Research On Numerical Simulation Of Extrusion Process And Die Optimization Method For Hollow Aluminum Profiles

Energy, environmental protection and security are three difficult problems that concern human existence and development. Because of its advantages of light weight, high strength, beautiful appearance, and ease of recycling, promoting the application of aluminum profiles is an important approach to alleviate the above problems. In recent years, the application scope of aluminum profiles has been expanded continuously. In the1950s and1960s, the aluminum profiles were mainly applied in civil architecture, but now it has been widely used in many fields, such as machinery manufacturing, traffic transportation, aviation, aerospace and communication, etc.Extrusion die structures and process parameters play a key role in aluminum profile production, which determine product quality and service life of extrusion die. Yet in practice, the die design and the selection of process parameters are mainly dependent on the experience and intuition of the die designer. Thus it is impossible to guarantee product quality and productivity, and many times of modifications and experiments should be undergone until the acceptable product is gained. On the contrary, the numerical simulation can describe the extrusion process on the computer and gain the information of stress state, strain state, temperature and velocity distribution of the aluminum profile, which are usually unmeasurable in the production field. In addition, with numerical simulation, one can predict the potential defects in the real extrusion process, so proper adjustments could be taken to the process parameters and die structures in time before the die is manufactured. Thus the numerical method can not only improve the profile quality, but also shorten the die design cycle and reduce the cost of production.Usually, the extrusion process is a non-linear one with large deformation, high temperature, high pressure and complex friction, thus the flow behavior of material and deformation mechanism in porthole die are difficult to investigate by means of traditional measurement techniques. In this paper, firstly, aluminum profile extrusion process is systematically investigated by means of numerical simulation, and the effects of extrusion die structures and process parameters on extrusion process are summarized. Secondly, the multi-objective optimization model for extrusion die is established, and the porthole automatic optimization system is developed. Thirdly, the extrusion die design method for wallboard profiles with large and complex cross-sections is presented, and its mechanical property, microstructure and fracture mechanism are investigated by experimental method. The main contents and conclusions in this paper are as follows:(1) Numerical simulation models of hollow aluminum profile extrusion process have been established on the basis of HyperXtrude software. The effects of extrusion die structures (the step of welding chamber, the number and layout of portholes, etc.) and process parameters (extrusion ratio, extrusion temperature, ram speed, etc.) on metal flow, temperature distribution, welding quality, extrusion load, die wear behavior, die stress status and deflection have been investigated. The metal flow rules and deformation mechanism in die cavity have been obtained.(2) Two optimization models for porthole extrusion dies based on modern intelligence algorithms have been established. In the first optimization model, choosing standard deviation of the velocity field, maximum die stress and mandrel deflection as optimization objectives, Pareto-based genetic algorithm with Kriging model is applied to optimize porthole extrusion die of irregular cross-section profile. In the second one, combining with Box-Behnken experimental design and response surface method, prediction models for standard deviation of the velocity field, maximum extrusion force and maximum temperature in the extrudate are established, and the porthole shape of the extrusion die is optimized by means of particle swarm optimization method.(3) Considering the consistency rule of the ratio of mass flux in each porthole to area of corresponding part of the extrudate, an automatic optimization program has been developed for porthole structure based on finite volume method during steady extrusion process. With the developed program, porthole shapes and locations could be adjusted and optimized by analyzing status of metal flow in die cavity. (4) The constitutive equation of AA6N01aluminum alloy used in high-speed train is established and die design methods for large and complex cross-section profiles are proposed. Through optimization design of extrusion die, the flow velocity distribution becomes more uniform and the weld quality of the extrudate is improved. Through experimental examinations, its dimensional accuracy, mechanical property and micro structure satisfy practical engineering requirements.