热轧厚板件冲压成形与回弹分析.pdf

第42卷第9期Vol． 42 No． 9FORGING 其次,通过3种软件对同一纵梁外板进行模拟分析对比。为获得真实可靠的实测值,成形前在板料上利用激光绘制基圆,依据成形后基圆尺寸变化计算主次应变,并选取断面及检测点,测量回弹尺寸与厚度变化,与3种软件分析结果进行对比。结果表明: MARC的实体单元对厚度和主次应变分析最为准确;对于回弹, Dynaform计算更为准确, Autoform和MARC回弹结果均与实测值产生较大偏离。关键词:热轧厚板件;冲压成形;回弹;主次应变; Autoform; Dynaform; MARCDOI: 10． 13330/j． issn． 1000-3940． 2017． 09． 010中图分类号: TG386． 1 文献标识码: A 文章编号: 1000-3940 (2017) 09-0051-06Analysis on stamping and springback of hot rolled thick plateZhou Hailong, Zhang Yaqi, Mu Chuankun, Wang Bin, Mao An, Ruan Yingyan(Technical Center of Dongfeng Motor Corporation, Wuhan 430058, China)Abstract: For the certain differences of mechanical properties, forming type and dimensional accuracy between hot rolled thick and thinblank and difficulties in accurate simulation on the forming and springback of thick plate by common sheet stamping analysis software, theforming characteristics and springback of the vehicle longitudinal beam were analyzed and compared by Autoform, Dynaform and MARC,and the software which is more suitable for thick plate simulation analysis was selected. Firstly, thick plate forming characteristics and thedifferences were analyzed by the three kinds of software. Secondly, their longitudinal beam simulation results were analyzed and comparedrespectively. In order to obtain true and authentic measured values, base circle on sheet metal before forming was drawn by the laser, thenthe primary and secondary strain was determined based on the changing size of base circle. Finally, the corresponding section and checkpoints were selected, the springback and thickness change were measured, and their results were compared by three kinds of software.The results show that the thickness and primary and secondary strain analysis can be obtained precisely by the physical unit of softwareMARC, and the springback can be gained more precisely by software Dynaform. However, the springbacks deviated from the measuredvalues largely by software MARC and Autoform.Key words: hot rolled thick plate; stamping forming; springback; primary and secondary strain; Autoform; Dynaform; MARC收稿日期: 2017 -04 -05;修订日期: 2017 -07 -01作者简介:周海龙(1989 - ),男,学士,高级工程师E-mail: zhl6541234@163． com随着CAE仿真技术的发展,相继出现了众多冲压分析类软件,如Autoform、 Deform、 Dynaform、PAM-STAMP、 JSTAMP、 PRO/ MECHANICA、 ALGOR、ROBUST、 MARC等[1 -5],这些软件在成形缺陷分析和工艺方案布置与优化方面具有可操作性强、计算时间快、结果变量可方便查阅等优点。但由于薄板类与厚板类零件在成形方面存在一定差异,传统的分析软件对薄板件分析较为准确,但对厚板件分析结果并不准确,因为在相同弯曲半径下,厚板具有更小的弯曲半径厚度比(半径/厚度),当该比值小到一定程度时,零件表现为三向应力状态,此时若采用壳单元仿真显然是不合适的,而传统的冲压分析软件一般将板料当作壳单元处理,其分析结果很难达到预期。厚板件结构简单,一般以伸长类或压缩类翻边为主,其成形缺陷主要是裂纹与回弹,相对于薄板,厚板件缺乏统一的失效判定准则和分析规范,且回弹计算没有明确的方法。现有回弹计算分析方法并万方数据不完善,厚板的CAE分析技术远远落后于薄板;薄板的回弹分析方法也无法移植到厚板,致使厚板回弹分析存在一定盲区。为此,有研究人员提出厚板理论,厚板理论是平板弯曲的精确理论,充分考虑横向剪切变形,从3D弹性力学出发研究弹性曲面的精确表达式。各分析软件的核心算法不尽相同,寻求更适合厚板回弹分析的软件尤为重要,本文对比分析了3款软件对厚板回弹的计算结果,结果表明Dynaform的厚壳单元更适合厚板回弹分析。1 厚板的应用及冲压成形特性分析1． 1 厚板的应用厚板在汽车上的应用见表1。由表1可知,厚板件一般用于支架类、悬置类或梁类零件,厚度在2． 5 mm以上;厚板件在汽车上仍大量存在,短期内无法用其他材料完全替代,汽车上仍有部分厚板零件存在[6 -7]。表1 厚板在汽车上的应用Table 1 Applications of thick blank in automobile分类用途厚度/ mm结构用钢板乘用车中使用最广,主要用于前后托架及摆臂的上下板、管梁、安装支座、加强板、支架,以及车架纵梁加强板、横梁、安装支架、后防撞梁1． 6 ~ 6, 2, 2． 5, 3, 3． 5最常用高屈服强度钢板前托架、三角臂半壳、加强板,扭力梁横梁,驻车制动拉索支架,座椅靠背锁扣座25, 2． 5使用较多大梁用钢板军车用,轮罩上板、安装垫板、发动机罩竖梁、蓄电池框、支架、风扇箍带、刻度盘、限位块等2, 2． 5, 4, 5双相钢前防撞梁、门槛加强梁1, 1． 4, 31． 2 厚板成形特性分析汽车上的结构冲压件大多采用高强度厚板成形,零件性能直接影响车辆可靠性,外观质量要求相对较低,相比于薄板,厚板成形具有以下特点。(1)材料力学性能的差异。厚板型材具有屈服强度高、料厚一致性差、表面质量差及伸长率低等特点,致使其在汽车上应用范围受限,无法应用在外观件和覆盖件中。(2)变形类型不同于薄板。厚板材料本身高屈服和低伸长率使其无法成形复杂的零件,一般以简单翻边的梁类件存在,成形方式主要以弯曲为主,有时局部存在伸长类或者压缩类翻边,无压料成形,其工艺相对简单。(3)尺寸公差的差异。厚板主要以弯曲类翻边为主,在无压料成形过程中,料片容易窜动,导致产品尺寸公差较大,对于公差精度要求较高的部件,需经过二次整形方能保证尺寸要求。此外,同一批次的厚板零件,其尺寸一致性较差。(4)模具间隙与凸凹模圆角半径的差异。厚板成形时模具圆角半径和凸凹模间隙应适当放大,一般凹模圆角半径比相应薄板件成形时的规定值大1 ~3倍,凸凹模间隙也要适当放大。(5)模具寿命的不同。厚板件一般是热轧高强度钢板材料,成形时所需的压机吨位更大,模具磨损严重,使用寿命低于薄板件模具,且在工作过程中噪声较大,加工环境较为恶劣。由于厚板相对薄板存在以上差异,其在数值模拟时也表现出以下特点。(1)材料属性定义不同。厚板理论认为横向剪力Qx, Qy引起的变形不能忽略,即薄板理论的基本假设γxz = γyz =0不成立;且该理论不再采用直法线假定,而是采用直线假定,同时板内各点的挠度不等于中面挠度。(2)板料单元选取不同。厚板在成形过程中是三向应力状态,厚向应力不能忽略,若对厚板料进行壳单元划分,其分析结果与实际值存在较大差异。因此,厚板料一般采用厚壳单元或者实体单元进行分析。一般单元类型选取原则如下:厚度远小于( 5% , 10% )的面应采用实体单元。(3)摩擦效应的不同。厚板型材厚度一致性较差,表面质量低,相应的摩擦系数较大,且大的成形力在成形过程中必然产生大的摩擦力,使材料流动阻力加大,若凹模圆角过小时,易产生开裂缺陷,所以,在厚板成形时,应适当加大凸凹模间隙和模25锻 压 技 术 第42卷万方数据具的圆角半径。(4)成形速度的不同。对于无压料的厚板成形,若成形速度过快,模具与料片间产生的碰撞效应会使板料偏离工具体中心,这必然导致零件出现尺寸偏差。所以,相对于薄板,厚板的成形速度较低。(5)时间步长的差异。当分析厚板采用实体单元时,其厚度方向的层数不能少于4,对于厚度小于6 mm钢板而言,其单元最小尺寸不大于1． 5 mm,单元的最小尺寸决定了分析迭代时最小时间步长,时间步长过小会使计算成本大大增加。2 结果对比分析2． 1 成形结果分析本文以某车型纵梁外板为例,分别采用Auto-form、 Dynaform、 MARC这3款软件对其进行成形性分析和回弹分析,材料和模具设置参数保持一致。Autoform、 Dynaform是专业冲压分析软件,操作相对简单,而MARC是CAE分析的基础性软件,没有响应的冲压分析模块,需根据实际情况,自行搭建冲压仿真模型, 3类软件厚板分析设置对比见表2。表2 3款软件分析设置对比(厚板)Table 2 Comparison of analysis settings for three kinds of software (Thick blank)类别Autoform Dynaform MARC求解器Increnmental LS-DYNA MARC前后处理器自带ETA/ FEMB Mentat算法静力隐式动态显式静力隐式材料屈服准则Hill48准则Mises准则Mises准则硬化曲线真实应力-应变曲线真实应力-应变曲线真实应力-应变曲线材料各向异性参数R0, R45, R90 R0, R45, R90 R0, R45, R90网格类型三角形四边形+三角形四边形单元类型弹塑性壳单元BT/ BWC单元厚壳或实体单元网格划分自动分网单元尺寸参数可控单元尺寸参数可控摩擦摩擦系数恒定库伦摩擦定律库伦摩擦定律成形缺陷分析起皱有相应结果变量直接查看有相应结果变量直接查看无对应的结果变量破裂、减薄有相应结果变量直接查看有相应结果变量直接查看无对应的结果变量回弹有相应回弹模块有相应回弹模块无坯料生成、导入生成、导入导入厚向积分点个数厚板回弹11层回弹分析7层实体单元最少4层回弹补偿有有无产品数模如图1所示。材料相关数据见表3,料片实际厚度为4． 13 mm。产品翼面共选取10个断面、腹面取1个断面进行分析,每个断面均匀选取9个检测点,如图2所示。成形后的工件见图3。利用超声波测厚仪对样件检测点进行厚度测量,并与分析数据对比,断面4、断面10的厚度变化如图4、图5所示。由图4和图5可知:翼面不存在伸长图1 产品数模Fig． 1 Product model表3 材料参数Table 3 Material parameters材料屈服强度/ MPa抗拉强度/ MPa 伸长率/ %厚向异性参数(R0 / R45 / R90)硬化指数n强化系数K弹性模量/ GPaDL510 456 568 14 0． 72/1． 3/0． 82 0． 1246 912 19435第9期周海龙等:热轧厚板件冲压成形与回弹分析 万方数据图2 检测点标记Fig． 2 Labels of detected points图3 成形后产品Fig． 3 Product after forming图4 断面4的厚度变化Fig． 4 Thickness change of section 4图5 断面10的厚度变化Fig． 5 Thickness change of section 10或压缩变形时, 3种软件计算的厚度结果相差不大,当存在伸长类或压缩类翻边时,其厚度出现明显的减薄区和增厚区, 3种软件对厚度的模拟结果区别不大。为得到成形后产品的真实应变,采用激光打标的方式在初始板料上绘制直径为Φ10 mm的圆,根据成形结束后基准圆尺寸变化最大的两个方向确定主次应变,如图6所示。图6 主次应变方向的确定Fig． 6 Direction determination of the primary and secondary strain图7、图8分别是断面4的主、次应变,由图7和图8可知:对于断面4处的主、次应变, MARC的分析结果更为准确,这主要是由于在MARC中分析时采用的是实体单元,四边形网格。由此可见,厚板主、次应变分析时采用实体单元更为准确。图7 断面4的主应变Fig． 7 Primary strain of section 42． 2 回弹分析对比回弹是影响零件尺寸精度的重要因素,不同材料、不同冲压环境下回弹结果都存在一定差异,因此,回弹方法的移植性很差[8 -13]。本文以翼面存在伸缩变形的纵梁为例,对3种软件分析结果进行对比,归纳总结出哪种软件更适合分析厚板成形与回弹。沿纵梁长度方向等间距选取3个截面,每个截面上取9个点,腹面取一个断面,每隔200 mm取一个检测点,实测值通过3D扫描得到。图9、图10分别为断面3和腹面回弹结果。45锻 压 技 术 第42卷万方数据图8 断面4的次应变Fig． 8 Secondary strain of section 4图9 断面3回弹结果Fig． 9 Springback results of section 3图10 腹面回弹结果Fig． 10 Springback results of ventral surface由图9和图10可知, Dynaform计算的回弹结果更为准确, Autoform的计算结果与实际值偏离过大,虽然MARC在主次应变分析时有良好表现,但回弹结果跟实测值偏离较大,这主要是由于在计算回弹时涉及到节点的分离与再接触,多次分离与接触会使局部节点产生牵拉,形成分离拉应力,对回弹结果产生较大影响,而Dynaform回弹的结果更为准确,并且对厚度、主次应变同样具有较高的准确率。3 结语由于厚板材料性能、成形类型、尺寸精度以及模具寿命与薄板均有所不同,传统的薄板冲压软件无法适用于厚板,本文通过3种常用软件对其成形性和回弹进行分析对比。分析结果表明:当翻边存在伸长或压缩变形时, 3种软件分析结果均与实测值产生一定偏离; MARC的实体单元对厚度和主次应变最为有效,但3种软件分析结果区别不大,结果均可接受;对于回弹, Dynaform计算更为准确, Auto-form和MARC回弹结果均与实测值产生较大偏离。参考文献:[1] 周朝辉,曹海桥,吉卫,等. 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In order to conquer the difficulties in straightening process, a modelwas established for a 10 - roll straightening machine, and the process parameters were studied. Therefore, a 10 - roll straightening modelof thin-walled tube was established by finite element software ABAQUS, and the optimal bending and compressed values were obtained byanalyzing the X, Y direction linear deviations and radial deviations of the tube under different conditions. Finally, a formula was fittedbased on the optimal process parameters. Process parameters of tubes under two different conditions were calculated according to the for-mula, and then the reliability of the formula was verified through simulation and experiments, which lay a theoretical foundation of themanufacture of thin-walled tube fine straightening machine.Key words: thin-walled tube; straightening; bending value; compressed value; simulation伴随工业水平的提高,不锈钢薄壁细管在精密收稿日期: 2016 -12 -21;修订日期: 2017 -02 -20基金项目:河北省自然科学基金资助项目(E2012203008)作者简介:张 爽(1987 - ),女,硕士,助理实验师E-mail: guojialengzha@ sina． com通讯作者:孙登月(1964 - ),男,博士,博士生导师,教授E-mail: 1344890502@ qq． com仪器等领域的应用越来越广泛[1]。矫直作为管材生产的最后一道工序,决定着薄壁超细管材最终的产品精度。但目前仅国外少数公司能够生产Φ5 mm以下薄壁细管精密矫直机[2],所以,为了国内薄壁细管矫直机的开发制造,对其进行研究极为必要。由于这种规格薄壁细管的精度要求很高,矫直过程中工艺参数的设定需要足够精确,所以,在矫直机确■ ■ ■ ■ ■ ■ ■ ■ ■ ■ ■ ■ ■ ■ ■ ■ ■ ■ ■ ■ ■ ■ ■ ■ ■ ■ ■ ■ ■ ■ ■ ■ ■ ■ ■ ■ ■ ■ ■ ■ ■ ■ ■ ■ ■ ■ ■ ■[10]阮光明.基于响应面法的DP800高强钢冲压回弹工艺参数优化[J].锻压技术, 2015, 40 (4): 40 -44.Nguyen Q M. Technological parameters optimization of springbackfor DP800 high strength steel based on response surface method[J]. Forging & Stamping Technology, 2015, 40 (4): 40 -44.[11]阮锋,朱寅,周旭辉.板材成形的回弹预测和控制的研究[J].机电工程技术, 2011, 40 (10): 1 -7.Ruan F, Zhu Y, Zhou X H. Sheet metal forming springback pre-diction and control research [J]. Mechanical & Electrical Engi-neering Technology, 2011, 40 (10): 1 -7.[12]杨蕊.基于非弹性回复的先进高强板回弹研究[J].锻压技术, 2015, 40 (12): 35 -42.Yang R. Research on springback of advanced high-strength-steelplate based on non-elastic recovery [ J]. Forging & StampingTechnology, 2015, 40 (12): 35 -42.[13]张铁山,张友良,王建中,等.较厚板料成形的数值仿真[J].机械设计与制造工程, 2003, 32 (10): 101 -103.Zhang T S, Zhang Y L, Wang J Z, et al. Numerical simulationof thicker sheet metal forming [J]. Machine Design and Manu-facturing Engineering, 2003, 32 (10): 101 -103.万方数据