Optimization Research On Die Structure For Aluminum Shape Flat-plate Extruding

Large-sized aluminum alloy flat-plate, with some characteristics like high specific strength, corrosion resistance, unfailing performance and attractive appearance, has been widely used in railway transportation, air transportation, ship transportation and so on. It is usually formed through extruding by combined flat container. Thus the die cavity is very important for forming process, which is closely related to deformation degree, forming velocity, stress states in deforming area, and has a great influence on the products quality, extrusion energy and die life. In this dissertation, the optimization of die cavity structure is carried out by comprehensive application of mathematics, fluid mechanics, numerical simulation and physical simulation. Through the research, the extrusion forming discipline of flat-plate is got, and some useful conclusions and instructional achievements are obtained.According to conformal mapping theory of complex function, the mapping function of Schwarz-Christoffel integral is introduced from physics field, electromagnetics field to plastic forming process. By this function, the extrusion inlet and outlet are mapped to a unit circle, and then the mapping modeling approach is put forward. First, the forward and reverse solution procedure for Schwarz-Christoffel integral is analyzed. Handling the problem of mapping accuracy, the convex-concave expansion technology for Taylor series expansion is adopted. To improve the solution efficiency, the fast-solution mode is developed on the MATLAB platform. By this mode, the mapping function from a simple polygon to a unit circle can be acquired quickly, and other complicated mapping functions from rectangle, trapezoid, I-section polygon to unit circle can also be solved accurately.Based on the upper bound theory, the flowing model for aluminum alloy rod extrusion is constructed, and then the kinematically admissible velocity field, the strain rate field and the deformation power are deduced with five different die containers. In addition, aiming at reducing extrusion power, the forming process optimization is carried out, from which the best container length with the less extrusion load is got. According to this, the boundary condition of transitional surface between flat extrusion container cavity and die outlet is established based on the flow function method, then the streamlined mathematic model of die cavity is constructed, and the streamlined 3D model of transitional surface is obtained by using CAD software.In order to verify the influence of different die cavity on extrusion process, the forming process of aluminum rod and complicated flat-plate extrusion are simulated by 2D elastic-plastic FEM and 3D rigid-plastic FEM respectively. Through the simulation, the displacement field, velocity field, stress-strain field and temperature field distribution discipline in forming process are obtained. In addition, some important factors that connected to forming process, such as the extrusion center etc, are discussed. The simulation results show, with the same area reduction ratio, streamlined cavity has great advantages in improving metal flowing, reducing forming load and enhancing products quality.Furthermore, flat extrusion container is working with the environment of high temperature, high pressure and high friction, which leads to the poor operating life. The hybrid optimization method, combining finite element method (FEM), artificial neural network (ANN), multi-objective genetic algorithm (MOGA) together, is adopted to optimize the container structure. Considering the strength of flat extrusion container and dimensional accuracy of inner layer, the multi-objective structural optimization of three-layer combined flat extrusion container under the non-uniform shrinkage design is realized. With analyzing, comparing and demonstrating, a feasible method of structural optimum design for flat extrusion container is obtained. Meanwhile, in order to reduce extrusion power and improve flat-plate quality, the important forming parameters, including extrusion velocity, calibrating length, die temperature and so on, are optimized with the combination of orthogonal experimental design, response surface method (RSM) and genetic simulated annealing algorithm (GSA). From this multi-objective optimization, the best procedure parameters are obtained.In the last, the streamlined extrusion process of trapezoid flat-plate is analyzed by photo-plasticity method. Based on the experiments, the best forming temperature and the reasonable heat treatment regime for experimental material are acquired. By the analysis of product sections, the strain distribution discipline along different path in the parts is got. And there is little difference between experimental and simulation results, thus it can prove the advantage of streamlined die cavity in extrusion process.Our results will have significant reference to extruding die design for flat-plate, and it can provide technical supports for other complicated flat-plate forming.