| By simulating forming process of auto engine rocker,I analyse affection of material parameter r,die corner,binder force ,and characteristic of middle-thick sheet drawing forming ,achieve finite element method for middle-thick sheet forming .Above all ,this thesis discuss step of finite element method ,partition of element gridding ,yield theory ,choice of simulation computation method ,disposal of contact ,disposal of forming bug and so on .Then ,this paper analyse finite element method of sheet and discuss finite element method of middle-thick forming .In sheet forming process ,we import classical Kirchhoff supposition ,consider that line of uprightness middle face before deformation is still line after deformation and plumb middle face .So we ignore transverse shearing impact ,As a result it is called sheet theory .For middle-thick sheet drawing of complicated shape ,there is obvious bend impact at die corner element ,and the basal condition of sheet supposition is not satisfied .Now there is consequentially more error if we still use sheet theory to analyse .Now most universal shell element is all based upon Mindlin theory .It considers rotational impact ,imports transverse shearing impact .It does not apply thin shell analysis ,but also apply middle-thick sheet analysis ,and it is easy to achieve transition with 3-dimension solid element .It is perfect element model .The middle-thick FEM of this thesis imported anisotropy yield function ,element model adopted Mindlin shell element ,consequently established FEM for complicated shape middle-thick sheet drawing forming .This thesis took example for auto rocker ,compared simulating result with actual forming ,draw a conclusion that the simulation error is more when bend corner is smaller ,the simulation result is according with actual result when bend corner is bigger .This thesis firstly from theory explained the finite element method of middle-thick sheet big-displacement finite forming .The wall thickness is the important studying object to estimate crinkling or cracking .The major factors are the cutting ratio ,the friction coefficient ,the angle of die ,the ring force and so on ,for these factors conditioned with each other .For achieving the curves of relatively changes ,finding the effect to crinkling ,designing reasonably mould and processing project ,and getting the rule of this kind of problem ,this thesis applied the CAE software (DYNAFORM) to simulate the drawing process of the car-engine rocker ,and analysed the breaking phenomena and its cause .To confirm the practicability and the reliability of the simulating result we designed a series of moulds for trial ,collecting trial data and contrasting the trial data with the simulating result .In this text ,we designed the relevant mould based on the processing project ,and do trial with the pressure .The car-engine rocker had achieved steady production in actual manufacture ,but in the process of confirming the technics project we need make a lot of mould and sample ,wasted time and resource .If we can use the CAE software to simulate and achieve corresponding relation curve by back-disposal module ,the trials will be very simple ,economize time and outlay .But the research is not perfect for middle-thick sheet forming limited analysis ,the report about middle-thick sheet CAE analysis is infrequent .Now CAE software simulating result is perfect for thin sheet forming ,but is not perfect for middle-thick sheet .So we bringed forward this project for it .The application of middle-thick sheet forming is very broad .we applied LS-DYNA for finding a viable method to simulate middle-thick sheet forming process . LS-DYNA is most famous FEM software in the world . LS-DYNA is a general purpose finite element code for analyzing the large deformation dynamic response of metal sheet ,which can simulate the whole forming process ,pick up important parameters ,help users to improve the design of moulds and technics parameters .this thesis analysed the characters of LS-DYNA and the theor... |
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