Axisymmetric Drawing Research Articles

Microstructural evolution and mechanical behavior of pearlitic steel under multi-directional forging

The mechanical behavior and the microstructural evolution of a pearlitic SAE 1080 steel were analyzed along 12 Multi-Directional Forging (MDF) cycles at room temperature and strain amplitude Δε ≈ 0.30 (MDF0.30). The resulting cumulative strain flow curve is typical of metals undergoing extensive dynamic recovery, displaying appreciable work hardening up to a strain εt ≈ 0.9, followed by a very low work hardening, where flow stress rises from ≈1400 MPa to ≈1510 MPa. Similarly, the microhardness raises up to a total cumulative strain εt ≈ 1.8 and seems to stabilize for further straining, reaching ∼3626 MPa after εt ≈ 10.8. Conversely, yield strength initially rises and then falls remarkably after εt > 5.4. This behavior is related with directional cross effects that favor dynamic recovery as the total applied strain increases. These results differ remarkably from those connected to a monotonic deformation process such as axisymmetric drawing. In addition, directional cross effects decrease the material yield stress as the total applied strain increases. Microstructural results revealed that MDF0.30 leads to increasing shearing, bending and fragmentation of the cementite lamellae into particles <50 nm in diameter dispersed in the ferritic matrix as the total imposed strain rises. As a consequence, only limited alignment and changes in the cementite interlamellar spacing are observed, up to a total applied strain ≈10.8. It is considered that the work hardening of pearlitic steel deformed through MDF0.30 is dominated by the dynamic recovery of the interlamellar ferrite and a limited contribution from the cementite. Such results have never been reported in the literature and are of practical importance, since extensive cold working of eutectoid steel through MDF can be performed with standard presses and large specimens.

Corrugation prediction in process of sheet drawing based on the results of modeling in the DEFORM environment

In a process of sheet drawing technology developing, the probability of workpiece buckling during deformation and the necessity of blank holder using to prevent corrugation, is estimated in accordance with the recommendations of the reference book. However, reference literature does not have clear recommendations, or it gives contradictory recommendations for blank holder use cases for some deformation conditions. In these cases, problem solving requires additional experimental research. Possibility and efficiency establishing of computer simulation using DEFORM environment of axisymmetric drawing processes to forecast the buckling of a thin-sheet workpiece during deformation. Technological processes of sheet drawing with a high probability of workpiece buckling were investigated by means of finite element computer simulation in DEFORM 3D. Research has established that simulation of thin-sheet workpiece drawing process in DEFORM 3D, allows to visualize the process of corrugation, and predict workpiece buckling with high probability, provided that the deformation occurs relatively simple geometry of the workpiece and deforming tool. In more complex deformation conditions, the experiments results, and computer simulation may differ (simulations may not indicate corrugation). This somewhat complicates corrugation prediction, but the problem is solved by an extended analysis of the stress-strain state and workpiece behavior in the deformation zone. The emergence of areas in the workpiece with an unpredictable and uncontrolled contact loss of the workpiece material with the deforming tool, or appearance of areas with significant irregular velocity of workpiece points movement, clearly indicates problem areas with high probability of corrugation in the real sheet drawing process. Obtained results allow to increase the efficiency of expecting places of corrugation appearance prediction by means of computer simulation of sheet drawing process in the DEFORM 3D environment.

Axisymmetric Drawing of Parts from Brass Sheets with Regulated Thinning

This paper describes the results of a study that looked at the effect of the dimensions and mechanical properties of L63 brass alloy sheets on the drawing forces and the dimentions of axisymmetrically drawn tubs. Specifically for tubs made of L63 brass, the paper presents a number of different options in terms of the actual process and the pre-hardening parameters for sheet metal. Computer modelling was performed based on the results of pilot passes conducted on a two-high mill 350&times;450 operated by Kolchugino Non-Ferrous Metal Working Plant. For this, 380&times;380 mm square 1.5&ndash;1.7 mm thick sheets with accumulated strain were driven through the mill, and the workpieces were turned around before the second pass. Due to varying properties of annealed sheets, the yield strength doubled rising from 145 to 280 MPa, whereas the plasticity dropped. The simulation study helped determine that as pre-deformed material becomes 10 % harder, it tends to form more evenly in the Tub stamping operation with L63 brass material used. At the same time, the thinning effect in critical areas decreases. Due to this process solution, the workpiece thickness could be decreased from 1.7 to 1.6 mm. The reduced thinning of the round part is combined with a slight thickening of the flange edge. The paper also decribes a drawing option which could help save half of the required operations due to a 5 mm bigger diameter of the workpiece (leading to an only 3% increase in the surface area of the workpiece). Due to the use of pre-hardened sheet metal, one can avoid big cross-sectional thickness variations in axisymmetrically drawn parts. To implement this process, one is advised to use a single-action press of the P2228A type designed for 630 kN.

Analytic Methods of Flange Deformation Region in Axisymmetrical Drawing Process

Analytic Methods of Flange Deformation Region in Axisymmetrical Drawing Process

Incorporation of a Fracture Criterion in Ideal Flow Design

The theory of sheet and bulk ideal plastic flows is used for the preliminary design of metal forming processes. The present paper develops an approach to incorporate the Cockroft and Latham ductile fracture criterion in this design method for stationary bulk flows. In particular, it is demonstrated that the initiation of ductile fracture can be predicted without having the ideal flow solution for stress and strain in the plastic zone (it is only necessary to know that the solution exists). Using the approach proposed the initiation of ductile fracture in axisymmetric drawing is predicted.

A new method for predicting drawing load of shape drawing process

The shape drawing process is a very useful metalworking process that can produce an elongated component with a constant cross-sectional shape. The prediction of drawing load is critical for evaluating the potential of shape drawing. However, it is challenging to predict the drawing load of shape drawing because of the complex cross-sectional shape of the drawn material. In this study, a new theoretical method is proposed to predict the drawing load of shape drawing. The proposed method is based on the geometric division of the cross section and an axisymmetric drawing load prediction model. The drawing loads of square and hexagon shape drawings from round material are predicted by using the proposed method. The effectiveness of the proposed method is verified through finite element analysis and a shape drawing experiment.

원형소재를 이용한 프로파일 다단 형상인발 공정설계

Multi-pass shape drawing is very important to produce steel profiles in round samples. In the current study, a process design system is developed for a multi-pass shape drawing. In general, the number of passes for a multi-pass shape drawing is 2 to 3 when the reduction ratio, drawing stress, and productivity are considered. Therefore, calculating the drawing stress and designing the intermediated die shapes are very important. In order to calculate the drawing stress, a shape drawing load prediction method is proposed using a general axisymmetric drawing load prediction model. An intermediate die shape design method is proposed using the initial and the final product shapes. Based on this analysis, a process design system is developed for multi-pass shape drawing for steel profiles. The system works with AutoCAD. The system was applied to design a shape drawing of a spline.

Effect of bulge formation on strain inhomogeneity in axi-symmetric metal drawing of light reductions

Bulge formation occurs in drawing with light reductions and large die angles. Reports concerning its effect on strain inhomogeneity in axi-symmetric drawing are limited. In this study, bulge formation is characterized by the occurrence of outward radial velocities in the finite element analysis. Strain distributions, including axial, radial, circumferential, shear, and effective strains, were analyzed to explain the effect of bulge formation on strain inhomogeneity. Hardness tests for the drawing experiment were conducted to verify the findings of the FE simulation. Optical microscopy of the microstructures produced by drawing under both a near homogeneous condition and a bulging condition was performed. The results indicate that bulging causes a peak in the axial strain distribution near the drawn workpiece’s surface, leading to a slight fall-off of effective strain on the surface. The peak is caused by the excessive redundant deformation of a local reversion from compressive to tensile axial strain. The strain peak is greater when drawing with light reductions and large die angles and becomes more noticeable with small strain-hardening exponents or large friction factors. Bulge formation also causes fibrous flow lines near the surface of the drawn workpiece.

PROFILING CHANNEL DRAWING TOOLS WITH THE CHANNEL OF TWO CONES

In the design process multiple drawing a long axially symmetric continuous and composite products at the stage of rough drawing it is advisable to use drawing tools with the channel of two cones, in which input cone ensures a low compression and improved conditions of friction compared with standard drawing tools, and the compression occurs in the second cone of the working part of the channel drawing tool. The formulas for calcu- lating the pressure of drawing axisymmetric drawing products and optimum geometry of the channel drawing tool with the channel of the two cones. It is shown that the drawing tool with the channel of the two cones at the expense of improvement of conditions of friction can reduce pressure of drawing and, accordingly, to provide the best power parameters of the process of drawing, reduce the filament and the defectiveness of a work piece, which is specially important in the process of drawing composite products.

DRAWING FEATURES OF AXISYMMETRIC COMPOSITE ARTICLE WITH FIBER CORE OF NONFERROUS METALS AND ALLOYS

The mechanism of plastic deformation of axisymmetric composite articles with heterogeneous components in the course of drawing is more difficult than in case of monometal processing. Because of the specificity of stress and strain state, the axisymmetric drawing is characterized by permanent inhomogeneity of strain, which depends on the reduction value in pass, reducing die cone angle, relative length of drawing cylinder of the reducing die, coefficient of friction between wire and reducing die in the deformation zone, core/cover separation surface joint strength factor, relative size of the core, and ratio of flow stress of the cover and core. By means of experimental studies the features of composite article drawing process with mono- and multi-fiber core and the conditions of implementation of homogeneous proportional flow of both components without tearing the core continuity, surface tears of the cover and break of the article itself have been found.

Features of drawing axially symmetric composite wares with a filament core made of nonferrous metals and alloys

The mechanism of plastic deformation of axisymmetric composite wares with dissimilar components during drawing is more complex than with a similar treatment of a monometal. By virtue of the specifics of the deformation mode, the constant nonuniformity of deformation is inherent to axisymmetric drawing; it depends on the reduction in the passage, the die cone angle, the relative length of the calibrating die rib, the friction ratio between the wire and die in the deformation region, the coefficient of connection strength of the core and sleeve interfaces, the relative core size, and the ratio of stresses of the plastic flow of the sleeve and the core. The features of drawing the composite wares with a monofilament and a multifilament core and implementation conditions of the uniform proportional flow of both components without the formation of fractures of the core continuity, the surface sleeve fracture, and the fracture of the ware itself are established by experimental investigations.

Axisymmetric extrusion and drawing through a die of arbitrary form

Axisymmetric extrusion and drawing through a die of arbitrary shape is analyzed by the Orowan method. The stress state in a representative element is determined by solving a boundary value problem of plasticity theory.

극박판 사각 드로잉에 있어서 드로잉속도와 블랭크홀딩력의 영향

Micro-drawn parts have received wider acceptance as products become smaller and more precise. The subject of this study was the deformation characteristics of ultra thin sheet metal in micro drawing of a rectangular shaped part. The influence of drawing speed and blank holding force on the product quality was investigated in micro-drawing of ultra thin sheet of beryllium copper (C1720) alloy. The specimen had a diameter of 4.8 mm and a thickness of <TEX>$50{\mu}m$</TEX>. Experiments were carried out in which, different blank holding force and drawing speed were considered. The product quality was evaluated by measuring the thickness and hardness along two specified directions, namely, the side and diagonal directions. The distribution of the thickness strain showed severe thinning especially around the punch radius in both directions. In the diagonal direction, thickening occurred in the flange area due to the axi-symmetric drawing mode. The increase of blank holding force and/or drawing speed was found to cause severe thinning around the punch radius. The blank holding force had a greater effect on thinning of the product than the drawing speed.

Critical parameters of axisymmetric drawing during plastic deformation of a transversally isotropic, radially inhomogeneous material

The effect of the anisotropic factor and the distribution irregularity of yield strength for a sheet material upon the critical parameters of axisymmetric drawing is analyzed. Two kinds of dependences (linear and quadratic) for the irregularity of yield strength of the sheet material and the piecewise-linear criterion of yielding are considered. In addition, the Mises ellipse is analyzed. Calculation formulas are obtained that connect the limit coefficients of axisymmetric drawing with the irregularity parameter and the anisotropic factor of the initial material.

Defects in axisymmetrically drawn bars caused by longitudinal superficial imperfections in the initial material

Metallic wires and bars are produced by axisymmetric drawing of hot rolled material and must not display surface defects that impair their service use or whose opening during subsequent cold forming is unacceptable. Experimental and numerical (Finite Element Analysis – FEA) analyses of the evolution of longitudinal superficial defects in copper bars during seven successive axisymmetric drawing passes are presented. The initial experimental defects displayed a rectangular cross-section, 1mm wide and 0.3, 0.6 or 0.9mm deep; the two latter evolved after drawing into the “inverted Y” defect already reported in the literature, but the former led to a newly reported “double V” defect. There was a good agreement between the results from experiments and FEA and further analyses were then carried only through FEA, covering two other materials (a carbon steel and aluminum), a decrease in the defect width (from 1.0 to 0.5mm) and an inclination of 15° or 30° of the walls of the 1.0mm wide rectangular defect. The defect evolution was similar for the three materials; the decrease in the defect width enhanced the incidence of “inverted Y” defects, and indicated the formation of newly reported “Radial” and “Inverted V” defects. The inclination of the defect walls led to the possibility of a change from the “inverted Y” defect to a “double V” one. Defects 0.3mm deep and with walls at 30° were eliminated by the present drawing sequence. A novel approach for the prediction of the effect of the initial superficial imperfections on the final drawn stock, through the so called “defect evolution maps” is presented.

Nonuniformity of deformation in drawing corrosion-resistant steel and alloy wire

Analysis of the nonuniformity of deformation over the wire cross section in axisymmetric drawing is based on the additional shear strain, determined analytically or by measuring the microhardness distribution. An expression for the additional shear strain is determined by the upper-limit method, using the kinematically possible disruptive velocity field. The influence of the geometric parameter of the deformation source on the nonuniformity is analyzed. As an example, the calculated and experimental data are compared for the drawing of X18H9T steel wire.

Analysis of the Redundant Deformation Factor in the Axisymmetric Drawing of AISI 304 Stainless Steel Bars through Experimental Techniques

One of the most significant aspects of the axisymmetric drawing operation is the occurrence of non-homogeneous deformation in the cross section of the metal. This phenomenon is associated with an internal distortion process that takes place in the bar as it flows through the die, leading to the development of higher drawing forces and affecting the subsequent mechanical behavior of the material. An adequate analysis of the process and of the work hardening of the drawn metal, therefore, must involve a detailed study of the deformation features in the forming operation. In the present work, the deformation in the single-pass drawing of AISI 304 stainless steel bars was investigated through the evaluation of the relationship between the redundant deformation factor and the parameter . Two experimetal procedures were employed in the study: the visioplasticity and the stress-strain curves superposition techniques. The first one, previously considered as the method leading to the most realistic solutions to various forming processes, allowed the establishment of an increasing linear relationship between de redundant deformation factor and the parameter . A similar behavior was observed through the stress-strain curves superposition technique. In this case, however, the redundant deformation factor values were lower or higher than those obtained through visioplasticity according to the drawing conditions and more sensitive to variations of the parameter . The results were compared to those exhibited by the AISI 420 stainless steel, revealing the influence of the structural features on the behavior of the metal.

The Evolution of Transversal Surface Defects in the Axisymmetric Drawing of Copper Bars

Surface defects are an inevitable characteristic of the raw material employed in the drawing of copper wires. These defects may cause problems in the processing of the material, both during the drawing down to wires and in the final manufacturing of artifacts with the produced wire. The literature reports few analyses covering the importance of these initial defects, as well as concerning their evolution or eventual healing during the drawing. The present paper presents such an analysis for a 12.7 mm diameter copper bar displaying artificial defects 1mm wide and 0.3mm deep. Low angle drawing led to the almost complete healing of the defect after three drawing passes with a 10% reduction of area each. The use of a high semi-angle die led to a completely different situation, where no such defect healing was observed.

The Anomalous Redundant Deformation and Work Hardening of the AISI 420 Stainless Steel During Axisymmetric Drawing

The cold axisymmetric drawing of metals leads to effective strains that increase from the centerline to the surface of the material cross section. This strain heterogeneity depends on the die semi-angle and reduction in area related through a “Δ” parameter. The average strain in the product is evaluated through a redundant deformation coefficient, “ϕ,” which has a minimum value of unity and rises as Δ is increased. Anomalous experimental results for this relationship (ϕ values below unity and insensitive to variations in Δ) have been reported for the AISI 420 stainless steel. Strain path affects the work hardening of metals during sheet forming, where some materials harden more and others less than under pure tension, for the same strain path. The present paper analyses the possibility that a similar dependence of the work hardening on the strain path, during the axisymmetric drawing of AISI 420 stainless steel causes the anomalous ϕ versus Δ relationship. The strain path followed along various material streamlines in axisymmetric drawing involves the superposition of a radially varying reversed shear strain on a basic radial compression/longitudinal tension pattern. A new method was developed for the determination of the effective stress versus effective strain curves of the material along three material streamlines, located close to the material surface, along its centerline and following a midcourse between these two flow lines. A relationship between the local microhardness of the material and its flow stress was established and visioplasticity was employed for the determination of local strains in the deformation region. Data were obtained for six situations resulting from the combinations of two reductions of area (8% and 20%) and three die semi-angles (3 deg, 8 deg, and 15 deg). The various strain paths followed in axisymmetric drawing of AISI 420 stainless steel led to effective stress versus effective strain curves tending to be often lower than that obtained in pure tension. The degree of lowering seems to depend on the reduction in area and die semi-angle. The effect of strain path on the work hardening during axisymmetric drawing causes the anomalous experimental results for the ϕ versus Δ relationship of the AISI 420 stainless steel. The present paper seems to be the first report in literature covering such effects under cold bulk forming conditions.

The Deformation and the Redundant Work Factor in the Axisymmetric Drawing of AISI 420 Stainless Steel Bars—Strain Path Effects Analysis

In the present work, experimental techniques for evaluating the deformation and the redundant work factor in the axisymmetric drawing of ferritic AISI 420 stainless steel bars were investigated. Six operation conditions, involving two reductions of area and three die semi-angles, were employed in the study. Regarding the redundant deformation analysis, the visioplasticity technique was considered as the most adequate procedure for estimating the average deformation in drawing. In this case, an increasing relationship between the redundant deformation factor and the parameter A was obtained. On the other hand, the stress-strain curves superposition technique led to redundant deformation factor values almost insensitive to variations of the parameter A and below unity, a phenomenon which was associated with strain path effects. Concerning the redundant work factor study, the experimental results were lower than those obtained through a theoretical approach and, in some conditions, below unity. This was also attributed to strain path effects.