Three-dimensional Surface Parts Research Articles

Influence of thickness reduction on the forming results in the three-dimensional surface rolling process with rigid arc-shaped rollers

Three-dimensional surface rolling with rigid arc-shaped rollers (TSRRAR), a new method for manufacturing double-curved metal sheets, can be used to realize the rapid forming of 3D surface sheets. The non-uniform roll gap is generated by a pair of rollers with different axial radii with appropriately reduced sheet thickness. After passing through the roll gap, a flat sheet is bent in the rolling direction. Meanwhile, it deforms perpendicular to the rolling direction, resulting in a three-dimensional surface part with curvatures in both directions. The work adopted the elastic-plastic finite element (FE) method to simulate aluminum alloy sheets with different maximum thickness reductions. The results showed that the longitudinal curvature of sheets rose as the reduction increased. Moreover, a slightly increased reduction caused a significant variation in the longitudinal curvature radius of sheets. Different bending curvatures of sheets could be obtained by changing the reduction, indicating the flexible forming of three-dimensional curved surface metal sheets. Also, the changing trend of longitudinal curvatures of testing parts obtained by rolling experiments was substantially in agreement with the FE simulation results. Therefore, the established FE models can be used for exploring the manufacturing process of TSRRAR.

Numerical simulation and experiment of dimple for flexible clamp multi-point stretch forming of spherical part

The structural character of flexible clamp stretch forming machine is introduced. The real stress and strain curve of Aluminium alloy 2024-O is tested by uniaxial tensile. Numerical simulation of dimple for spherical part with flexible clamp multi-point stretch forming (FCMPSF) is carried out by ABAQUS, and the generated result of dimple is elaborated. The effects of transitional length, sheet thickness and spherical radius on dimple are investigated by lots of numerical simulations, and the thickness strain of spherical part along the objective line ef with different forming suitation is extracted. Then polyurethane sheet is chosen as elastic cushion to depress dimple, and series of numerical simulations are put forward for spherical part of FCMPSF with different thicknesses of polyurethane sheet. Finally, FCMPSF experiment is done and forming precision is measured. Consequently, the spherical part has good forming shape and surface accuracy, which illustrates that the FCMPSF technology is feasible and practional to forming three-dimensional surface part.

Research on Contact State and Its Effect on Forming Precision in Uniform-Contact Stretch Forming Based on Loading at Multi-Position

Uniform-contact stretch forming based on loading at multi-position (UC-SF) was designed to substitute for conventional stretch forming (C-SF) in the manufacturing of qualified three-dimensional surface parts of a specified shape. Since the integral rigid clamps are replaced by discrete clamps, the sheet metal can be bent in a transverse direction (perpendicular to the stretching direction), and the sheet metal can be automatically warped to the die surface during the loading process. In this paper, finite element numerical simulations were performed to research the contact state evolution and its effect on forming precision by two kinds of loading modes (UC-SF and C-SF). The evolutions of contact state for spherical and saddle-shaped parts were analyzed in different steps, and the results reflect that, in UC-SF, the contact region of curved surface parts is gradually extended in a long strip, and the effective formed regions of the final parts can be in contact with the die surface. However, in C-SF, it is difficult for the final parts to be completely in contact with the die surface, especially spherical parts of a large curvature. Moreover, it is found that the noncontact region of the saddle-shaped part is susceptible to wrinkling in C-SF. Conversely, in UC-SF, the sheet metal can be constrained by contact with a die surface, such that the noncontact region and wrinkle defect disappear and high-precision parts are formed. Finally, stretch forming experiments were carried out and the perfect curved surface part was formed; thus, the experimental results verify the feasibility and effectiveness of UC-SF.

Research on flexible rolling process of three-dimensional surface part using auxiliary rolls

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.

Elongation Rule of the Longitudinal Fiber of the Continuous Roll Forming Part

Continuous roll forming is a novel technique for low-cost, high-efficient manufacturing of three-dimensional surface part. Comparing with conventional continuous forming (using at least three rolls), continuous roll forming employs an upper and a lower flexible rolls to shape the sheet metal. The desired forming shape can be obtained by controlling the profile of the flexible roll and the gap between upper and lower flexible rolls. Modeling and simulation of the continuous roll forming process based on finite element analyses is established to investigate the elongation rule of the longitudinal fiber of the continuous roll forming part. The length of the longitudinal fiber at different positions across the thickness direction is discussed, and the mechanism of the longitudinal deformation is clarified. The following conclusions are obtained. When the flexible roll profile and the roll gap distribution meet certain conditions and make length of the longitudinal fiber linearly distributed, the longitudinal deformation of the sheet metal can be generated.

Research on flexible asymmetric rolling process for three-dimensional surface parts

To realize rapid fabrication of three-dimensional surface parts, flexible asymmetric rolling process for continuously forming surface parts is developed. This process employs an auxiliary roll, a pair of upper and lowers bendable rolls as forming tools. By adjusting the height of the auxiliary roll, the sheet metal is inclined before non-uniform rolling, which is conducive to longitudinal bending deformation of the sheet metal after rolling. Meanwhile, the non-uniform thickness reduction of the sheet metal caused by the non-uniform roll gap between the upper and lower rolls makes itself bend in the transverse and longitudinal directions. Owing to small bending behavior of the bendable roll in the experiment, the forming precisions of formed parts are not ideal by the 3D rolling process without the auxiliary roll. In this paper, the flexible asymmetric rolling process is introduced to improve the 3D rolling process for surface parts with well forming precisions. An auxiliary roll is employed in the flexible asymmetric rolling process except a pair of upper and lower rolls. The formation mechanism of the curved surface is set forth, and the parametric equations of the formed surface in flexible asymmetric rolling process are derived. Typically simulations and experiments for forming spherical and saddle surfaces have been performed. The dimensional accuracies of the forming parts are measured, and the differences of the 3D rolling and flexible asymmetric rolling processes are investigated though numerical simulations. The forming results with good dimensional accuracies show that the flexible asymmetric rolling process is feasible for manufacturing three-dimensional surface parts with a broader range.

Investigation of deformation in stretch forming based on distributed displacement loading

Stretch forming based on distributed displacement loading is a new stretch forming process, in which distributed displacements are applied at a series of discrete points, therefore, the deformation in different positions of sheet metal can be individually controlled. To investigate the deformation of sheet metal in stretch forming, the rational loading trajectory is designed, and it is determined by the respective length of longitudinal cross-section curve. The numerical simulation results show that, the loading trajectory is valid to form three-dimensional surface parts, and the relatively small shape errors between the simulated results and target results make it possible to form qualified parts. Meanwhile, the longitudinal strains are uniformly distributed along the longitudinal material lines, and longitudinal strains increase evenly with the process of stretch forming. Finally, experimental tests proved the effectiveness and feasibility of the stretch forming based on distributed displacement loading.

The shape analysis of three-dimensional flexible rolling method

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.

Research on Transition Zones of Spherical Surface Parts in 3D Rolling Process

3D rolling is a novel technology for three-dimensional surface parts. In this process, by controlling the gap between the upper and lower forming rolls, the sheet metal is non-uniformly thinned in thickness direction, and the longitudinal elongation of the sheet metal is different along the transverse direction, which makes the sheet metal generate three-dimensional deformation. In this paper, the transition zones of spherical surface parts in 3D rolling process are investigated. Spherical surface parts with the same widths but different lengths are simulated in condition of the same roll gap, and their experimental results are presented. The forming precision of forming parts and the causes of transition zones in the head and tail regions are analyzed through simulated results. The simulated and experimental results show that the lengths of transition zones of spherical surfaces in the head and tail regions are fixed values in condition of the same sheet width and roll gap.

An investigation on roll adjusting radius in three-dimensional rolling process for three-dimensional surface parts

Three-dimensional rolling is a novel forming process for three-dimensional surface parts, which combines the rolling process with multi-point forming technology. This process employs a pair of forming rolls as a forming tool; the residual stress of sheet metal makes the sheet metal generate three-dimensional deformation by controlling the nonuniform distribution of roll gap of the forming rolls. In this article, two types of forming processes are investigated for three-dimensional surface parts with the same target shape in different roll adjusting radius. The roll adjusting radius of a forming process is much larger than the target transverse curvature radius of the forming part, and the roll adjusting radius of another forming process is equal to the target transverse curvature radius of the forming part. Finite element analysis models are established; spherical and saddle surfaces are simulated. The corresponding experimental results are obtained. The dimensional accuracy of the forming parts using the two types of forming processes is compared, and the difference between the two types of forming processes for forming parts is analyzed through simulated results. The bendable roll rotates around its bent axis easily if its bending deformation is small; therefore, the forming process that the roll adjusting radius is much larger than the target transverse curvature radius of the surface part has relatively extensive application prospect. The comparison and analysis of the forming results may provide useful guidance on optimizing the three-dimensional rolling process for three-dimensional surface parts.

Continuous-forming method for three-dimensional surface parts combining rolling process with multipoint-forming technology

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.

Research on forming precision of flexible rolling method for three-dimensional surface parts through simulation

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.

Research on three-dimensional surface parts in multi-gripper flexible stretch forming

Multi-gripper flexible stretch forming (MGFSF) is a novel flexible forming process of sheet metal based on the multi-point forming principle. The straight jaws in traditional transverse stretch forming (TSF) are replaced by several discrete clamping mechanisms on both sides. To help understand the forming characters of MGFSF, spherical and concave–convex parts were selected as the research objects and finite element analyses on TSF and MGFSF were implemented using an explicit nonlinear finite element code. The influence of the transition length on the forming results in MGFSF was also taken into account in the present work. The simulation results reveal that a shorter transition length in MGFSF would result in an easier conformability of the sheet metal to the desired shape as well as a smaller strain variation in the forming zone. It is also found that, compared to TSF, the sheet metal can be formed without transition zone by utilizing MGFSF, which could significantly improve the material utilization and save the manufacturing costs. Finally, experimental validations were conducted on the self-developed MGFSF apparatus and the experimental results show a good agreement with the numerical results.

Investigation on Forming Precision of Flexible Rolling Process for Three-dimensional Surface Parts of Different Sheet Materials

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 2.0mm excluding the head and tail regions of the forming parts in rolling direction.

Numerical Investigation of Continuous Roll Forming for Three-Dimensional Surface Parts

Continuous roll forming is a new technology for manufacturing three-dimensional surface parts. Extensive numerical simulations of continuous roll forming process were carried out. The influence of the middle curve and the magnitude of the roll gap on the longitudinal curvature of formed parts is investigated. Wrinkling is one of the most important defects for the formed parts in continuous roll forming process. A simplified model was established for analyzing the wrinkling of saddle-shaped part and torus-shaped part. The simulated results show that the wrinkling of saddle-shaped part is located at the edges, and the wrinkling of torus-shaped part emerges in the vicinity of middle region.

Surface flexible rolling for three-dimensional sheet metal parts

To realize highly effective and continuous fabrication of three-dimensional (3D) sheet metal parts, a new forming method, surface flexible rolling forming, has been investigated. This method takes only two integral flexible rolls as the forming tool. In the forming process, a non-uniform elongation in the rolling direction and a bending deformation in the thickness direction occur simultaneously, and finally three-dimensional surface parts are formed. In this work, the basic principle and forming mechanism of surface flexible rolling are studied. A method to calculate the transversal curvature radius of the arc-shaped roll is brought forward, while the feasibility is verified by the explicit dynamic finite element analysis. An experimental device has been developed and the forming experiments have been performed. Typical 3D surface parts including the convex and saddle surface parts have been obtained. Finite element model of surface flexible rolling is established and the effect of forming parameters such as reduction, velocity, bending radius and friction on the surface shape is analyzed. The forming effects including shape errors and thickness changes are studied by the deviation analysis. The results indicate that the formed surface is quite close to the criteria one; the thickness of the parts changes gradually and keeps within a narrow range. The experimental formed parts are measured and the forming accuracy is investigated. The results show that the accuracy is high, and are consistent with the simulation.

Modeling and Simulation of Continuous Flexible Roll Forming Process

The continuous flexible roll forming process is a novel sheet metal forming technique for effectively manufacture of three-dimensional surface parts. In this study, two types of finite element (FE) models were developed under the ABAQUS/Explicit environment. The difference of the two models is that the rolls are defined as discrete rigid bodies in model No.1 and are deformable in model No.2. An experiment was carried out using the continuous sheet metal forming setup. The comparison of the numerical computation results with the experimental results shows that the model No.2 can be used for the shape prediction of continuous flexible roll forming process well.

Rolling Process for the Continuous Forming of Curved Surface Parts Based on Bended Rolls

A new sheet metal forming process which can form three-dimensional surface rapidly, effectively and with lower-cost has been proposed. This paper mainly focuses on the fundamental aspects of the process. The principle of the rolling process based on bended rolls is introduced, and the methods to calculate the longitudinal bending deformation and to design the roll gap are presented. Experiments for typical surface parts are carried out. The forming results of convex surface and saddle shaped surface parts are measured and analyzed, the analyzed results demonstrated that the proposed process is a feasible and effective way of forming three-dimensional surface parts.

Mechanical Mechanism of Continuous Roll Forming for Three-dimensional Surface Parts and the Calculation of Bending Deformation

Continuous roll forming(CRF) is a new forming method for sheet metal,the three-dimensional surface part can be formed by using two bended forming rolls.The mechanical analysis on the deformation process from sheet blank to the curved surface in CRF is carried out,the deformation and material models are simplified,according to the equilibrium of internal force in the formed surface,the basic equations for governing bending deformation in longitudinal direction(rolling direction of forming rolls) are set forth,the formulations for calculating the radius of bending curvature in longitudinal direction based on the rolling strain are presented,and the method to design the gap between the upper and lower rolls is given.Analysis results show that,when the initial rolling strain is linearly distributed in the height direction,there are no residual stresses in the final formed surface,in addition,the bending curvature in longitudinal direction is determined by the maximum height difference and the compression ratio difference in the cross-section.Through the analyses on the process of CRF,the condition to realize the continuous roll forming for curved surface is achieved and the effects of the compression ratio difference and the geometrical parameters of the curved surface on the bending deformation in longitudinal direction are obtained.Experimental examples of CRF verify the effectiveness and practicability of the proposed theory and formulations.

Development of Flexible Rolling Device for 3D Plate

To effectively form three-dimensional sheet metal parts with various curvatures produced in small quantities, flexible rolling forming, a new flexible forming method is being developed. Firstly, concept of the flexible rolling forming is introduced and its characteristics and working principle are analyzed by the combination of conventional rolling and multi-point forming. Secondly, the equipment design scheme of flexible rolling forming is put forward and the relevant device is developed. Thirdly, the feasibility and practicality of flexible rolling forming are verified by rolling several typical three-dimensional surface parts such as spherical and saddle surface parts by self-developed device. Finally, verifies the reasonableness of the device and at the same time possesses the important guiding significance to the research and development of practical flexible rolling forming equipment.