Study On Preform Shape Optimization In Forging Process Based On Quasi-equipotential Field Method

Forging is one of primary material forming processes. Generally, one or more preform processes are required before final forging. Research on the number of performs processes and preform shape design is fundamental and difficult for the plastic forming technology and die design, which has not been settled perfectly and effectively. Furthermore, it is difficult to get advisable preform shape using preform design methods based on experience, physical simulation or numerical simulation. Therefore, study on preform design method is of great theoretical significance and engineering significance.By Quasi-equipotential Field Method which is a non-numerical optimization algorithm, the equi-potential lines generated between two conductors of different voltages show similar trends for the minimum work paths between the undeformed shape and the deformed shape. Based on this similarity, the Quasi-equipotential Field Method has the broad application prospect in preform shape optimization for complex3-D forgings. In this paper, preform shape optimization methods for3-D axisymmetric and complex forgings (with3-D preform shapes) using Quasi--equipotential Field Method, plastic finite element modeling and engineering optimization algorithm are proposed.(1) Combing Quasi-equipotential Field Method with the principle of forging preform design optimization, a new approach to do the preform shape multi-objective optimization in two-stage die forging based on Quasi-equipotential Field Method is developed, which is effectively applied to preform design of both3-D axisymmetric forgings and non-axisymmetric complex forgings.(2) Research on preform shape multi-objective optimisation in two-stage die forging based on Quasi-equipotential Field Method is conducted by the example of H-section axisymmetric part. First, electric field distribution distribution of equipotential line between the undeformed shape and the deformed shape is obtained by electrostatic field simulation method. Second, with the potential value of an equi-potential line and volume ratio of preform to final shape as the design variables, forging filling ratio as the optimization goal, response surface analysis about forging forming process of H-section axisymmetric forging is carried out. Accordingly, the optimum volume ration and the appropriate range of potential lines for the preform of is determined. Finally, with the potential value of an equi-potential line as single factor variable, preform shape multi-objective optimization design controlling deformation uniformity and deforming force for H-section axisymmetric forging is performed using the conjugate gradient optimization algorithm. Consequently, flashless final forging with complete die fill and optimum deformation uniformity and deforming force is obtained(3) A new approach to optimize preform shape in multi-stage die forging for3-D complex forgings based on Quasi-equipotential Field Method is proposed, which is based on stepping backward method. In the first stage of preform design, optimum pre-forging shape is determined combining Quasi-equipotential Field Method, response surface optimization with finite element analysis. In the second stage, Vertical and horizontal Cross-section Curves Method is introduced to design advisable preformed blank based on the optimized pre-forging shape. The two-stage preform design method is suitable to eliminate underfill and fold which easily occur in the forming process of three dimensional complex forging.(4) Research on preform shape optimization in multi-stage die forging for3-D complex forging part based on Quasi-equipotential Field Method is conducted by the example of pendulum mass part. First, three dimensional electric field distribution between the undeformed shape and the deformed shape is obtained by electrostatic field simulation method. The material flow characteristics in the forming process are analyzed by the distribution of three dimensional equipotential surface so that the possible defects in the forging process can be predicted. The equipotential surfaces in3-D electrostatic field are extracted as pre-forging shapes by cross section curve lofting method. Based on the electrostatic field simulation results, response surface analysis about forging forming process of3-D complex pendulum mass part is performed with the potential value of an equi-potential surface and volume ratio of preform to final shape as the design variables, forging filling ratio as the optimization goal. Consequently, the optimum shape and volume of pre-forging is determined for obtaining final forging with complete die fill.(5) Vertical and horizontal Cross-section Curves Method is introduced to design advisable preformed blank based on the optimized pre-forging shape. The equal horizontal cross-section curve and longitudinal cross-section curve of symmetry plane are designed according to material flow characteristics and forming defects in the pre-forging process. As a consequence, the advisable preformed blank is found, ensuring pre-forging with complete die fill on the basis of finite element simulation results of the first and second preform processes. Final forging with complete die fill and without folding defect is obtained after two-stage preform forging processes,...