Formability Parameters Research Articles

Forming limit diagram for Indian interstitial free steels

In this work, the suitability of interstitial free steel sheets of thickness 0.6 and 1.6 mm for press forming operations were examined by obtaining the forming limit diagram. The microstructural aspects, tensile properties and formability parameters were studied. Forming limit diagrams (FLD) were evaluated for the above sheet metals of two different thicknesses and they were compared. Strain distribution profiles were obtained from the forming experiment. The fracture surfaces of the formed samples were observed using scanning electron microscope. Using the fractography, the fracture behaviour and formability were analyzed. The tensile properties and formability parameters were correlated with the FLD. It was found that the formability of both sheets is good and the sheet with 1.6 mm thickness was superior.

Forming limit diagram for interstitial free steels Part I

The suitability of interstitial free (IF) steels of thickness 0.9 and 1.2 mm for press forming operations were examined. The microstructural aspects, tensile properties and formability parameters were studied. Forming limit diagrams were evaluated for the above sheet metals and they were compared. Strain distribution profiles were obtained from the forming experiment. The fracture surfaces of the formed samples were viewed using scanning electron microscope (SEM). Using the fractography, the fracture behaviour and formability were analyzed. The tensile properties and formability parameters were correlated with the FLD. From the analysis, it was found that IF steel having 1.2 mm thickness is superior compared to the other one.

Optimizing homogenization parameters for better stretch formability in an Al–Mn–Mg alloy sheet

The present study examines the effect of homogenization of roll-cast material on the formability and microstructure of Al–Mn–Mg alloy sheets under uniaxial and biaxial deformation modes. The effect of various process variables investigated and an optimized homogenization cycle for improving the stretch formability are presented. The stretch formability of sheets have been characterized in terms of limit strains in forming limit diagrams (FLDs). The phenomenon of recrystallization and the effect of second phase particles have been investigated in cold rolled sheets and the limiting grain sizes at different annealing temperature calculated on the basis of the Zener limit equation. It appears that surface roughening which is in turn a result of grain coarsening is an important formability parameter in the homogenized materials annealed at high temperatures.

Formability analysis of extra-deep drawing steel

In the present work, formability of five sheets of aluminum-killed extra-deep drawing (EDD) low carbon steel sheets (with a wide variation in thickness) has been characterized. Forming limit diagrams (FLDs) have been determined experimentally by conducting punch-stretching experiments using suitably designed and fabricated tools. Formability, observed from FLDs, has been correlated with microstructure, mechanical properties and formability parameters like strain hardening coefficient ( n) and normal anisotropy ( r ̄ ). The strain distribution in the material during punch-stretching under different states of strain has been studied. From the experimental results, it has been found that four of the five sheets have a favorable grain size and mechanical properties to meet the requirements of good formability. The suitability of these sheets for critical deep-drawing applications has been examined in terms of the level and range of critical strains in the FLD. These results correlated well with formability parameters. Earing tendency during drawing is expected to be high for one sheet due to its high planar anisotropy. The level of the FLD increased significantly with the sheet thickness. The effect of n and r ̄ on the strain distribution characteristics has been analyzed.

Optimization of initial blank shape to minimize earing in deep drawing using finite element method

Deep drawing of highly anisotropic sheets causes earing in the formed cup (formation of wavy edge at the top). In the present work, an attempt has been made to study this earing problem in deep drawing of cylindrical cups using a flat bottom punch from extra-deep drawing steel sheets using a finite element method based software LSDYNA. The mechanical properties and the formability parameters of the sheets were determined from the simple tensile tests. These properties along with experimental design parameters were used as input for simulation of deep drawing. Significant earing was observed and it compared with experimentally determined earing (by measuring cup height at several points) with reasonably good accuracy. To optimize the initial blank shape to minimize earing, the flow of material was observed at various steps during the process and accordingly blank shape was modified. Simulation of blanks with modified initial shape showed significant reduction in earing. Experiments were carried out on a 40 t hydraulic press using the modified blank shapes and it has been found that results agreed well with the analysis results.

Effects of strain rate and anisotropy on the tensile deformation properties of extruded AlZnMg alloys

Two extruded AlZnMg alloys have been investigated in uniaxial tension, emphasizing the mechanical anisotropy and strain-rate effects. A strong mechanical anisotropy was found in the extruded profiles which had recrystallized and nonrecrystallized microstructures. The recrystallized alloy had a lower strength level and less variation in ductility and formability parameters than the nonrecrystallized alloy. Mg in solid solution causes dynamic strain aging (DSA) in both alloys. With increasing strain rate, the DSA became less effective and the strain localization caused by DSA vanished. Thus, the room-temperature formability, in the solution heat-treated and quenched condition, may be improved significantly by a sufficient increase of the strain rate. Additional tests on an as-cast sheet-ingot AlMg alloy were performed to isolate the effect of Mg from Zn in solid solution. These tests confirmed the effect of strain rate on the tensile behavior.

Formability of two aluminium alloys

The suitability of two recently developed aluminium alloys (an Al–Mg–Mn alloy and an Al–Li–Cu alloy) for press forming applications has been examined. The characterisation involved the experimental determination of microstructural aspects, tensile properties, and formability parameters such as average plastic strain ratio and planar anisotropy. The forming limit diagram has been experimentally evaluated. A detailed analysis of the strain distribution profiles obtained from punch stretching experiments has been attempted. An attempt has been made to correlate the crystallographic texture with the formability parameters. The fracture surfaces of the punch stretched samples were observed using scanning electron microscopy with a view to obtaining a correlation between fracture behaviour and formability. The alloys, in particular the Al–Mg–Mn alloy, have been found to possess good stretchability but both show very limited drawability. Texture analysis indicated negligible earing during deep drawing. These alloys are suitable for stamping applications where stretching constitutes the major proportion of the deformation.

Influence of inclusion characteristics on the formability and toughness properties of a hot-rolled deep-drawing quality steel

In industrial practice, variations in the steelmaking process may cause significant change in inclusion characteristics. During hot rolling of flat steel products, manganese sulfides, which are plastic at elevated temperatures, are elongated in the rolling direction. These elongated inclusions affect the formability properties, such as ductility, strain hardening exponent, average plastic strain ratio, critical strain represented by the forming limit diagram, and Charpy V- notch (CVN) impact energy as well as fracture behavior. The inclusion characteristics and microstructural features of three commercially produced hot- rolled deep- drawing quality steels were evaluated and their effects on formability and impact properties were investigated. All three heats were made in a basic oxygen furnace. Two heats were teemed into ingots while the other heat was argon purged and continuous cast. These heats were then processed into 3.10 mm thick strips with identical processing parameters. Manganese sulfide stringers were found to reduce the transverse ductility, whereas yield and tensile strengths remained virtually the same in all directions. The formability parameters were not significantly affected by small variations in inclusion characteristics. However, CVN impact energy and impact transition temperature data were observed to improve with steel cleanliness. The sulfide stringers were also found to adversely affect the impact energy, transition temperature, and fracture behavior in the transverse direction.

On the formability of sheet steels

Formability of sheet steel in stamping operation primarily depends on strain hardening exponent (n), average plastic strain ratio (\(\bar r\)) and the maximum strain the material can undergo before the onset of localized necking. The formability parameters (n and\(\bar r\)) and the forming limit diagrams have been evaluated for a variety of sheet steel products, extensively used for press forming of components of diverse shapes e.g. extra deep drawing quality auto-body sheets, high strength cold rolled sheets, LPG steel for gas cylinders, austenitic and ferritic stainless steels, etc. The effect of sulphide shape control on formability of hot rolled HSLA steel has also been studied. Additionally, the press performance of auto-body sheets and austenitic stainless steels have been monitored and evaluated at customer’s end for complete information on the formability.

The development of a computer software system for the prediction of formability parameters of sheet metals form X-ray diffraction data

A computer software for the prediction of formability parameters of sheet metals from X-ray diffraction data has been developed. There are two functional parts in the software system. One of them is to complete the calculation and analysis of the crystallographic texture, and the another is to predict the formability parameters such as the plastic strain ratios, yield loci and Taylor factor from the experimental textures. A new algorithm using Fast Fourier Transform to calculate the crystallite orientation distribution function is used, and the volume fraction of texture components are determined automatically. A conception of cubic equivalent spreading width is proposed to describe the degree of texture spreading and is used for the prediction of the plastic anisotropy of sheet metals. The prediction results agree well with experimental data obtained from an AlCu alloy. The software will be useful for engineers in the quality control and testing of sheet metals in industry.

Measurement of texture and formability parameters with a fully automated, ultrasonic instrument

A fully automatic, ultrasonic instrument to measure texture and formability parameters on metal sheet is described. Arrays of EMAT transducers are used to transmit and receiveS o Lamb waves propagating at 0°, 45°, and 90° with respect to the rolling direction. By analyzing the frequency dependence of the phase of the received signals, the long wavelength limit of the velocities is obtained. Included is a discussion of this algorithm, and subsequent processing steps to predict the ODC'sW400,W420, andW440. On steel, the prediction of drawability parametersr and Δr based on a correlation developed previously by Mould and Johnson is also discussed. Results of blind field trials at facilities of three suppliers/users of steel sheet for automotive applications and one supplier of aluminum sheet for beverage can production are reported. The former confirmed the Mould-Johnson correlation for lowr material but indicated that refinements are needed for modern steels with highr. The aluminum data suggest a correlation between W440 and the degree of four-fold earing.

Contractile strain ratios of textured cp-titanium (Grade II) sheet

The mechanical anisotropy and strain localization were investigated on cp-titanium sheet using grid analysis method which yielded the transverse contractile strain ratios (R,P), formability parameter (B), and critical strains to necking and fracture. Crystallographic texture pole figures were determined using X-ray diffraction (XRD) techniques from which crystallite orientation distribution functions (CODFs) were derived. The anisotropy and formability parameters were evaluated using CODF in conjunction with crystal plasticity models, and are correlated with experimental results.

A Plane Strain Tensile Apparatus

A simple clip-on apparatus has been designed to deform a modified sheet tensile specimen in a state of plane strain. The apparatus consists of a sprung clamp having four knife edges to prevent specimen edge pull-in. Both the plane strain limit strain and fracture strain are obtained from measurements on the fractured sample. Results compare favorably with previously published data. In addition, the apparatus has been used to measure the plane strain formability parameters at non-ambient temperatures.

A theory of plastic anisotropy based on yield function of fourth order (plane stress state)—II

Examples of the yield function of fourth order are shown for commercial Al-killed steel and Cu-( 1 4 ) H sheets. Points in which they differ from the quadratic yield function are shown by illustrations with respect to yield loci and dependence of r-values and uniaxial yield stresses σ a on tensile directions. Comparison of the theories and the experiments shows that r-values by both theories are in good agreement with experimental results, and that σ a is also predicted very well by the fourth-order theory but not so well by the conventional quadratic theory. The theory in the case of planar isotropy is discussed. The yield function contains two parameters − r and X (= equi-biaxial (E.B.) yield stress σ b /uniaxial stress σ n ). For higher r- values the yield locus shrinks on the tension-compression ( T- C) side, but no effect on its E.B. side exists. Enlargement of the yield locus on this side (i.e. texture hardening) is dependent only on a higher X- value and then the T- C side also enlarges a little. Formability parameter Y(= σ b/✓(3)σ s ; where σ s is the yield stress for T- C) and S (= 5 n X which is proportional to ϵ eq at diffuse necking in E.B. tension; with n ̄ the strain-hardening exponent) are proposed with respect to the deep-drawing (and/or combined forming) and stretching, respectively.

Some Considerations on the Formability Parameter in Sheet-Metal Forming

The applicability of the relative load-carrying capacity as a formability parameter is examined for deep-drawing, combined-forming, and pure stretch-forming tests, using various kinds of sheet metals. High correlations are observed between this parameter and the forming depth throughout these forming tests with all of the sheet metals used. In combined-forming the correlations are grouped according to the fracture mode, which are classified into three types: punch profile, intermediate, and wall fracture. The experimental results can be confirmed also by a simple theoretical analysis. Moreover, it is found that the parameters measured in each forming test are markedly correlative.

On new magnetic actions, and on the magnetic condition of all matter

A method for using non-contact infrared thermal imaging for determining the processing history of bulk metallic glass matrix composites (BMGMCs) during semi-solid forging is presented. The technique allows for the first estimations of the relevant parameters associated with semi-solid forging, including the heating profile, forging temperatures, cooling rates, and formability parameters. The processing parameters are correlated with microstructure and a new forging viscosity estimation is developed and compared with other techniques. The research offers a new strategy for thermal measurements that is widely applicable to other manufacturing processes.