Numerical Simulation Study Of Multi-Point Forming With Highly Flexible Blankholder

Multi-point forming (MPF) is a flexible manufacturing technology forthree-dimensional sheet metal parts. In MPF, the conventional monolithic die isdivided into a matrix of discrete elements. Each element's height and velocity canbe controlled by computer. The forming process of sheet metal is implemented bythe contour surface of elements group. MPF has found its extensive applicationfields such as the manufacturing of the fuselage of aircraft, the hull of ship,covering components of vehicle, city sculpture and modern architecture etc. Based on the plasticity theory, the MPF of sheet metal parts is a nonlinearprocess which includes both material and geometry nonlinearity. It is difficult toanalyse spring-back and the defects during process of MPF. Numerical analysismethod is necessary for optimizing mould&die design, predicting defects andanalyzing forming quality. Among the Numerical analysis methods, finite elementanalysis is the most efficient one. In recent years, it has been extensivly applied intechnical analysis of sheet metal forming, not only in the analysing of practicalforming process, but also predicting wrinkle, dimple, calculating the magnitude ofspring-back, improving the raw material design, and so on. During the MPFprocess, because the contacting condition between elements and sheet metal variescontinuously and the load condition is complex, so the dynamic explicit algorithmFEM is the best choice. In this thesis, dynamic explicit finite element algorithm isused in the simulation of the MPF process. In multi-point forming, a blankholder is used to improve the forming quality ofsheet metal which is composed of dozens of hydraulic cylinders, and each of themis driven by its respective independent hydraulic equipment. When an appropriatethickness blankholder is selected in MPF, the rigid blankholder or the high flexibleblankholder multi-point forming can be realized. But when the rigid blankholder isused, forming defects such as wrinkles, fractures and dimples easily occur, With thecommercial FEA software, both the MPF process with the high flexibleblankholder and the MPF process with the rigid blankholder have been simulated.The results show that MPF with high flexible blankholder can eliminate or avoidforming defects and improve the forming qauality. Main works are as following: 60吉林大学硕士研究生学位论文 1) Building of the finite element analysis model for MPF and research on the keyalgorithms and parameters of numerical simulation. Based on the concept of dynamic explicit algorithm, how to make the dynamicequation solution explicit utilizing the central difference method has been discussed.the key parameters and algorithms that have a great influence on the simulationprecision and efficiency have been studied, such as, element formulas, materialmodels, fictitious velocity and the algorithms for the spring-back analysis. And thefinite element models for different multi-point forming principles have been built. 2) Comparision reasearch on the numerical simulation of MPF with the highflexible blankholder and with the rigid blankholder Simulation with forming defects, such as wrinkle, dimple and crack and so on,have been done in MPF with the rigid blankholder. Wrinkle is arose by press stress,which can be eliminated by increasing BHF. But increasing BHF easily bringscracks and dimple at the vertical transmiting force area. By comparesion researchon MPF with high flexible blankholder and rigid blankholder, it is clear thatmulti-point forming with high flexible blankholder can effectively restrict formingdefects, and the crack force and the forming force during the forming are bothsmaller than that with rigid blankholder. 3) Research on the numerical simulation of MPF with high flexible blankholder The multi-point forming process with high flexible blankholder has beensystemicly studied by means of fi...