【作者】 郑再象；

【导师】 徐诚； 樊黎霞；

【作者基本信息】 南京理工大学 ， 机械工程， 2007， 博士

【摘要】 管件液压成形工艺因具有减轻重量、节约材料、降低能耗、简化生产流程、降低生产成本、表面质量高、机械性能好等优点，近年来已在欧洲、北美、日本、韩国等国家的汽车、航天、航空、国防、化工、医疗等领域中得到了广泛的应用。但过高的初期设备投资和苛刻的工艺条件使得这项被称为“贵族工艺”的技术在我国的发展步履维艰。因此，加强低成本的液压成形设备特别是大吨位大工作台面液压成形设备的研究，完善与之配套的材料制备、工艺设计准则制订等相关工作，对促进该项技术在资源相对贫乏的我国实现产业化具有重要的意义。本文的主要内容如下：结合国内的制造水平和加工能力，简要分析了柱梁式和板框式机架的优缺点，并对大吨位管件液压成形设备所采用的预应力钢丝缠绕机架进行了可行性论证，继而给出了克服预应力钢丝缠绕机架抗侧推能力较差的解决方案。在此基础上，先后完成了设备合模机构的优化设计、超高压动密封结构和液压系统的设计、以及控制系统的设计、建模与仿真等工作。利用金属塑性成形理论，通过解析的方式揭示了管坯外径、管坯初始厚度、管坯与模具之间的初始接触长度、以及摩擦条件等参数对成形结果的影响规律。在此基础上，建立了汽车仪表板梁液压成形的有限元模型，通过仿真分析，研究了直接成形和分步成形、内压加载路径与轴向补料位移的匹配关系、摩擦条件、补料量等不同工艺方案和主要工艺参数对成形结果的影响规律，提出了该类零件液压成形工艺方案设计和工艺参数制订的准则。针对副车架等大型结构件成形工序多、成形困难、以及上道工序对下道工序的影响较大等问题，文中建立了副车架预弯曲、预冲压和液压成形全过程的有限元模型，通过数值方法研究了预弯曲、预冲压对液压成形的影响规律，给出了该类零件的数值仿真精确建模、工艺方案设计和工艺参数制订的原则。针对传统寻优方法的不足，文中提出了一种新的优化方法，即将基于精英保留非劣排序遗传算法(NSGA-Ⅱ)的多目标优化求解器与基于动态显式算法的有限元软件LS-DYNA集成起来进行工艺参数的寻优方法。在简要介绍NSGA-Ⅱ算法原理及流程之后，建立了加载路径和补料量的多目标优化模型，并进行了优化运算。与传统寻优方法所获得的结果相比，多目标优化所获得的结果更为理想，取得了较好的效果。在数值模拟及优化的基础上，以仪表板梁为例，通过试验对液压成形过程中的金属变形机理展开研究，分析加载路径、补料量、摩擦条件等工艺参数对成形结果的影响规律，并将试验结果与数值模拟结果进行对比分析，不仅证明通过仿真方法进行工艺方案设计和工艺参数制订是可行的，还给出了仪表板梁工艺方案设计和工艺参数制订的准则。更多还原

【Abstract】 As a near-net shape metal forming technology, tube hydroforming, compared withconventional manufacturing via stamping and welding, has many advantages, such aslightening weight, improving material utilization ratio, stinting energy, reducing operation,potentially economizing tooling costs, improving surface quality, enhancing mechanicalproperties, and so on. In Europe, North America, Japan, and South Korea, it has beenwidely used in the fields of automobile, aeronautics, astronautics, national defence,chemical engineering, medical apparatus, etc. Tube hydroforming is labeled as ablue-blooded process, because it requires high cost of equipment investment and rigorousprocess, which lead it to move forward difficultly in our country. Therefore, the researchon low-cost hydroforming equipments, especially large-tonnage andlarge-operating-platform hydroforming equipments should be strengthened. Correlativematerial preparation and process design guidelines should also be completedsimultaneously. All these works are strategically meaningful for achievingindustrializations of tube hydroforming in our country, where natural resources are poor.The main work and creative harvests in this paper is listed blow:Based on the manufacturing level and working ability of equipment at home, theadvantages and disadvantages of frameworks with beam column and also with sheet frameare introduced briefly, and the feasibility for tube hydroforming equipment to adoptprestress wire-winded framework is confirmed. The solution to improve the resistance ofprestress wire-winded framework to side thrust is also brought forward. Subsequently, theclamping structure of hydroforming machine is optimized, and ultra high pressure sealstructure and hydraulic system is carefully designed. In addition, design, modeling andsimulation of the control system are carded out.Hydroforrning process is heavily influenced by process parameters such as initialoutside diameter and thickness of tube, initial contact length between tube and dies, andfriction conditions. Hence, it is essential to analyze the effect laws. Based on metal plasticdeformation theories, analytical equations are built and the laws are obtained. The equationon relationship between stress and strain under plastic state is built using Levy-Mises’syield criterion. By taking expansion region as instance, variations of stress, strain and tubedimension under different internal hydraulic pressures and axial loads are discussed.Aiming at the problems coming from geometrical nonlinearity, material nonlinearity and boundary condition nonlinearity in tube hydroforming process, nonlinear geometricalequation and constitutive equation of elastoplastic material are derived, and contactalgorithm and friction model used in numerical simulation are also introduced briefly, andsubsequently the dynamic explicit approach used for hydroforming process analysis andthe static implicit FEA used for spring back analysis are analyzed. Instrument panel beamand sub frame are taken as the case to perform the numerical simulation analysis ofhydroforming process. Effect laws of process planning and parameters, such as one-stepforming and multi-step forming, loading paths (internal hydraulic pressure via time andaxial feeding displacement via time), friction conditions, feeding amount, and materialproperties etc., on forming results are also investigated.In order to overcome the disadvantages of conventional optimization methods, thispaper presents a new optimization method to seek optimal hydroforming processparameters, which integrates dynamic explicit FEM into multiple-objective optimizationsolver based on elitist nondomiuated Sorting genetic algorithm (NSGA-Ⅱ). Using themethod, the feeding amount and loading paths of instrument panel beam hydroformingprocess is optimized. The optimization results obtained by this method are better than theresults obtained by the trial-and-error approach from experience or experimental studies. Inaddition, some pareto results are obtained by running simulation program at a time, andwhich offer a wider choice for process parameter design and designer’s decision-making.To validate the accuracy of simulation and optimization results, a series ofexperiments about instrument panel beam are performed. From the experimental results,some laws are obtained, that hydroforming process is influenced by process parameterssuch as loading paths, axial feeding amount, and friction conditions. The results fromexperiments are compared with the results from the FEA simulation and optimization.Finally, design guidelines of process parameter are given.更多还原