【作者】 阳德森；

【导师】 周杰；

【作者基本信息】 重庆大学 ， 材料加工工程， 2010， 博士

【摘要】 在能源短缺和温室效应等环保问题的双重压力下,汽车轻量化步伐不断加快。采用高强度钢板不仅可以实现汽车的轻量化,而且能提高汽车的安全性能,因此高强度钢板等轻量化材料在汽车车身上的应用逐年增加。由于高强度钢板的成形性能一般较普通钢板差,塑性变形能力低,冲压成形时更容易出现破裂、起皱以及回弹等缺陷,因此寻求新的成形工艺方法提高高强度钢板等轻量化材料的成形性能已经成为当前的研究热点。板料冲压成形具有高度的几何非线性、材料非线性、边界非线性等特点,影响冲压件成形质量的工艺参数诸多,主要包括压边力、拉深筋形式及分布方式和润滑条件等。上述工艺参数中,拉深筋是控制材料流动的重要手段,其设计得合理与否是拉深成败的关键,它可以在相对较小压边力条件下提供较大的拉深阻力。国内外学者对拉深筋在板料冲压成形中的作用和影响规律进行了大量研究,但大多限于固定拉深筋的研究,其几何尺寸在整个拉深成形过程中不发生改变,因此固定拉深筋在提供拉深阻力方面基本是恒定的。有研究表明零件的拉深成形过程中如果能够提供可变的拉深阻力,零件能获得更优的应变路径,其拉深性能可以得到改善,在这方面国内外大量研究人员主要是依靠变压边力工艺实现拉深阻力的变化,而对于通过实时调整拉深筋的高度以控制拉深阻力变化的研究工作很少。基于上述研究背景及高强度钢板成形性能低的特点,本文提出一种新的成形技术——可控拉深筋技术,将其应用到高强度钢板成形过程中。在拉深筋几何尺寸中,高度对拉深阻力的影响较大,而且拉深过程中最容易被调节。因此本文提出的可控拉深筋技术是通过实时调节拉深筋高度来改变高强度钢板拉深过程中的拉深阻力,实现提高高强度钢板成形性能的目的。本文以JAC590Y高强度钢板为研究对象,结合数值模拟、优化理论与算法、液压与电气控制等关键技术,通过有限元分析及物理实验的方法,较为系统地研究了可控拉深筋技术对高强度钢板拉深性能及回弹方面的影响规律。主要对下列三个方面进行了研究:①可控拉深筋技术对高强度钢板拉深性能的影响及优化1)首先对高度阶跃变化的拉深筋与固定拉深筋高强度钢板盒形件进行模拟分析与实验验证,结果表明可控拉深筋在改善高强度钢板拉深性能方面具有综合优势,并验证有限元分析的可靠性;2)在可控拉深筋技术中,拉深筋高度变化与凸模行程的匹配运动轨迹对高强度钢板的拉深性能有重要影响。根据拉深过程中成形力的需求特点,设计六种拉深筋形式下的三种不同类型的拉深筋高度连续变化运动轨迹,通过正交试验确定相应的试验方案,采用Dynaform软件进行模拟计算,比较各种类型运动轨迹下的极限拉深深度、应变分布以及流入量状况,确定了最优的拉深筋运动轨迹类型(最优轨迹类型)为上升——停止——下降的轨迹,并得到了影响零件极限拉深深度的主要因素和较佳的因素水平组合;3)基于最优轨迹类型得到的数值模拟数据,建立各拉深筋形式下的可控拉深筋运动轨迹与极限拉深深度的GA-BP神经网络,经测试样本验证,构建的GA-BP神经网络具有较好的预测能力,可以代替真实模型预测各因素对高强度钢板拉深性能的影响,通过建立的GA-BP神经网络与拉丁超立方抽样法相结合建立最优轨迹类型的可控拉深筋主要影响因素H 1和H 2与极限拉深深度之间的响应面;4)提出了分区域的可控拉深筋优化策略,研究表明长筋比短筋后上升,或长筋比短筋先下降,高强度钢板的极限拉深深度能够进一步提高,为考虑控制的方便性和材料流动的稳定性,采用短筋和长筋相同的运动速度为宜。②可控拉深筋技术对高强度钢板成形回弹规律的研究首先对不同的固定拉深筋高度对高强度钢板回弹的影响状况进行研究,结果表明拉深筋高度对高强度钢板的回弹有较大的影响,随着拉深筋高度增大,回弹量相应减小。然后设计与拉深过程中类似的三种轨迹对U型高强度钢板冲压件的回弹状况进行分析,研究结果表明可控拉深筋的运动轨迹对高强度钢板回弹量有重要影响,拉深筋上升——停止的轨迹有利于回弹的减小,而有利于高强度钢板拉深性能改善的上升——停止——下降的轨迹对高强度钢板的回弹量减小效果最差。③可控拉深筋实验装置与控制系统的设计基于可控拉深筋运动原理与传统的拉深模具结构,设计了可控拉深筋高强度钢板盒形件拉深实验装置,通过该实验装置对固定拉深筋以及高度阶跃式变化的拉深筋进行试验验证。同时,比较驱动拉深筋运动的不同机构形式的优缺点,选择杠杆机构与液压系统联合作用模式,并设计相关的液压与电气控制原理图。通过对可控拉深筋技术的研究,表明该技术可以极大地改善高强度钢板等难成形材料的拉深性能,为高强度钢板冲压成形提供了新的优化途径,同时为该技术应用于实际生产奠定技术基础。本文的研究结果对于拓宽高强度钢板新的工艺研究、扩大高强度钢板材和超高强度钢板的应用范围有着较为重要的学术意义和工程应用价值。更多还原

【Abstract】 The pace of lightweight automobile has been quickened under the dual pressures of energy shortage and greenhouse effect. Lightweight automobile can be realized and the safety performance of automotive can be improved by using the high strength steel(HSS). So the lightweight material such as HSS for the autobody parts has been widely used year by year. These defects such as crack, wrinkle and springback will appear in the stamping process of HSS because of its high strength and low plasticity. So the new forming technology which will improve the formability of HSS is becoming the research focus.Sheet metal forming is a complicated deformation problem, which involves material nonlinearity, geometrical nonlinearity and boundary nonlinearity. The factors including blankholder force, the shape and layout of drawbead, lubrication have great influence on the quality of stamped parts. The drawbead, which provides the larger drawing resistance in the conditions of smaller blankholder force, is a important method to control the material flow. The reasonable design of drawbead is the key to success or failure of drawing. Up till now, although the scholars at home and abroad have done a large amount of research work on studying the influence law of drawbead in sheet metal forming, their researches are mostly limited to the fixed drawbead whose geometry size and drawing resistance is almost invariant in sheet metal forming. The research shows that part optimal strain path will be obtained and the drawability will be improved by the variable darwing resistance in sheet metal forming. Now the scholars at home and abroad mostly are always adopting the variable blankholder force to obtain the variable darwing resistance, but the research on the variable flow resistance by adjusting the height of drawbead has been seldom studied.Because the height has great influence on darwing resistance and can be controlled easily, a new controllable drawbead technology was put forward to improve the formability of HSS by the real-time height adjustment of drawbead based on the low formability of HSS.The JAC590Y HSS was selected as research object, and its drawability and springback laws were systematically studied based on the controllable drawbead technology by the method of finite element analysis and physics experiment combined with the key technologies such as numerical simulation, optimization algorithm and hydraulic and electric control technology. Three following ascepts were mainly investigated.①The effect of controllable drawbead technology on drawability of HSS and the optimization of controllable drawbead trajectory1)Firstly, the height step-like change and fixed drawbead of HSS box was simulated and experimental verification. It shows that the controllable drawbead has the comprehensive advantage in the aspects of improving the drawability of HSS and reliability of simulation results are verified by physics experiment.2)The trajectory of drawbead height variation matching punch travel has great influence on the drawability of HSS. Three different types of height continuous change drawbead trajectories with six different drawbead forms were designed accroding to the need of forming force in the drawing process. The test schemes were determined by orthogonal test design and the processes were simulated by the software Dynaform. The drawing depth, strain distribution, material inflow are analyzed in different trajectories. The optimal type trajectory, ascent——halt——descent, is determined and the major influencing factors of drawing depth and the optimal combination of each factor level are obtained.3)The GA-BP neural networks of controllable drawbead trajectory factors—limite drawing depth with six drawbead forms are constructed based on the simulation results of the optimal drawbead trajectory. Through the verification of test samples, the GA-BP neural networks have good prediction ability. So the GA-BP neural networks can replace the real model to predict the effects of factors on the drawability of HSS. And the response surfaces composed of main influence factors H1&H2 and limit drawing depth with the optimal controllable drawbead trajectory are established based on the GA-BP neural networks and Latin Hypercube.4)The regional separation optimization strategy of controllable drawbead was proposed. The simulation results show that the limite drawing depth of HSS will be further improved by long drawbead increasing later than short drawbead or long drawbead decreasing earlier than short drawbead. It should adpot the same velocity of the long drawbead and the short drawbead to ensure the convenient control and material flow stability.②Study on springback of HSS based on the controllable drawbead technologyFirstly, the influences of different fixed drawbead heigth on springback of HSS were studied. The results show drawbead heigth has great influence on springback of HSS and springback decreased with drawbead heigth increased. Then three different controllabe drawbead trajectories similar to the trajectories in the drawing process were designed. The influence of these trajectories on springback of HSS U-shaped part was studied by numerical simulation. The results show controllabe drawbead trajectories have great influence on springback of HSS. The trajectory of ascent——halt can decrease springbak, but the trajectory of ascent——halt——descent which improve the drawability of HSS is worst on decreasing springbak.③Design of experiment device and control systemThe HSS box drawing experimental device with the controllable drawbead driven by hydraulic and electric control system was designed based on the controllable drawbead movement principle and the conventional structure of drawing die. The tests of step-like changed in drawbead height and fixed drawbead were carried out by the experimental device. The driving mode with the Leverage and hydraulic unit is chosen by comparing the advantages and disadvantages of different motion mechanisms. The corresponding hydraulic and electrical control principle diagrams are designed.The controllable drawbead technology has great potential for improving the drawability of light materials, such as HSS, which are difficult to deform. The technology provide a new optimization method for the forming of HSS. And the research results laid a technology foundation for further application of controllable drawbead technology in practical production. Furthermore, the research on the controllable drawbead can give a new development in technology of HSS and has both important academic meaning and engineering value to enlarge application range of HSS and AHSS.更多还原