【作者】 孙雪梅；

【导师】 赵国群；

【作者基本信息】 山东大学 ， 材料加工工程， 2014， 博士

【摘要】 铝合金型材是应用最为广泛的铝合金产品,世界各国均将铝合金型材挤压技术及其产业作为重点发展方向之一。铝合金型材挤压技术是挤压筒内的铝锭材料在外力作用下发生塑性变形、流经挤压模具的导流室、分流孔、焊合室、工作带并最终形成所要求的截面形状的铝合金型材的过程。铝合金型材挤压过程是一个复杂的大变形、高温、高压、摩擦等条件下的非线性热力耦合成形过程。铝合金型材是实现高速列车、汽车、船舶、航空航天器等的轻量化和性能提升的关键结构材料,目前正在向高性能、大型化、复杂化、精密化、多品种、多规格、多用途方向发展,对铝合金型材的结构、力学性能、组织性能等的技术要求日益苛刻,这类型材具有中空薄壁、断面形状复杂、断面尺寸大、力学性能高的特点,材料在变形中的流动行为复杂,增加了模具结构设计、材料流动行为分析和工艺模具参数的优化设计的难度,若模具设计和工艺参数选择不合理,则极易造成型材扭拧、波浪、弯曲、开裂等缺陷,并影响模具使用寿命。因此,迫切需要研究铝合金型材挤压过程的数值建模方法,研究材料变形规律,揭示工艺与模具参数的影响规律,探讨复杂截面型材的模具结构优化设计方法等,以便为铝合金型材质量控制提供理论指导。本文首先针对带有大长悬臂的复杂铝合金型材挤压过程中存在的常规平模或导流模结构设计容易导致模具悬臂部位损坏的问题,提出并建立了一种伪分流模具结构设计方法及其长悬臂梁分解技术,建立了长悬臂梁铝合金型材在伪分流模具中的挤压变形数值模型,对比分析了常规模具设计与伪分流模具设计对铝合金型材挤压速度分布、温度分布、材料粒子运动轨迹等的影响规律,研究了不同模具结构对其强度的影响规律。研究表明,采用伪分流模具不仅能够大幅度降低模具应力,而且通过材料流动优化可获得良好的材料流动规律和型材质量。最后总结提出了伪分流模具结构的一般设计原则和方法。复杂铝合金型材往往需要二级焊合,本文研究了具有二级焊合室的铝合金型材挤压过程数值模拟建模方法和挤压模具二级焊合室结构优化设计方法,针对某一典型铝合金型材,建立了以模具工作带出口处型材截面流动速度均匀性为目标、以二级焊合室的形状和高度为设计变量和以满足模具强度校核为限制条件的二级焊合室优化模型。采用Box-Behnken试验设计方法,建立了基于HyperXtrude的铝合金型材挤压过程的数值模型,分别获得了不同试验设计时的型材出口处流速、温度等场量的分布规律,采用响应曲面方法,建立了目标函数的响应曲面公式,并采用遗传算法作为优化方法,实现了基于响应曲面法和遗传算法的挤压模具二级焊合室的优化设计,优化获得了型材出口速度分布相对均匀的二级焊合室的结构尺寸,保障了铝合金型材的挤压质量且满足模具结构强度要求。高速列车车体壁板型材多为宽体多腔、薄壁超长的大截面型材,型材材料多为AA6N01和AA7N01,针对这类大断面复杂铝合金型材,本文首先进行了AA6N01和AA7N01铸锭材料的热模拟实验,分别建立了材料的本构关系模型,检验和分析了铸锭材料的微观组织。研究了高速列车车体壁板铝合金型材挤压过程数值建模方法,设计了壁板型材挤压模具,以型材出口处流速为优化目标,研究揭示了模具结构形状对型材截面流速、筋部供料等的影响规律,分析了导致型材弯曲和扭拧变形的根本原因,对挡块、焊合室结构等进行了优化设计,详细分析了材料在优化模具中的挤压变形行为、流线分布、温度分布以及模具变形和应力分布等,总结给出了壁板型材挤压模具优化设计结果,进行了实际生产挤压实验,验证了模具设计和工艺参数选择的正确性,分别研究和对比了型材制品在挤压方向、横向和筋部的力学性能、显微组织和断口形貌,并揭示了型材在不同方向上的试样断裂机制,结果表明,采用优化设计的分流模具和选择的挤压工艺参数能够获得质量优异的车体壁板型材产品。针对目前复杂截面铝合金型材挤压模具设计仍然依赖设计者的经验和缺少计算机CAD设计系统的问题,本文研究了铝型材平面分流组合模的设计流程和关键技术,运用反推分析法,从模具结构向工艺参数反推,构建平面分流组合模CAD系统总体框架,分析了分流组合模具结构实体建模方法,实现了各个模块的具体设计,采用UF对象模型进行了逐步建模,开发了复杂截面铝合金型材分流组合模具CAD系统。基于该CAD设计系统,对一典型的复杂截面铝合金型材挤压分流组合模具进行了CAD设计,进行了挤压过程数值建模和分析,研究揭示了挤压材料的流动规律和型材截面变形扭拧状态,通过对引流槽、挡块、工作带的局部修正,优化获得了出口截面流动速度相对均匀的优化模具结构和形状。结果表明,采用本文开发的平面分流组合模CAD系统设计的模具形状完全可以作为初始模具设计方案,根据挤压过程数值模拟结果并对模具进行局部优化,能够获得使出口型材断面流速均匀的模具设计方案。该系统可对任意空心型材进行平面分流组合模设计建模,提高了模具设计效率。更多还原

【Abstract】 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.更多还原