Search

AbstractFlexible rolling (FR) is a novel process for manufacturing doubly curved shallow shells with various shapes based on a pair of small-diameter bendable rolls. In this paper, the fundamental reason for bi-directional bending of the sheet metal in FR is explained. For the purpose of predicting the forming radii in the transverse and longitudinal directions more effectively, the exit velocity is divided into linear velocity and interference velocity, with the latter so small as to be considered to cause only elastic deformation of the sheet. The theoretical calculation model of the pre-curvature radius resulted from linear velocity is established. Using the mechanical theory of the doubly curved shallow shell, the transverse and longitudinal curvature changes caused by the interference velocity are derived and solved by the analytical approach, which are added to the transverse and longitudinal pre-curvatures respectively so that the actual curvature radii are obtained. In order to verify the reliability of the proposed shape prediction method of FR, numerical simulations and forming experiments for convex and saddle-shaped parts are carried out. Through measurement and comparison, it is found that the simulated and experimental results are extremely consistent with the theoretical data. Besides, the effect of important parameters on elastic deformation is investigated by means of the deduced formulas. [ABSTRACT FROM AUTHOR]

With the development of electronic devices, conductive composites are receiving more and more attention, the demand for electrically conductive composites (ECC) is also increasing. However, the existing preparation process does not allow for the continuous preparation of electrically conductive composites. Therefore, we report a continuous spatial‐confining network assembly (CSNA) technique method to achieve an efficient and controllable preparation of electrically conductive composites. Short carbon fiber (SCF) and polydimethylsiloxane (PDMS) are used as conductive fillers and polymer matrix to prepare conductive composites, and the filler content of the prepared composites is 6 wt%. The electrical conductivity of the PDMS/SCF conductive composite is 73.72 S m−1, when flexible roll with a Shore hardness of 12.5 A and a roll pressure of 126 N is used. The effect of increasing pressure, the higher the number of rolls and the roll speed on the electrical properties of the composite, is also investigated. To sum up, the PDMS/SCF composite prepared by this preparation method is expected to achieve continuous production and application in medical, biological, thermal management, etc. [ABSTRACT FROM AUTHOR]

Flexible rolling is important for increasing rolling production capacity. Since the wear rolls withdrawn and new rolls launched into the rolling process causing thermal deformation parameters variation, such as deformation temperature, strain rate, and strain. This paper studies the coupling behavior of static recrystallization (SRX), metadynamic recrystallization (MDRX), and thermal deformation parameters based on the double-pass thermal simulation experiments, analyzes the flow stress curves and reveals the variation law of recrystallization with thermal deformation parameters. The result shows that the second-pass flow stress of SRX is significantly dependent on the inter-pass time, deformation temperature and strain rate, Compared to MDRX, SRX requires time to nucleus of conception and is more influenced by initial strain. Considering the recovery effect and the multi-pass static softening solution algorithm of materials, the kinetic models of SRX and MDRX are established, and the predicted values of the models are in good agreement with the experimental values. The EBSD microstructure characterization technique is used to characterize the morphology of SRX and MDRX. The result shows that increasing inter-pass time, deformation temperature and strain rate can promote the SRX and MDRX process and improve static softening effect. Under the condition of constant deformation temperature and strain rate, increasing the initial strain can increase the SRX volume fraction. However, deformation temperature and strain rate have a more significant effect on the static softening than the initial strain. This paper provides a theoretical basis for designing and optimizing recrystallization behavior of flexible rolling gaps.

The continuous tube-rolling method has been widely used to manufacture high-quality seamless pipes and tubes. However, the analytical model for determining the roll pitch diameter in three-roll continuous retained mandrel rolling from first principles has not yet been presented, which has, thus, hindered the development of rolling control technology in tube manufacturing. In this work, a new analytical model has been established from the force–equilibrium principles. The modelling has taken the tube-roll contact geometry, roll pressure, mandrel pull forces, inter-stand tensions, and friction coefficients into account for its formulations. Seen from the experimental results of the rolling at the plant, the maximum deviation of the predicted projected contact area is less than 6% and the maximum deviation of the calculated roll speed from the satisfactory data in field operation is less than 3.9%. The proposed model has enabled the influence of the friction coefficients on the roll pitch diameter to be quantified in theoretical analysis, and it was found that the changing amplitude of the theoretical roll pitch diameter corresponding to the commonly used data range of the friction coefficients can be above 9%. Having overcome the shortcomings of the empirical model, this model has the required prediction accuracy and flexibility for being applied to flexible tube rolling. By building the key algorithms around physical models, this modelling has advanced not only the rolling control at the plant, but also our scientific understanding of the mechanics of the continuous tube-rolling process. [ABSTRACT FROM AUTHOR]

The continuous tube-rolling method has been widely used to manufacture high-quality seamless pipes and tubes. However, the analytical model for determining the roll pitch diameter in three-roll continuous retained mandrel rolling from first principles has not yet been presented, which has, thus, hindered the development of rolling control technology in tube manufacturing. In this work, a new analytical model has been established from the force–equilibrium principles. The modelling has taken the tube-roll contact geometry, roll pressure, mandrel pull forces, inter-stand tensions, and friction coefficients into account for its formulations. Seen from the experimental results of the rolling at the plant, the maximum deviation of the predicted projected contact area is less than 6% and the maximum deviation of the calculated roll speed from the satisfactory data in field operation is less than 3.9%. The proposed model has enabled the influence of the friction coefficients on the roll pitch diameter to be quantified in theoretical analysis, and it was found that the changing amplitude of the theoretical roll pitch diameter corresponding to the commonly used data range of the friction coefficients can be above 9%. Having overcome the shortcomings of the empirical model, this model has the required prediction accuracy and flexibility for being applied to flexible tube rolling. By building the key algorithms around physical models, this modelling has advanced not only the rolling control at the plant, but also our scientific understanding of the mechanics of the continuous tube-rolling process.

Dynamic recrystallization (DRX) is the predominant softening mechanism under high‐temperature large‐plastic deformation and determines the microstructure evolution of steel. Herein, an equivalent substitution method is proposed to investigate the coupling effect of deformation conditions on microstructural evolution during the flexible rolling process. Low‐carbon steel is compressed using a Gleeble 3800‐GTC thermal–mechanical physical simulation system at temperatures ranging from 900 to 1100 °C and strain rates ranging from 0.01 to 10 s−1. The flow stress behaviors under different deformation conditions are discussed. Accordingly, the relationship between strain rate and temperature is established using the Zener–Hollomon equation. Further, a new DRX model is proposed by combining the theoretical implications of previous models. The effectiveness of the experimental model and predicted model is statistically evaluated to accurately determine the DRX volume fraction of the experimental steel. Based on the dynamic material model, a hot processing map of the experimental steel is also developed to evaluate the steel's hot workability. Finally, the microstructure of the experimental steel is analyzed under specific deformation parameters. The results demonstrate that DRX behavior decreases as the upper roller is raised and the lower roller is lowered during the flexible rolling process. [ABSTRACT FROM AUTHOR]

The 3D curved part rolling method based on the rigid arc-shaped rollers is a novel sheet metal rolling process to rapidly manufacture 3D surface parts for various parameters. The flow of material inside the sheet metal is complicated during the cold rolling forming process of the 3D curved parts, whose quality of products is sensitive to process parameters. The work analyzed the friction force for the sheet metal inside the roll gap during rolling as well as the reason for the instability of the forming process. The instability of the forming process significantly affected the forming accuracy of curved parts. Therefore, the method of using an auxiliary plate was proposed to improve the stability of the rolling process. The finite element numerical simulation models were established for two rolling processes, with and without the auxiliary plate, and the forming errors of the two processes were computed. The numerical simulation results showed that the rolling process with the auxiliary plate can obtain a more stable rolling process, and the forming error of formed curved parts was smaller. The reliability of the numerical simulation results was verified through experiments. [ABSTRACT FROM AUTHOR]

Flexible asymmetric rolling process has been conceived to manufacture sheet metal parts with high efficiency. In the asymmetric rolling process, the metal plate is fed into the roll gap at a tilted angle. The nip angles of the top and bottom rolls are not equal, and inconsistent thickness thinning occurs on the two surfaces of the metal plate. It is easy to bend the metal plate during the asymmetric rolling process. Then, desired metal parts with three-dimensional deformation are generated though non-uniformly rolling in the thickness direction. Compared with the 3D rolling technology, shape precision of the metal part with desired configuration is significantly improved. In this paper, the forming sequences of the auxiliary roll height are investigated for forming surface parts. A series of auxiliary roll heights are selected for the metal plate in condition of same roll gap distribution. Numerical simulations and experiments for typically surface parts have been performed. Deformation degree and shape accuracy of the surfaces parts formed in different auxiliary roll heights have been respectively compared and analyzed. Through analyzing deformation degree and shape accuracy of the surfaces parts, it is beneficial for parameters optimization of the flexible asymmetric rolling process. [ABSTRACT FROM AUTHOR]

Flexible rolling is a sheet metal forming process used to rapidly manufacture three-dimensional (3D) surface parts for various industries. In this paper, a flexible rolling method of 3D surface parts using auxiliary rolls is introduced, and a forming mechanism of curved surface parts is described. The generation of instability of a convex surface part in the rolling process was analyzed, and the calculation for longitudinal bending deformation was deduced to obtain an effective design method for the roll gap shape. Numerical simulations and experimentation were performed for two rolling processes, with and without auxiliary rolls, for surface parts, for which the curvature distribution and dimensional accuracy were measured and analyzed. The simulation results show that the flexible rolling process with auxiliary rolls offers a more stable rolling process with smaller curvature fluctuation of the formed parts. The experimental results further verify that the process with auxiliary rolls is better than that without auxiliary rolls, as indicated by the shape error that can be controlled in a narrower range and the smaller error value of fluctuation. Overall, the proposed flexible rolling process with auxiliary rolls offers a feasible method to effectively form 3D surface parts with good forming quality and accuracy. [ABSTRACT FROM AUTHOR]

Flexible rolling is a novel and effective process for double curvature parts and it is suitable for various shapes and small batch production. Taking spherical surface parts as an example, the utilization rate of the processed curvature part in flexible rolling was studied for the first time. In the finite element model, the processed surface part is divided into three areas by forming characteristics. The formation mechanisms of forming areas are discussed. Meanwhile, the effect of the ratio among length, width, and thickness on the utilization rate of processed surface part is studied deeply. The results show that the processed surface part is divided into three areas by plastic deformation in the longitude direction. The bending deformation distribution is continuously changing in the transition-forming areas and stable in the stable-forming area. The ratio among the length, width, and thickness has a great effect on the utilization rate of processed surface part. When the width and thickness remain constant, the utilization rate is increasing with increasing length ratio. When the length and thickness remain constant, the utilization rate is increasing with decreasing width ratio. When the length and width remain constant, the utilization rate is increasing with decreasing thickness ratio. The numerical simulation results are in accord with experiment results. [ABSTRACT FROM AUTHOR]

Flexible rolling is a forming process based on thickness reduction, and the precision of thickness reduction is the key factor affecting bending deformation. The major purpose of the present work is to solve the problem of bending deformation error caused by insufficient thickness reduction. Under the condition of different rolling reductions with the same sheet thickness and the same thickness reduction with different sheet thicknesses, the thickness reduction error of sheet metal is analyzed. In addition, the bending deformation of sheet metal under the same conditions is discussed and the influence of the multi-step forming process on the thickness reduction error is studied. The results show that, under the condition of the same sheet thickness, the thickness reduction error increases with increasing rolling reduction because of an increase in work hardening. As rolling reduction increases, the longitudinal bending deformation decreases because of the decrease of the maximum thickness difference. Under the condition with the same thickness reduction, the thickness reduction error increases because of the decrease of the rolling force with increasing sheet thickness. As the sheet thickness increases, the longitudinal bending deformation increases because of the increase in the maximum thickness difference. A larger bending deformation is divided into a number of small bending deformations in a multi-step forming process, avoiding a sharp increase in the degree of work hardening; the thickness reduction error is effectively reduced in the multi-step forming process. Numerical simulation results agree with the results of the forming experiments. [ABSTRACT FROM AUTHOR]

In this study, a new design for tensile specimens made from tailor rolled blanks (TRB) with longitudinal thickness transition zone (TTZ) has been proposed. To this end, an additional lateral wedge angle is introduced to obtain a uniform stress field along the gauge length, which enables one to study the tailored properties of TRBs via stress-strain curves without considering the effects of geometrical inhomogeneities. Parallel finite element simulations were carried out to study the stress and strain fields resulted from different geometries of tensile specimens. The results were then used to obtain stress triaxiality factors to analyze the deformation prior to failure. In addition, a mathematical model was developed to study the contribution of different parts of TTZ to the total deformation. The results of uniaxial tension test along with results of simulation revealed that the deformation is controlled by the side with lower load-bearing ability in the new-developed tensile specimen. Furthermore, it was concluded that the conventional tensile specimens are more appropriate to study the effect of thickness changes on the elongation of TRBs. However, the presented tensile specimens can be used to study the strength of TRBs. Finally, the fracture mechanisms were investigated utilizing SEM and optical observations. [ABSTRACT FROM AUTHOR]

As the local forming non-uniform of the formed curved surface part with larger bending deformation is the one of common defects, the utilization ratio of metal plate greatly reduces due to this defect, and cost of production is also increasing. In this paper, the differential speed rotation technology of flexible rolling process was proposed firstly to solve this forming defect. The finite element model was established, the reason of the local forming non-uniform was discussed; the effect of differential speed rotation technology on the forming uniform was studied. The results show that: Flexible rolling is a process based on thickness reduction, in this forming process, the thickness reduces sharply near the back end of metal plate, the local forming non-uniform of formed curved surface part is caused during this process; the differential speed rotation technology is applied in flexible rolling, with increasing rotation speed difference between upper and lower roll set, the forming uniformity of the formed curved surface part is greatly improved. The results of numerical simulation are in agreement with the result of forming experiments.

In this study, effects of different deformation conditions on the rolling force were studied during variable gauge rolling processes. To this end, variations of rolling forces with rolling times were analyzed at different roll diameters, absolute thickness reductions and friction coefficients. Considering the rolling force variations, an abrupt change in the outlet section of downward and outward rolling was observed at all deformation conditions. The experimental data, along with the results obtained from finite element method (FEM) simulations, revealed that this drop in the rolling force (DRF) is strongly dependent on the deformation conditions. It was found that the DRF value increases with increasing absolute thickness reduction, roll diameter and friction coefficient. Furthermore, dependency of contact length on the roll radius and wedge angle (slope of the thickness transition zone) was investigated. Accordingly, it was concluded that the variations of the DRF value can be mainly attributed to the changes in the contact length during variable gauge rolling. Moreover, slab method analysis was used to model the effects of deformation conditions on DRF.

A new forming method, three-dimensional flexible rolling, is proposed for three-dimensional surface parts, which can form the parts effectively with the dieless characteristics. In this study, the shape of bending rolls is circle and the bending radii of upper and lower rolls are different; therefore, the roll gap is non-uniform. Because of the roll gap, an uneven compression appears at the transversal direction, which leads to a non-uniform elongation in feeding direction. The parts bend in two directions at the same time, and the three-dimensional surface shape is obtained. The forming rules of flexible rolling are proposed to analyze the relationship between the pressure ratio and the deformation extent of double-curved surface. The function between the non-uniform roll gap and the bending radius is deduced from the theory of invariable volume. An experimental device is developed to do the forming experiments. The feasibility of the device and the advantage of the method have been validated through numbers of experiments. Typical three-dimensional surface parts such as the convex and saddle parts have been completed for researching and analyzing. Some fine numerical simulation results of flexible rolling have been obtained. Finally, the simulation results are compared with the actual results to analyze the shape and illustrate the forming effect. [ABSTRACT FROM AUTHOR]

Continuously increasing demands for consumption-optimized automotive concepts require steady development of weight-saving potentials. In the area of steel lightweight design, flexible rolling of tailor-rolled blanks, TRB, is a well-established technology applied worldwide in all automotive categories. In the future, with the current tendency towards an increased application of aluminium sheets in the car body and chassis, flexible rolling of aluminium will become more and more attractive. In the present paper, the status of the process and materials development of Al-TRB is presented and the prospective of the future development is outlined. First, the possible development directions are addressed, followed by an outline of the process chain for the Al-TRB fabrication together with several application examples. Considering work-hardening AA 5xxx series and age-hardening AA 6xxx series alloys for automotive applications, lab-scale experiments have been conducted in order to elucidate the range of properties which can be realized through flexible rolling while maintaining reproducible constant materials properties according to specification. Large-scale trials were performed to demonstrate that the manufacturing of Al-TRBs is feasible, in that these alloys can be processed in industrial scale to provide homogeneous materials properties over the relevant thickness range for automotive applications. [ABSTRACT FROM AUTHOR]

Flexible rolling is a novel forming process for three-dimensional surface parts combining the rolling process with multi-point forming technology. By controlling the distribution of the gap between the upper and lower forming rolls in the rolling process, the sheet metal is thinned non-uniformly in thickness direction, and the longitudinal elongation is different along the transverse direction, which makes the sheet metal generate three-dimensional deformation. In this paper, the comparison of the forming precision with different sheet materials is presented by measuring the shape errors of the simulation results, the materials of sheet metal are low carbon steel 08Al sheet and aluminum alloy 2024-O sheet. Torus and saddle surface parts of different sheet materials are simulated and their experimental results are presented. The simulated results are consistent with the experimental results which verify the feasibility of the use of simulation to guide the experiment. The shape errors of simulated results show that the forming precision of the 08Al sheet is better than that of the 2024-O sheet, but all the deviations of the forming parts are less than 2.0 mm excluding the head and tail regions of the forming parts in rolling direction. [ABSTRACT FROM AUTHOR]

Flexible rolling is a novel forming process for three-dimensional surface parts, which combines the rolling process with multipoint-forming technology. This process employs a pair of forming rolls as a forming tool. By controlling the gap between the upper and lower forming rolls, residual stress caused by the longitudinal non-uniform elongation of sheet metal makes the sheet metal generate three-dimensional deformation. In this paper, the improvement of the process is introduced that the middle curve radius of the roll gap is much larger than the transverse curvature radius of the forming surface in the forming process. The forming roll rotates around its own axis easily because of the small bending deformation which is suitable for producing three-dimensional surface parts including the wide sheet metal with a relatively small transversal curvature radius. The forming principle is set forth, and corresponding formulations are presented. Finite element analysis model is established, and spherical and saddle surface are simulated. The forming precision and the causes of the shape errors are analyzed through simulated results. The experimental equipment is designed and their experimental results are obtained. Simulation results are in well agreement with the experimental results, which verifies the feasibility of using simulation to guide the experiment. The results of both numerical simulations and experiments show that the proposed process is a feasible and effective way of forming three-dimensional surface parts. [ABSTRACT FROM AUTHOR]

Flexible rolling is a novel forming process for three-dimensional surface parts using a pair of bendable rolls. By controlling the distribution of the gap between the upper and lower forming rolls in the rolling process, the sheet metal is nonuniformly thinned in the thickness direction and the longitudinal elongation is different in the width direction of the sheet metal, which makes the sheet metal deform in rolling direction. With the rotation of the bendable rolls, the sheet metal is deformed consecutively and a three-dimensional surface part could be obtained. A small experimental device has been designed. Finite element analysis (FEA) model is established. Spherical surface and saddle surface are simulated, and their experimental results are presented. The major purpose of the present work is to analyze the forming precision of flexible rolling and the reasons for the shape errors through simulated and experimental results. The results demonstrate that the proposed process is a feasible and effective way of forming three-dimensional surface parts. [ABSTRACT FROM AUTHOR]

Abstract: To meet targeted reductions in CO2 emissions by 2050, demand for metal must be cut, for example through the use of lightweight technologies. However, the efficient production of weight optimized components often requires new, more flexible forming processes. In this paper, a novel hot rolling process is presented for forming I-beams with variable cross-section, which are lighter than prismatic alternatives. First, the new process concept is presented and described. A detailed computational and experimental analysis is then conducted into the capabilities of the process. Results show that the process is capable of producing defect free I-beams with variations in web depth of 30–50%. A full analysis of the process then indicates the likely failure modes, and identifies a safe operating window. Finally, the implications of these results for producing lightweight beams are discussed. [Copyright &y& Elsevier]

In recent years, steel production has increased rapidly in China, to approximately 489 Mt in 2007. However, any further growth in production presents problems related to the shortage of energy and resources, environmental pollution, and the high cost of raw materials. In view of this, the government of China has changed its steel policy from tax return for export of steel products to adding extra tax on it. The steel companies in China are now forced to devote more attention to reducing the cost of steel production. This articleputs forward idea of rolling steel with declining resources. It includes: 1) Flexible Rolling Technology (FRT) based on the technology of online control of microstructure and properties, which will facilitate using a slab with the same chemical composition to produce the steel products of different properties by means of using different rolling and cooling parameters; 2) new generation cooling system and new generation Thermo-Mechanical Control Processing (TMCP), including High Rate Cooling (HRC) and Cooling Path Control (CPC) for plate mill, hot strip mill, and bar mill; 3) development of high performance steel products with low cost, such as super steel, fine grained steel, and Advanced High Strength Steel (AHSS), such as Dual Phase (DP) and TRIP steels with simple chemical composition. The key points are to save energy and reduce resource consumption (especially the consumption of microalloying elements), aiming at reducing manufacturing cost and helping to protect and conserve the environment, which is considered to be the best way to ensure sustainable development of steel rolling industry. [ABSTRACT FROM AUTHOR]

3D-Strip Profile Rolling should enable the production of blanks with a defined thickness profile in latitudinal and longitudinal direction. The production chain of 3D-Strip Profile Rolling will combine Flexible Rolling in a first production step with Strip Profile Rolling in a second step. The control system to adjust the roll gap during 3D-Strip Profile Rolling is currently under development. Nevertheless, some first experiments have shown the general feasibility to produce 3D-profiled blanks. In 3D-Strip Profile Rolling the material will strain harden differently on different locations. This results in a variation of the material properties of the strip. Lateral spread, elastic roll stand deformation and local deformation will be influenced by this variation. To investigate these influences on the complete production process, the complete production chain needs to be modelled in the future with aid of finite element simulations. In this publication a first simulation model is used to study the influence of different grades of strain hardening in a Taylor Rolled Blank on the bulge formation that occurs during the rolling of a rill in this Tailor Rolled Blank. [ABSTRACT FROM AUTHOR]

As the local forming non-uniform of the formed curved surface part with larger bending deformation is the one of common defects, the utilization ratio of metal plate greatly reduces due to this defect, and cost of production is also increasing. In this paper, the differential speed rotation technology of flexible rolling process was proposed firstly to solve this forming defect. The finite element model was established, the reason of the local forming non-uniform was discussed; the effect of differential speed rotation technology on the forming uniform was studied. The results show that: Flexible rolling is a process based on thickness reduction, in this forming process, the thickness reduces sharply near the back end of metal plate, the local forming non-uniform of formed curved surface part is caused during this process; the differential speed rotation technology is applied in flexible rolling, with increasing rotation speed difference between upper and lower roll set, the forming uniformity of the formed curved surface part is greatly improved. The results of numerical simulation are in agreement with the result of forming experiments. [ABSTRACT FROM AUTHOR]