板料增量成形的研究进展

板料增量成形是采用简单模具对板料进行逐次塑性加工的一种工艺,不需要专用的模具就可以成形较为复杂的零件,同时还具有成形力小、柔性高的特点,特别适合多品种小批量零件的生产方式,因此得到国内外学者的重视。本文重点从板料的增量压弯成形、增量拉深胀形、增量微成形3个方面对板料增量成形的发展进行综述,还对板料增量成形工艺的发展前景进行了展望,指出进行理论创新、开发新的模拟软件、探索新的成形方案、开发增量成形新设备是发展趋势。     

A geometrical model of the kinematics of incremental sheet forming for the prediction of membrane strains and sheet thickness

The sine law is a simple geometrical model for incremental sheet metal forming (ISF). It is based on the assumption that the deformation is a projection of the undeformed sheet onto the surface of the final part. The sine law provides approximations of sheet thinning for shear spinning and ISF at negligible computational cost, but as a plane strain model it can be applied only when plane strain deformation prevails.     

Feature-based tool path generation approach for incremental sheet forming process

Incremental sheet forming (ISF) is a highly versatile and flexible process for rapid manufacturing of complex sheet metal parts. Although tool path plays an important role in the ISF process, there is only limited development in the tool path generation strategy and the conventional contour based strategies have been proven to cause problems in surface quality and geometric accuracy. This paper presents a new feature-based tool path generation algorithm for incremental sheet forming process. In this algorithm, tool paths are generated according to the specified critical edges. To obtain a better understanding of forming mechanism using the new tool path generation method, the thickness distribution, geometric accuracy and surface quality of the ISF formed shapes by using the feature-based tool path approach are compared with the traditional ISF tool path method based on three case studies including a truncated cone with double bottoms, a non-symmetrical cone and a car fender. The results suggest that the new tool path stretches the sheet in a different way and results in different thickness distributions. The results of these case studies also demonstrate the advantages of the feature based tool path generation especially in surface quality, geometric accuracy and forming time.     

In-situ springback compensation in incremental sheet forming

Limited geometric accuracy in incremental sheet forming is a major obstacle for its wide adoption in industry. This paper develops a generic methodology, suitable for arbitrary part geometries and various ISF processes, for addressing one of the main causes of geometric inaccuracy, i.e., in-process springback. The methodology consists of three main elements: determination of key control points to treat geometric complexity, simplified simulation models to predict springback offline, and in-situ toolpath modification during forming. It is shown experimentally that the method provides an efficient and robust solution for various geometries with negligible setup cost.     

基于韧性断裂准则的铝合金板材成形极限预测

为了准确地预测铝合金板材成形极限，将韧性断裂准则引入到数值模拟中。在数值模拟获得的应力应变值基础上，采用简单拉伸试验和数值模拟相结合的方法确定了韧性断裂准则中的材料常数，并应用该韧性断裂准则预测了铝合金LYl2(M)的圆筒件拉深和半球形凸模胀形的成形极限。预测结果与实验值吻合较好，该韧性断裂准则能够预测铝合金板材成形极限。     

TRIP590板料渐进成形失效研究11,2111

通过胀形试验和以沟槽法为基础获取普通板料渐进成形极限图的方法,分别获取TRIP590板料的传统成形极限图和渐进成形极限图。为了直观地比较TRIP590板料在不同成形方式中具有的成形性能以及验证获取的渐进成形极限图是否满足于TRIP590板料成形,设置了变角度圆锥台和变角度方盒进行验证。两组试验证明:TRIP590板料在渐进成形中的成形性能远强于传统成形,并且获取的线性方程为ε2=0.525 4ε1+0.989 1的渐进成形极限图也适用于TRIP590板料的成形。     

电磁平板自由胀形3D数值模拟(英文)

电磁成形是一种高速率成形方法,它能够有效提高金属板材的成形极限。但是电磁成形过程复杂,涉及到磁场?结构场之间的耦合分析。数值模拟提供一种手段去解决耦合问题。然而,大多数的数值模拟都限于2D。建立3D有限元模型去分析电磁平板胀形。成形过程中考虑了板料与底模的接触和板料变形对磁场的影响。板料中心节点和半径20mm处节点的位移随着时间的变化与实验结果一致。分析了塑性应变能和塑性应变。     

The mechanics of incremental sheet forming

The deformation mechanism of incremental sheet forming (ISF) is examined experimentally through forming specially prepared copper sheets. Strain distributions through the thickness of the sheets are measured for two configurations of ISF: two-point incremental forming (TPIF) and single-point incremental forming (SPIF), and a comparison is made to pressing. The measurements show that the deformation mechanisms of both SPIF and TPIF are stretching and shear in the plane perpendicular to the tool direction, with shear in the plane parallel to the tool direction. Strain components increase on successive laps, and the most significant component of strain is shear parallel to the tool direction. Increasing stretching and shear perpendicular to the tool direction account for differences between the sine law prediction and measured wall thickness for both SPIF and TPIF. The observed mechanisms of SPIF and TPIF differ from a mechanism of pure shear that has previously been assumed.     

镁合金板材正反向快速气压胀形实验

采用两种不同轮廓的反向预成形模具进行高应变速率气压胀形实验,结果表明,内外凹圆弧预成形模的成形效果好于半圆弧预成形模,反向胀形的时间可控制在10s,表面和微观组织均无明显缺陷。利用上述预成形模进行半球件正反向气压自由胀形实验,研究正反向胀形的效果,正反向胀形可以显著提高AZ31B镁合金板料的成形能力,使胀形件高径比从0.344提高到0.522,并使壁厚均匀度从19.4%提高到半圆弧预成形模具的32.3%,内外凹圆弧预成形模具的45.5%。在400℃温度下胀形300s,可以成形出高径比为0.522的完好半球件。     

LZ91镁锂合金板材的超塑性气胀成形研究

本文利用热拉伸实验、气胀成形实验、金相分析和扫描电镜观察,研究LZ91镁锂合金板材的超塑性、气胀成形性能及其组织结构。结果表明:在热拉伸变形温度为573 K、应变速率为0.001 s-1时,其伸长率可达343.7 %,应变速率敏感指数为0.697,轧制态的LZ91合金板材表现出优良的超塑性;在胀形温度573 K,胀形气压0.06 MPa条件下,板材成形高度为51.14 mm,高径比达1.279,说明该镁锂合金板材具有良好的超塑性成形潜力;在热拉伸变形和超塑性气胀成形过程中,均有动态再结晶现象产生,可有效提高该合金的塑性成形能力;在拉伸断口和胀形件破裂处断口均存在典型的超塑性空洞形貌特征,说明两者的主要变形机制均为晶界滑移,且合金超塑性失效的主要原因是空洞的长大和连接。     

Incremental forming by continuous bending under tension—An experimental investigation

The Continuous Bending under Tension (CBT) test has been applied to study aspects of incremental forming. Effects of experimental conditions like speed and bending angle have been studied in particular. The results illustrate an essential aspect of incremental sheet forming (ISF): localized deformation. The actual bending radius is the most important influencing factor and this turns out to be controlled by both the pulling force and the bending angle (depth setting). Material thickness had only a minor effect. The maximum elongation before fracture of mild steel was significantly better than that of aluminium. The material is subjected to additional repetitive bending; this does affect material behaviour in general. The aspects of bending under tension as a governing mechanism in incremental sheet forming are discussed.     

Exergy analysis of incremental sheet forming

Research in the last 15 years has led to die-less incremental forming processes that are close to realization in an industrial setup. Whereas many studies have been carried out with the intention of investigating technical abilities and economic consequences, the ecological impact of incremental sheet forming (ISF) has not been studied so far. Using the concept of exergy analysis, two ISF technologies, namely single sided and double sided incremental forming, are investigated and compared to conventional forming and hydroforming. A second exergy analysis is carried out with the purpose of examining the environmental impact of different forming technologies from a supply chain perspective. Therefore, related upstream activities (die set production, aluminum sheet production and energy conversion and supply) are included into the exergy analysis. The entire supply chain is modeled with Matlab/Simulink. The results of both analyses suggest that ISF is environmentally advantageous for prototyping and small production runs.     

背压对AZ31镁合金板材快速气压胀形的影响

利用快速气压胀形实验,研究背压对AZ31镁合金轧制板材胀形时空洞体积分数、胀形高度和壁厚分布的影响。研究结果表明,在胀形温度为350℃的工艺条件下,胀形件顶部在无背压和加载背压时,空洞的比率分别达到了21%和16%。在相同的应变下,加载背压时获得的胀形件中的空洞比率小于无背压时的空洞比率。背压的加载,能有效降低板材中空洞的分布比率,提高板材的胀形高度,进而提高成形极限。     

Investigation of material deformation mechanism in double side incremental sheet forming

Double side incremental forming (DSIF) is an emerging technology in incremental sheet forming (ISF) in recent years. By employing two forming tools at each side of the sheet, the DSIF process can provide additional process flexibility, comparing to the conventional single point incremental forming (SPIF) process, therefore to produce complex geometries without the need of using a backing plate or supporting die. Although this process has been proposed for years, there is only limited research on this process and there are still many unanswered open questions about this process. Using a newly developed ISF machine, the DSIF process is investigated in this work. Focusing on the fundamental aspects of material deformation and fracture mechanism, this paper aims to improve the understanding of the DSIF process. Two key process parameters considered in this study include the supporting force and relative position between master and slave tools. The material deformation, the final thickness distribution as well as the formability under varying conditions of these two process variables are investigated. To obtain a better understanding from the experimental results, an analytical model has been developed to evaluate the stress state in the deformation zone. Using the developed model, an explicit relationship between the stress state and key process parameters can be established and a drop of stress triaxiality can be observed in the double contact zone, which explains the enhanced formability in the DSIF process. Based on the analytical and experimental investigation, the advancements and challenges of the DSIF process are discussed with a few conclusions drawn for future research.     

DC04钢板胀形-渐进复合成形锥形件成形能力的实验研究

为了提高渐进成形过程中板料的成形极限和加工效率,提出了胀形-渐进成形的复合成形方法,通过胀形-渐进成形复合成形锥形件实验,研究了DC04钢板胀形-渐进成形复合成形锥形件和纯渐进成形锥形件的成形极限角和应变变化以及壁厚分布规律。结果表明:预成形高度为h=15 mm和h=25 mm时,复合成形零件的成形极限角分别为α极=66°和α极=69°;采用胀形-渐进成形复合成形锥形件,当胀形的最大减薄量发生在局部渐进成形区内,并且胀形和渐进成形的最大减薄量位置方向相反时,锥形件壁厚趋于均匀,提高了胀形-渐进成形的复合成形能力。     

铝板弯曲电磁校形实验研究

回弹是弯曲成形的主要缺陷,传统的弯曲工艺消除回弹的效果并不理想.电磁成形是一种高速成形技术,能提高成形性能,改善应力分布,有效地控制回弹.以1060铝板为研究对象,提出一种用于V形件弯曲校正匀压力线圈,以利于提高成形效率,对不同厚度的铝板毛坯进行电磁弯曲校形实验.实验结果表明:随着放电能量的增加,V形件回弹逐渐减小直至消除;坯料越厚,消除回弹所需的能量越大;坯料宽度对工件回弹没有影响;在较低的能量下对工件进行多次放电,随着放电次数的增加,回弹逐渐减小,最终被消除;离折弯线区域越近,工件塑性变形功越大.     

AZ31B镁合金板热渐进成形的精度研究

成形精度差是限制单点渐进成形发展的重要因素,针对单点渐进成形技术难以实现对材料高温处理再加工的问题,提出一种基于液体介质加热的单点渐进成形方法,并通过依次提高温度的方法,探索了适合进行AZ31B镁合金板料单点渐进成形的实验温度。同时,研究了在该温度下采用单点渐进成形方法加工AZ31B镁合金方锥件时,成形角对精度的影响。结果表明:液体介质加热的方法对单点渐进成形有效,在加热油温达到200℃时能够完成镁合金板料的单点渐进成形过程;方锥成形件的精度影响分两种形式——侧壁鼓凸和棱边回弹,并且随成形角的增大,侧壁鼓凸和棱边回弹的回弹量都减小。     

应用韧性断裂准则预测不同材料的胀形极限

为了准确地预测板料成形极限 ,将韧性断裂准则引入到有限元模拟中。在有限元模拟获得的应力应变场基础上 ,应用韧性断裂准则预测板料断裂的发生。本文应用作者提出的韧性断裂准则及材料常数的确定方法预测了铝合金板和钢板的半球形凸模胀形的成形极限。与实验结果比较表明 ,该方法能在较宽的材料范围内预测胀形成形极限。     

板料成形极限的理论预测与数值模拟研究

本文针对目前板料成形极限的实验、理论计算和数值模拟方法以及成形极限应力图的研究进展 ,进行了综述与分析 ,提出了通过数值模拟方法预测板料成形极限所存在的一些问题。认为找到一种能够尽量减少对外部条件的依赖 ,从而更本质地反映材料性能的方法。     

基于人工神经网络的板料激光成形工艺优化

采用BP算法的人工神经网络系统，以激光能量、光斑大小、扫描速度、矩形板料的厚度和宽度作为输入层节点，预测板料激光成形的温度峰值和弯曲角度，并将该系统用于08F薄钢板激光弯曲成形的工艺参数优化之中，可以快速获得最大成形角度所对应的最优工艺参数组合。