Numerical Analysis Of Wrinkle And Springback In Multi-point Forming For Sheet Metal

Multi-point forming(MPF) is a flexible manufacturing technology for threedimensional sheet metal forming. In multi-point forming, the conventional solid dieis replaced by "flexible Multi-point die" composed by a series of discrete elements(or punches). The forming process of sheet metal is implemented by the envelopesurface of punches. Multi-point Forming can be applied extensively in a lot offields such as aircraft, stream and navel ships, vehicle, large sculpture and modernarchitecture etc. Sheet metal forming in MPF without blank holder, which is a commonprocess method, is usually applied in processing those kinds of surface parts whichhave not big deformation amount. In this process condition, the original materialconsuming and the press cost can be reduced to a low level as well as simplifyingthe press structure and leaving out trimming procedure in metal sheet formingprocess. without blank holder, the deformation inside the surface is distinctlysmaller than the bending outside the surface. Wrinkle is a key factor to determinewhether the part could be formed and become one of primary forming defectsespecially for thin metal sheet in MPF. On the other hand, in this condition, springback was more serious than thoseforming with blank holder. Springback was affected by numerous factors, such asthickness of metal sheet, material property and deformation amount and so on. Andthe last content of this paper was to research the springback eleminating methodthrough controlling the forming surface of the elements group for metal sheet inmulti-point forming process.1.Numerical simulation of wrinkling in multi-point forming formetal sheet without blank holder As view from mechanics, wrinkle is a kind of plastic ?in metal sheet surface.It is more difficult with static implicit algorithm than dynamic explicit in analyzing 73吉林大学硕士研究生学位论文wrinkling problem. Based on the explicit algorithm, there must be offered as fineelement as to make the wrinkle to simulate with adequate small wavelength. Obtained the numerical simulation results of wrinkle with different size offinite element, establishing the finite element model for wrinkling numericalanalysis. The Multi-point forming process of sphere, saddle surface of differentmaterials with different thickness and deformations were simulated, and thoseresults show that metal sheet thickness, deformation and material property haveeffect on wrinkle defect. With metal sheet thickness increasing, deformationdiminishing, wrinkle can be gradually weakened. Simultaneously, wrinkle wasaffected by material property too. In this paper, two material, 08Al steel and L2Y2pure aluminum are simulated, and found L2Y2 pure aluminum are more sensitiveto wrinkling than 08AL steel because the Elastic modulus of 08AL is greater thanthat of L2Y2. In this paper, the wrinkling growing up process was also analyzed, anddiscovered that wrinkling in multi-point forming for metal sheet without blankholder, derives from metal sheet under an half-baked restraining which comes fromthe elements group. The maximal of wrinkle depth appear in the anaphase of theforming processing, and some wrinkle can be planished at the end of forming. Inaddition, the non-wrinkling limit of sphere and saddle surface were obtained.2. Numerical simulation of springback in multi-point forming formetal sheet without blank holder There were included loading and unloading course in an intact metal sheetforming. Based on explicit-implicit algorithm, the finite element model fornumerical simulation of springback was established. Dynamic-explicit formulationwas employed to analyze the loading process and implicit formulation to unloadingprocess. This method not only overcomes the time consuming and convergenceproblem in explicit algorithm but also avoids the contact difficult in implicitalgorithm, with go...