【作者】 马宁；

【导师】 胡平；

【作者基本信息】 大连理工大学 ， 车辆工程， 2011， 博士

【摘要】 热成形技术是将传统热处理技术及冷冲压技术相结合的最新制造技术,刚兴起已受到国家产业政策、工业界及学术界的高度重视,具有广阔的发展前景和长远的发展生命力。本文从热成形技术工艺、热成形理论及实验方法、热成形过程的多场耦合本构关系、热成形过程的数值模拟、热成形复合材料技术及热成形技术的工程应用等方面对热成形技术进行了系统全面的研究。本文的主要研究成果如下：一、在热成形工艺方面基于独立自主开发的拥有自主知识产权的国内第一条热成形生产线介绍了直接热成形工艺和间接热成形工艺,分析了两种热成形工艺的特点,给出了选择不同成形工艺的方法。分析了高强度钢板热成形技术的关键技术和装备,总结了连续加热炉的核心技术要求、给出了热成形模具关键制造技术及设计方法,以及对热成形专用压机需具备快速动作、保压等关键技术进行了论述。研究了热成形工艺参数及其优化控制方法,分析了热成形工艺的关键工艺参数,即加热温度及保温时间、高温板料传递时间、冲压成形速率及模具冷却速率控制等,并对这些工艺参数的技术要求、优化控制方法进行了说明；结合热成形实例,提出了利用传统冲压数值模拟技术与高温材料参数相结合的手段对热成形参数进行快速辅助优化控制方法。二、在热成形理论和实验研究方面对热成形材料常温下的微观组织及其基本力学性能进行相关实验研究及理论分析；对热成形材料常温下的热成形性能进行了成形极限实验研究。对热成形过程中影响材料成形性能的硬化能力参数进行了实验研究；通过对材料硬化性能的分析,给出了热成形材料具有较好成形性能的温度区间。分析了热成形过程中板料各向初始轧制各向异性的实验方法,提出了一种新的方便高精度的实验方案用于测试材料的高温轧制各向异性。在热成形钢板进行高温拉伸及淬火实验的基础上,建立了马氏体相变点Ms、马氏体转变速率θ及相变塑性系数k与应力之间关系,进而建立了硼钢热成形过程中的热、力、相变耦合模型。引入了混合定律,对多相混合组织的热容、导热系数、热膨胀系数等热物性参数、弹性模量E及屈服极限等力学性能参数进行了等效分析。对热成形应变组成及其形成机理进行了分析,引入了相变体积应力及相变塑性应力等新概念。三、在热成形过程的数值模拟技术方面在建立的高强度钢板热成形热、力、相变耦合本构方程的基础上,发展了热成形非线性大变形动力显式有限元方程；通过定义接触控制参数的概念,将材料的高温性能引入接触与摩擦模型；将热成形过程中的相变潜热引入温度场,并进行了有限元分析；在自主开发的商业化金属成形CAE软件KMAS (King-Mesh Analysis System)基础上,开发了考虑多场耦合的非线性、大变形热成形动力显式数值模拟模块。基于虚功率方程及持续平衡方程建立了热成形静力显式多场耦合有限元列式,在KMAS软件基础上,开发了热成形静力显式数值模拟模块。四、在热成形金属复合材料技术方面发现了热成形分层金属复合材料及其制造工艺;分析了这种热成形新型金属复合材料各层的硬度、强度及塑性性能的连续梯度分布规律；通过对比车门防撞梁新型金属复合材料与内部各相材料在冲击载荷作用下的冲击力、吸能等性能对比,说明了金属复合材料综合了各单相材料的优秀性能,适合用于承受冲击吸能构件的选材。给出了热成形连续梯度分布金属复合材料成形工艺,通过控制热成形过程中的加热温度及模具冷却管路布局,得到了材料性质呈连续梯度分布的特殊金属复合材料。通过实验及数值模拟分析,说明了这种金属复合材料特别适合于耐碰撞冲击材料的选材。五、在热成形技术工程应用方面提出了判断耐冲击零部件性能的数值模拟方法,即根据零部件在整车碰撞中的约束情况对零部件进行相应约束,然后进行准静态或者动态冲击数值模拟。基于上述方法对某车型前保险杠横梁进行了热成形材料厚度的优化设计,在性能提升的同时重量减轻40%。对热成形金属复合材料零部件的优化设计进行了研究。首先通过对B柱进行冲击数值模拟证明了所提出的判断耐冲击零部件性能的数值模拟方法的可行性。进而通过对车身典型零部件B柱及S型梁应用热成形复合材料工艺进行优化设计,得到了比传统结构耐冲击能力更好的热成形金属复合材料零部件,同时给出了热成形金属复合材料零部件的优化设计方法。对热成形零部件在车身设计中的应用方法进行了研究,提出了热成形零部件用于车身设计的“功能设计”方法,通过4种工况下整车侧面碰撞结果的对比分析,说明了热成形零部件在车身设计中的作用机理,并详细阐述了“功能设计”方法的内容。更多还原

【Abstract】 Hot forming of ultra high strength steel is the advanced technology that integrates traditional heat treatment and cold stamping. It represents the best solution to increasing the strength-to-mass ratio of sheet components, and then it can meet the need of higher passive safety and weight reduction. The prospect of hot forming technology has attracted the attention of national industrial policy the academic and engineering community, which mainly focus on the high temperature mechanical properties of materials, numerical simulation and experiments. Hot forming technology is systematically researched on these aspects including hot forming technique, theory and experimental methods of hot forming, multi-field coupled constitutive relationships of hot forming, numerical simulation of hot forming, metal composite material in hot forming and their engineering application. The main researching results of this dissertation are in the following:Hot forming techtique:According to the different forming and quenching process, two methods can be employed in hot forming:multi-step method and one-step method. The key technology of the two methods and their die design are studied. The application methods of these two hot forming processes are given. Based on independently developed mass production line of hot forming, the key technology and equipments are proposed, which include die manufacturing with cooling system, continuous heating furnace technology and integrated manufacturing system composed of the advanced interdisciplinary technology of machining, electronic control, material and chemical engineering.Hot forming technique parameters and their optimization method are investigated, which include heating temperature, temperature preservation time, blank transferring time forming speed and die cooling rate. Feasibility methods including theoretical analysis, numerical simulation and experiment are used to the design of the die and its manufacturing process of vehicle HFS (hot forming steel) components. The fast aid optimization method of hot forming parameters is obtained, which integrated numerical simulation of traditional cold stamping and material properties at high temperatures.Theory and experimental research of hot forming:Microstructure and basic mechanical properties of hot forming are introduced. FLD (forming limiting diagram) experiments are carried out at room temperature.The hardening ability of hot forming material is investigated tensile testing at high temperature, which influences material forming ability. The best temperature range for hot forming is obtained. A new experimental method is provided to investigate the anisotropic property due to rolling process of steel.Thermal-mechanical-transformation coupled relations of boron steel are investigated in the hot forming (HFS, hot stamping) process by tensile and quenching experiments at high temperature. In the experiment a plate specimen of boron steel is austenitized for five minutes at 950℃, then tensile forming and quenching take place simultaneously and the force, displacement, expansion and temperature in the experimental process are measured. Based on the analysis of the above physical quantities’variation and the specimen’s microstructure, thermal-mechanical-transformation coupled relations of boron steel are researched and the thermal-mechanical-transformation coupled constitutive models are developed. The multi-phase mixed relationship is introduced to analyze the effective thermo-mechanical parameters and mechanical properties of multi phases during the hot forming. The components of strain and their evolved mechanism for hot forming are investigated. By defining the concepts, the phase-transformation volume stress and phase-transformation plastic stress are expressed to explain the mechanism of thermal-mechanical-transformation coupled relations. Based on the above research, the thermal-mechanical-transformation coupled models are introduced into the constitutive equations of hot forming and the integrated and incremental constitutive equations are respectively developed.Numerical simulation of hot forming:Based on the characteristic of hot forming process, the main difference of numerical simulation between hot forming and cold forming is investigated. The key questions in numerical simulation of hot forming are analyzed.Based on developed thermal-mechanical-transformation coupled constitutive models of hot forming, the nonlinear large-deformation dynamic explicit finite element equations are proposed. By defining the concepts, the contact control parameter is expressed to reflect material contact and friction properties at high temperatures. The phase transformation latent heat is introduced into the analysis of temperature field during the hot forming process. Based on the independently developed commercial CAE software for sheet metal forming, named KMAS (King-Mesh Analysis System), the numerical simulation module of dynamic explicit for hot forming is developed.The rate-dependent constitutive equation of hot forming and the finite strain virtual power equation and continuous equilibrium equation based on updated Lagrange method, the large-deformation, multi-field coupled, static explicit finite element equations of hot forming are established. Based on KMAS software, the numerical simulation module of static explicit for hot forming is developed. Metal composite material of hot forming:The multi-layer metal composite material and its manufacturing technique are discovered. The automotive components and parts formed in this technique show that the hardness in the exterior is low and that in the interior is high. The material properties present gradient distributions in the thickness direction. Then the new type multi-layer metallic composite materials is formed. By comparing the crash force and energy absorption between the metallic composite materials and its every single phase material, it is found that the metallic composite materials have the comprehensive performance of every single phase material. So the new metallic composite material is a good alternative material in application of absorbing energy.A new type of metal composite material can be manufactured by controlling heating temperature and designing the layout of cooling pipes in hot forming process of ultra high strength steel. The experimental results show the mechanical properties of the new metal composite material have the characteristics of continuous distribution along the main direction of energy absorption during crash process. The top-hat thin-wall structure consisting of U-shaped metal composite material is employed to analyze the crashworthiness of the new type of metal composite material. The numerical simulation results indicate the new type of metal composite material has the comprehensive performance of every single phase material. So the metal composite is a good alternative material in application of crash resistance.Engineering application of hot forming:The numerical simulation method of impact resistance is provided:according to the constraint and load conditions of the component in the whole vehicle car, the quasi-static load or dynamic load is employed to implement numerical simulation. Based on this method, optimization design of the front bumper beam is carried out by hot forming technology. The results show not only the bumper beam of hot forming improve the impact resistance, but also its weight is reduced by 40%.The optimization design of HFS metal composite material is investigated. The simulation result of B pillar proves the validity of the developed method, which is employed to investigate the impact resistance of HFS metal composite material. The optimization designs of B pillar and S-shape rail are carried out respectively by metal composite material of hot forming technology. Then the hot forming components with better ability of impact resistance are obtained.The new design method-functional design is provided, which applies the parts by hot forming to vehicle body design. Three models are design by using hot-forming parts to compare the numerical simulation results in the vehicle side impacts. Based on the comparison, the mechanism of the improved impact resistance of the whole vehicle by using hot-forming parts is analyzed. The parts by hot-forming should be the overall skeleton layout and form the ultra high strength car-protecting cab and passenger living space. The single part by hot-forming should not be simply employed to the vehicle body design in order that it thrusts into the vehicle body when vehicle crashes. Finally the functional design methods of hot-forming parts used in the vehicle body design are summarized.更多还原