【作者】 张磊；

【导师】 赵国群；

【作者基本信息】 山东大学 ， 材料加工工程， 2013， 博士

【摘要】 热冲压工艺是一种基于模内淬火的高温板料成形技术,其技术特点是将板料在高温下冲压成形,并利用模具实现对成形工件的淬火处理。在热冲压工艺中,冲压过程板料处于奥氏体化温度以上,这将显著降低高强度钢对成形力的要求,提升单工序成形能力。冲压前,高温板料进行了充分的奥氏体均匀化,冲压后模具仍然要保持压力闭合一段时间,对成形零件进行快速冷却淬火,提升淬后零件的力学性能和组织性能。热冲压工艺可以有效的消除利用传统工艺对高强度钢成形时极易出现的断裂、回弹、变形抗力大等工艺问题,显著改善高强度钢的成形能力；有效提高了成形工序集合程度,降低了工艺复杂性,提高了生产效率。显然,热冲压工艺作为一种多种工艺、多种技术高度集合的新型工艺,极大地扩展了高强度钢的应用范围,具有广阔的应用前景和巨大的市场潜力。本文从工艺原理、工艺流程、硼钢材料的淬后性能、模具温度场控制、冷却系统的优化设计、材料模型的建立及相关关键技术研究等方面对热冲压成形工艺进行了系统的研究。针对硼钢材料的淬后性能,利用对比实验的方法,研究了淬后工件力学性能和微观组织形态,通过对比分析不同加热温度、不同保温时间、不同冷却介质(水、铜砧板、钢砧板)条件下淬后工件的抗拉强度、硬度、微观组织形态等性能指标,研究揭示了相关工艺参数对材料淬后性能的影响规律,并据此提出了该材料的热处理工艺参数推荐方案。分析了热冲压工艺原理和模具系统各部位热传递过程,构建了热冲压工艺热平衡分析模型,建立了热冲压成形过程数值模拟模型,利用数值模拟方法研究了热冲压模具温度场的分布形态和历史演变规律,并提出了需要重点关注的模具主要换热通道；建立了热冲压工艺实验模拟装置,制定了合理的实验模拟热冲压工艺流程,提出了平均温度、平均温增、温度极值、平均周期四个温度场考量指标,利用实验数据,分析了工艺过程中模具温度场的分布和变化规律,研究了成形温度、冷却介质和工艺周期对模具温度场考量指标的影响规律；将模拟结果与实验数据进行了对比分析,验证了所建模型及相关设置方案的可靠性。基于热力耦合数值模拟分析、响应曲面法和粒子群优化算法,研究了热冲压模具冷却系统相关参数对冷却效率、温度场均匀性和疲劳寿命的影响规律；利用最小二乘法的回归分析,建立了热冲压模具表面平均温度、表面温度的标准差和模具上最大等效应力的响应曲面膜型；通过变异数分析和随机试验,验证了响应曲面模型的有效性。提出了冷却效率优先、模具温度均匀性优先和疲劳寿命优先的三种优化设计策略,基于所建立的响应曲面计算模型,分别建立了相关优化模型,利用自主开发的优化设计程序目标函数进行了优化计算,扶得了模具冷却系统布局相关推荐参数,利用与原设计方案进行对比分析的方法,证明了优化结果的积极意义。基于相关实验测试,自主构建了热—力—组织三场耦合的的材料模型，实现了对热冲压工艺温度场、应力应变场和相变过程的耦合分析；根据热冲压工艺特点,建立了U型件热压工艺过程的数值模拟模型，利用自行开发的材料模型，研究了成形温度对板料厚度、回弹变形、残余应力场及相变过程的影响规律,建立了相关成形零件工艺指标随工艺条件的变化规律；通过对U型件的热冲压成形的实验研究,研究了成形温度和模具冷却方式等成形零件力学性能和微观组织形态的影响规律,为热冲玉成形零件工艺规范的设计提供了理论依据和科学指导。更多还原

【Abstract】 Hot stamping process is a kind of sheet metal forming technology at high temperature which based on die quenching process, in which the sheet metal stamping is formed at high temperature, and the workpiece is quenched using the mould. In hot stamping process, the blank at pressing progression is heated up to austenitizing temperature and above. This will significantly reduce the requirement of the forming force and promote deformation ability in single process. Before pressing, the high temperature austenite has been fully homogenization. After pressing, the mould will be closed keeping pressure for a period of time, in order to rapidly cool and harden the forming part, improving the mechanical properties and microstructure morphology. Hot stamping process can effectively eliminate the technology problems such as fracture, springback, large deformation resistance which easily appear when forming high strength steel using traditional process, and greatly improve the high strength steel forming ability. Hot stamping process can effectively improve the collection of forming process, which has positive significance for reducing process complexity and improving the production efficiency. Obviously, hot stamping process is a new technology which highly collected variety of process and variety of technology. It greatly expands the scope of the application of high strength steel, making which won a wide application prospect and huge market potential.In this paper, hot stamping will be given a systematic and in-depth study in the aspects of technology principle, technological process, performance of boron steel after quenching, mold temperature control technology, mold cooling system optimization design and related key technology research.Aiming at the chosen boron steel material, the mechanical properties and microstructure morphology after quenching are selected as key points. The heat treatment parameters (austenitizing temperature, holding time) and cooling medium (water, copper block, steel block) has been made a permutation and combination. And series of experiments with simplified process are carried out. Then the mechanical property is tested and microstructure is observed. Through contrast analyzing the experiments results, the influence law of process parameters on the materials performance after quenching is studied. And recommended proposals for applicable heat treatment parameters are give out.By analyzing the technology principle and the heat transferring process between the different parts of mold, the reasonable experimental simulation of hot stamping is presented and the experimental device is set up. Based a U-part forming process, hot stamping experiments are carried out. Using the mold temperature data obtained in experiment, the mold temperature distribution pattern during the single process and the variation rule during continuous process are studied. Combined experimental situation, the numerical simulation model is built based the software ABAQUS. With appropriate settings of related interfacial property, the mold temperature distribution pattern and its history variation rule are simulated using numerical method. The reliability of numerical model is checked by contrast with the former experiment result.Based on thermal-mechanical coupled simulation, response surface method and PSO (Particle Swarm Optimization) optimization algorithm, the iniluence rule of mold cooling system parameters on cooling efficiency, temperature uniformity and fatigue life is analyzed. Using the regression analysis with least square method, the response surface models are set up including average temperature of mold surface, the standard deviation of mold surface temperature and the maximum equivalent stress on mold. By means of ANOVA and random experiment, the availability of these response surface models are proved. Three optimization design strategies are proposed including cooling efficiency first, mold average temperature first and fatigue life first. Based the established response surface model, the related optimal models are set up respectively. The optimal calculation of object function is carried out using self-developed optimal design program. As a result, recommend parameters of mold cooling system layout are obtained. It is experiment verified using numerical method. The optimal result is proved having positive significance on improve the related index such as cooling efficiency by comparing with the original design method.Based on experimental test result, a material model is self-developed which coupled the calculation of thermal-mechanical-phase field. Importing it into the numerical simulation process using the ABAQUS subroutine function, the three field coupled simulation of hot stamping is realized. According to the hot stamping technological characteristics, the numerical model for U-part hot stamping process is built. It is studied that the influence of forming temperature on blank thickness, on the springback deformation, on residue stress field and on the phase transformation. It is obtained that the variation rule of formed parts process index with process conditions. It is experimental studied on the U-part hot stamping process. With the experiment result, it is analyzed the influence rule of forming temperature and mold cooling method on the mechanical properties and microstructure morphology. This provided a theory basis and scientific instruction for process specification of hot stamping part.更多还原