The Study Of Finite Element Analysis On Multi-Point Forming Process Of Sheet Metal

Multi-Point Forming(MPF) is a flexible manufacturingtechnology for three-dimensional sheet metal forming, which utilizesa collection of adjustable discrete elements arrayed regularly toapproach "flexible Multi-point die". MPF applies numerical controltechnology to control the displacement and velocity of elements, so itcan form alterable envelope, and achieves flexible forming. Relativeto the forming method of the conventional solid die, the same MPFpress can be used for different purposes. MPF press with blank holder device can realize the sheet metalforming. Based on the mechanics theory, the MPF process of sheetmetal concerns nonlinear field problems both on material andgeometry. It has elastic deformation and plastic deformation. It mustanalyze the spring back after sheet metal forming and all defectsduring the process of MPF. Numerical analysis method is necessaryfor optimizing mould & die design , prognosticating defects ,analyzing forming quality. Among the Numerical analysis methods,finite element analysis is the most efficient method. At the recentyears, finite element analysis method is applied in technical analysisof sheet metal forming more and more pervasively. Not only finiteelement analysis method can be applied to technical analysis ,practical forming process simulation of sheet metal forming, but alsoprognosticating wrinkle,impressed mark,calculating the magnitudeof spring back, solving the origin rough material design, and so on.Because during the MPF process of sheet metal, the contact statebetween elements and sheet metal changes continuously and the loadcondition is complex, so it has obvious superiority to apply thedynamic explicit algorithm. In this thesis, the author used dynamicIVABSTRACTexplicit finite element algorithm to simulate the MPF process ofsheet metal. Main works are as follows for making this dissertation: 1. Research on MPF types, fundamental theory and formingcharacteristics The main characteristics of MPF can be summarized that it canrealize many kinds of three-dimensional sheet metal forming. Duringthe forming process, the relative movement state of elementsdetermines MPF path for sheet metal and load distributing, namely,determines the forming effect and qualities of product, so it is the keytechnology of MPF to control the relative movement state of elements.Relative movement state types of elements includes changeless type,passive type and active type. There are six forming methods throughcombining three different types of elements, among them, thereare four forming methods which have emblematize andpracticability: multi-point die forming,half multi-point die forming,multi-point alternating forming,half multi-point alternating forming.In MPF of sheet metal, the conventional solid die is replaced by"flexible multi-point die" composed by a series of discrete elements,and it can choose rigid blank holder device or flexible blank holderdevice according to material performance and the complexity ofproduct shape, and it can control the pressure of blank holder devicethrough adjusting hydraulic pressure, so it can prevent the wrinkleduring MPF process of sheet metal. The top surface shape of elements which contact with sheetmetal influences the product quality during MPF process. If the topsurface shape is flat, the product contacts with elements at the edges,so it can produce some defects. In order to realize differentthree-dimensional sheet metal forming, convenient for calculate andcontrol the elements' displacement, the top surface shape can adoptsphere. V吉林大学博士研究生学位论文 2. Research on the finite element analysis model and the keyalgorithms and parameters of numerical simulation. There are twoboundary conditions, one is load, the other is movement constraint.Different boundary c...