Numerical Simulation On Bending For Conical Cylinders With Differential Rollers

As a common sheet forming parts, conical cylinder widely applied in many fields such asaerospace, automobile, petrochemical, shipbuilding and so on. At present, the roll bendingforming of conical cylinder is mainly by bending machine. The traditional ways of forminginclude partition bending method, auxiliary sleeve method, cone-roller bending method andfour-roller clamping method. Although the above methods have their own characteristics, thereare some defects: Partition roll bending is a time-consuming method, which has low formingprecision; auxiliary sleeve and cone-roller methods are not suitable for bending of high-taperconical cylinder; four-roller clamping bending method needs higher requirements for controlsystem of the equipment. In order to improve the above forming methods, this paper adoptsdifferential-roller bending forming technology. Though changing roll speeds of two ends rollers,it can achieve any taper conical cylinders’ forming, in addition, the technology equipment has theadvantages of simple structure, high forming precision and stable forming process.In this paper, using finite element analysis software ABAQUS and the dynamic explicitmethod to simulate the differential-roller bending forming process of conical cylinders, anddetailed analyzing the influence of roller’s speed ratio and descending distance on the formedparts. It provides theory guidance for the design of forming equipment and the optimization offorming technology. The main contents and results are as follows:(1) It mainly discusses the principle of differential-roller bending forming and the geometricrelationship between mainly components. It also details the establishing process of finite elementmodel, including material property settings, selection of element type, meshing method, settingof boundary conditions and contact conditions, determine of material direction in localcoordinates. Finally, verify the rationality of settings through the simulation examples.(2) Firstly establish the finite element model for the traditional cylindrical roll bending, andanalysis the influence of the virtual roll speed on forming radius. Then change the two endsrollers’ speeds, and discuss the impactof roller speed ratio on forming results. The simulationresults show that the optimum roll speed ratio increase with increase of the radius ratio between large and small circle of conical cylinder, and the speed ratio will keep unchanged if the radiuratio is constant.(3) Firstly deduces the geometric relationship between the descending distance and theforming radius of cylinder in traditional three-roller bending process, numerical simulationresults show that the simulation value is consistent with the theoretical value on the relationshipbetween descending distance and forming radius, and the radius of cylinder is a power functiondecreasing with increasing of desending distance. On the basis of the above study, simulate thedifferential-roller bending forming process of conical cylinders, and analyze the impact ofover-roller’s descending distance on forming radius, the result show that the radius of large andsmall circle decrease with the increase of descending distance for the same basic size of sheet.But for different basic size of sheet, even the descending distance is constant, the large and smallcircle radius are still different. Similar to the cylindrical roll bending forming, the correctiveaverage radius of conical cylinders is also decreasing in power function relationship withincreasing of the desending distance.(4) It analyses in detail that the distribution of stress and strain which in thickness directionas well as on the top surface and bottom suface of sheet. The simulation results show that in theloading process of sheet, the stress change of both ends in thickness direction are roughly thesame, but during the process of unloading, the stress change trend on the two ends are different.After forming of conical cylinder, the stresss distribution on the surface has a big difference fromwhich after forming of traditional cylinder. With the increase of descending distance, the plasticstrain valur increase gradually and the tensile stress area increase at first and then tend to bestable.