Length Of Deformation Zone Research Articles

Approach Based on Response-Surface Method to Optimize Lining of Dies Used in 3D Free-Bending Forming Technology

In three-dimensional free-bending forming (3D-FBF), the tube is not overly constrained, and the plastic deformation behavior and forming quality of the bent tube are significantly affected by the critical structure of the forming die lining. However, the effects of die-lining structural parameters on the tube quality, and a method to determine the combination of die-lining structural parameters is yet to be devised. This study aims to propose a new framework that allows one to understand the effects of various die-lining structural parameters on tube quality and to propose the best combination of die-lining structural parameters. First, finite-element modeling is performed to simulate 3D-FBF and examine the effects of individual die-lining structures on the quality of tube formation. The simulation results show that the deformation-zone length and die gap are positively correlated with the tube-section distortion and wall-thickness variation, whereas it shows an opposite trend with respect to the bending radius. Additionally, the lining chamfer radius of the bending die and the guide lining chamfer radius minimally affect the tube forming quality. Subsequently, the optimal die-lining structure is obtained using the response-surface method. The tube cross-sectional distortion rate reduced from 2.73 to 2.53% after the die lining is optimized. Additionally, the average inner-wall thickness reduced to 1.06 mm, whereas the average outer-wall thickness increased to 0.97 mm. This paper proposes a method for optimizing the forming-die-lining mechanism and for improving the tube forming quality in 3D-FBF.

Forming characteristics of thin-walled tubes manufactured by free bending process-based nontangential rotation bending die

The free-bending process of a metal tube involves a geometric relationship between the eccentricity, the rotation angle of the bending die, the deformation zone length, and the bending radius. Ideally, during the forming process, the contact position between the bending die, and the outer bend of the tube remains tangent. However, due to factors such as the clearance of the bending die and material properties, the rotation angle can be adjusted within a specific range while still ensuring smooth tube formation. The tangential state is disrupted when the rotation angle changes, resulting in overbending or underbending. Thus, in this study, a new theoretical analysis of the free bending process, accounting for clearance, was developed to analyze the material flow and changes in the bending radius during the nontangential contact between the bending die and the tube. In addition, the reasons for achieving smooth tube bending even after adjusting the rotation angle were explained, and the deformation mechanism of the tube under the combined effects of additional tangential force from the bending die and axial propulsive force was analysed. Furthermore, the impact of the rotation angle on the bending radius and the displacement of the strain neutral layer (strain NL) was determined. Afterwards, finite element (FE) modeling and forming experiments were conducted to verify the proposed theoretical analysis under different deformation zone lengths and eccentricities conditions. Besides, the distribution of the inner and outer wall thicknesses of the tube under the nontangential rotation of the bending die was further analysed. The simulation and experimental results fit well with that obtained from theoretical analysis.

Influence of deformation zone length on bending radius of SS304 tubes with small diameters manufactured via free bending-based active motion

In three and six-axis free-bending equipment, the deformation zone length (A) is a fixed mechanical structure parameter modified when the relevant structure is redesigned and manufactured. In this study, a six degree of freedom (6-DOF) parallel mechanism was used as the control mechanism of the bending die, and a new method of changing the deformation zone length (A) was proposed. Firstly, an idealized geometric model of free bending-based active motion was established. Then, the influence of the deformation zone length (A) on the bending moment and the bending radius of the tube was analyzed. In addition, the finite element simulation and a kinematic model of free bending-based active motion controlled by the 6-DOF parallel mechanism were established, and bending processes of the SS304 tube with different deformation zone lengths were investigated. Afterwards, the impact of the deformation zone length (A) on the bending radius, bending moment, wall thickness, and motion of the parallel mechanism were analyzed. Finally, experiments were carried out on the free-bending equipment based on the 6-DOF parallel mechanism. Experiments verified the rules in the theoretical analysis, finite element simulation, and kinematic simulation.

Increasing the crack resistance when pressing pipes made of 08Kh13N4M1F steel

The main factor determining the possible appearance of continuity defects in hotpressed pipes is the physical nature of the material subjected to deformation, namely, its plasticity. Alloying of a metal contributes to a decrease in its plasticity and an increase in the resistance to plastic deformation, which, on the one hand, increases the stress level during hot deformation, and, on the other hand, reduces the threshold stress value corresponding to the onset of metal fracture. The introduction of computer simulation tools, in particular software products based on the finite element method, made it possible to perform an analytical study of the features of the stress-strain state of the metal during hot pressing of steel pipes. Particular attention in the modeling is paid to the deformation conditions of the surface layers of the metal, since one of the characteristic surface defects of hot-pressed pipes is cracks and ruptures. The dependences of the stress-strain state on the technological parameters of the pressing process are revealed, namely, the nature of the change in the stress-strain state of the surface layers of the pressed shell along the deformation zone length, the effect of temperature, elongation coefficient and friction coefficient on the change in the stress-strain state are determined, the degree of the plasticity resource use by the Kolmogorov failure criterion is assessed. On the basis of the results obtained, a set of theoretical and experimental studies was carried out to investigate the mechanisms of the formation of surface defects in hot-pressed pipes, technological parameters and technological tool parameters that contribute to the elimination of surface defects were determined.

Autowave Criteria of Fracture and Plastic Strain Localization of Zirconium Alloys

Plastic deformation and fracture of Zr–1% Nb alloys exposed to quasi-static tensile testing have been studied via a joint analysis of stress-strain curves, ultrasound velocity and double-exposure speckle photographs. The possibilities of ductility evaluation through the εxx strain distribution in thin-walled parts of zirconium alloys are shown in this paper. The stress-strain state of zirconium alloys in a cold rolling site is investigated considering the development of localized deformation bands and changes in ultrasound velocity. It is established that the transition from the upsetting to the reduction region is accompanied by the significant exhaustion of the plasticity margin of the material; therefore, the latter is more prone to fracture in this zone exactly. It is shown that traditional methods estimating the plasticity margin from the mechanical properties cannot reveal this region, requiring a comprehensive study of macroscopically localized plastic strain in combination with acoustic measurements. In particular, the multi-pass cold rolling of Zr alloys includes various localized deformation processes that can result in the formation of localized plasticity autowaves. Recommendations for strain distribution division over the deformation zone length in the alloy in the pilger roll grooves are provided as well.

Springback analysis of different A-values of Cu and Al tubes in free bending forming technology: experimentation and finite element modeling

In tube free bending forming technology, the springback behavior affects the bent tubes’ forming accuracy and quality. Thus, in this investigation, the springback behaviors of T2-Cu and AA6061-T6 tubes manufactured by free bending technology were studied experimentally and using finite element modeling. The bending radius of the formed tubes was measured in ABAQUS combined with the geometric calculation. After investigating the different A-values (sufficient length of deformation zone) of Cu and Al tubes, it was found that the higher the A-value, the higher the bending angle, the lower the bending radius, and the larger the springback angle. The changes of both bending and material properties affect the springback to specific values. The tube forming’s stress peak occurred in the forming segment, where the springback angle is the highest, and the outer springback is higher than the inner side at the same A-value and position. Under the same forming parameters, each section’s strain variation and springback angle in the bending process of T2-Cu tubes is higher than that of AA6061-T6 tubes. The simulation results were in remarkable agreement with those obtained from experimentation, proving the simulation’s reliability and accuracy.

Mathematical simulation of seamless pipes extrusion and rational calibration of die

Technology of seamless pipes production by extrusion enables to deform pipe workpieces made of low-plastic materials. However, low durability of the working instrument restricts the area of the technology application. The purpose of the work was to specify optimal parameters of technological processes of pipes extrusion. Minimization of energy and force parameters of the deformation zone and an increase of once-only metal deformation were accepted as criteria. They will enable to increase the presses productivity, increase durability of working instrument and accuracy of pipes geometric dimensions. A mathematical model of deformation zone and stressed state of pipe workpiece were elaborated. Influence of the die generatrix calibration and deformation zone parameters on the character of energy and force parameters change revealed. Dependence of energy and force parameters on the die calibration and geometric parameters of deformation zone for the press 50 MH was established. The results of mathematical simulation of pipes extrusion showed that along the whole deformation zone length, increase of metal flow speed results in an increase of tangential and normal stresses on the forming mandrel and calibrated die. The task of parametric optimization of die profile (calibration) was accomplished in interpretation of base variation Euler’s task for a determined functional of pipes extrusion. It was established that while the extrusion speed is increasing, the energy and force parameters of the deformation zone are getting pronounced dynamic character. At that, by optimization of die calibration, an increase of the extrusion press 50MH working instruments durability was reached, as follows: dies – by two times, mandrels – by 4 times, container bushes – by 40% and press-washers – by 2 times.

Stress-strain state of metal in deformation zone during production of steel section billets on the unit of combined continuous casting and deformation. Report 2

Stress state of metal in deformation zone during introduction of the separating collars of the grooved die into continuously casted steel slab was calculated for production of section billets on the unit of combined continuous casting and deformation. Calculation of axial, tangential and equivalent stresses arising in deformation zone of metal was made in four sections of deformation zone and its results are presented in specific points and lines. View of the section of deformation zone and location of specific points are provided. The stress state of metal in zone of cyclic deformation at formation of three steel section billets from continuously cast slab by separating collars of grooved die on the unit of combined continuous casting and deformation was determined by solving extensive problem of elasticity with the finite element method using the ANSYS package. The results of calculation of axial, tangential and equivalent stresses according to Mises in deformation zone are given in form of graphs and tables for working surfaces in four cross sections. The values and regularities of distribution of these stresses along the length and width of deformation zone were determined. The character of axial stresses distribution by characteristic lines located along the length of deformation zone is shown. Values of the highest compressive and tensile axial stresses arising in deformation zone during introduction of separating collars of grooved were obtained for the unit of combined continuous casting and deformation.

A novel single pass severe plastic deformation method using combination of planar twist extrusion and conventional extrusion

Forward shear normal extrusion (FSNE) as a new single pass severe plastic deformation (SPD) method was based on conventional extrusion combined with planar twist extrusion. The proposed method was studied by finite element analysis to investigate the effect of FSNE die geometrical parameters, i.e. deformation zone Length (LDZ) and distortion angle (α), on uniform stress-strain distribution during deformation. Consequently, the optimum condition was considered in design and the process was experimentally performed on aluminum alloy (0.27% Fe, 0.08% Si and balance Al (wt. %). It was found that L = 15 mm and α = 40° are the optimum die parameters that can result in higher effective plastic strain with a more uniform distribution. Microstructural evolution was also studied to demonstrate the capability of this technique in grain refinement and microstructure observations revealed the presence of ultra-fine grains after FSNE. Tensile testing results indicated that yield (YS) and ultimate (UTS) strengths increase 2.7 and 2 times for the processed sample compared to the annealed sample. Hardness results showed increase in hardness level from 25HV0.3/10 for non-processed to 53 HV0.3/10 for the processed state. The uniform distribution of hardness values in both transverse and longitudinal directions was achieved due to the uniform distribution of effective strain resulting from the optimum die design. Compared to other SPD methods, the present technique resulted in high accumulated plastic strain and hardness with uniform distribution and significant grain refinement after one pass.

Microstructural evolution of twin-roll-cast Al–Mn alloy during cold rolling and subsequent annealing: Effect of number of cold-rolling passes

Variations in the shape and microstructure of a 3003 Al alloy strip fabricated by twin-roll casting during cold rolling and subsequent annealing are investigated as a function of the number of cold-rolling passes under the same total rolling reduction. With an increase in the number of cold-rolling passes, the length and width of the cold-rolled sheet increases and decreases, respectively, owing to a reduction in the ratio of the deformation zone length to the mean deformation-zone thickness. A homogenized twin-roll-cast strip has much coarser grains and more particles in the surface region than in the center region. The shape, amount, and distribution of the particles remain unchanged after cold rolling and subsequent annealing, and they are independent of the number of cold-rolling passes. However, as the number of cold-rolling passes increases, the amount of plastic deformation accumulated in the surface region of the cold-rolled sheet increases. As a result, the size of recrystallized grains in the surface region of the subsequently annealed sheet gradually decreases with increasing number of cold-rolling passes owing to the enhanced recrystallization behavior. Therefore, the grain size difference between the surface region and the center region of the annealed sheet reduces significantly, and the homogeneity of the microstructure in the thickness direction of the sheet improves with an increase in the number of cold-rolling passes.

Numerical Analysis of Twin-Roll Casting of Strips With Profiled Cross-Section

The relatively high production costs of innovative materials with tailored properties such as Tailor Welded Blanks, Patchwork Blanks, Tailor Heat Treated Blanks and Tailor Rolled Blanks are responsible for a growing interest in new cost-effective production methods. One of the promising energy-saving and environmental friendly technologies for the production of tailored blanks is twin-roll casting. In the study a new alternative method for twin-roll casting of strips with profiled cross-section is proposed, which uses one or more preloaded endless steel strips with an antiadhesive coating for profiling of the formed strip on a pair of the common cylindrical shells. As a primary stage for the practical process design, numerical simulation of the process using the finite element software package ANSYS is realized. In this way, dependencies of the strip elements outlet temperature, deformation zone length and elements outlet speed on the varied strips thickness and total solidification-deformation zone length are established. Based on the simulation results, a procedure for the twin-roll casting process design is suggested.

Deformation Zone Length and Plastic Strain in Twin-Roll Casting of Strips of Al-Mg-Si Alloy

An original method for determination of the deformation zone length and corresponding plastic strain is suggested. The method is based on microstructural analysis of wedge-shaped specimens produced by controlled rapid process interruption. Electron backscatter diffraction analysis followed by grain orientation spread (GOS) characterization allows description of the grain evolution during the passage through the roll gap. The appearance of the first elongated grains and increase in GOS values detected in the microstructure of the strip core zone were used for exact identification of the deformation zone origin.

Effect of Shear Deformation on Closure of a Central Void in Thin-Strip Rolling

Central voids or voids at the middle layer are often found in thin strips produced by twin-roll casting. These strips are in general so thin that they are unable to take a required reduction in thickness to close the voids. In the present investigation, equal-speed rolling and differential-speed rolling were compared to assess the effect of differential speed on closure of the voids by the rigid-plastic finite-element analysis. As a result, shear deformation developed in differential-speed rolling was found to reduce the reduction in thickness required for void closure. An increase in speed ratio, length of deformation zone, or friction coefficient at the interface expedited the progress in void closure. However, as the speed ratio exceeded thickness ratio, a portion of rolling power was dissipated extensively by excessive slip at the interface. Moreover, tensile stress developed which would cause cracks in the strip.

Effect of die design parameters on the deformation behavior in pure shear extrusion

Abstract Influences of die design parameters in terms of diameter ratio and length of the deformation zone on the distribution of effective strain, filling fraction of the die exit channel and pressing load in pure shear extrusion (PSE) are studied using finite element method (FEM). Dimensional stability, pressing load and hardness measurements are used to validate the predictions of the simulation. Acceptable agreements between the predictions of simulation and experimental results are observed. It is found that strain is inhomogeneously distributed which increases from the center to the corners. Effective strain, inhomogeneity of strain, filling fraction of the die exit channel and pressing load are increased with increasing diameter ratio. In addition, the work-piece is deformed more homogeneously at lower pressing load by increasing the length of deformation zone. However, filling fraction of the die exit channel initially increases by the length of the deformation zone up to 60 mm after which it reduces. The optimum die design parameters covering a range of acceptable effective strain and strain homogeneity, filling fraction of the die exit channel and pressing load are proposed as being 60 mm and 2 for length of the deformation zone and diameter ratio, respectively.

Finite-element analysis of severe plastic deformation in differential-speed rolling

Differential-speed rolling can impose severe plastic deformation on a metallic sheet by developing extensive shear strain. Plastic deformation by a single pass with a speed ratio of 3 was found to be as high as 3.5 in terms of the effective strain. Although the speed ratio, the friction coefficient and the length of deformation zone are important parameters in controlling the differential-speed rolling, their effects on plastic deformation are yet unknown. In the present study, these effects were investigated by the rigid-plastic finite-element analysis, and as a result logics in dissipation of power, mechanisms in development of plastic deformation and an upper limit of the speed ratio were found. Moreover, a double-pass differential-speed rolling was introduced to achieve a symmetric distribution of the effective strain through thickness of a sheet. An excessive speed ratio would waste unnecessarily a portion of the power through friction at the interface between the sheet and rolls, and also exert a tensile stress in the sheet, which could result in fracture if the material of the sheet is as brittle as a magnesium alloy.

Upsetting Process Analysis and Numerical Simulation of Metal Pipe’s End

Upsetting is a common method in the production of connectors, a new technology to avoid instability of long pipe under compression was taken in this paper, which would get the upsetting shape of long pipe by changing the length of deformation zone. Forming process was simulated by finite element, and some mechanisms of metal deformation and load were obtained. The simulation results showed that: instability was not occurred and one could have specified shape by using conical die upsetting only once. Then the upsetting experiment was conducted, the trail had a good match with simulation results, which expanded upsetting rules, and provided a reference for design of die.

Extrusion die geometry effects on the energy absorbing properties and deformation response of 6063-type Al–Mg–Si aluminum alloy

The response of 6063-type Al–Mg–Si alloy to deformation via extrusion was studied using tool steel dies with 15°, 30°, 45°, 60° and 75° entry angles. Compressive loads were subjected to each sample using the AVERY DENISON machine, adapted to supply a compressive load on the punch. The ability of the extrudate to absorb energy before fracture was calculated by integrating numerically the polynomial relationship between the compressive stress and sample strains. Strain rate was calculated for each specimen and the deformation zone length was mathematically derived from the die geometry to decipher its influence on both lateral and axial deformations. Results showed that extruding with a 15° die was the fastest as a result of the low flow stress encountered. Outstanding compressive strength, plastic deformation, strain rate and energy absorbing capacity were observed for the alloy extruded with a 75° die angle. Increase in die angles led to a decrease in deformation zone length and samples deformed more in the axial direction than in the lateral except for the 45o die which showed the opposite; the sample also showed the least ductility.

Deformation and Heat Transfer Analysis for High Speed Dieless Drawing of AZ31 Magnesium Alloy Tubes

The effect of drawing speed and heating length on deformation behavior was investigated by numerical approach for AZ31 magnesium alloy tubes to realize high speed dieless drawing process. The length of deformation zone expands with increasing the feeding speed. The increase in heating length leads to expanding length of deformation zone. The mean strain rate increases with increasing the feeding speed firstly, and then rate of increase in the strain rate becomes gradual under condition of any length of heating band. Based on these results, a limiting reduction in area of 52.5% under higher speed and larger heating length conditions can be realized experimentally.

Comparison of evolution laws of stress and strain fields in hot rolling of titanium alloy large rings with different sizes

For hot rolling of titanium alloy large rings, evolution laws of stress and strain fields in rings with various sizes were explored and compared based on a reliable coupled thermo-mechanical three-dimensional (3D) finite element (FE) model. The results show that for forming processes of different rings, as γ ¯ (the equivalent distribution ratio of feed amount per revolution of a process) decreases, the final peak Mises stress may transfer from the biting point at the driver roll side to that at the idle roll side, and the final peak equivalent plastic strain may transfer from the outside surface to the inside surface; as L ¯ (the equivalent deformation zone length of a process) increases, the final peak Mises stress may appear in the middle layer. The final positions of peak Mises stress and equivalent plastic strain are the combined effects of the above two aspects. In the deformation zone of a deformed ring, the surface layers are in the 3D compressive stress state, while the middle layer is in the 1D compressive and 2D tensile stress state or 2D compressive and 1D tensile stress state; the whole ring is in the 1D compressive and 2D tensile strain state.

Simulation of contact stresses and forces during hot rolling of thin wide strips with allowance for a stick zone and elastic regions in the deformation zone

A new procedure for the calculation of contact stresses and hot-rolling forces for wide strips 0.8–1.5 mm thick has been developed and tested. This procedure takes into account the presence of a stick zone in the deformation zone and stress distributions in both elastic and plastic regions in the deformation zone. The average error in the force calculation according to the new procedure is 5%, which is more than two times smaller than the calculation error of well-known force calculation procedures. The developed procedure is used to simulate the contact stresses in the deformation zones of working stands in a six-stand 1700 mill during rolling of strips thinner than 1.0 mm. A number of new relations for the state of stress in a strip have been revealed upon simulation. Some of these relations are as follows: in the last stands, the length of elastic regions accounts for 10–17% of the total deformation-zone length; the maximum normal contact stresses are 1300–1400 MPa, which corresponds to the stresses in the deformation zones of cold-rolling mills; the stick-zone length accounts for 85–99% of the deformation-zone length; and the contact stresses in the stick zone are virtually independent of the friction coefficient. The developed calculation procedure can be used to optimize the technological regimes of wide-strip mills.