金属薄板超塑胀形极限系数

本文从连续介质塑性力学的基本理论出发,并应用变m值超塑性本构方程,求得超塑恒压自由胀形高度极限系数D和恒压胀形充填型槽半径极限系数D',进而给出用D和D'对应地确定极限高度和极限半径的简便方法。由于理论与实验结果符合,故可把D和D'作为超塑胀形的重要工艺参数。     

数控渐进成形不等层间距等高线轨迹生成

考虑数控渐进成形中层间距对成形质量的影响,提出了一种基于等残余高度的、并对成形角不同曲面区域生成不等层间距的等高线轨迹生成方法。首先生成等残余高度的等高线轨迹,然后在大成形角、大层间距区域中插入等高线来优化层间距。最终生成能满足等残余高度要求、并能通过减小成形力来减小反弹变形的轨迹。数值模拟分析与试验结果表明,该方法生成的不等层间距成形轨迹与等残余高度轨迹相比,成形件所受的等效应变均匀性好,成形件轮廓精度高,能够获得较好的工艺质量。     

微热压印过程聚合物流动形貌研究

为研究模具结构对聚合物流动形貌的影响,利用Deform-2D对微热压印成型过程进行了有限元模拟。首次系统的研究了模具占空比、宽厚比、阴模、阳模及不对称结构对聚合物流动形貌的影响。模拟结果显示随着占空比的减小,聚合物截面流形从单峰过渡到双峰,从陡峭过渡到平坦,当宽厚比大于1.5时,截面流形开始表现为双峰形式。其仿真结果和相关实验结果吻合。和阳模压印时没有明显的高度差相比,使用阴模压印时,微结构之间存在较大的高度差。针对压印过程易出现的填充效率不佳,提出了模具拓扑结构优化策略,通过在模具边缘布置一些流动坝,达到降低边界处聚合物流动率、促进聚合物有效填充的目的。仿真结果表明优化策略对促进聚合物填充具有很好的效果。     

Blank optimization for free bulging of Inconel 718 to maximize bulged height at high temperatures

Thickness profiled blank is designed via the optimization technique to maximize the bulged height in free bulging for Inconel 718. The thickness of the blank is described by the Bezier curve by using four control points. The location of each control points is used for the design variables of optimization. The material parameters for the flow stress equation of Inconel 718 are obtained from the free bulging test at constant pressure condition by using a flat blank and verified via numerical analysis. The objective function and constraints for optimization are the maximization of the bulged height within a limited strain range. The equivalent static load method for non-linear static response structural optimization with a move limit scheme is used for optimization. The result of optimization shows 21.95% increased bulged height and uniformly distributed strain after bulging. The free bulging test using blank with optimized profile is conducted to verify the optimization process. The results of bulged height and deformed shape are compared with those from numerical analysis, and the comparison shows good agreement.     

Analysis of the bulging process of an AZ31B magnesium alloy sheet with a uniform pressure coil

As the lightest metal material, magnesium alloy is widely used in the aerospace, automobile, and consumer electronic industries. However, magnesium alloy sheet has poor formability at room temperature. Electromagnetic forming is a high velocity forming technique that can promote the formability of low ductility materials, improve the strain distribution of workpieces, and reduce their wrinkling and springback. In this work, a uniform pressure coil was used to bulge AZ31B magnesium alloy sheets. The finite element method was then used to analyze this bulging process. The bulging contours and displacements of AZ31B magnesium alloy sheets were consistent with the experiment results. The distribution of the magnetic field intensity and magnetic field forces were found to be better than using a flat spiral coil. The deformation rule of AZ31B magnesium alloy sheet using the uniform pressure coil differed from that using the flat spiral coil. The largest strain occurred at the center of the sheet.     

空间弯管仿真与回弹补偿

回弹是空间弯管成形的主要成形缺陷。为了预测和补偿空间弯管成形中的回弹,通过编写用户幅值子程序（UAMP）,将有限元法应用于空间弯管的成形和回弹分析,提出了一种从仿真结果中提取管材中心线的方法。通过圆柱螺线形弯管成形的仿真计算,建立了管材回弹前后中心轴线曲率、挠率的关系。提出了一种基于求解曲线基本方程的空间弯管模具型面补偿方法,论述了曲线几何补偿的数学依据。通过对曲率和挠率(均为非常值)曲线进行补偿计算和成形仿真,对该方法进行了验证。结果表明该方法能够有效补偿回弹误差,保证弯管精度。     

The study for stability of closed-loop control system based on multiple-step incremental air-bending forming of sheet metal

To solve the springback problem for sheet metal forming, feedback control idea in automatic control theory is introduced to incremental air-bending forming process. The advanced control techniques are used to solve precision forming for workpiece of sheet metal. However, stability, accuracy, and rapidity of closed-loop control can directly affect system normal operation. Aiming to analyze the effect of stability on the quality of the formed workpiece, a closed-loop control system model for incremental air-bending forming is established. The transfer function and characteristic equation of the closed-loop system are solved through theory deduction and minor incremental linearization method. Both simulations with Matlab/Simulink and root locus results show that, as the overall gain is equal to one, the shape of formed part could converge to the target shape at the fastest rate. Finally, a semiellipse-shape workpiece is manufactured with the corrected mold obtained by the closed-loop forming method. The experimental results show that the closed-loop forming way is feasible and the means of correcting the mold parameters by iterative compensation of the stable closed-loop control system is effective. It can be taken as a new approach for sheet metal incremental air-bending forming and mold design.     

翻车机系统定位车和推车机的改造

黄骅港翻车机的定位车、推车机大臂俯仰系统原设计不合理,大臂高度靠液压缸的伸出长度来定位,且定位精度受液压油的温度影响,致使大臂定位十分不准。设计了四连杆结构,使大臂的落臂高度靠机械定位,避免了上述情况。通过在液压系统中加入压力管路过滤器,有效消除了系统中的杂质,提高了液压系统的寿命。通过程序改造,提高了作业效率,消除了众多的事故隐患。     

自由锻造液压机控制策略

自由锻造液压机工作压力高、换向频繁,须要对大运动惯量部件进行平稳和精确控制,难度很大,现有控制方法无法很好地解决这一难题。通过研究自由锻造液压机工作特性,提出一种应用于自由锻造液压机的预测型多模式模糊控制策略。对液压机的不同区段分别进行模糊速度、位置和Bang-Bang控制,获得较高的快速性、平稳性和定位精度;使用预测算法,解决液压系统执行机构存在的动作滞后和惯性对控制特性与控制精度的影响。应用预测型多模式模糊控制策略,以减少液压机动作滞后的影响,使自由锻造液压机活动横梁的控制精度达到±1 mm,最高锻造次数达到120次/min,系统的液压冲击和主机振动也得到有效控制。     

切边工艺对冲压件回弹影响的研究

作为冲压产品生产的重要工序之一,切边对零件形状精度产生明显影响。针对目前关于切边回弹研究比较少的情况,以某矿用防爆灯灯罩为研究对象,在Dynaform平台下,对切边回弹的产生、构成、切边线位置变化及切边工序安排对冲压件形状精度的影响进行了仿真分析,研究结果认为:切边回弹一方面是由于切边导致零件形状结构变化、内应力重新分布而引起的,另一方面是因为切边线附近应力、应变状态变化而产生的。其中前者占主导地位,在冲压加工中必须予以充分考虑,后者占总体回弹比例较小,对大型、复杂冲压件拉深成形后的切边可忽略其影响;另外,切边线位置变化、切边工序的顺序安排,对零件回弹变形影响明显,实际生产中,可通过适当选择切边线位置、合理安排切边工序在整个工艺路线中的顺序来有效控制切边回弹。     

Rapid springback compensation for age forming based on quasi Newton method

Iterative methods based on finite element simulation are effective approaches to design mold shape to compensate springback in sheet metal forming. However, convergence rate of iterative methods is difficult to improve greatly. To increase the springback compensate speed of designing age forming mold, process of calculating springback for a certain mold with finite element method is analyzed. Springback compensation is abstracted as finding a solution for a set of nonlinear functions and a springback compensation algorithm is presented on the basis of quasi Newton method. The accuracy of algorithm is verified by developing an ABAQUS secondary development program with MATLAB. Three rectangular integrated panels of dimensions 710 mmx750 mm integrated panels with intersected ribs of 10 mm are selected to perform case studies. The algorithm is used to compute mold contours for the panels with cylinder, sphere and saddle contours respectively and it takes 57%, 22% and 33% iterations as compared to that of displacement adjustment （DA） method. At the end of iterations, maximum deviations on the three panels are 0.618 4 mm, 0.624 1 mm and 0.342 0 mm that are smaller than the deviations determined by DA method （0.740 8 mm, 0.740 8 mm and 0.713 7 mm respectively）. In following experimental verification, mold contour for another integrated panel with 400 ram~380 mm size is designed by the algorithm. Then the panel is age formed in an autoclave and measured by a three dimensional digital measurement devise. Deviation between measuring results and the panel＇s design contour is less than 1 mm. Finally, the iterations with different mesh sizes （40 mm, 35 mm, 30 mm, 25 mm, 20 mm） in finite element models are compared and found no considerable difference. Another possible compensation method, Broyden-Fletcher-Shanmo method, is also presented based on the solving nonlinear fimctions idea. The Broyden-Fletcher-Shanmo method is employed to compute mold contour for the second panel. It only takes 50% iterations compared to that of DA. The proposed method can serve a faster mold contour compensation method for sheet metal forming.     

高温超塑胀形实验装置

超塑变形具有很强的结构敏感性，其变形规律与应力状态和变形路径有关，因此在处理二维胀形问题时，不能直接引用一维拉伸的实验数据，胀形实验装置便成为理论研究和制定工艺方案的重要手段。设计了高温超塑胀形实验装置，并针对实验装置进行了程序设计。该实验装置具有氩气净化、炉外加热、温度和压力闭环控制，能同时施加正压、背压并按设定的恒压、恒极点胀形速度和应变速率进行实验，同时可以无接触地记录胀形件极点高度与时间的关系，并观察其形貌变化过程。     

Study on design of progressive dies for manufacture of automobile structural member using DP980 advanced high strength steel

Advanced high-strength steel (AHSS) is widely used in automobile manufacturing to reduce the weight of vehicles, thereby improving fuel efficiency. However, the high yield and tensile strength of AHSS leads to a serious springback problem in the cold sheet metal forming process. This phenomenon has delayed the implementation of AHSS in vehicle parts due to the resulting negative impact on part accuracy. In this study, parameter optimization and multi-stage die compensation were conducted with Finite element (FE) analysis to develop a progressive forming process for automobile structural members using DP980. The FE simulation used the Yoshida-Uemori model to predict the springback phenomenon accurately. The key parameters that significantly influence the springback behavior were optimized using FE simulation and the Taguchi method. The simulation results were used to determine the die and mold compensation. After the parameter optimization and multi-stage die compensation, the final part was obtained with acceptable dimensional accuracy.

     

内补液增压式THF性能测试装置开发及试验研究

材料性能对液压胀形工艺(THF)及产品质量有重大影响,传统单向拉伸试验所得材料性能不能很好反映管材液压胀形性能。开发了一种简单实用可在单动压力机上使用的试验装置,可用于不同材料及尺寸管材的液压胀形试验,以确定管材胀形性能。该装置不需要复杂的外部供液系统,而是利用其内部的补液腔自动、同步地建立起胀形所需液压力及轴向载荷,两载荷比值可通过合理设计补液腔直径得到。可以实现管材自然胀形、轴向压缩胀形、两端不同约束下的胀形和一定程度的比例加载胀形。一系列胀形对比试验表明：管端约束方式对自然胀形有较大影响,而对轴向压缩胀形影响较小;液压力、轴向载荷及其比值对轴向压缩胀形有较大影响。     

T2紫铜箔材的U型弯曲变形

设计了箔板U型弯曲试验方案,使用不同凹模槽宽尺寸和圆角半径的微型模具,在三思微型试验机上完成了试验,分析了模具几何尺寸、箔板厚度等对箔板U型弯曲变形中冲头载荷、回弹以及表面质量的影响。研究结果表明,槽宽尺寸或圆角半径减小时,最大冲头载荷显著增加,且冲头载荷上升和下降速率都明显增大;对比两种不同厚度箔板的冲头载荷显示,冲头载荷减小速率明显快于横截面面积的减小速率,说明产生了明显的尺寸效应;另外,圆角半径或板厚减小,导致回弹角度增大,成形件精度降低;虽然成形件表面比较平整,但侧面出现划痕提示需要提高模具表面质量和采取润滑措施。以上研究结果对指导箔板微成形工艺设计具有重要意义。     

薄壁深抛物线形零件固体颗粒介质成形工艺

薄壁抛物线形壳体成形过程为拉深和胀形两种变形模式的复合,极易发生起皱和破裂。固体颗粒介质成形是采用固体颗粒代替刚性凸模或凹模(或弹性体、液体)对板料进行成形的工艺。板材在颗粒介质内压的作用下成形,可以有效防止抛物线形件拉深成形过程中侧壁的起皱;由于颗粒内压是非均匀分布的,故可以有效控制抛物线形件成形过程中的破裂,提高板材的成形极限。根据固体颗粒介质成形工艺的特点,提出了两次成形薄壁深壳体零件的工艺,建立了数值分析模型,通过数值模拟和试验对该成形过程和工艺参数进行了分析。结果表明,采用固体颗粒介质成形工艺过程简单、成形工件壁厚分布均匀、表面质量好、回弹小。     

小型桥壳液压胀形初始变形条件分析及成形试验

介绍了小型汽车桥壳的液压胀形工艺,提出了初始胀形内压的表达式,预测了初始胀形内压与轴向推力的匹配关系（即经向应力比的大小）对预胀形时各部分变形顺序的影响。在普通液压机上进行了两种加载路径下的液压胀形试验,在初始经向应力比小于零并保持恒内压的条件下,预胀形管坯先变形成两侧高、中部低的双鼓形,经增压后将中部胀起;在初始经向应力比大于零且内压恒定的条件下,预胀形管坯中部沿轴向胀裂;两种加载路径下,管坯扁锥体凸起与胀形区之间均产生了明显内凹缺陷。理论分析与试验结果均表明,初始变形条件对小型桥壳的预胀形有重要影响。     

多角弯曲件冲压回弹规律研究

通过ABAQUS软件中动态显式模拟方法就材料的厚度、冲压力、模具间隙及摩擦系数四个因素对冲压回弹的影响进行了模拟研究,分析了各个因素对回弹影响情况和影响的规律,在模具设计和制造中具有预告和指导意义,克服了试错法带来的周期长、成本高的缺点。     

中小型内高压成形机液压系统的设计与仿真

为研发节能高效、经济实用的三侧缸内高压成形设备,设计了合模力可变且最大为10 MN,三轴向进给、组合式充液胀形且最高胀形压力为300 MPa的中小型内高压成形机液压系统,并对系统主要部件选型。将整机液压系统分为合模压机、充液胀形、轴向进给和下缸退料4个子系统,并基于AMESim对各子系统进行建模与仿真测试。在此基础上建立整机液压系统完整仿真模型,并应用工程成形实例进行仿真试验。仿真实验结果表明:系统设计合理,主要参数控制精度达到设计要求,设计的液压系统为研发此类装备提供参考。     

热压罐成型框架式模具温度场分析

模具成型型面的温度均匀性对复合材料制件的成型精度具有重要影响。某大尺寸高平面度复合材料蜂窝夹层板构件利用热压罐工艺成型,模具为大型框架结构模具。文中采用有限元数值模拟方法,利用Simcenter12.0 软件对该大型框架结构模具热压罐成型工艺过程的温度场特性进行了模拟分析,模拟值与试验值误差小于10%,证明了模拟方法的准确性。模拟结果表明：成型固化工艺参数设置合理,模具型面温度均匀性较好,金属边框对模具的整体温度场影响较大;模具在热压罐内的位置在所设定的2.1 m 范围内沿长度方向移动对模具温度场的影响可以忽略。