双板件电磁翻边成形效率研究北大核心CSCD

针对电磁翻边成形技术成形效率低的问题,提出了双板件电磁翻边成形技术。在阐明双板件电磁翻边成形原理的基础上,构建了传统单板和双板件两组仿真模型,并从驱动线圈电流波形、磁通密度、电磁力、塑性应变能、成形效率5个方面进行对比分析。结果表明:在相同的放电能量下,双板件仿真模型的塑性应变能比传统单板提高了52.28%;在相同的翻边角度下,双板件仿真模型所需的放电能量仅为传统单板仿真模型两次放电能量的60.60%,能量利用率提高了39.40%。双板件电磁翻边成形技术可使用单个驱动线圈同时实现两个板件的翻边,能够有效地解决电磁翻边成形效率低的问题,促进了电磁翻边成形技术在工业领域的广泛运用。     

基于弹性介质的铝合金板材小尺寸凸角电磁成形试验研究

针对6014铝合金板材的V形凸角成形,开展了基于弹性介质的带驱动板的电磁成形工艺试验研究,探究磁脉冲放电、弹性介质硬度、凹模空腔真空度以及弹性介质形状尺寸等因素对铝合金薄板小尺寸凸角成形能力的影响。试验结果表明,磁脉冲放电电压越大、弹性介质硬度越小、凹模空腔真空度越高,成形的凸角高度越大。并通过对弹性介质形状、尺寸和模具结构的优化,最终在放电电压为3. 5 kV、聚氨酯硬度为A90、凹模空腔真空度为3. 2 Pa的条件下获得了较为理想的V形凸角成形效果,凸角高度为2. 92 mm,凸角顶端圆角半径为R1 mm,达到了小圆角特征的成形精度要求。     

超声振动效应对TA2钛合金板材力学及胀形性能影响

针对钛合金板材塑性变形能力差的问题,进行了超声振动辅助成形工艺的研究,分析超声振动对钛合金TA2板材力学性能及与接触面之间摩擦系数的影响。在此基础上进行了不同宽长比坯料的超声振动辅助胀形实验,分析超声振动对TA2板材胀形力、极限胀形高度的影响。同时,基于网格应变原理,通过不同宽长比坯料极限应变的测量,建立TA2板材的成形极限图。研究结果表明,选择合适的超声振动辅助成形工艺参数, 不仅可以提高TA2板材变形能力,还可以减小摩擦对板材成形性能的影响,从而有效提高了TA2板材的成形极限。     

不同热处理状态下成形速率对2219铝合金成形极限的影响

分别对完全退火态和固溶淬火态2219铝合金板材进行准静态成形条件和电磁成形条件下的单向拉伸实验、平面应变实验和双向拉伸实验,建立了2219铝合金的成形极限图并研究了不同热处理状态下成形速率对2219铝合金成形极限的影响规律。结果表明,固溶淬火会显著提高2219铝合金的强度,降低2219铝合金的断后伸长率;准静态成形条件下,完全退火态2219铝合金在以上三种典型应变状态下的极限应变比固溶淬火态2219铝合金分别高14.76%、37.98%、39.54%;电磁成形条件下,完全退火态2219铝合金在以上三种典型应变状态下的极限应变比固溶淬火态2219铝合金分别高14.51%、38.03%、33.33%;完全退火态2219铝合金在电磁成形条件下以上三种典型应变状态下的极限应变比准静态成形条件下分别高16.08%、24.38%、18.76%;固溶淬火态2219铝合金在电磁成形条件下以上三种典型应变状态下的的极限应变比准静态成形条件下分别高16.34%、24.20%、30.94%,电磁成形可有效提高2219铝合金的成形极限,改善2219铝合金的成形性能。     

链模式变截面成形机理分析

链模式成形是一种新型的板金属成形工艺,对链模式变截面成形过程中的材料流动规律和特点进行了计算机模拟仿真。模拟结果表明:变截面成形件的弯角处最大主应变较大,方向垂直弯曲面向外,边腿的凹弧区域最大主应变为拉应变,沿边腿的高度方向从高到低,最大主应变逐渐减小;边腿高度和成形角度对成形件纵向应变的影响较大,增大边腿高度和成形角度会增加边腿的纵向应变,材料属性对成形件的纵向应变影响较小。提取了仿真模型里变截面零件的纵向应变,结果显示,在变截面型材边腿上的4个圆弧位置纵向应变比较大,它们在成形的过程中发生了拉伸或者压缩的变形,而等效塑性应变主要集中在变截面型材的弯角部分。通过链模式变截面成形实验对模拟结果进行验证,实验结果与仿真结果基本吻合。     

TA34钛合金波纹管成形研究

采用恒应变速率拉伸方法研究了普通退火态(M态)和等温退火态(HT态)TA34钛合金管坯的冷成形性能，结果表明：M态TA34钛合金管坯的强度更高，最大应变硬化率更低，冷成形性能更好，更适用于波纹管的成形。采用有限元模拟的方法对DN85波纹管的成形参数进行仿真计算，得到最佳鼓波压力、成形压力和最大波深系数等成形参数。根据仿真模拟结果进行DN85波纹管成形工艺的探索，HT态管坯在波深系数1.162时即出现开裂，M态管坯在波深系数1.165、1.169、1.178时均未出现表面质量缺陷。以M态TA34钛合金管坯为坯料，选择合适的波纹管成形工艺参数可以制备出质量优良的TA34钛合金波纹管。     

TA1纯钛板成形极限图测定及应用

采用机械划线法制作网格,利用通用板料成形性能试验机和网格拓印测量的方法,获得了TA1纯钛板在不同应变路径下的极限应变值,以此数据为基础绘制了TA1纯钛板室温下的成形极限图,并基于最小二乘法对成形极限图进行拟合建立了成形极限图的预测模型。此外,将成形极限预测模型导入到有限元模拟软件中,作为成形破裂的判据,对TA1纯钛板胀形成形的破裂缺陷进行预测,并通过工艺试验对预测结果进行了验证。对比结果表明,采用成形极限预测模型作为破裂判据的有限元数值模拟能够较为精确的预测出TA1纯钛板的极限胀形高度和胀形发生破裂的部位。     

薄板曲面微结构电流辅助滚压成形工艺研究

针对燃料电池等系统中的薄板曲面微结构制造,提出了薄板曲面微结构滚压成形工艺,并借助电流辅助成形技术,提高了薄板曲面微结构的成形质量。采用单向拉伸实验,研究了脉冲电源参数如电压、频率、脉宽等对T2紫铜薄板单向拉伸变形行为的影响;开展了薄板曲面微结构滚压变形有限元模拟,优化坯料结构,抑制了曲面微结构件的翘曲失稳;在此基础上,开展了电流辅助滚压成形实验。结果表明,脉冲电流在达到一定阈值时,流动应力显著降低,断裂应变明显提高;采用梯形板坯,可优化板料受力状态,抑制翘曲失稳;脉冲电流辅助滚压成形时,曲面微结构高度分散性变小,成形件一致性更好,微结构尺寸精度更高。     

汽车前梁多道次内高压成形

基于动力显示有限元软件eta/DYNAFORM,以汽车前梁为例,开展了回转拉伸弯曲和模具压弯多道次内高压成形工艺过程数值模拟。结合各种成形工艺下汽车前梁内高压成形极限图,分析其成形质量。在此基础上进行管坯回转拉伸预弯曲和内高压成形试验,给出了典型截面的壁厚分布,并与模拟结果进行了比较。研究结果表明,模拟结果与实验结果相一致。预弯曲成形后,管坯壁厚分布对内高压成形结果中壁厚分布具有一定的影响。多道次内高压成形模拟能够提高内高压成形模拟精度。管坯模具压弯的壁厚分布较回转拉伸弯曲的壁厚分布好,利于汽车前梁内高压成形性能提高。     

树脂板多点热成形本构模型研究

介绍了树脂板多点热成形装置和成形原理,进行了聚碳酸酯(PC)板鞍面件多点热成形实验,获得了形状轮廓较好、厚度分布均匀的实验件。测试了PC板的玻璃态转变温度和其在不同拉伸温度和速度条件下的真实应力-应变曲线,获得了广义Maxwell模型和PC-DSGZ模型的参数。建立了树脂板多点热成形有限元模型,开展了两种本构模型下PC板多点热成形数值模拟。结果表明两种本构模型鞍面件均实现贴模成形,PC-DSGZ模型可以获得更加均匀的应变和厚度分布。数值模拟与成形实验件的厚度对比结果显示PC-DSGZ模型模拟得到的鞍面件厚度与实验结果更接近。     

基于BP神经网络的TA15钛合金热变形工艺-性能预报

将经过热约束变形的TA15钛合金进行力学性能测试,获得了工艺(温度、应变、应变速率及冷却方式)、性能(抗拉强度、延伸率)参数数据,利用BP人工神经网络建立起其间的关系网络模型.研究表明:所建立的网络可以很好地反映出本材料的工艺-性能之间的关系并且具有一定的精度,网络模型可以用来预测不同变形条件下TA15钛合金的性能.     

Shape controlling and property optimization of TA32 titanium alloy thin-walled part prepared by hot forming

The hot flow behaviors, microstructure evolution and fractographs were studied to optimize the hot forming process of the TA32 titanium alloy thin-walled part. A set of microstructure-based constitutive equations were developed based on the experimental data, which described the relationships among the hot flow stresses and the evolution of phase volume fraction, dislocation density, grain size and damage. The constitutive model was imported into ABAQUS 6.14 to simulate the hot forming process for a typical thin-walled part. The effective strain, dislocation density and damage distribution as well as forming defects of formed parts under different process parameters were predicted. A qualified part without wrinkling and fracture defects was produced at a loading speed of 5 mm/s at 800 °C by the modified blank shape, where the maximum damage value was only 18.3%. The accuracy of constitutive model and finite element (FE) simulation was verified by the microhardness tests, which indicates that the FE model based on physical internal-state variables can well optimize the hot forming process of TA32 titanium alloy complex parts.     

Reverse effect of tensile force on sidewall curl for materials with tensile/compressive strength difference

Sidewall curl occurring by the removal of tool surfaces after forming is one adverse phenomenon that should be effectively reduced in sheet metal forming operations. Among several process parameters controlling sidewall curl, a constraint tensile force is widely used along with attainable formability by introducing blank holder and drawbead. The classic but common knowledge is that sidewall curl is suppressed for conventional sheet metals as the constraint tensile force increases. Interestingly, however, for magnesium alloy sheets that have unusual asymmetry in tension and compression it has been recently reported that springback increases as the tensile force increases within a specific range of tension. The major deformation in the sidewall usually consists of bending and unbending under tensile force. Therefore, this unique stress-strain response of sheet materials with strength-differential, including magnesium alloys, should be considered for an accurate estimation of sidewall curl. In the present study, a semi-analytical bending/unbending theory incorporating characteristic constitutive behavior of magnesium alloys was developed to evaluate the moment-curvature relationship for various levels of constraint tensile forces. The present analysis proved that the reverse effect of constraint tensile force on sidewall curl was caused by the lower resistance to plastic yielding in compression with proper combination of applied tensile force.     

Relationship among microstructure,mechanical properties and texture of TA32 titanium alloy sheets during hot tensile deformation

The relationship among microstructure, mechanical properties and texture of TA32 titanium alloy sheets during hot tensile deformation at 800 °C was investigated. In the test, the original sheet exhibited relatively low flow stress and sound plasticity, and increasing the heat treatment temperature resulted in an increased ultimate tensile strength (UTS) and a decreased elongation (EL). The deformation mechanism of TA32 alloy was dominated by high angle grain boundaries sliding and coordinated by dislocation motion. The coarsening of grains and the annihilation of dislocations in heat-treated specimens weakened the deformation ability of material, which led to the increase in flow stress. Based on the high-temperature creep equation, the quantitative relationship between microstructure and flow stress was established. The grain size exponent and α phase strength constant of TA32 alloy were calculated to be 1.57 and 549.58 MPa, respectively. The flow stress was accurately predicted by combining with the corresponding phase volume fraction and grain size. Besides, the deformation behavior of TA32 alloy was also dependent on the orientation of predominant α phase, and the main slip mode was the activation of prismatic 〈a〉 slip system. The decrease of near prism-oriented texture in heat-treated specimens resulted in the enhancement of strength of the material.     

Electromagnetic incremental forming (EMIF): A novel aluminum alloy sheet and tube forming technology

Large parts cannot be shaped by conventional electromagnetic forming method due to the limitation of the strength of working coil and the capacity of capacitor bank. In this paper, based on the principle of single point incremental forming, a new method named electromagnetic incremental forming (EMIF) has been proposed. The method makes use of a small coil and small discharge energy to cause workpiece local deformation in a high speed. Finally, all local deformations accumulate into large parts. For the electromagnetic incremental sheet forming, the effect factors of processing parameters namely discharge voltage, vent hole, discharging times in a fixed position and the number of discharge region, on final sheet shape are investigated by using AA3003 aluminum alloy parts. In addition, two different simulation strategies are proposed to predict electromagnetic incremental sheet and tube forming process. For method 1: the technology like “birth–death element” is used to indirectly describe the movement of the coil and the morphing technology is used to make the air change with the workpiece deformation. For method 2: the coil can directly move to a special position and the remesh technology is used to consider the effect of the workpiece deformation and the movement of coil on magnetic analysis. It is found that method 1 cannot be used for electromagnetic incremental sheet forming process if overlap region exists in two adjacent discharge regions. However, method 1 can successfully predict electromagnetic incremental tube forming. And method 2 can be used for electromagnetic incremental sheet or tube forming. Both of the experimental and simulation results demonstrate that this new technology is feasible to produce large part.     

显微组织对TA11钛合金棒材力学性能的影响

通过对TA11钛合金不同组织状态的棒材进行组织、性能检测分析,研究了初生α相含量和尺寸对TA11钛合金室温拉伸性能、热稳定性能、蠕变性能的影响。研究结果表明,初生α相含量对TA11钛合金的拉伸性能影响较小,但对合金的抗蠕变性能影响明显:初生α相含量在50%~90%范围内时,合金的室温拉伸性能、热稳定性能随初生α相含量的增加变化不明显,抗蠕变性能随初生α相含量的增加而提高;初生α相尺寸对TA11钛合金的拉伸性能、蠕变性能具有一定的影响,随着组织粗大程度的增加,拉伸强度降低,抗蠕变性能提高。     

TA32钛合金马鞍形零件热冲压工艺数值模拟

建立了TA32钛合金本构模型,在模具上添加了不同的拉延筋,并对其进行了优化以消除皱纹。使用Barlat 89和Hill 48屈服准则来比较有限元模拟的预测精度。通过热冲压成形实验,测量了TA32钛合金马鞍形零件的厚度分布,并与模拟结果进行比较。结果表明;添加X轴和Y轴拉延筋可以有效消除皱纹,实现马鞍形零件精确成形,并且无任何缺陷。采用Barlat 89屈服准则的有限元模型比采用Hill 48屈服准则的模型具有更好的预测精度,该有限元模拟具有较好的理论预测意义。研究了成形后零件的力学性能和显微组织,各项性能均达到了实际工程需要。     

基于元胞自动机的TA15板材累积叠轧微观组织预测

为研究累积叠轧过程中TA15钛合金微观组织的演变规律,首先利用DEFORM有限元软件模拟了不同累积叠轧工艺对板材成形热参数的影响,在此基础上通过元胞自动机模拟了TA15钛合金累积叠轧后组织的动态球化过程。结果表明,在累积叠轧过程中,通过减少单道次变形、降低轧制速度并保持一定的温度,可有效地改善TA15钛合金的微观组织和性能。将元胞自动机动态球化模型导入Deform-3D软件,成功地模拟了在热压缩和累积叠轧过程中微观组织的演变。     

TA2纯钛板的成形极限

为了探究TA2纯钛板的成形极限,通过电化学腐蚀方法印制网格,在室温下使用BCS-50AR板材试验机分别对厚度为0.5和0.8 mm的TA2纯钛板进行了Nakizima胀形试验。通过网格分析系统采集网格的畸变,获得材料的主、次应变,并绘制了TA2纯钛板在室温下的成形极限图。根据单位体积塑性功相等的原理改进了Hill48屈服准则,并求出了TA2纯钛板对应的各向异性系数。将M-K失稳准则和改进的Hill48屈服准则相结合,对TA2纯钛板的成形极限进行了理论预测,理论预测结果与试验结果基本吻合,但整体略低于试验结果。所做研究对于今后板料成形极限的研究提供了重要的研究方法,并且对实际生产具有着重要的工程应用价值。