【作者】 杨兵；

【导师】 张卫刚； 李淑慧；

【作者基本信息】 上海交通大学 ， 车辆工程， 2006， 博士

【摘要】 在汽车制造领域,与传统的冲压、焊接工艺相比,采用管件液压成形工艺制造的汽车零件具有重量轻、刚度好、强度大、耐撞性好、节约材料、结构紧凑、加工工序少等诸多优点。这很好地满足了汽车轻量化发展的要求。随着计算机控制技术和超高压液压控制技术的发展,管件液压成形技术已开始进入实用化的阶段。可以预见,该技术将有力地促进汽车、航空、航天、船舶等产业制造技术的进步。在管件液压成形过程中,由于管坯材料、模具形状和加载工艺条件的影响,管件容易产生整体屈曲、起皱、破裂等成形缺陷。因此,防止成形缺陷的产生并提高成形性能,已经成为各汽车制造企业增强竞争力的关键技术之一。在零件形状、模具条件和管坯材料已给定的情况下,合理控制内压力、轴向推力的大小以及两者间的匹配关系即加载路径是管件液压成形工艺的关键。近几年来很多学者在管件液压成形加载路径的控制方面开展了广泛的研究,取得了一定的成果。然而这些研究对加载路径的控制规律、加载路径变化对管件液压成形性影响的内在机理、合理加载路径的设计原则以及合理加载路径的设计方法等方面仍不够全面深入,研究结果还不能直接用于实际生产。本文以数值模拟为工具并结合试验对管件液压成形的加载路径问题开展深入研究。自主研制了一台计算机控制管件液压成形设备,设备最大成形内压力达到200MPa超高压,设备可同时实现内压力、轴向推力和轴向位移的联动精确控制;以典型的自由胀形件为例,研究了管件液压成形时避免各种缺陷产生的临界载荷变化规律以及不同因素对临界载荷的影响规律;从加载路径影响应力状态,应力状态影响成形性能的角度揭示了提高管件液压成形性能的加载机理,并确定了合理加载路径的设计原则;在此基础上,提出了基于自适应仿真与模糊控制相结合的加载路径设计方法,并将该方法应用于若干典型试验件的成形。本文主要研究内容和主要创造性工作包括以下几个方面:1、计算机控制管件液压成形设备研制本文自主研制了一台内压力达200MPa的计算机控制管件液压成形设备。对设备的整体结构、液压控制系统、计算机控制系统、模具与超高压密封系统等若干关键技术进行了探索性的研究;并通过大量的试验调试实现了设备在工艺控制精度上的先进性。为研究提供实验基础。2、管件液压成形的数值模拟与试验本文开展了提高管件液压成形数值模拟精度的三维有限元建模方法的研究,分析了进行数值模拟时仿真参数的选取原则,研究了采用动力显示有限元算法进行仿真计算时虚拟加载时间对管件液压成形预测精度的影响。通过仿真与试验结果的比较,为研究提供准确的数值模拟基础。在试验基础上,分析加载路径对管件液压成形结果影响的两个层面。提出了管件液压成形性的几种评价准则,并采用数值模拟和试验研究了几种典型的加载路径对圆形截面零件成形性的影响。3、管件液压成形的临界载荷变化规律研究将成形过程中发生密封泄漏以及管件发生屈曲、起皱、破裂等成形缺陷时对应的临界内压力、临界轴向推力加载关系曲线所围成的载荷区间称之为“临界加载窗口”(critical loading window diagram)。加载路径应该位于临界加载窗口内才可以成形零件。本文基于塑性稳定性理论和成形工艺特点建立了完整的自由胀形件临界加载窗口的理论模型,并通过试验验证该模型的正确性。分析了管坯尺寸、管坯材料、模具形状等参数对临界加载窗口的影响规律,从而实现根据材料、管坯尺寸和模具参数来约束加载路径的范围。从理论上解决了如何避免零件成形缺陷的产生问题。4、提高管件液压成形性的加载路径规律研究在临界加载窗口内,能成形零件的加载路径很多,但采用不同加载路径时零件的成形性不同。为确定合理的加载路径以提高管件液压成形性,本文对管件液压成形的塑性变形过程展开了进一步的理论研究。首先分析管件液压成形工艺过程中的应力应变特点,揭示应力状态对成形性能的影响规律,获得提高成形性能的理想应力状态。提出获得理想应力状态所需理想加载路径的基本构想,并以自由胀形件为例,从理论上建立理想加载路径的计算模型。利用获得的加载路径分别进行仿真与试验研究,根据仿真和试验结果,提出了合理加载路径的设计原则。从理论上解决了如何提高管件液压成形的成形性问题。5、基于自适应仿真与模糊控制相结合的加载路径设计方法研究根据合理加载路径的设计原则,如何有效地设计确定具体的加载路径轨迹仍然是一个难题。本文结合管件液压成形的工艺特点和合理加载路径的设计原则,提出一种基于自适应仿真与模糊控制相结合的管件液压成形加载路径设计方法。采用自适应仿真方法克服了传统仿真中反复试错的缺点,利用所建立的成形缺陷趋势评价函数,将当前的仿真结果及时地反馈给下一步的仿真计算,实现成形过程缺陷的“预发现、预纠正”,从而减少有限元模拟次数、提高效率。在成形缺陷趋势程度的识别和成形工艺参数的调整过程中,采用模糊逻辑控制的策略,从而更加合理地判断成形缺陷、调整工艺参数。本文最后对典型组合截面的试验件进行加载路径设计和试验验证,结果表明了该方法的正确、有效性,也表明了本文提出的加载路径设计原则的正确性。从实际上解决了具体加载路径设计的方法问题。本文的研究以理论推导、数值模拟为主,并结合大量试验数据的对比分析,自主研制了计算机控制管件液压成形设备,在前人研究的基础上揭示了提高管件液压成形性的内在机理和加载路径设计原则,提出了合理加载路径的设计方法,将依赖于试验和经验的加载路径设计上升为依据严密理论推理的科学过程,为管件液压成形的加载路径设计提供了理论指导和方法选择。更多还原

【Abstract】 In automobile manufacturing industry, tube hydroforming (THF) will offer several advantages as compared to conventional manufacturing via stamping and welding. These advantages include: weight reduction, improved structural strength and stiffness, part consolidation, lower tooling cost due to fewer parts, fewer secondary operations. These advantages satisfy the requirements of the development of lightweight car. The THF technology has now been used in industry with the development of the computer and the super-high hydraulic pressure controlling technology. It can be forecast that the manufacturing technology of the automobile industry, aeronautics and astronautics industry, and shipbuilding industry will be improved by this technology.Because the effects of the material, the die shape and the loading condition, the forming workpieces may be limited by the failure modes of buckling, wrinkling and bursting during the THF process. To avoid the forming failures and improve pats’formability is a key technology for improving the competence of the enterprise. For a given part shape, die condition and tube material, the key technology is to reasonably control the internal pressure, the axial force and its relationship, that is loading path. Lots of literature research into the loading paths of the THF process, and achieved some usable results. But few efforts have been put into the rules of the loading paths, the mechanism of improving the formability by controlling the loading paths, the design principle and the design method of the reasonable loading paths.This dissertation studies on the loading paths of the THF through FEM and experiments methods. Firstly, a computer controlling THF equipment has been research and developed, its maximal internal pressure is 200MPa. The internal pressure, the axial force and the axial displacement can be controlled accurately. Then, the variation laws of the critical loading for avoiding different forming failures and the effect of different conditions on the critical loading forces for the free bulge process are studied. Thirdly, the mechanism of improving the formability by controlling the loading paths are analyzed from the view that stress station has effect on the formability, and the loading path has effect on the stress station. After that, the design principle for the reasonable loading paths is proposed. Based on this analysis, a design method integrated the adaptive simulation and the fuzzy logical control is proposed. At last, the method is used for some typical experiment parts.The main content of this thesis can be divided into five parts: 1. Research and develop a computer controlling THF equipmentA computer controlling THF equipment has been research and developed, its maximal internal pressure is 200MPa. The dissertation takes an exploratory study on the key technique of the integral structure, the hydraulic controlling system, the computer controlling system, the THF die system and the sealing system and so on. Then equipment is verified to be precise through quantities of experiments. It is the experiment tool for research.2. Simulation and experiment study on THFThis dissertation studies the three-dimensional FEM modeling method to improve the THF simulation precision, and put forward some guidelines for parameters selection of simulation process. The effect of the virtual time on the prediction precision in the THF process is analyzed when the dynamical explicit FEM is used. Through the comparison between experimental and simulation results, the FEM tool for the research is achieved. Then, two effects of the loading paths on the forming results are analyzed based on some experiment results. On the basis of the study above, this dissertation studied on the effect of several typical loading paths on the tube hydroformability, using numerical simulation and experiments.3. Study on the variation laws of the critical loading in THFThe critical loading window diagram (CLWD) is a diagram that is enclosed by the loading path of the critical internal pressure and the critical axial force, which are the critical loading when failures such as buckling, wrinkling or bursting have happened. The loading paths for forming a part should lies within the CLDW. Based on the plasticity theory and THF technology, this dissertation constructs the whole theoretical model for the CLWD, which is validated through experiments. Then, the effect laws of tube size, material and die shape on the CLWD are analyzed, and then put forward the selection range for different material, different tube size and die parameters, which limit the bound of the loading paths and avoid the forming failures of TFH. The CLWD can answer the question of how to avoid the forming failures from the theory.4. Study on the loading paths that improves the tube hydroformabilityIn CLWD, there are many loading paths for selection, but there is great differences formability for the hydroformed tubes between different loading paths are selected. To select an appropriate loading path, this dissertation studies the tube plastic deformation process in THF with theoretical methods, analyzes the stress and strain characteristics in hydroformed parts and finds the effect of the stress station on the formability. Then, obtains the ideal stress states for improving the formability in THF process. This dissertation proposes the basic concept to obtain the ideal loading path that leads to the ideal stress states in hydroformed parts, and then the theoretic model of the ideal loading path for the free bulge process are studied. According to the simulation and experiment results at different loading paths, this dissertation also put forward the design principle of reasonable loading paths, which answer the question of how to improve the formability of the tube from the theory. 5. Study on loading paths design method based on the combination of adapted simulation and fuzzy logical controlHow to obtain the reasonable loading path is still difficult for people, although its design principle is known. Based on the characteristic of THF technology and the design principle of loading paths, this dissertation put forward a design method for reasonable loading path, this method integrated the adaptive simulation and fuzzy logical control. The adaptive simulation avoids the try-and-error process of conventional loading path design method, it constructs a target function that assesses the defects tendency in hydroformed process, and then returns the simulation results to the next simulation step. In this way, the program can predict and rectify the forming process defects, which means fewer simulations and higher efficiency. In the identification of forming results and the modification of the process parameters, the fuzzy logical control method is used. In this way, more reasonable prediction of forming defects and adjustment of process parameters can be achieved. To validate the efficiency of the loading path design method, several experiments are used in the end. From the results, it’s found that the design principal and the design method for loading path proposed in this dissertation are right and advanced. This method can answer the question of how to design the loading path in industry.This dissertation studies on the loading paths of THF mainly through theoretical deduction, numerical simulation and large amounts of experiments. The THF equipment, the mechanics of hydroforming, the design principle and the design method of loading path are researched into in this dissertation. It transforms the loading path design process that depended on experiments and experiences to a refined theoretical deduction process. Which provides theories guidance and a new method for the loading path design in THF.更多还原