Numerical Simulation Analysis And Experimental Research On Roll Bending Forming Process Of Three-dimensional Surface

Three-dimensional sheet metal parts are widely used in the manufacturing of automobiles,high-speed trains,urban architectures and airplanes,etc.Large batch and single type curved parts are usually manufactured by conventional mold forming process.Considering the high cost and low flexibility of mold forming,a new flexible forming technology needs to be developed to manufacture single-piece or small batch curved parts with personalized,diversified,and large sized characteristics.The roll bending forming for curved parts was developed by combining the multi-point shape-adjusting principle with conventional roll forming,employing an upper flexible roller and two lower flexible rollers as forming tools.This process can meet the requirements of manufacturing hyperbolic curved parts with personalized,diversified,and large-sized characteristics.In this paper,the longitudinal and transverse deformations of sheet metal during the roll bending forming process were studied from three aspects: theoretical analysis,numerical simulation and forming experiment.The control method for forming process was given,which can provide theoretical guidance and support for the development of forming process.The main research works and conclusions are as follows:1.The transverse deformation process of convex and saddle curved parts under different downward displacement of the upper flexible roller were investigated.The setup and selection schemes of key parameters involved in the finite element model of roll bending forming were provided,including the material model,mesh element,local coordinate system,analysis step,friction model,contact model and boundary conditions.Finite element model of the saddle and convex curved parts were established.The variation law of transverse curvature radius of sectional lines for saddle and convex curved parts were analyzed.In the roll bending forming process,the sheet metal being formed is divided into the predeformed zone,deformed zone and formed zone.The transverse deformation degree varies with different zones for the saddle and convex curved parts.Under the same downward displacement of the upper roller,the transverse curvature of the finally formed convex curved part is larger than that of the saddle curved part.2.The longitudinal and transverse curvature radii of convex and saddle curved parts under different downward displacements of the upper roller were studied.The influence of main process parameters,including thickness,width,and material properties of sheet metal,the bending radii of flexible rollers,as well as the downward displacement of upper roller on the longitudinal and transverse curvature radii were analyzed.The relationship curves of longitudinal and transverse curvature radii versus the downward displacement and bending radii of flexible roller for with different sheet thickness were presented.The mutual influence law between the longitudinal deformation and transverse deformation in roll bending forming process were studied.The effect of transverse deformation on longitudinal deformation is mainly reflected in the influence of bending radius of flexible rollers on the longitudinal forming curvature radius.The effect of longitudinal deformation on transverse deformation is mainly reflected in the influence of downward displacement of upper flexible roller on the transverse curvature radius.3.Based on small-scaled roll bending forming experimental equipment,the forming experiments were conducted and the forming accuracy of the curved parts was analyzed.The main structures of the forming equipment were introduced and the main parameters were provided;the working process of forming sheet metal was discussed.This equipment can form sheet metal with a maximum width of 300 mm and a maximum thickness of 3mm.The 3DSS optical scanner for surface measurement was introduced,and the principle and characteristics of surface measurement were described.The small forming equipment was used to form curved parts with different types.The three-dimensional optical scanner was used to scan and measure the formed curved parts.The forming precision and surface smoothness of the formed curved parts were analyzed.The results demonstrated that there are relatively large shape errors at the edges of the saddle and convex curved parts.On the leading edge and the trailing edge,the forming errors mainly result from the so-called straight-end effect.On the side edges,the forming errors result from the springback of deformed sheet metal.The forming errors can be reduced by properly designing the shapes of flexible rollers so as to compensate for the springback and mutual influence of the longitudinal and transverse deformation.4.Based on large-scaled roll bending forming experimental equipment,the forming experiments were carried out and the forming accuracy of the curved parts was analyzed.The main structures of the forming equipment were introduced with the main parameters provided.The working process of forming a circular sheet and square sheet were discussed.This equipment can manufacture metal plate with a thickness of 2~6mm.It can manufacture metal plate with a maximum diameter of 1200 mm by the double-sided working region,and with a maximum width of 500 mm by the single-sided working region.The dish-shaped,convex and saddle curved parts with different materials were formed by this forming equipment.The three-dimensional optical scanner was used to scan and measure the formed curved parts,and the forming precision and surface smoothness of the formed curved parts were analyzed.The thicknesses of curved parts were measured by an ultrasonic measuring instrument,and the thicknesses distribution laws of the curved parts were analyzed.The results demonstrated that the final curvature radius of the formed curved parts would approximate to the target values,and a doubly curved part with good surface smoothness can be obtained by roll bending forming process.