Numerical Simulation And Forming Technology Research On Rolling And Stretch Forming For Surface Of Sheet Metal

Rolling and stretching technology (RST) that combines with traditional rolling andstretch forming is proposed to fabricate three-dimensional (3D) surface parts usingpolyurethane roller. Compared to traditional rolling and stretch forming, RST not onlyrealizes continuous and flexible forming of3D surface parts but also reduces springbackso as to improve forming quality.The finite element models of RST to form spherical surface, saddle surface and free-form surface were built, also forming process were simulated. Distribution of stress andstrain and springback were compared to RST and traditional stretch forming, and theparameters influencing on rolling and stretch forming were studied, and relevantexperimental parts were performed.The characteristic of RST was introduced, in contrast to traditional rollingtechnology, the three-dimensional compressive stress of material leaded to the lowdeviator of stress, which impeded the plastic deformation of sheet, and larger deformationwill not occur. During traditional stretch forming, the unidirectional tensile stress ofmaterial came up, which induced plastic deformation. When using RST to form, the twosides of the element shows two-dimensional tensile stress and one-dimensionalcompressive stress in the lateral bending direction, and three sides of element showedthree-dimensional compressive stress in the inside bending direction, but the deviator ofstress increased, the plastic deformation is more easily to occur.Based on finite element theory, the finite element model of spherical surface, saddlesurface and free-form surface were established, and their forming processes weresimulated. The numerical analysis of parameters of extensive displacements and rollingtimes as well as thickness of sheet on forming processes of spherical surface, saddlesurface and free-form surface parts were studied. The results showed that the equivalentplastic strain value increases with the increasing of extensive displacement. But breakagewill happen on the formed part when the extensive displacement is so big. Procedure ofrolling with many times is in favor of the extension of plastic strain form inside andoutside surface to the middle layer, so that the plastic deformation of forming part is morefully. As to spherical parts, with the increasing of sheet thickness, the compressiondeformation degree of inner surface and tensile deformation degree of outer surface ofsheet increase, so the value of plastic strain increases.As to saddle surface parts, with theincreasing of sheet thickness, the maximum value of plastic strain decreases and the minimum value shows a trend of increasing. For free-form surface parts, with theincreasing of sheet thickness, the maximum value of plastic strain decreases and theminimum value shows a trend of increasing.The effect of rolling times and the thickness on springback for forming partsincluding spherical surface, saddle surface and free-form surface parts were studied. Theresults indicated that the springback of spherical surface, saddle surface and free-formsurface parts decrease with the increasing of sheet thickness. Rolling for many times willsignificantly reduces the springback of spherical surface, saddle surface and free-formsurface parts.The research methods and the conclusion of this paper have significant guiding inengineering to form curved surface of sheet metal using the RST.