Cross-shear Zone Research Articles

Study on the Influence of Mandrel Speed on the Titanium Tube Continuous Retained-Mandrel Rolling Process

The continuous retained-mandrel rolling process is a promising method for titanium tube production with high efficiency and a short process. The importance of mandrel as a deformation tool supporting the inner wall is crucial. This paper thoroughly examines the influence of mandrel velocity on the deformation characteristics at the groove vertex using three approaches: numerical simulation, shear-deformation observation experiments, and microstructure analysis. The following conclusions are drawn: Decreasing the mandrel velocity enhances the penetration of shear deformation into the inner wall of the titanium tube, improves thickness uniformity, and shifts the deformation mechanism near the inner wall from twinning to dislocation slip. As a result, the volume fraction of recrystallization increases from 18.4% to 42.3%. However, the mean shear strain increases first and then decreases to a certain value as the mandrel speed decreases, which is attributed to the combined influence of the cross-shear zone and the rolling force.

Research on microstructure and mechanical properties of TC4/304 clad plates by asymmetric rolling with local strong stress

In order to solve the problems of complex traditional preparation process and low bonding strength of titanium/steel clad plates, TC4/304 clad plates were prepared by asymmetric rolling with local strong stress (ARLSS), the effect of rolling temperature on the interface bonding of clad plates was studied. The two-dimensional simulation model of TC4/304 clad plates rolling was established by finite element method, and its accuracy was verified by experiments. The experimental results show that the interfacial bonding strength of the clad plates increased with the increasing temperature, but when the temperature reached 950 °C, the brittle intermetallic compounds (IMCs) formed extremely fast, which greatly weakens the bonding strength. The clad plates showed the best bonding strength at 900 °C. After corrugated roll bonding (CRB) (33 % reduction ratio), the bonding strength at the peak was lower than that at the trough. After FRB (46 % reduction ratio), the interface bonding strength was slightly improved. The final peak bonding strength reached 519 MPa, and the trough bonding strength was 527 MPa. The improvement of bonding strength mainly came from the improvement of TC4 matrix strength. The finite element simulation results showed that multiple cross shear zone in the deformation zone of the CRB stage were beneficial to the bonding of dissimilar metals. While the deformation of the clad plates material in the FRB stage was consistent, which effectively avoided the cracking of the bonded area and further improved the bonding strength. Therefore, the strong non-uniform plastic deformation of ARLSS process had a significant effect on the deformation coordination of dissimilar metals and the quality improvement of clad plates.

Study on minimum rollable thickness in asymmetrical rolling

A new model for the asymmetrical rolling is proposed to calculate the minimum rollable thickness simply and fast by the slab method. The calculation formulas of the rolling pressure, the rolling force, the critical roll speed ratio, and the critical front tension under different deformation zone configurations are proposed, and the deformation zone configuration-rolling parameter relationship diagram is given and analyzed. The results show that the minimum rollable thickness can be reached when the rolling parameters keep the deformation zone configuration as cross-shear zone + backward-slip zone (C + B) or all cross-shear zone (AC). The calculation formulas of the minimum rollable thickness and the required rolling parameters for different deformation zone configurations are proposed, respectively. The calculated value agrees well with the experimental result.

Formation mechanism of dynamic multi-neutral points and cross shear zones in corrugated rolling of Cu/Al laminated composite

Corrugated rolling technology is a new method to produce metal laminated composite. Compared with flat rolling, the corrugated rolling can effectively promote the deformation of hard-deformed metal, refine metal grains and obtain laminated composite with superior mechanical properties. A three-dimensional simulation model of Cu/Al laminated composite produced by the corrugated rolling process is set up through finite element method, and its accuracy is verified by experiments. The friction stress of contact surfaces between the plate and the roll are obtained to analyze the dynamic multiple neutral points and the distributions of the cross shear zones at different moments. Corrugated rolling greatly increases the friction stress values and cross shear zone areas without the changing of rolling mill equipment capacity, and the microstructure characteristics in different position of deformation zone reflect the fact. The stress state of whole rolling process is further analyzed by stress triaxiality and Lode parameter plane in which the cross shear zones are close to considerable shear state, and greater shear deformation makes the rupture of the oxide layer and hardened layer at the bonding interface easier. Therefore, the corrugated rolling can coordinate the deformation of metals with different resistances and then improve the composite quality.

Analysis of asymmetrical rolling of strip considering two deformation region types

Analytical models of two deformation region types considering the percentages of three regions in the plastic deformation zone are proposed for analyzing asymmetrical rolling of strip and used to calculate the critical speed ratio, three region percentages, roll force, and roll torque. The effective range of speed ratio on thickness reduction increases with increasing critical speed ratio. When the deformation region type is backward-slip zone + cross-shear zone + forward-slip zone (B+C+F), with increasing speed ratio, the thickness reduction in asymmetrical strip rolling increases evidently, but remains unchanged when the critical speed ratio is exceeded, where the deformation region type is backward-slip zone + cross-shear zone (B+C). It is achievable to increase thickness reduction by increasing the roll force and front tension, which can not only increase the reduction rate, but also increase the critical speed ratio. The effect of asymmetrical rolling on thickness reduction is enhanced with decreasing of the roll force and front and back tension because of the increasing cross-shear zone percentage.

Analysis of asymmetrical rolling of strip considering percentages of three regions in deformation zone

An analytical model based on slab method considering the percentages of three regions in deformation zone is proposed for analyzing asymmetrical rolling of strip and used to calculate the percentages of three regions, the roll force, and roll torque. The asymmetrical rolling is more effective in reduction than the symmetrical rolling due to the existence of cross-shear zone. The percentage of cross-shear zone increases with the increasing of speed ratio and friction coefficient and decreasing of back and the front tensions, thickness of the strip, and roll force. With increasing of the percentage of cross-shear zone, the contribution ratio of reduction increases. The proposed model has good accuracy for the analysis results are in good agreement with the results measured in experiments.

Experimental study on deformation region types and percentages of each region in asymmetrical rolling of strip

A simple method for dividing the deformation type and a practical model for calculating the percentages of each region in various deformation types are proposed. The percentage of cross-shear zone gradually increases to 100% and the percentages of forward-slip and backward-slip zone gradually decrease to 0 as rolling pass increases with huge roll force and tensions and better lubricating conditions. The method and the model can provide a good reference for better operations during asymmetrical rolling, which is good for rolling industry.

Study on the relationship between asymmetrical rolling deformation zone configuration and rolling parameters

A new model for analyzing asymmetrical cold rolling process is proposed by the slab method, which solves the problem of insufficient applicability of existing models in the face of multiple asymmetric rolling conditions. In the new model, six configurations of the deformation zone are proposed as, forward-slip zone + cross-shear zone + backward-slip zone (F + C + B), cross-shear zone + backward-slip zone (C + B), all cross-shear zone (AC), forward-slip zone + cross-shear zone (F + C), all forward-slip zone (AF) and all backward-slip zone (AB). By analyzing the effects of rolling parameters such as reduction rate, roll speed ratio, tension and friction coefficient on the deformation zone configuration, the critical roll speed ratio and critical tension required for different deformation zone configurations are proposed. According to the variations of the critical roll speed ratio and critical tension with different rolling parameters, the deformation zone configuration - rolling parameters relationship diagram is obtained. Based on this diagram, the deformation zone configurations produced by different rolling parameter ranges can be determined, and the reasonable asymmetrical rolling technology can be selected for different production objectives. The proposed model can comprehensively and accurately calculate the rolling pressure, rolling force and torques under various rolling conditions, the calculated values agree well with the experimental results, the maximum error is 9.97%.

The mechanical parameters modeling of heavy steel plate snake/gradient temperature rolling with the same roll diameters

The grains in the center of the heavy steel plate can be refined by the snake/gradient temperature rolling, and the deformation penetration, the microstructure, and the properties of the steel plate will be improved. The existing rolling mechanical models are not suitable for the snake/gradient temperature rolling, so it is necessary to establish the mechanical parameters model of the snake/gradient temperature rolling to instruct production. The yield criterion of rolled material was modified based on the idea of equivalent flow stress. The element stress analyses were carried out based on the uniform normal stress and nonuniform shear stress in the vertical sides of each slab. Then the equilibrium equation of the unit pressure based on the slab method was established on this basis. The deformation region was divided into three layers (the top layer, the bottom layer, and the central layer) and maximum four zones (back slip zone, front slip zone, cross shear zone, and reverse deflection zone) according to the temperature distribution and position of the neutral point, and then the 12 zones were formed during the snake/gradient temperature rolling. The boundary conditions of the existence of the back slip zone, the front slip zone, and the cross shear zone were established according to the relationship between the threading angle and the neutral angle. The accurate mechanical parameters model of the rolling force and rolling torque of the snake/gradient temperature rolling with the same roll diameters was set up on this basis. The ANSYS software has been used in the rolling process simulation by many scholars, and the calculating precision has been verified. So the rolling processes were simulated by the ANSYS software to validate the model precision. The results show that the maximum relative deviation of the rolling force analytic model is less than 7% compared with the numerical method, and the maximum relative deviation of the rolling torque analytic model is less than 11% compared with the measured results. The mechanical parameters model can accurately predict the rolling force and rolling torque during the snake/gradient temperature rolling with the same roll diameters, so as to provide a theoretical basis for the design of rolling mill and the setup of the process parameters.

Analysis of deformation mechanism in corrugated rolling of composite plate

The corrugated rolling is a new rolling technology to obtain the composite plate. Compared with the flat rolling, the corrugated rolling can promote the plastic deformation of hard metal effectively and gain a composite plate with superior mechanical properties. In this paper, the finite element analysis of the copper/aluminum composite plate in corrugated rolling process was carried out. The correctness of the model was verified by experiment. The distributions of rolling normal stress, shear stress, equivalent strain and cross shear zone in corrugated rolling were obtained, and the differences between these from flat rolling were contrasted. Cross shear zone and shear stress in corrugated rolling are larger than flat rolling, which is beneficial to metal composite.

Theoretical and experimental analysis of the deformation zone and minimum thickness in single-roll-driven asymmetric ultrathin strip rolling

Although asymmetric rolling is employed extensively to produce ultrathin strips in micromanufacturing, microelectronics, and other high precision engineering fields, very limited attention has been given to the deformation zone, which is a direct result of the material thickness reduction behavior during asymmetric rolling. In this study, theoretical analysis of the minimum thickness of single-roll-driven asymmetric rolling is performed by combining FE (finite element) and theoretical analytical models to complete a comprehensive investigation. Based on the FE model calculation results, the deformation zone contour varies with reduction ratio, strip thickness, and yield strength; the Fleck model can be used to describe single-roll-driven asymmetric ultrathin strip rolling when the thickness is small enough. Different from symmetric rolling, a cross-shear zone is inevitably formed during asymmetric rolling, but the cross-shear force resulting from asymmetric rolls decreases and approaches 0 with smaller strip thickness, smaller reduction ratio, and higher yield strength, which means the rolling status of single-roll-driven asymmetric ultrathin strip rolling is very similar to symmetric rolling when the strip reaches its limiting minimum thickness. Therefore, a minimum thickness model is developed for single-roll-driven asymmetric ultrathin strip rolling with different roll diameters, mean tensions and strip yield strengths, and the elastic modulus and Poisson ratio of the two rolls are considered. Eventually, the minimum thickness for single-roll-driven asymmetric rolling of ultrathin strips is estimated using the new minimum thickness model, with further experimental verification by the single-roll-driven asymmetric rolling of various materials, including aluminum, 304 stainless steel, and both non-annealed and annealed copper. Compared with experimental results, the model is shown to be a possible alternative for more accurate minimum thickness prediction in single-roll-driven asymmetric rolling.

The analytic study on the heavy steel plate snake rolling with the different roll diameters

The deformation in the inner region along the thickness of the heavy steel plate can be improved by snake rolling method. Then the microstructure and property will be refined and the crack in the inner region may be avoided. So the in-depth research on snake rolling method mechanics parameter modeling should be conducted to guide production. The rolling deformation zone will be divided into back slip zone, cross shear zone, front slip zone and reverse deflection zone according to the direction of the friction during the snake rolling process. The four zones may not exist at the same time. The boundary conditions of existence of the back slip zone, cross shear zone and front slip zone were established by calculating the position of neutral point by a special method. The calculating models which were used to calculate the snake rolling mechanical parameters including the rolling force and rolling torque were setup. The calculated models of unit compressive pressure in the four zones were setup by the slab method, and at this basis, the accurate calculating models of the rolling force and rolling torque were setup according to the composition of the rolling deformation zone and the boundary condition. The mechanical parameters were calculated by the analytic method and the numerical method, and the relative deviation is less than 5% which can satisfy the industrial requirement. The present analytical model can predict the characteristics during snake rolling easily and quickly and it is also suitable for online control applications.

A fast calculation method of large-cylinder asymmetrical rolling force considering shear effect

An analytical model for large-cylinder asymmetrical rolling is proposed based on an improved slab method, which can predict the rolling force more quickly. In this method, uneven normal and shear stresses acting on the vertical side are supposed. In the solution, the upper and lower contact lengths are different, and the roll gap is divided into four slabs. Moreover, the effects of the rolling parameters such as roll speed ratio, roll radius, exit thickness, and radius of cylinder on the rolling force and cross-shear zone ratio are investigated. The cross-shear zone ratio, which means the shear effect, is a key parameter in reducing rolling force and microstructure refinement. This method is conducted with the experimental and finite element verification, and good agreement has been found. It should be noted that the calculation result can be obtained rapidly and easily by this proposed model. Therefore, the present model is suitable for online application.

The Analytic Study on the Heavy Steel Plate Snake Rolling with the Same Roll Diameters

The deformation in the inner region along the thickness of the heavy steel plate can be improved by snake rolling method. Then the microstructure and property will be refined and the crack in the inner region may be avoided. Therefore, the in-depth research on snake rolling method mechanics parameter modeling should be conducted to guide production. A snake rolling process with the same roll diameters and different angular velocity was conducted in this paper. The rolling deformation zone will be divided into back slip zone, front slip zone, cross shear zone, and reverse deflection zone according to the direction of the friction during the snake rolling process. The four zones may not exist at the same time. The boundary conditions of existence of the back slip zone, front slip zone, and cross shear zone were established according to the relationship between threading angle and neutral angle. The calculating models which were used to calculate the snake rolling mechanical parameters including the rolling force and rolling torque were set up. The calculated models of unit compressive pressure in the four zones were set up by the slab method, and on this basis the accurate calculating models of the rolling force and rolling torque were set up according to the composition of the rolling deformation zone and the boundary condition. The mechanical parameters were calculated by the analytical method and the numerical method, and the relative deviation is less than 6% which can satisfy the industrial requirement. The present analytical model can predict the characteristics during snake rolling easily and quickly and it is also suitable for online control applications.

Microstructure, Texture, and Mechanical Properties of Alternate α/β Mg–Li Composite Sheets Prepared by Accumulative Roll Bonding

Mg–5Li–1Al sheet and Mg–12Li–1Al sheet are used to prepare α/β Mg–Li composite sheets with accumulative roll bonding (ARB). The microstructure, texture, and mechanical properties of the specimens are investigated. Results show that, Mg–5Li–1Al alloy and Mg–12Li–1Al alloy alternatively distribute with uniform deformations and a good continuity, during the ARB process. With the increase in ARB passes, the hardness values of α layer and β layer increase, and the strength of composite sheet first increases, then maintains in a stable range. During the initial several passes, the elongation decreases, and it increases again after five passes. As for the texture density, with the increase in ARB passes, it first increases, then decreases. In the interface areas between sheets, a cross shear zone exists.

Analysis of strain variation in cross shear zone of plate during snake hot rolling

In order to study the distribution of equivalent and shear strain of aluminum alloy plate during snake hot rolling, several coupled thermo-mechanical finite element models (FEM) are established. Effects of speed ratio and offset distance on strain distribution of the plate are analyzed. The length of cross shear zone is defined to have a better understanding of the deformation characteristic in cross shear zone, which is the essential difference from symmetrical rolling in deformation zone. The results show that the equivalent strain and shear strain of lower part both increase with the increase of speed ratio, while the upper part decreases; the equivalent strain through the whole thickness decreases with ascending offset distance, while the shear strain of lower part increases. The length of cross shear zone quickly increases with ascending speed ratio and slightly decreases with ascending offset distance. The “positive” and “negative” cross shear zones are formed with the increase of speed ratio and offset distance, respectively. The value of the sensitivity coefficient of speed ratio is an order of magnitude bigger than the offset distance. However, the shear strain at center point increases with the ascending speed ratio and offset distance for different mechanism. As speed ratio increases, the asymmetry of the distribution of equivalent is becoming larger and the shear strain is generated in the same direction in cross shear zone. The FEM results agree well with experimental results.

Experimental and theoretical study on minimum achievable foil thickness during asymmetric rolling.

Parts produced by microforming are becoming ever smaller. Similarly, the foils required in micro-machines are becoming ever thinner. The asymmetric rolling technique is capable of producing foils that are thinner than those produced by the conventional rolling technique. The difference between asymmetric rolling and conventional rolling is the ‘cross-shear’ zone. However, the influence of the cross-shear zone on the minimum achievable foil thickness during asymmetric rolling is still uncertain. In this paper, we report experiments designed to understand this critical influencing factor on the minimum achievable thickness in asymmetric rolling. Results showed that the minimum achievable thickness of rolled foils produced by asymmetric rolling with a rolling speed ratio of 1.3 can be reduced to about 30% of that possible by conventional rolling technique. Furthermore, the minimum achievable thickness during asymmetric rolling could be correlated to the cross-shear ratio, which, in turn, could be related to the rolling speed ratio. From the experimental results, a formula to calculate the minimum achievable thickness was established, considering the parameters cross-shear ratio, friction coefficient, work roll radius, etc. in asymmetric rolling.

Permissible Minimum Thickness in Asymmetrical Cold Rolling

The minimum rolling thickness in asymmetrical rolling was analyzed compared with that in symmetrical rolling. The differential equilibrium equations on forces were established to calculate the asymmetrical rolling force equation by slab method. An implicit expression of the minimum rolling thickness was then derived from the rolling force equation and Hitchcock equation. The results show that permissible minimum rolling thickness of asymmetrical rolling only exists within a specific range of cross-shear ratio, which is termed the cross-shear zone proportion of the whole deformation zone. Numerical computation was carried out to obtain a discrete solution of the minimum rolling thickness. Experiments were designed to investigate the influence factors on cross-shear ratio. Finally, experimental results prove the correctness of the improved formula given.

A photoelastic investigation on the contact stresses developed in rolls during asymmetrical flat rolling

Experiments are described which give results of stress distribution in rolls during the asymmetrical rolling of pure lead. The asymmetry was due to both the rolls having different angular speeds and to the rolls having different diameters. The results of this work show a variation of the shear stress at both surfaces of contact accompanied by a change of sign at the neutral point. A cross shear zone was evident when asymmetry was due to difference in angular speeds, the extent of the cross shear zone increased with the increase of speed mismatch. The results also indicated that the asymmetry due to difference in roll radii had no significant effect on the size of cross shear zone. However, greater peak normal pressure was observed on the roll with the smaller diameter. The experimental results also indicated that with angular speed mismatch, the peak normal pressure did not necessarily coincide with the position of the neutral point.