Numerical Simulation On Spirngback’s Control Of The Flexible Spinning

The flexible spinning on Multi-point adjusting principle is a new technology for sheetflexible forming developed by Jilin University. Compared with traditional half-mouldspinning forming, the flexible spinning do not need mould and is a real flexible formingmethod. The method not only has reduced the processing cost, but also improved theworking efficiency. Different form the traditional spinning, the sheet metal is rolled formingby three flexible rolls which has been adjusted figuration and remains3-D bending. Thisstress、strain state leads to strong springback of spun parts and decrease its processingaccuracy. Thus, how to control spun parts’ springback the main problem the flexible spinningfaces.The flexible spinning forming involves3-D bending problem, stress、strain inside ofsheet metal are more complex. Numbers of scholars at home and abroad ever tried to solvethe problem and gained some formulas in the thesis, but these formulas are based onsimplified models、hypothesis conditions、limited shapes and only apply to particular shape,the error between calculated result and experimental result is larger.With the development of computer technology, numerical analysis technique has madea great progress. In the field of sheet metal forming, numerical analysis results of formingand springback are accurate. Therefore, this paper analyzes the forming and springbackprocess of the flexible spinning by ANSYS/LS-DYNA finite elements software, aims to gainthe law of springback and explore the method of springback control. The main contents andresults of this paper are as followed:1. The flexible spinning forming and springback mechanismFirst, the mechanisms of flexible roll forming and springback process are analyzed, andcompared with the traditional spinning. Elements of the traditional spun parts all remainbiaxial compressive and uniaxial tensile stress state, the stress state is benefit to thedeformation of sheet metal, the parts only have a smaller springback value. But for theflexible spinning, the sheet metal is rolled forming by three flexible rolls which has beenadjusted figuration along radial direction and pressed bending by upper roller and lower rollers along circular direction. Elements on inside of the neutral layer are under triaxialcompressive stress state, elements on outside of the layer remain uniaxial compressive andbiaxial tensile stress state. This stress、strain state leads to strong springback of spun partsthan the traditional spinning.2. Finite element simulation method of springback in the flexible spinning processIn the flexible spinning process, the sheet metal is anchored by a centering device andonly allowed to spin around its own axis, rollers adjusted push down and drive the sheetmetal spinning, thus realize sheet metal progressive forming. The sheet metal remains in astate of loading-unloading–loading circle, springback process is more complex, the commonexplicit-implicit FEM method would not apply. So the flexible spinning springback isanalyzed through the explicit dynamic analysis method and the damp technology isintroduced in this paper. The numerical simulation result is consistent with the experimentresult.3. Establishment of FEA model of the flexible spinningNumerical simulation is based on the right FEA model, which greatly influences theaccuracy of numerical simulation results. This paper introduces the element type、 theelement algorithm、the material model、the boundary conditions and load in more detail,establishes FEA model for the flexible spinning.4. The finite element analysis of the factors which influence springback in theflexible spinning processSpringback is an inevitable and universal phenomenon in sheet metal forming andinfluenced by numerous factors. Sensitivity for factors is different in different formingmethods. This paper analyzes how material、thickness、radius、distance between lower rollersaffect springback, and the general rule of the effect is summarized in the end, in order that itcan guide the test. The results show that the Elastic Modulus、yield strength of the sheet arehigher, the springback value is larger, but the sensitivity is great high; the springback valuedecrease with increasing thickness of the sheet, and the decreasing trend raises whenthickness of the sheet is smaller than2mm; the smaller the forming radius, the lower thespringback value, the accuracy of parts is quite high when the forming radius is smaller than150mm, the error is only2%; it can decrease springback to increase distance between lowerrollers, but the force between rollers and sheet metal will decrease with increase of thedistance between lower rollers, the sheet metal may result in wrinkling, the analysissuggested that the high quality product can be gained when the distance between lowerrollers remains in35mm. 5. The control of springback in the flexible spinning processThe springback analysis aims to effectively control it and improve the accuracy of parts.This paper discusses the control methods in the spinning times、 the reduction compensation、the radius compensation. The springback value may be decreased through increasing thespinning times, but the effect is limited. Under the precondition of the equal reduction,springback may be effective controlled by increasing the reduction of upper roller, but theradius error will get bigger with increase of the reduction. In order to dealing with theproblem, this paper presents a new method that is to decrease the adjusting radius of lowerrollers while increasing properly the reduction of upper roller. Simulation resultsdemonstrate that the error is reduced obviously and can be controlled within4%.