基于DYNAFORM的筒形件拉深成形数值模拟技术

应用数值模拟技术对金属板料成形规律进行研究越来越受到重视。对影响筒形件拉深成形的主要因素压边力、凹模圆角半径、凸模圆角半径、摩擦系数进行了分析,并研究了单元技术、求解格式、本构关系等金属板料成形模拟中的关键技术。应用DYNAFORM数值模拟软件,对筒形件的两道次拉深成形四种主要因素的工艺参数进行了模拟优化。模拟结果分析表明,各因素对金属板料拉深系数影响的主次顺序在不同拉深道次下是不相同的,不能一概而论,与实验结果基本吻合。     

数值模拟分析工艺参数与拉深件壁厚变化的关系

在分析板料拉深成形有限元理论的基础上建立数值模拟的分析模型,利用数值模拟技术系统地对拉深过程进行模拟。主要研究模具圆角半径、摩擦因数、压边力与模具间隙等工艺参数与拉深件壁厚最大变薄率的内在关系。     

矩形拉深件材料流动变形规律的有限元分析

用有限元模拟矩形盒拉深成形过程并剖析拉深中材料流动变形规律。选用更接近拉深过程本质的动力显式算法和效率更高的壳单元来模拟非回转对称体的成形过程。实验验证了矩形盒成形有限元模拟结果的可靠性。     

高盒形件多道次变薄拉深工艺机理研究及数值模拟模型确立

盒形件有限元模拟通常采用壳单元进行建模,由于薄壳单元在计算中忽略了厚向应力,因此在多道次拉深成形及变薄拉深成形工况下的适用性存在质疑。以3003H14高盒形件多道次变薄拉深为研究对象,利用Dynaform并结合LS-DYNA有限元软件进行数值模拟,对比壳体单元与实体单元的模拟计算数据,通过分析外观模拟结果和Levy-Mises增量理论中瞬时本构关系系数的模拟数据,得到单元类型对薄板多道次变薄拉深成形模拟计算精度的影响规律。利用实际工程中的毛坯尺寸样本数据对建立的盒形件拉深毛坯尺寸计算程序进行训练,从而实现了盒形件拉深工艺毛坯尺寸预测软件的开发。此外,在明确建模方法后,结合实体单元有限元模拟结果研究板料在变薄拉深过程中材料的减薄与增厚的机理,揭示了材料流动规律。研究表明:实体单元模拟计算结果与实际更接近。若以坯料单元在工序前后的理论变形厚度的百分比差值作为变形程度衡量指标,当变形程度为0~11.1%时,两种单元计算差异为0.5%~27.8%;当变形程度为24.2%~34.9%时,两者计算差异为44.4%~79.3%。经多道次变薄拉深后,金属材料增厚区域多发生在凸缘及长边与短边交界处的圆角上;在模具的限制作用下,减薄区域多发生在底部圆角,长边与短边区域都有一定减薄;除工序1外,其他各个工序长边侧直壁平均厚度比工艺设计的理想值大1.00%~2.02%,短边侧直壁平均厚度比工艺设计的理想值小0.86%~12.90%。     

球形件反复拉深成形工艺有限元模拟及试验

提出了球形件反复拉深成形工艺,对该工艺进行了有限元模拟与试验验证。与一次拉深成形工艺进行了对比分析,结果表明：凹模圆角区与法兰区应力状态及大小基本相同,但在球底区,反复拉深时径向应力和周向应力都远小于一次拉深的应力,球底区径向应力和周向应力基本为压应力或很小的拉应力;反复拉深时球底区厚度方向应变明显减小,一次拉深、二次反复拉深、三次反复拉深成形的制品最薄点减薄率分别为0.189、0.122、0.049,三次反复拉深可实现近等壁厚制品的拉深成形。该工艺与筒底冷校形工艺相结合,可实现近等壁厚深筒形零件的拉深成形。     

正交试验设计在TA2筒形件拉深成形过程中的应用

研究了TA2筒形件的拉深成形过程,对无压边圈情况下拉深成形的5个因素(凹模入口圆角、凸凹模间隙、模具与板坯之间润滑系数、凸模圆角、坯料直径)进行了有限元数值模拟及其正交试验,提出了采用成形后板坯最大厚度与最小厚度之差Δt的概念来作为描述零件成形结果的评价标准,且论证了采用该评价标准的合理性。对试验结果进行了直观分析和方差分析,得出了各因素对拉深成形过程的影响次序及显著性。     

基于有限元逆算法的拉深筋工艺设计和优化

汽车覆盖件拉深成形中，一般通过设置适当的拉深筋控制成形过程中的板料塑性流动规律来提高覆盖件成形质量。针对覆盖件工艺设计需求，提出一种基于有限元逆算法的拉深筋工艺优化算法。该算法以灵敏度优化方法为基础，考虑了板料的成形度、破裂和起皱等成形缺陷。在板料成形模拟FASTAMP系统中，开发了拉深筋优化模块，并以实际覆盖件为例，验证了该算法能快速准确地模拟等效拉深筋力的布置情况以及优化板料的成形性。     

基于正交试验和能量转换的精密级进模多步拉深成形研究

应用正交试验方法,采用Dynaform对精密级进模多步拉深成形进行有限元数值模拟。结合能量转换原理,研究各步拉深中凹、凸模圆角半径、拉深高度以及压边力等工艺参数对成形件厚度和回弹的影响,并找出各因素影响的主次顺序。以射频(RF)连接器的壳件为例,通过上述方法优化各步成形参数,用以指导模具设计。     

非轴对称抛物面反射镜拉深成形数值模拟研究

利用板料成形分析软件Dynaform建立了合理的有限元模型,分析了典型的非轴对称拉深件——汽车前雾灯反射镜在拉深过程中的厚度分布、裂纹和起皱预测、成形极限图等;对板料形状、凹模圆角和压边力等多参数进行了优化,改进了传统的模具设计模式,对同类件的生产有一定的借鉴意义。     

镀锌钢板圆筒拉深件表面损伤行为的研究

采用不同凹模圆角半径下的圆筒拉深实验,对热镀锌钢板DC53D+Z和合金化热镀锌钢板DC53D+ZF拉深成形工件表面损伤行为进行研究。实验结果表明,在不同凹模圆角半径下,DC53D+Z表面损伤有熨平纹和表面划痕两种形式,而DC53D+ZF的表面损伤则有镀层龟裂和表面划痕两种形式;随着凹模圆角半径的减小,DC53D+Z熨平纹现象增加,DC53D+ZF垂直拉深方向的裂纹增加。利用ANSYS/LS-DYNA有限元分析软件,建立基于界面结合的镀锌板圆筒拉深有限元模型,对镀锌钢板拉深过程进行模拟。模拟结果表明,随着凹模圆角半径的减小,镀层沿拉深方向的第一主应变增加。数值模拟结果与实验结果对比表明,镀层沿拉深方向的第一主应变是影响表面损伤程度的主要原因。     

The application of abductive networks and FEM to predict the limiting drawing ratio in sheet metal forming processes

The deep drawing process, one of the sheet metal forming methods, is very useful in the industrial field because of its efficiency. The limiting drawing ratio (LDR) is affected by many material and process parameters, such as the strain-hardening exponent, the plastic strain ratio, friction and lubrication, the blank holder force, the presence of drawbeads, the profile radius of the die and punch, etc. In order to verify the finite element method (FEM) simulation results of the LDR, the experimental data are compared with the results of the current simulation. The influences of the process parameters such as the blank holder force, the profile radius of the die, the clearance between the punch and the die, and the friction coefficient on the LDR are also examined. The abductive network was then applied to synthesize the data sets obtained from the numerical simulation. The predicted results of the LDR from the prediction model are in good agreement with the results obtained from the FEM simulation. By employing the predictive model, it can provide valuable references to the prediction of the LDR under a suitable range of process parameters.     

金属板料冲压成形的数值模拟

本文采用有限元动力显式算法模拟金属板料冲压成形的加工过程。四结点蜕化壳单元和刚体壳单元分别用来建立权和模具的有限元模型;更新Ｌａｇｒａｎｇｅ法和速率型本构关系被用来处理板料变形中的大应变和大转动;材料模型采用塑性各向异性屈服与等向强化模型;通过主从面模型定义板料和模具的接触,接触算法采用运动约束法,摩擦力用库仓定律计算;并利用动力松弛法对回弹过程进行了计算。模拟结果和实际零件比较,证明模型合理,算法稳定,结果可靠,具有良好的应用价值。     

采用试错接触算法的板料成形有限元模拟技术－

以金属板料成形过程为对象,采用基于板壳理论的８节点壳单元,以Ｋｉｒｃｈｈｏｆｆ应力张量和Ｇｒｅｅｎ应变张量作为应力与应变的度量,采用有限变形的Ｕｐｄａｔｅｄ　Ｌａｇｒａｎｇｉａｎ列式,研究有限元方法模拟成形过程的技术。在此基础上,提出了一种直接试错的接触算法,将非线性的接触边界条件线性化处理,接触处理与有限元计算相对独立。通过试验结果与计算结果的比较,说明采用的模拟算法是合理可行的。     

On the prediction of side-wall wrinkling in sheet metal forming processes

Prediction and prevention of side-wall wrinkling are extremely important in the design of tooling and process parameters in sheet metal forming processes. The prediction methods can be broadly divided into two categories: an analytical approach and a numerical simulation using finite element method (FEM). In this paper, a modified energy approach utilizing energy equality and the effective dimensions of the region undergoing circumferential compression is proposed based on simplified flat or curved sheet models with approximate boundary conditions. The analytical model calculates the critical buckling stress as a function of material properties, geometry parameters and current in-plane stress ratio. Meanwhile, the sensitivities of various input parameters and integration methods of FEM models on the prediction of wrinkling phenomena are investigated. To validate our proposed method and to illustrate the sensitivity issue in the FEM simulation, comparisons with experimental results of the Yoshida buckling test, aluminum square cup forming and aluminum conical cup forming are presented. The results demonstrate excellent agreements between the proposed method and experiments. Our model provides a reliable and effective predictor for the onset of side-wall wrinkling in sheet metal forming processes.     

Rigid-plastic finite element analysis of sheet metal forming processes using continuous contact treatment and membrane elements incorporating bending effects

An improved method of contact treatment is developed in which both the FEM (finite element method) mesh and the tool surfaces are described with parametric patches which have C¹ continuity or more. The FEM mesh at the current configuration is globally converted into smooth surface patches of net form. A continuous sheet surface normal scheme is devised by using the globally smoothed mesh surface. A robust and efficient contact search algorithm is also developed in connection with the proposed continuous contact treatment. As an improved version of conventional membrane element, the BEAM (abbreviated from Bending Energy Augmented Membrane) element is newly developed based on node spring. In order to verify the effectiveness of the proposed continuous contact treatment and BEAM element, deep drawing processes of complicated parts including actual auto-body panel are analysed. Comparisons with the available experiment and analysis show that the proposed continuous contact treatment in connection with BEAM elements can be effectively applied to the analysis of sheet metal forming processes for arbitrarily curved parts with deformation regions in which the bending effect must be taken into account.     

板材软模成形二维断面有限元分析界面接触摩擦处理

板材软模成形是板材和柔性传力介质耦合变形过程,存在板材和刚性模具及板材和柔性传力介质两种类型的界面接触。采用罚函数法计算接触力,推导了Mindlin轴对称壳单元和实体单元两种不同单元类型之间接触摩擦的有限元列式。采用静力显式的时间积分方法,通过控制载荷步长保持接触状态稳定。粘弹塑性软模材料的板材变形数值算例表明该算法是有效的。该算法也适用于其他类型软模材料的板材变形接触摩擦问题的处理。     

Prediction of limiting dome height using neural network and finite element method

Using neural network to predict limiting dome height (LDH) based on the result of finite element analysis is a high efficiency work in spite of little error. Finite element results are presented with different working condition parameters, such as material thickness, punch speed, friction coefficient between punch, die and sheet metal, and blank holder force. Then, a two-layer back propagation network is developed to best fit this discrete engineering problem. Different number of neurons in the hidden layer, three commonly used training algorithms, and two performance functions are adopted and compared to choose the suitable one to minimize the error between the predictive value and the simulation results (one with ideal output). After comparison, the neuron number in the hidden layer is determined to be 12 and the appropriate learning algorithm is Levenberg–Marquardt algorithm. The difference between two performance algorithms is small. The mean square error between the predicted value and targeted one is less than 0.2%. Finally, five sheet metal forming processes under various working conditions are predicted and compared with the finite element method (FEM) result to verify the validity of this neural network model. The small difference indicates that this neural network can predict the LDH in a certain range of working conditions.     

Optimisation of springback in bending processes using FEM simulation and response surface method

The aim of this work includes the springback optimisation of bending processes using the concept of experimental design and response surface methodology (RSM). The optimisation method includes two phases. The first involves the objective function prediction using design of experiments and response surface method, while the second is an optimisation process using a FORTRAN gradient algorithm. Springback of sheet parts during bending processes is simulated using finite element model (FEM) including damage evolution effects within the sheet. The numerical simulation of the damage evolution has been modelled by means of continuum damage approach. The Lemaitre damage model, taking into account the influence of triaxiality, has been implemented into ABAQUS/Standard code in order to predict the external fibres rupture evolution during the process and the material characteristics changes after bending. The simulation included die corner radius and punch-die clearance as the main variables.     

Tool path correction algorithm for single-point incremental forming of sheet metal

There exists some error between the manufactured part shape and the designed target shape due to springback of this part after forming. To reduce the error, an iterative algorithm of closed-loop control for correcting tool path of the single-point incremental forming, based on Fast Fourier and wavelet transforms, has been developed. Moreover, the data of the springback shapes, after unloading, of the sheet metal parts formed with the trial and corrected tool paths, used for iterative correction of tool path in the algorithm, are obtained with finite element model (FEM) simulation. Then, a truncated pyramid-shaped workpiece, whose average errors are +0.183/?0.175 mm, was made with the corrected tool path after three iterations solved by the above algorithm and simulation data. The results show that the tool path correction algorithm with Fourier and wavelet transforms is reasonable and the means with FEM simulation are effective. It can be taken as a new approach for single-point incremental forming of sheet metal and tool path design.     

拉深孔成形的工艺参数优化与实验研究

为了探讨拉深孔成形技术对提高板料成形性能的有效性，以圆筒形件为研究对象，研究了拉深孔成形条件下的成形性能。采用数值模拟、人工神经网络和遗传算法进行板材成形工艺参数优化，得到了最优化的压边力和拉深孔相对密度等拉深工艺参数。根据优化后的结果设计并完成了相关的工艺实验，取得了与有限元模拟相一致的结果，证明了拉深孔成形技术是一种提高板材成形性能的行之有效的方法。