Inverse finite element approach and its application in sheet metal forming

The inverse finite element approach (IFEA) was derived from ideal forming to predict the development blank of sheet metal and the thickness strain distribution according to the geometry of final product. The flange portion of stamping product under blank-holder is a free parameter that is mostly dependent on the shape of the initial flat blank. Based on the IFEA, this paper proposed a node relocation technique to estimate the influence of flange shape and evaluate the final geometry and thickness strain distribution from the prescribed flat blank. The applications of the IFEA cover the backward and forward evaluations: from given product to initial blank and from given initial blank to final product. Those applications make the design of sheet metal forming easy and fast. A door-like product experiment confirmed that the precision of the IFEA satisfied the manufacturing requirement.     

体积成形有限元模拟软件CASFORM的开发研究

简要介绍了作者自主开发的体积成形有限元模拟软件CASFORM及其关键技术，并给出了大量的实例分析。CASFORM主要由前处理模块，有限元分析模块，后处理模块，有限元网格生成模块和网格再划分及数据传递模块以及材料数据库和模拟数据库等构成，该软件能够分析各种体积成形工艺，包括锻造、挤压、拉拔等。能够预测缺陷的生成，验证和优化工艺/模具设计方案，该软件既能模拟等温成形过程，也可以模拟非等温成形过程，即可进行单工位成形分析，也可进行多工位成形分析。该软件界面友好，使用方便，可靠性和自动化程度高，是模具和工艺设计方案验证和优化的有力工具。     

基于理想形变理论的有限元逆算法在板料成形中的应用

基于理想形变理论,研究了金属板料成形的有限元逆算法,并开发了计算程序.采用线性三角形膜单元和厚向异性的刚塑性材料模型,计算了一个带凸缘的方盒形件,并与Dvnaform的一步逆向法和增量法的计算结果进行了比较.实例分析结果表明,在工程允许精度范围内,本文方法能够有效分析零件的成形性能.由于该方法计算速度快,所以可用于零件...     

有限元反向法计算筒形件毛料形状

合理地选择冲压件的毛料外形 ,可以提高板料的可成形性 ,同时也可以提高材料利用率。选用反向法来计算冲压件的毛料外形 ,开发了独立的有限元源程序 ,并提出了一种简单的求解毛料初步解方法。通过例子证明 ,该算法计算的结果与实际情况比较吻合 ,而且程序比较稳定 ,能较准确较快地求得冲压件的毛料外形     

Gas detonation forming process and modeling for efficient spring-back prediction

Aluminum cylindrical cups are formed with gas detonation forming technology and finite element modeling of aluminum cylindrical cup production with the detonation forming technology is performed. The forming process simulation is carried out in two-step analysis. 2D and 3D computational models are constructed with both explicit and implicit dynamic analyses are performed. The effects of detonation pressure and die design parameters also are investigated. The thickness distribution and deformed geometry of the cups are compared with the experimentally determined values. The spring-back predictions based on the explicit and implicit methods are criticized in terms of deformed shape accuracy and elapsed time.     

Finite element modeling and optimization of superplastic forming using variable strain rate approach

Detailed finite element simulations were carried out to model and optimize the superplastic blow forming process using a microstructure-based constitutive model and a multiscale deformation stability criterion that accounts for both geometrical instabilities and microstructural features. Optimum strain rate forming paths were derived from the multiscale stability analysis and used to develop a variable strain rate forming control scheme. It is shown that the proposed optimization approach captures the characteristics of deformation and failure during superplastic forming and is capable of significantly reducing the forming time without compromising the uniformity of deformation. In addition, the effects of grain evolution and cavitation on the superplastic forming process were investigated, and the results clearly highlight the importance of accounting for these features to prevent premature failure. This paper was presented at the International Symposium on Superplasticity and Superplastic Forming sponsored by the Manufacturing Critical Sector at the ASM International AeroMat 2004 Conference and Exposition, June 8–9, 2004, in Seattle, WA. The symposium was organized by Daniel G. Sanders, The Boeing Company.     

剪挤成形工艺分析及数值模拟研究

为了研究不同剪挤成形工艺参数对成形零件质量的影响,本文使用Deform 2D有限元软件建立二维轴对称模型,采用Ludwik硬化流动应力模型和能够同时反映空穴损伤发展和空穴形状变化对损伤程度影响的韧性损伤模型,进行剪挤成形弹塑性有限元分析.分析归纳出板厚、凸凹模间隙、凸模半径、压边力和反顶力等工艺参数对剪挤成形质量和成形...     

改进型逆有限元法在某轿车翼子板快速成形模拟中的应用

为提高一步成形逆有限元法的模拟精度,将四节点等参膜单元应用于一步成形计算,并对空间四边形单元的四个节点可能不在同一平面引起的单元翘曲进行了修正,编写了计算机程序,对某轿车翼子板进行了实际模拟,通过一步模拟结果与增量法模拟结果和实验结果的对比,发现改进后的一步成形模拟结果与增量模拟结果已非常接近,而计算时间不到增量法的1/30,进而验证了本文方法的有效性。     

An axisymmetric forging approach to preform design in ring rolling using a rigid–viscoplastic finite element method

In this paper, a new method for approximately predicting the deformation of material in ring rolling is presented. The plastic flow of material in ring rolling is assumed to be axisymmetric and thus the ring rolling process is considered as a sequence of consecutive forging processes. The problem, having tool velocity as well as material velocity field as unknown variables, is formulated by an axisymmetric rigid–viscoplastic finite element method. The unknown tool velocity is determined by making the circumferential stress on the ring cross-section exist in the range of user-specified values. The approach is applied to preform shape design in ring rolling of bearing races. The predicted results are compared with the experimental ones. It has been shown that the approximate approach presented is useful for engineering design of preform in ring rolling of bearing race-like rings.     

Flexible forming tool concept for producing crankshafts

Forging, casting and machining compete on quality and price for the production of crankshafts. Forging and casting are commonly utilized for mass production because the capital investment in equipment and tooling are very high. Machining is employed only in case of small production batches of high quality crankshafts made from materials that are normally difficult to forge or cast because it is time and energy intensive, generates a lot of waste and is generally more costly than forging and casting.As a result of this, conventional manufacturing routes for crankshafts are not suitable for flexible small to medium-batch production and, therefore, are not appropriate for the growing agile manufacturing trends requiring very short life-cycles and very short development and production lead times.This paper is concerned with these issues and is focused on the development of an innovative forming tool concept for producing small to medium-batches of cost competitive crankshafts. The proposed tool concept combines knowledge on buckling of solid rods under compression with flexible construction solutions based on modular dies to allow crankshaft production to change output rapidly. Single cylinder to multi cylinder crankshafts including multiple main bearing journals, crankpins and crank webs can be easily produced by fastening or removing appropriate die modules in the overall tool set.The presentation is illustrated with test cases obtained from finite element modelling and experimentation with a laboratory prototype tool conceived to operate exclusively with lightweight materials exhibiting high ductility in cold forming.     

Z形环复合成形工艺与模具

通过对Z形环零件的结构工艺分析,指出了Z形环零件多工序成形的方案及多工序成形的不足之处。为提高加工效率并降低零件成本,提出了将翻边、拉深、成形融于一体的加工工艺方案,设计了模具结构,阐述了模具工作原理,生产实践证明其效果良好。同时针对零件脱模轻微变形问题及类似零件加工提出了模具改进方案。     

双凸板材件的数控渐进成形研究

针对数控渐进反向成形中无法直接成形加工双凸板材件的问题,提出了基于双面挤压的双凸板材件数控渐进反向成形方法。该方法通过设计从正反两面可接近各形体的支撑模,并把板材用两个支撑模装夹,从正反两面挤压板材来实现双凸板材件成形。给出了双凸板材件的成形工艺方案和支撑模设计方法,研究了双凸板材件数控渐进反向成形过程数字模拟分析的方法并运用数值模拟分析了该方案的可行性,并且通过成形试验,完成了双凸板材件的制作。研究结果表明,基于双面挤压的数控渐进反向方法可应用于双凸板材件的制作。     

Surface topography and energy of grain boundary triple junctions in copper tricrystals

Copper tricrystals with a common crystallographic axis 〈1 0 0〉, 〈1 1 0〉, 〈1 1 1〉 were fabricated by the Bridgman technique. Utilizing atomic force microscopy, the topography of the grain boundary triple junctions for the three crystallographic systems were investigated. The grain boundary free surface energy and the grain boundary triple line energy were determined for specific crystallographies of tricrystals.     

小变形高温退火对Hastelloy C-276合金晶界特征分布和晶界平面分布的影响

Hastelloy C-276合金经1150℃+30 min固溶处理后,进行不同变形量的冷轧高温退火处理。采用电子背散射(EBSD)技术对退火后的晶界特征分布和晶界面分布进行表征。结果表明,在退火过程中,Σ1小角度晶界比例减小,变形存储能释放,晶界发生迁移,促进了晶界相互作用,从而导致Σ9和Σ27晶界比例增加。与此同时,晶粒发生异常长大并促进了特殊晶界的形成,产生的特殊晶界阻断了大角度晶界的连通性。合金经变形高温退火之后,Σ3晶界分布在{111}晶界面扭转晶界,Σ9晶界分布在[110]晶带倾斜晶界。不同变形条件下,Σ3晶界面与Σ9晶界面分布演变规律不同,原因在于变形退火导致Σ3晶界比例的不同和晶界之间的相互作用的结果。     

Simulation of bulk metal forming processes using one-step finite element approach based on deformation theory of plasticity

The bulk metal forming processes were simulated by using a one-step finite element(FE)approach based on deformation theory of plasticity,which enables rapid prediction of final workpiece configurations and stress/strain distributions.This approach was implemented to minimize the approximated plastic potential energy derived from the total plastic work and the equivalent external work in static equilibrium,for incompressibly rigid-plastic materials,by FE calculation based on the extremum work principle.The o...     

Grain boundary migration and grain rotation studied by molecular dynamics

We report on molecular dynamics simulations of an isolated cylindrical grain in copper shrinking under capillary forces. At low temperatures, the coupling between grain boundary (GB) migration and grain translation induces rotation of the grain towards higher or lower misorientation angles, depending on the initial misorientation. The dynamics of the GB motion and grain rotation are studied as functions of the initial misorientation angle and temperature. The effects of imposed constraints blocking the grain rotation or exerting a cyclic torque are examined. The simulation results verify several predictions of the model proposed by Cahn and Taylor [Acta Mater 52, 4887 (2004)]. They also indicate that the GB motion is never perfectly coupled but instead involves at least some amount of sliding. This, in turn, requires continual changes (annihilation or nucleation) in the GB dislocation content. Dislocation mechanisms that can be responsible for the motion of curved GBs and dislocation annihilation in them are proposed.     

动力显式有限元法辊弯成形全流程仿真技术研究

辊弯成形是大位移、大转动、有限应变的过程,具有复杂的非线性特征,成形规律难以通过传统“试错法”把握。为避免成形缺陷,降低开发成本,采用有限元法对辊弯成形进行全流程仿真,可以准确预测辊弯成形过程中应力-应变分布与变化规律,辅助工艺设计与产品开发。采用动力显式算法,可以缩减计算规模,避免隐式算法的迭代收敛问题等限制,容易实现大规模并行计算,减少计算时间。通过对槽型件的辊弯成形进行全流程仿真实例,验证了该方法的有效性。