Research On Flexible Blank-drawer Forming Process And Numerical Simulation For Sheet Metal

Sheet metal forming is one of the most important manufacturing technologies in the modernindustry with the advantages of high precision, easy mechanization and automation, are widelyused in many industrial productions. However，with the development of society, the requirementof products towareds diversification and individuation. The more complex the forming parts are,the more obvious the stamping process limitation is. In traditional stamping, blank-holder deviceis used, but it mainly limits the flow of sheet passively. The uneven blank-holding force betweenthe sheet blank and blank-holder results in wrinkles and cracks easily. New sheet metal formingtechnologies are needed urgently due to narrow range of current stamping techniques, especiallyin forming complex shape and large panels.The principle of flexible blank-drawer forming (FBDF), a new type flexible formingmethod, is studied for the first time based on the existing stamping process and the flexiblestrech-forming. The FBDF technology replacing the traditional blank-holder forming (TBHF)technology, employ a set of blank-drawer device combined with different fixed dies ormulti-point dies to realize the flexible forming of three dimensional(3D) surface parts (e.g.saddle, spherical, non-rule, square box, convex-boss panels and so on). The new technolegy canreduce the production cost, suppress the deformation defects such as wrinkling and cracking,produce high quality parts with even stress, strain distribution and small springback, and offerprofound prospects of academic research significantly.The main contents and conclusions are summarized as follows:1. Researh on FBDF equipment and forming processThe FBDF device was designed according to the FBDF principle which was studied for thefirst time. The technical features and the forming advantages of the equipment were pointed outand two FBDF processes were discussed including the processes with pre-streching and withoutpre-streching through analyzing the advantages, disadvantages and application rang of eachprocess. The research on FBDF device and forming process will solve the deformation problemsof wrinkling and cracking, and broaden the application range of stamping process. 2. Building finite element models of FBDFBased on relative theories of plastic forming, the basic equation, virtual work principle andconstitutive equations of materials under plastic deformation were gived; the FE models ofFBDF process were built and the related element selection, meshing, boundary conditions, thecontact and friction were stated, especially the modeling method of the blank-drawer apparatuswas discussed deeply, which is the base of numerical simulation study of the FBDF process.3. Effects of the blank-drawer apparatus on formed parts by the FBDFTaken the spherical parts and non-rule surface parts as investigating examples, numericalsimulations on FBDF process with finite element method were done. The effects of configuration,number and shape of grippers on the the stress and strain distributions of formed parts werestudied. The results show that the stress and strain distributions are uniform while blank withhexagonal and more grippers, without clamping at the four corners of the blank.4. Effects of the process parameters on the FBDFTaken the multi-point forming of saddle parts and rigid-die forming of spherical parts asinvestigating examples, the effect of different forming processes on the stress and straindistribution and springback values were studied. The results show that forming process withpre-stretching can obtain better parts with even stress, strain distribution and small springback;the saddle parts formed with different blank-drawing forces were compared in distributions ofstress, strain and wrinkles, through which effects of the blank-drawing force on the formabilitywas discussed. The results show that the blank-drawing force can supress the wrinking of sheetmetal; at the same time, the blank-drawing force changes in forming sheet blanks in differentthickness and materials were discussed. The results show that the thicker the sheet blank, thegreater the yield stress and the elastic modulus of material are, the bigger the neededblank-drawing force is. The research on the numerical simulation of the friction coefficientpoints out that the better the lubrication condition is, the higher quality of the part is.5. The comparative analysis between the FBDF and TBHF processNumerical simulations on multi-point forming of saddle parts, rigid-die forming of squarebox parts and convex-boss panels on TBHF (e.g. rigid blank-holder, flexible blank-holder) andFBDF process with finite element method were done. The results show that the FBDF process isbetter controllable, for forming the parts with even stress, strain distribution and smallspringback through suppress wrinking and craking. In short, the FBDF is prority to the TBHF,which can fabricate3D curved panels in better quality and can be used in stamping processes.