Research And Numeircal Simulation On Stretch Forming With Flexible Rollers For Curved Parts

Stretch forming technology, a common method of metal sheet forming, is widely used in thefield of aerospace to form the aircraft skins, the head of high-speed trains and automotivepanel, etc. The conventional stretch forming technology often need fantastic amount of timein manufacturing the dies and waste much money to debug dies, as well as much storagespace. Meanwhile, stress concentration is easily generated from the collective clamp used inthe conventional stretch forming, which will affect the quality of forming parts. And thecontrolling of the conventional stretch forming device is so hard. Therefore, concerning theabove factors, exploring a stretch forming device with excellent controllability, high formingprecision, good forming quality, easy application and simple structure will greatly promotethe development of Chinese aerospace industry, high-speed railway and automotive industry,etc.Flexible rollers stretch forming technology is a new metal sheet forming technology.The principle is that, designed between the clamps and die, the flexible rollers generate theloading, and the sheet constrained by the discrete clamps will produce bending deformation.Due to the constraint of the clamp, the deformed sheet will be stretched in the tangentialdirection of the die’s generatrix. With the increasing of the loading by the rollers, the stretchdeforming will augment. Then the sheet attaches the die and gains a certain amount of plasticdeformation.The main research content and conclusion of this paper are as follows:1. Study on the principle and forming device of flexible rollers stretch formingThe principle of flexible rollers stretch forming technology was analyzed and3Dcomputer aided design software was utilized for the design of flexible rollers and discrete clamps. By contrast with the traditional stretch forming, flexible rollers stretch formingtechnology has the advantages of forming double-curvature parts. By deducing thefundamental theory and introducing Bauschinger effect, the drawbead restraint force (FDBR)of the clamps were researched, meanwhile, the correlative formulas were given. Eachcomponent of the device of flexible rollers stretch forming device was introduced, and maintechnical parameters of the device were given.2. Research on finite element modeling and simulation of flexible rollers stretchformingThe finite element model traditional stretching forming and flexible rollers stretchingforming were established. By the analysis of technical parameters for flexible rollersstretching forming, reasonable loading pressure and geometry location of the roller as well asthe friction coefficient of the clamp were fixed. Adopting both of these methods to form thespherical parts, the conclusions showed that the effective stress and effective plastic strain ofthe spherical parts were more uniform by using the flexible rollers stretching forming, andthe distribution of thickness was well-proportioned.3. Study on the sheet movement with two different kinds of clampsStudy on the sheet movement with two different kinds of clamps, the researchconclusions showed that the sheet clamped by the drawbead clamp had a better flow in theforming process. However, the plate clamp had only a little flow in the interior of the clamp.The conclusion was verified by approach of the experiment.4. Establish the finite element model of flexible rollers stretching forming for theS-shaped curved part formingThe S-shaped part formed by flexible rollers stretching forming technology was studied.Finite element model of flexible rollers stretching forming for the S-shaped part forming wasestablished. By method of numerical simulation, comparing the distribution of stress andstrain with the different thickness of plastic cushion, the result showed that the dimple wasnot obvious with the increasing of the plastic cushion thickness. Effective stress andeffective plastic strain of forming part influenced by the different thickness of plastic cushionwas analyzed, and the result indicated that the thickness of plastic cushion was reasonablyselected in20~25mm.5. The study about the springback theory and numerical simulation of springback for stretch formingSpringback theory of stretch forming was studied. By method of theoretical derivation,the theory of bending springback in stretch forming was researched. Springback of formingparts for different thickness plastic cushion was researched, the result indicted that thespringback of thickness30mm was larger than that of thickness25mm and20mm.Meanwhile, the result of simulation also demonstrated that the bending springback was thedominant factor of the stretch forming springback.