve high surface quality but also reduce the extent of thickness reduction of the material.