【作者】 吴磊；

【导师】 李光耀；

【作者基本信息】 湖南大学 ， 车辆工程， 2010， 博士

【摘要】 扭曲回弹是冲压成形过程中常出现的一种回弹形式,随着汽车用钢强度的提高,扭曲回弹更加明显。汽车零件产生的扭曲回弹非常难以控制,往往涉及到对零件型面的调整,风险较大且工程繁琐,使得工程师对于采用高强度钢板的零件比较慎重,然而基于汽车轻量化和安全性的考虑,高强度钢板在汽车车身上的应用越来越普及。扭曲回弹控制不了,会严重影响整车的装配精度和增加焊装的难度,因此,扭曲回弹问题一直是汽车工业界和学术界关注的热点。本研究基于工程实际应用,首先从实际生产中出现的各种扭曲回弹形式进行归类和总结,分析了产生扭曲回弹零件的基本特征,并对产生扭曲回弹的基本原因和影响因素进行了探讨研究。本文提出了高强钢零件冲压后扭曲回弹问题的分析方法、评价方法和控制方法。本研究的主要工作包括以下几个方面:1.在广泛调查扭曲回弹现象的基础上,对容易产生扭曲回弹的汽车车身零件进行了分类,研究整理出高强钢零件冲压后产生扭曲回弹的主要基本特征。通过实际零件如A柱铰链加强板、门槛件等零件的扭曲回弹现象分析,提出零件的“抗扭刚度”和“残余扭矩”是导致扭曲回弹的主要原因,并提出了常用的减小扭曲回弹的方法和工艺。2.提出一种考虑特征截面卷曲回弹的解析法用于预测特征截面的回弹量,并将卷曲效应叠加到回弹角的计算结果中,使得预测方法更加准确,通过U型冲压实例对该方法进行了验证,结果表明该解析算法具有较高的计算精度。提出基于该解析法预测零件整体扭曲回弹趋势的方法,将扭曲回弹定义为“初始回弹”和“相互影响”两个过程,通过解析法分析截面的初始回弹,结合零件的形状特点分析不同截面之间的相互影响作用,从而实现对零件扭曲回弹趋势的预测,并对具有拐角特征、变截面特征等的典型零件的扭曲回弹趋势进行了实例分析。3.分析了汽车冲压件产生扭曲回弹的基本特征,即不平衡拉深特征、变截面特征和拐角特征,以实验为基础,采用科学实验设计方法结合仿真分析手段分析了这些特征产生扭曲回弹的基本原因,并以这些基本特征为基础,研究了汽车零件的基本特征尺寸、冲压材料、成形工艺等因素对扭曲回弹的影响规律。4.提出可用于预测实际零件扭曲回弹趋势和规律的截面运动法,该方法采用回弹前后典型截面的运动参数作为零件扭曲回弹的评价指标,对零件的扭曲回弹进行了量化,通过特征截面和扭曲回弹参数描述零件的扭曲回弹。应用实例表明,该方法能够较准确地计算复杂零件的扭曲回弹量,对指导汽车零件扭曲回弹的控制具有较强的实用性。5.提出了一种基于截面运动规律的扭曲回弹控制方法,该方法应用截面运动法获取典型截面扭曲回弹参数,采用反向补偿因子计算扭曲回弹截面控制线,利用该截面控制线生成扭曲回弹补偿型面。应用实例表明,利用基于截面运动规律的扭曲回弹控制方法可对模具型面进行快速调整,节省了高强钢车身零件的制造时间,并可提高零件的尺寸精度。更多还原

【Abstract】 Usually there is a problem that the torsion springback of panel is difficult to be controlled in the stamping process, especially using HSS (High Strength Steel). Based on the consideration of lightweight and safety, the application of HSS in automotive panel is more and more popular. It will make a bad accuracy in the car assembly if the springback can’t be controlled well. Torsion springback of automobile part is one of the main forms of springback, which is complex and hard to control and brings difficulties of manufacture precision. So, torsion springback problem is always a hotspot in automotive industry group and academia.The research was based on practical application of engineering, Firstly, various forms of torsion springback were classified and summarized. Secondly, basic features of torsion springback were analyzed. Finally, basic reasons and effect factors of torsion springback were studied. Based on the engineering practice, this paper contains torsion springback analysis, evaluation methods and control methods. Main works of this paper are presented as follows:1.According to the widespread investigation on torsion springback, the auto parts which were more likely to bring torsion springback were classified, summaries of main basic characteristic of torsion springback were obtained. The general forms of torsion springback of the HSS by actual parts were explained, such as A pillar reinforcement, door threshold etc. A method named“torsion stiffness”was proposed to analysis the reasons for torsion springback and influencing factors, commonly used methods and techniques of production were proposed to reduce torsion springback by the aspects including remaining torque and the torsion stiffness.2.An analytical method to calculate the springback of characteristics section was suggested, sidewall curl was also considered and taken account into springback computation, this strategy improves the accuracy of the proposed method. The method was validated by the U stamping, and it indicated that the method has a higher accuracy. Furthermore, a method to predict tendency of torsion springback was proposed, the process of torsion springback can be divided into "primitive springback" and "mutual influence". Firstly, the primitive springback of section was calculated by analytical method, and then, shape features were taken into account to analysis mutual influence of different sections. Meanwhile, by this method, we could analysis the causes of torsion springback. Cases study for basic feature with turning shapes and various section shapes were carried out. The torsion springback of the given parts were analyzed by finite element method, and then some measures to promote accuracy and predict tendency of torsion springback were put forward.3.Some basic features such as parts with turning shapes, parts with various section shapes, non-uniform material flow in stamping process were proposed. Based on experiments and simulation of FEM, cases to the effect of torsion springback were studied, such as the basic feature size, properties of stamping materials, stamping techniques etc.4.A novel method to evaluate parts’ torsion springback by springback movement of characteristic cross-section method was proposed. This method could obtain the parameters of springback movement in the characteristic cross-sections, this paper attempts to represent parts’ torsion springback by parameters. A program was developed to determine the deformation of characteristic section, the deformable movement included displacement and rotation, and this program divided characteristic sections with several areas by convergence estimation. The paper studied on a part’s springback with arched surface by experiment and simulation analysis, the result verified validity of this model.5.A system which can control springback is presented based on the springback movement of characteristic cross-section method. Firstly, the result of springback could be calculated by FE system or obtained by scan way. Secondly, the parameters of springback movement in the characteristic cross-sections could be analyzed by springback movement of characteristic cross-section method (SMCS). Thirdly, springback control section could be obtained based on the parameters of springback movement by compensation factor method. Finally, based on the origin CAD surface and the control section of springback, the mould was compensated for springback by application of shape global deformation method. The practice engineering cases proved that the system can save more time to deal with springback of parts with arched surface, the result of springback compensation is right and applied and the method is worth to spread.更多还原