IF钢成形极限的研究

发布时间：2018-11-17 19:05

【摘要】：IF钢作为第三代深冲钢材因其优异的塑性变形能力,被广泛应用于汽车中的一些变形程度比较大的难成形零件。IF钢的使用从某种程度上代表了一个国家的汽车工业水平的高低。我国汽车工业虽然已经度过了发展最快的时期,但仍然处在一个高速发展的阶段,对IF钢的需求量很大。但一些汽车零部件厂并没有对所使用板材的成形极限进行研究,致使工艺分析与模具设计缺少判据。因此,研究IF钢的成形极限,充分利用其塑性成形性能,进而优化成形工艺,提高汽车冲压件质量具有重要研究意义和价值。成形极限是板材塑性变形过程中在不失稳的前提下达到最大应变的极限状态,是衡量板材成形性能的重要指标之一。通过实验获取成形极限图国内、外都指定由相应的标准,但从试样设计、制备到实验后的真实应变测量和数据处理都耗时费力,不便于应用。本文以DX54D+Z为例,通过成形极限的实验研究、理论分析和数值模拟,探讨用理论分析和成形模拟仿真方法快速获取IF钢成形极限图的途径。在实验研究方面,根据《金属薄板成形性能实验-成形极限图(FLD)实验》的规定,制作了矩形与阶梯形9组(27件)试样,矩形试样用于获取“拉-拉区”的应变数据,阶梯形试样用于获取“拉-压区”应变数据;采用电化学腐蚀法在板材上印制网格;利用杯突试验机完成成形实验;利用GMASystem系统进行网格应变自动测量;最终完成实验成形极限图的绘制,为后续理论分析与成形模拟提供参考。在理论分析上,基于M-K凹槽理论,利用Logan-Hosford屈服准则和Rossard硬化方程,建立了板材成形极限预测数学模型,结合弦截法迭代求解,通过MATLAB软件对DX54D+Z的成形极限图进行了理论预测。在此基础上,分析了不同屈服准则、应变强化指数、应变速率敏感系数和厚度不均值对理论预测的影响。在成形模拟方面,应用DYNAFORM软件对标准埃里克森杯突实验过程进行成形模拟。但由于有限元软件没有失稳判据判断材料破坏或是虚拟实验停止的时间节点,本文在分析应力应变状态的基础上,提出极限状态的判据,对比分析了不同判据的使用范围,并预测了IF钢的成形极限图,讨论了实验工艺参数对基于成形模拟预测结果的影响。最后,将理论和成形模拟成形极限图与实验成形极限图进行对比,验证了理论和模拟方法的可行性和结果的正确性,为零部件厂商在实际生产中快速获取成形极限图提供了新的途径。
[Abstract]:As the third generation deep drawing steel, IF steel has excellent plastic deformation ability. The use of IF steel represents the level of automobile industry in a country to a certain extent. Although the automobile industry of our country has passed the period of the fastest development, it is still in a stage of high speed development, and the demand for IF steel is very large. However, some automobile parts factories do not study the forming limit of the sheet metal used, which leads to the lack of criteria for process analysis and die design. Therefore, it is of great significance and value to study the forming limit of IF steel, make full use of its plastic formability, optimize the forming process and improve the quality of automotive stamping parts. Forming limit is the limit state of the maximum strain in the process of sheet metal plastic deformation, and it is one of the important indexes to evaluate the forming performance of sheet metal. At home and abroad, the corresponding standard is assigned to obtain the forming limit diagram by experiment. However, from sample design, preparation to the real strain measurement and data processing after experiment, it is time-consuming and difficult to apply. In this paper, taking DX54D Z as an example, through the experimental study, theoretical analysis and numerical simulation of the forming limit, the way to obtain the forming limit diagram of IF steel quickly by theoretical analysis and simulation method is discussed. In the aspect of experimental study, according to the rule of "sheet metal formability experiment-forming limit diagram (FLD) experiment", 9 groups of rectangular and stepped specimens (27 pieces) were made. The rectangular specimen was used to obtain the strain data of "pull-pull zone". The step specimen is used to obtain the strain data of "tension and compression zone"; The electrochemical etching method is used to print the mesh on the sheet metal, the forming experiment is completed by the cupping test machine, and the mesh strain is measured automatically by GMASystem system. Finally, the drawing of the experimental forming limit diagram is completed, which provides a reference for the subsequent theoretical analysis and forming simulation. Based on M-K grooves theory and Logan-Hosford yield criterion and Rossard hardening equation, a mathematical model of sheet metal forming limit prediction is established. The forming limit diagram of DX54D Z is predicted by MATLAB software. On this basis, the effects of different yield criteria, strain strengthening exponent, strain rate sensitivity coefficient and thickness non-mean on the theoretical prediction are analyzed. In the aspect of forming simulation, DYNAFORM software is used to simulate the standard Eriksson cupping process. But because the finite element software does not have the instability criterion to judge the time node of material failure or virtual experiment stop, based on the analysis of stress-strain state, the criterion of limit state is put forward, and the application range of different criterion is compared and analyzed. The forming limit diagram of IF steel is predicted and the influence of experimental process parameters on the prediction results based on forming simulation is discussed. Finally, the theoretical and simulated forming limit diagrams are compared with the experimental forming limit diagrams to verify the feasibility of the theory and simulation methods and the correctness of the results. It provides a new way for parts manufacturers to obtain rapid forming limit diagram in actual production.
【学位授予单位】：武汉理工大学
【学位级别】：硕士
【学位授予年份】：2015
【分类号】：TG301;TG142.1

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