Research On Initial Solution Of One Step Direct Forming Method

Faced with the increasing demand of low-carbon and energy-saving by all overthe world, as a result, the position of auto body lightweight program is improving.Meanwhile, the government or consumers who is buying a car, are taking the safetyas an important consideration when comes to judging a car of good or bad.Especially for auto body designing, this trend of the car design will be lasting for thenext20years.The new models of a car must be elegant for auto body designers, which meansto not only have sufficient stiffness, strength, durability, safety and other bodystructure properties, but also reduce development costs and make the developmentcycle short as much as possible.Development of computer technology and the out-coming of auto-bodystructure CAE analysis software are good news for those who needs analyse data ofthe thickness changes of the blank stamping on the cover body in the early stages ofdesign. It can be optimized parameters data, and then shorten the development cycle,reduce the cost as much as possible. While many scholars make a lot of research onthe direction of stamping numerical simulations, but there is no one can be fast andaccurate as a pre-analysis method. In view of the situations, draw lessons from thebasic theory of one step forming inverse method. A new method of one step formingdirect has been put forward in this paper. The main contents are as follows:The first chapter introduces the new situation of auto body technology’sdevelopment and the problems we have faced, it also summarize the method ofdomestic and foreign in sheet forming numerical simulation. There are two kinds ofmethod, mainly: the incremental approach and one step forming inverse finiteelement method, we analyze their strengths and weaknesses, and draw thesignificance of further research.The second chapter begins with the basic theory of one step forming inversemethod，then gives out a brief description of the basic assumptions and solving ideasin addition. After summary and inheritance the one step forming inverse method, we build up the theoretical system of one step forming direct method, brings out thelocal and global coordinate transformation of the physical, and the large deformationgeometric relationship by using of continuum mechanics theory. By Hill thick to theyield criterion, constitutive relation and important formulas can be deduced. Finally,according to the principle of virtual work, we build up finite element solvingequations and using the Newton-Raphson method to solve it.Begin with the basic theoretical system and initial solution of one step formingdirect method, the initial solution method–“Second projection method” has beenbring out in the third chapter.And step inverse forming the initial field of the finite element method to expandthe methods of starting, first proposed the third step is forming the finite elementmethod of initial field indicates--“twice projection method”. This method startsfrom flat blank, and make it projection to the blank of expanded which is thetwo-dimensional tool-shaped face. Then looks for the location of the blank grid nodein the tool-shaped surface mesh, and the formation of one relationship into the spacetool-shaped surface, so that completing the second projection, thus getting theindicating initial solution field in the three-dimensional space.On this basis, in order to solve the problem that there will be few and scatteredgrid when comes to larger curvature in tool surface, a new grid the encryptionrefinement algorithm has been put forward which based on the one step formingdirect forming method.The new algorithm is as the dihedral angle of space-shaped surface betweenadjacent grid a judgment, in accordance with the encryption refinement of the grid isgreater than the critical value, thereby improving the result of the indicating initialsolution field, improve the calculation accuracy in further. Finally, by usingnumerical calculations to examples, we verify the effectiveness of the newalgorithm.The fourth chapter summarizes the methods of improving grid computingprecision, which is by optimizing the finite element mesh shape. In order to improvethe calculation accuracy of the finite element mesh in further, we proposed a new method based on the average strategy of the grid homogenization algorithm. Basedon the existing ABM method, on the basis of geometric rotation and potential energyminimum conditions, we added grid side length of the optimal conditions for theoptimization goals of the polygon center position by adjusting the areas, bring aboutoptimizing local mesh shape so as to improve the purpose of calculation accuracy.Calculation examples can be seen, the optimized grid average minimum angle hasbeen improved, and the shape of the elements are similar to the regular polygon, soas to prove the effectiveness of the algorithm.A summary of the full text has been put forward in chapter5. The validity of theindicating initial solution fields in the one step forming direct method and itsoptimization algorithm has been calculated by introducing the advantages of speedand accuracy. And then describes the step is forming the finite element method to geta wider range of applications and in-depth research in the future.