Study On Numerical Modeling For Extrusion Process Of Aluminum Profiles With Complex Cross-section And Optimization Die Design

As aluminum alloy profiles have been the most widely used aluminum products, aluminum alloy extrusion technology and industry have become one of the most important development direction all over the world. The technology of aluminum alloy extrusion is a process that aluminum material inside the container with plastic deformation caused by the action of external force flow through the diversion chamber, porthole, welding chamber and bearing of the extrusion die, and eventually form the aluminum alloy extrudate with required shape. The aluminum alloy extrusion process is a non-linear and heat-stress coupled one under complex large deformation, high temperature, high pressure and friction.Aluminum alloy profile is one of the key structure materials to realize the lightweight and properties improving of the high-speed train, automobile, vessel, aerospace vehicle, etc. Now it develop in the direction of high properties, large-scale, complicate, accuracy, versatile, multi format and multipurpose. So it puts forward rigorous demands on aluminum alloy profiles structures, mechanical properties and microstructure property. With the features of hollow, thin-wall, complex cross section shape, high mechanical properties, materials have complex flowing during deformation which make it difficult to design extrusion die, analyze materials flowing and optimize the extrusion parameters. Unreasonable die design and process parameters may cause the defect of twisting, waving, bending and crack of the profile, which will reduce the die life. Above all, it is an urgent need to study the method of numerical model building of aluminum profile extrusion process, find the rules of material deformation, reveal the influence of the die structure and extrusion parameters on the extrusion process and analyze the methods of optimization die design. So that to gain the theoretical direction about the extrudate quality.For large and long cantilever aluminum alloy profiles, the conventional flat die and diversion die design usually causes the damage or failure of die in the cantilever area. Fake porthole die design method and cantilever decomposition technique are proposed to solve the question above. The material flow velocity, temperature, particle track and the die strength of the two different die design methods are studied and compared with numerical simulation. Especially, the die strength and stress distribution are researched. The results indicate that the fake porthole die design method is a useful die design method for large and long cantilever aluminum alloy profiles. It can decrease the die stress significantly and ensure the die strength. The sound material flow and profile quality are also obtained by optimizing the fake porthole die structure. The design rules for fake porthole die structure and the material flow based die shape optimization method are given.Second step chamber is usually used for complex aluminum profile extrusion process. The method of numerical simulation modeling and optimization second step die design is studied in this article. Using a typical aluminum alloy extrusion profile as the example, the shape and the height of second-step welding chamber of the extrusion die are selected as the design variables. Standard Deviation of the Velocity field in bearing exit (SDV) is used as the objective function. By combining Box-Behnken experimental Design (BBD) with Response Surface Method (RSM), a prediction model for SDV is established. The model is optimized by means of genetic algorithm, and the optimal extrusion die for the aluminum profile is obtained. In comparison with the initial die design, a more uniform velocity distribution in the cross section of the profile in the bearing exit is achieved by using the optimal die design. And die strength can also satisfy industry need.Most of the High-speed train extrudate have the characteristics of multi-cavity, thin wall and large cross-sections. Profiles usually use the materials of AA6N01and AA7N01. For this kind of complicated large cross-section aluminum alloy, thermal compression experiment of ingot casting material of the AA6N01and AA7N01were carried out. Two material constitutive relation models were established respectively. Then test and analyze the microstructure of ingot materials. Study the extrusion process numerical modeling method of aluminum alloy profiles used in High-speed train body plate and design profiles extrusion die. The research reveals the influence of die structure on the velocity at the die exit and muscle materials feeding. Analyze the reasons of profile bending and twisting deformation. Then optimize the baffle and chamber. Analyze deformation, streamline distribution, temperature, stress and die deformation of the extrusion process and so on. Experiments of the optimization die design were carried out to check out the die structure and extrusion parameters. Then the mechanical properties and micro-structures and fracture appearance were analyzed, and the fracture mechanism of the specimens was gained. The results show that extrudates with excellent quality can realized with the optimization designed die and the extrusion parameters in this example.At present, die design of complex section aluminum profile still rely on the designer’s experiences and the lack of computer CAD design system. In order to solve the problems mentioned, the CAD aluminum porthole die design process and key technology WRE studied with the back-stepping method which working backward from the die structure to process parameters in this paper. Porthole die system with CAD framework was build. Then analyze the die structure modeling method. Each part of the die structure modeling was realized. The UF object model is used for porthole CAD system modeling. A typical complex aluminum alloy profile extrusion die was designed based on the CAD design system built in this article. Then analyzed and numerical simulated the extrusion process. The research reveals the material flowing rules of extrusion process and extrudate deformation. Through local modification of the drainage channel, baffle plate, bearing, optimization die structure with uniform exit velocity was gained. Results show that the porthole die built with CAD system can be used as the initial designed die. Optimization designed die will gained by locally adjust. The system can be used for any hollow profile porthole die design, which will improve the efficiency of die design.