Finite Element Simulation On The Multi-Point Draw Forming Process For Sheet Metal Pyramid Boxes

Multi-Point Forming (MPF) is a novel technique for forming sheet panelproducts rapidly and digitally. Its main ideas are that the array of adjustableelements in height shapes a discrete tooling surface based on the digitalinformation of the panel product, and then the flexible tooling is used to form 3Dsheet metal panels without using other solid dies. This is a great innovation to thetraditional metal stamping technology. Comparing with the die forming technology,the MPF technology has cut down time in design, manufacturing and trial. So far,the MPF equipments have being applied in many fields and brought significanteconomical and social benefits.Pyramid box panels are broadly used in many panel products such as vehicleparts, kitchen and medical appliances. The study on the Multi-Point Draw Forming(MPDF) for the sheet metal pyramid box (SMPB) will widen the range of MPFapplication. The topics of the thesis involve in two projects -the study on theforming and controlling technology of the digital die for sheet metal, whichsupported by National Nature Science Foundation and -the exploitation andapplication demonstration of dieless forming equipment for automobile stampingparts, which is the key project of Changchun city. The thesis firstly discussed FEMalgorithms, shell theoretics and boundary conditions. Then FEM models of theMPDF for the SMPB were built and finally the whole processes were simulated.The main contents and results are as follow:1) The numerical simulation of the effect of elastic buffers on improvingsurface quality of the SMPB;Dimples are the special defects occurred to the MPF. The MPDF processes forSMPBs were simulated in the thesis by means of either the elastic buffers or not.The results show that there are many dimples on the surface of the part while notusing elastic buffers and surface quality of the part is improved while using theelastic buffers. This has proved that the elastic buffers can restrain the dimpleseffectively in the process of MPDF. The interior crimple is another defect in theparts by the MPDF. The results also show that the interior crimple disappearedwhile using the elastic buffers. This is because the conical walls were restricted bythe elastic buffers during the process of MPDF. The numerical simulation of theMPDF using elastic buffers in different thickness such as 5mm, 10mm and 15mmwere also studied in the thesis. The results show that too thin elastic buffer can notrestrain the dimples and interior crimples;the too thick elastic buffer affects theshape precision of the part;10mm in thickness of the elastic buffer is appropriatefor drawing a no dimples, no interior crimples and good precision pyramid box.2) The numerical simulation of the MPDF process for the square pyramidbox(SPB) and the prediction of the defects;The flowing rule of the blank and distributions of the stress and strain of SPBswere numerical simulated. The results show that the material in the flange regionflow into the conical walls incessantly during the drawing process, but the materialin the bottom of the box has little deformation. The analysis shows that the flangeand the corners are danger of the exterior crimple and cracking respectively. Thereasonable blank-holder force (BHF) can not only prevent the exterior crimple inthe flanges but also avoid the cracking in the corners of the conical walls.3) The effect of geometry parameter on the defects occurred during the MPDFprocess of the rectangle pyramid box(RPB).The numerical simulation on MPDF process of RPBs with different geometryparameters such as blank thickness, drawing depth and conical angle were studiedand the experiment was made to prove the simulation results. The results show thatthe thinner blank tends to occurring of the crimples in the flanges and the crackingin the corners of conical wall while the BHF is the same;with the decrease of thedrawing depth, the possibility of crimples and cracking improved;too big or toosmall conical angles are not suitable for the drawing. The limitations of the BHFswere obtained by analyzing the simulation results of the RPBs with differentgeometry parameter. The conclusions are that the range of the BHFs is widenedwith the increase of the thickness, shrank with the increase of the depth, and firstlyexpanded and then decreased with angle increase.