Study On Optimal Design Method Of The Microstructure In Forging Process Based On Preform Design And Application

Widely used in mechanical industry, metallurgy, shipbuilding, weapons and so on, metal forging has a very important position in national economy. Since the global competition becomes more and more intense, low cost high quality and efficiency become the crucial factors for the manufacturing factories to win in the competition. Therefore, the various process parameters involved in the metal forging and the cost, quality and efficiency should be considered into the process design. The evolvement and structure of the microstructure in the forging process have a direct influence on the mechanical property of the final parts. So, during the various parameters of the metal forging, the simulation and optimization of the microstructure are pivotal and integrant. The preform shape is corresponding to the shape of the final parts. It directly controls the reliability of metal. So, it directly influents the shape of the final parts and the capability of the microstructure. So the optimal preform design becomes the crucial aspect of controlling the quality of the product.With the development of the computer technology and the reliability of metal forming theory, the numerical simulation of metal forming processes can be realized on the computer. The numerical method such as finite element method are widely used in the metal forging.Based on the above analysis, an optimization design method of the microstructure in forging process is proposed in this dissertation. The current research situation of the simulation and optimization of the microstructure all over the world is reviewed in this dissertation. The optimal objective is to obtain the fine and symmetrical grain size. The optimal object is the preform shape. Combining the FEM simulation with the genetic arithmetic, the multiple objective optimal method whose optimal objective is to involve the shape of forging and the microstructure of forging is put forward. Using FORTRAN language, the software for optimal design method of the microstructure in forging process based on preform design is developed. The preform designs of the cylinder upsetting processand an H-shaped forging in plane strain deformation realize the optimization of the final microstructure.First, the basic theory of the visco-rigid plastic finite element method is presented in this dissertation. The basic assumption of the visco-rigid plastic finite element method and the basic equations of the plastic mechanics are given. The essential principles and the solution procedures of the visco-rigid plastic finite element are introduced. At the same time, the essential principles, common structures and routine operational steps of the microstructure are introduced in detail.The main contents and the normal principles of the optimal design are described in this dissertation. The optimal modeling of the shape of forging and the microstructure is analyzed respectively. The grain size sub-objective function, the shape sub-objective function and the whole objective function for the multiple objective function optimization are put forward, respectively in this dissertation. The method that the B-spline used to represent the preform die shape is presented. The coordinate of the control point of the B-spline is used as the optimal design variables. Using the genetic arithmetic, the simulation and the optimization to microstructure in forging process based on preform design are carried out.Using the genetic arithmetic and FEM simulation, the software for optimal design method of the microstructure in forging process based on preform design is developed by using FORTRAN language. It is composed of seven modules. They are the module for initialization, for preform parameter modification, for preform finite element simulation, for final forging parameter modification, for final forging finite element simulation, for calculation of objective function, and for evaluation. The software can automatically realize the optimal design of the microstructure in forging process based on preform design as long as the essential deformation manipulative parameter, technical parameter, the shape parameter of the die and final parts and initialization in genetic arithmetic are provided.The preform designs of the cylinder upsetting process and an H-shaped forging in plane strain deformation realize the optimization of the final microstructure by using the software developed in this dissertation. For the cylinder upsetting process, the average of the grain sizes declines 72% from 91.43μm to 25.19μm in isothermal process and the average of the grain sizes declines 47μmfrom 117.28um to 70.95μm in non-isothermal process. For an H-shaped forging , the average of the grain sizes declines 54.8% from 67.5 1μm to 30.51μm.After optimization, the recrystallized grain size becomes further more uniform and fine. The shape of the final forging gain optimization whose side has hardly any drum after optimization, while side has biggish drum initially.From the optimal result,it can be seen that, the optimal arithmetic that the software uses is greatly credible.