【作者】 陈浩；

【导师】 赵国群；

【作者基本信息】 山东大学 ， 材料加工工程， 2012， 博士

【摘要】 能源、环保、安全是关系到人类生存和发展的三大难题。由于铝合金型材产品具有重量轻、强度高、外形美观、易于回收等优点,因此,推广应用铝型材产品是缓解上述三大难题的重要途径之一。目前铝型材的品种规格不断增多,应用范围不断拓展,已由20世纪50～60年代民用建筑为主体,扩展到了机械制造、车辆、船舶、飞机、通讯等各个领域。挤压成形工艺是实现铝型材生产的关键技术,其工艺水平决定着型材制品的质量和模具的使用寿命。然而在实际生产中,挤压模具的设计和工艺参数的确定更多依赖设计师的经验,模具质量难以保证,需要多次试模和修模才能生产出合格产品。而采用数值仿真技术模拟实际的挤压过程,可以实时跟踪描述金属的流动行为,揭示金属的真实流动规律,获得速度、温度、应力、应变等实验现场难以测量的物理量,预测型材在挤压过程中可能出现的缺陷,并及时对模具结构及工艺参数进行调整,有效减少了试模修模次数,不仅能够提高挤压型材质量,同时也可降低生产成本,缩短模具生产周期。铝型材挤压成形是一个处在大变形、高温、高压、复杂摩擦条件下的非线性成形过程,涉及力学中的几何非线性和物理非线性,难以采用传统的测量和分析方法研究挤压模具型腔内材料的流动规律和变形机理。本文围绕空心铝型材挤压成形问题,采用数值仿真方法,对铝型材挤压成形工艺进行系统研究,总结模具结构参数和工艺参数对挤压成形过程的影响规律,建立挤压模具的多目标优化模型,开发挤压模具分流孔自动优化系统,探讨复杂大断面型材挤压模具的设计方法,并实验研究大断面型材的机械性能、内部组织缺陷及断裂机理。论文的主要研究工作和成果如下：(1)建立了空心铝型材稳态挤压过程的有限元模型,研究了挤压模具型腔内材料的流动规律及变形机理,获得了挤压模具结构(如焊合室级数、分流孔数量及布局等)和挤压工艺参数(如挤压比、挤压温度和挤压速度等)对材料流动、温度分布情况、焊缝质量、挤压力、模具磨损行为、模具受力状态及变形情况的影响规律。(2)建立了两种集成有限元模拟技术和人工智能算法为一体的挤压模具优化设计模型。在第一种优化模型中,以获得均匀的型材截面速度分布、最小的模具应力和模芯变形为目标,采用拉丁超立方法进行实验设计,并结合Kriging代理模型和基于Pareto法的多目标遗传算法对一异形空心型材挤压模具进行了优化设计。在第二种优化模型中,选取分流孔形状作为设计变量,结合Box-Behnken实验设计和响应曲面法,分别建立了以型材截面速度均方差、最大挤压力和型材截面最高温度为目标的预测模型,并利用粒子群算法实现了一多腔壁板型材挤压模具分流孔结构的优化设计。(3)基于各个分流孔通量与其所填充型材面积比的一致性原则,并结合稳态挤压过程的有限体积法,建立了挤压模具分流孔自动优化模型,开发了相应的计算程序。采用上述系统对模具型腔内的金属流动规律进行了模拟分析,并自动修改分流孔形状和位置,实现了模腔内金属的流动平衡。(4)建立了高速列车车体用材料AA6N01铝合金的本构方程,针对高速列车壁板型材,提出了一种数字化模具设计方法,解决了型材截面速度分布不均的问题,同时提高了型材的焊缝质量。通过测试发现,型材的尺寸精度、机械性能及内部组织均满足工程应用的要求。更多还原

【Abstract】 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.更多还原