粘性介质反向压力胀形对5A02铝合金板成形性的影响

粘性介质压力成形（Viscous Pressure Forming,VPF)是一种适合于难变形材料板金零件制造的软模成形工艺。采用粘性介质胀形实验研究了反向压力对5A02铝合金板料成形性能的影响，结果表明在一定范围内的反向压力有利于抑制板料的平面各向异性，而在更高的反向压力条件下板料具有更好的成形性。     

在反向压力粘性介质胀形铝、钛合金板实验研究

粘性介质压力成形是一种新发展起来的板金软模成形工艺，其对板料成形性能的影响可以通过胀形实验来检测和评价。文中采用一种具有应变速率敏感性的半固态粘性物质作为传力介质，采用胀形实验研究了在有、无施加反向压力的情况下，铝和钛合金板料的成形形状特征与应变分布，结果表明，粘性介质压力成形，尤其是存在反向压力时可提高板料的成形性能。     

粘性介质压力成形研究进展(下)

粘性介质压力成形(Viscous Pressure Forming，VPF)工艺非常适合于采用难变形材料的多品种、小批量零件的生产。当前的研究主要集中在成形过程中粘性介质粘度对板料成形的影响；介质排放口以及反向压力等工艺参数对成形性的影响。通过实验研究并结合数值模拟的方法对工艺进行优化，对于缩短板料件新材料应用研制周期、提高复杂形状板料件性能、控制板料成形件的厚度减薄具有重要意义。     

铝合金半球形件反向粘性介质压力成形及有限元分析

针对铝合金半球形零件在成形时容易出现拉裂、 起皱等问题,首次提出采用反向粘性介质压力成形方法进行此类零件的成形,并对其成形过程进行了有限元仿真分析和实验验证,得到不同反向粘性介质压力下试件的几何形状和壁厚变化规律以及粘性介质压力场的分布规律.结果表明,坯料在较高反向粘性介质压力作用下"反向拉深",形成了预反成形效果,改...     

半球形件粘性压力成形的实验研究

本文对半球形件的粘性介质胀形进行了实验研究。充分利用实验设备的特点 ,分析了背压、介质排放口等粘性压力成形中的工艺参数对板材成形性能的影响。实验结果表明 ,粘性压力成形中背压及介质排放口分布的变化可以引起模腔中介质压力场的变化 ,在板材表面形成不同的压力分布 ,进而改变了板料的流动模式及应力状态 ,选取合适的背压及介质排放口的分布可以改善板材的成形性能     

板料液压成形技术的发展动态及应用

介绍了板料压成形技术的发展，尤其是近几年发展起来的径向加压的液压成形，液压成对成形和粘性介质压力成形等3种金属成形技术，以及近几年国外板料液压成形设备的开发和应用情况。     

高温合金波纹件粘性介质压力成形过程危险点的数值模拟

粘性介质压力成形（Viscous pressure forming,VPF)适合于高强度难变形材料钣金零件的制造。本文应用有限元商业软件DEFORM^TM进行模拟，对比分析采用粘性介质压力和刚性凸模成形高温合金波纹形薄壁件过程中材料危险点的变化。发现前者板料成形的危险点会发生转移，释缓了应力集中，降低了缺陷了发生的可能性。因此，有利于提高板料的菜性。     

板料粘性介质胀形过程应变速率变化的模拟研究

采用半固态、具有应变速率敏感性的粘性介质作为板料软模成形传力介质, 这种粘性传力介质的抗力可随板料发生局部变形而迅速增加, 建立起适应于板料变形的压力, 对提高板料成形性十分有益。本文针对板料粘性介质胀形, 采用有限元模拟方法研究了板料与介质应变速率变化, 模拟结果显示介质应变速率与相接触的板料应变速率是一致的, 解释了粘性传力介质变形抗力 “自适应”于板料变形的原因。     

阶梯形件粘性介质压力成形的试验研究

介绿了用粘性介质压力成形（VPF）方法制造阶梯形件的工艺过程,通过调整压边力与介质注入压力的配合,分两步来控制板料的成形,成功地制出阶梯形零件。该方法在第一工步采用较小的压边力拉深预成形,使板料尽量流入型腔,第二工步则加大压边力和介质注入压力使板料最终贴模成形。结果表明采用这种新工艺成形的零件厚度分布均匀,减薄量小,表面质量好,尺寸精度高。     

粘性介质压力成形技术(VPF)研究——王仲仁教授指导的学术新方向

粘性介质压力成形技术(VPF),是20世纪90年代出现的板材软模成形新技术。介绍了粘性介质压力成形技术的基本原理,分析了粘性介质压力成形技术的特点,采用有限元方法数值模拟分析了粘性介质性质对板材变形的影响规律;给出了高强度镍基高温合金小半径曲面波纹形超薄壁厚构件、低塑性铝合金阶梯形构件、轴对称曲面件粘性介质局部内压扩径、外压缩径等粘性介质压力成形实例和分析。     

液体介质传热渐进温成形研究

由于液体介质的存在,在以导热油直接作为传热介质加热板料实现板料温热渐进成形中,成形初始的预胀以及成形过程中存在的背压是区别于其他渐进成形方法的显著特征。在数控渐进机床上,首先以2A12铝合金板料对成形过程中液体压力产生的板料预胀和过程背压的影响进行了研究,然后采用SUS304不锈钢板料对成形过程中的导热油温度影响进行了研究。研究结果表明：液体介质较小的压力产生的预胀和背压对成形过程没有显著影响,成形过程中为了保证导热油和板料充分接触,导热油可以保持一定的系统压力;采用液体介质直接作为传热介质加热板料进行板料温渐进成形是可行的;温度对SUS304不锈钢板渐进成形性能影响显著。     

变压边力对铝合金板冲压成形的影响研究

通过数值模拟和实验,研究了变压边力对铝合金板成形过程中应变路径的变化规律,基于MK法研究应变路径的变化对铝合金板成形极限(FLC)的影响,通过比较不同随时间变化的压边力对铝合金成形极限的影响,揭示变压边力改善铝合金板冲压成形性能的机理。实验和数值模拟结果表明,变压边力改善铝合金板成形性能的主要原因是变压边力对应变路径的影响,对杯形拉深来说,渐增型随时间变化的变压边力可以改善铝合金板的成形性能。     

Experimental Observations of Quasi-Static-Dynamic Formability in Biaxially Strained AA5052-O

To establish the efficacy of electromagnetically assisted sheet metal stamping (EMAS), a series of combined hydraulic bulging and electromagnetic forming (EMF) experiments are presented to evaluate the biaxial quasi-static-dynamic formability of an aluminum alloy (AA5052-O) sheet material. Data on formability are plotted in principal strain space and show an enhanced biaxial formability beyond the corresponding experimental results from conventional forming limit diagram. The plastic strains produced by the combined process are a little larger than or at least similar with those obtained in the fully dynamic EMF process. In addition, the biaxial forming limits of aluminum sheets undergoing both very low and high quasi-static prestraining are almost similar in quasi-static-dynamic bulging process. Limit formability seems to depend largely on the high-velocity loading condition as dictated by EMF. It appears that in quasi-static-dynamic forming, quasi-static loading is not of primary importance to the material’s formability. Based on these observations, one may be able to develop forming operations that take advantage of this formability improvement of quasi-static-dynamic deformation. Also, this could enable the use of a quasi-static preform fairly close to the quasi-static material limits for the design of an EMAS process.     

Observations on the Influence of Tool-Sheet Contact Conditions on an Incremental Forming Process

The influence of tool-sheet contact conditions on features such as surface roughness, forming force, and formability was evaluated for components produced by incremental forming, a highly flexible innovative sheet metal-forming process. Experimental tests were carried out on sheets of AA7075T0 to create two types of component: pyramid frusta (for the evaluation of roughness and force) and cone frusta (for the evaluation of formability). Four different types of tool-sheet contact were analyzed, using two types of tool. From the experimental tests, the influence on the surface finishing and on the trend of the forming forces depending on contact type was revealed. Contact types do not, however, influence sheet formability.     

Fundamental studies on the incremental sheet metal forming technique

The idea of incremental forming technique has been investigated for production of sheet metal components. With this technique, the forming limit curve (FLC) appears in a different pattern, revealing an enhanced formability, compared to conventional forming techniques. In the present study, the formability of an aluminum sheet under various forming conditions was assessed and difficult-to-form shapes were produced with the technique. By utilizing knowledge and experience obtained during the present study, it became possible to produce some free surfaces.     

Formability limits by fracture in sheet metal forming

The aim of this paper is twofold: first, to revisit the forming limit diagram (FLD) in the light of fundamental concepts of plasticity, damage and ductile fracture mechanics and, second, to propose a new experimental methodology to determine the formability limits by fracture in sheet metal forming. The first objective makes use of the theory of plasticity applied to proportional strain loading paths, under plane stress conditions, to analyze the fracture forming limit line (FFL) and to introduce the shear fracture forming limit line (SFFL). The second objective makes use of single point incremental forming (SPIF), torsion and plane shear tests to determine the experimental values of the in-plane strains at the onset of fracture. Results show that the proposed methodology provides an easy and efficient procedure to characterize the formability limits by fracture in sheet metal forming. In particular, the paper shows that the FFL determined by means of tensile and conventional sheet formability tests is identical to that determined from SPIF tests on conical and pyramidal truncated specimens. The new proposed approach is expected to have impact in the established methodologies to outline the formability limits on the basis of the forming limit curves (FLC's) at the onset of necking.     

7075-T6铝合金板温热成形极限图实验

研究7075-T6铝合金板在温热状态下成形性能,采用电化学腐蚀网格法,利用热力耦合条件下的通用板材成形性能实验机和网格应变自动测量分析系统,获得了7075-T6铝合金板在温热状态下(室温~200℃)的成形极限图(FLD)。实验表明,7075-T6铝合金板的成形极限曲线受温度影响显著,并随温度的升高而上升。基于实验数据,建立了不同温度下7075-T6铝合金板成形极限图的计算模型。     

Rate and Orientation Dependence of Formability in Fine-Grained AZ31B-O Mg Alloy Thin Sheet

Uniaxial tension and press forming tests were carried out at two different strain rates and temperatures to investigate the formability of fine-grained AZ31B-O Mg alloy thin sheet. Formability parameters were determined by tensile test results. The tensile properties and formability parameters were correlated with the forming limit diagrams. The present work focused on the effects of loading orientation and deformation rate on formability. Anisotropic behaviors were observed in the mechanical properties. Maximum strengths were obtained in the direction perpendicular to the rolling direction (RD). It can be concluded that the formability of the rolled fine-grained AZ31B-O Mg alloy sheet can be influenced by loading orientation and deformation rate. Stretch formability can be enhanced at a higher deformation rate, resulting from a lower anisotropy and a higher work hardening effect. In contrast, the drawing processes can be performed at a lower deformation rate to take advantage of a higher anisotropic behavior. Specimens with the RD parallel to the major strain in the press forming tests can enhance stretch formability, whereas specimens with the RD perpendicular to the major strain can improve deep-drawability.     

金属板料幂指型硬化模型应变强化系数K值研究

应变强化指数n值因同时体现金属板料胀形、压延等成形性能优劣,甚至与材料的宏观断裂和疲劳特性也存在一定关系,故已成为评价其冲压成形性能的主要材料参数而获得广泛关注。而幂指型硬化模型的另一重要参数——强化系数K值,前期研究虽表明其对板料的冲压成形性能也有重要影响,但目前对其在冲压成形性方面的研究甚少。文章以金属板料单向拉伸塑性失稳点特性为基础,结合硬化模型在该点附近较好地与板料真实应力-应变曲线相符合的基本假设,详细推导了K值与抗拉强度σb和n值之间解析关系,并基于该解析关系讨论了K值与n值在评价板料成形性能方面的一致性。结果表明,K值可作为衡量板料成形性能的综合指标,为研究金属板料成形能力评价方法打开了新的思路。通过实验证明了该解析结果的正确性及其工程适用性。     

A new formability indicator in single point incremental forming

Material properties play an important role in determining the sheet fracture in metal forming processes. However, the degree of influence of a material property on the forming extent depends on the nature of the forming process employed. In the current study, the effect of various material properties on the formability in SPIF has been investigated. Correlations of the formability with material properties under investigation were developed in order to establish a new formability indicator. An empirical model describing the effect of the newly introduced formability indicator has also been proposed.