板料成形的回弹预测方法研究

回弹是影响板料弯曲成形品质的主要因素之一,对回弹进行准确预测和有效控制是提高成形精度的关键.从理论研究、实验研究、有限元数值模拟以及人工神经网络4个方面综述了国内外关于板料成形回弹预测的研究现状,总结了基于两种塑性弯曲理论模型建立的回弹计算公式,并概述了有限元数值模拟技术在模拟板料成形及其回弹的应用情况,最后介绍了人工神经网络在回弹预测领域的应用.     

机油盘冲压过程截面的有限元模拟与实验验证

板料冲压过程的模具设计是一个费时费力的过程。采用有限元可以降低设计费用 ,缩短设计周期。本文采用有限元软件 MARC基于拉格朗日的弹塑性本构方程建立了一个有限元模型来分析机油盘的成形过程。模拟中考虑板料的厚向异性 ,接触面间的摩擦约束采用库仑摩擦模型。模具看作刚体 ,板料作为变形体。模拟和实验结果的比较表明模拟的壁厚变薄分布与测量结果吻合得很好 ,因而理论模拟的结果可用于真实情况的预测     

基于有限元分析的铝合金板料弯曲回弹的影响因素研究

铝合金材料的弯曲成形是飞机板材和型材零件常用的加工方式之一,在卸载过程中,由于板料的弹性回复,不可避免的会出现回弹现象,在实际加工中如何预测工件回弹后的形状,并对模具进行适当修正仍是一个比较难解决的问题。本文利用非线性有限元软件MARC对不同厚度的铝合金板材弯曲加工过程进行了模拟分析,给出了相对弯曲半径,弯曲中心角,及不同弯曲模式与回弹角度之间的关系,并与实验数据进行了比较。结果表明,有限元分析结果与实验结果比较吻合,有限元模拟能有效地分析和预测铝合金板料的弯曲回弹,为实际生产加工过程中工艺参数的选择提供有力的参考。     

汽车覆盖件冲压回弹仿真的研究

为了解决汽车覆盖件冲压成形过程中的回弹问题,以板料冲压成形有限元理论和仿真方法为基础,对某汽车U形梁采用板料成形仿真软件Dynaform,在计算机上模拟冲压成形及回弹的过程,预测出实际的模具制造过程中可能出现的回弹量,通过将仿真结果与实验对比,说明了仿真设计方法的实用性,从而总结出控制回弹的措施.     

铝合金板材冲压成形回弹有限元模拟研究

板料卸载后回弹变形对钣金件的成形精度影响很大。基于Numisheet1993的U形弯曲标准考题,考虑板材与模具间的接触演变过程,建立了一个有限元模型来预测铝合金板材弯曲过程的回弹。模拟中板材本构方程基于更新拉格朗日弹塑性材料模型,压边力采用凸缘边界的等效力表示,卸载过程采用模具反向运动方法。对有限元敏感度分析发现,回弹大小和整体精度受到元素大小、积分点和屈服准则的很大影响。有限元模型通过Numisheet1993和2005的考题进行验证,发现精度达90%以上。通过有限元分析得到了一个优化的模型,提供了一个更加精确的方法,该方法还可减少计算时间。     

基于ANSYS的铝制错列锯齿翅片成形回弹研究

以铝制错列锯齿翅片为研究对象,利用ANSYS/LS-DYNA非线性动力有限元求解功能,模拟了翅片成形过程与卸载后回弹变形的全过程,得到了成形过程中任意时刻各处的应力、应变和卸载后板料的回弹结果。研究翅片成形过程中压边力、板料厚度、冲压速度、刀具齿形组合、刀具圆角半径等对回弹的影响。利用回弹规律进行模具补偿设计,以此优化专用翅片成形机及模具的结构参数和工艺参数,从根本上提高铝制错列锯齿翅片的制造精度,为翅片的结构优化设计提供了可靠的依据。     

高强度钢冲压成形中扭曲回弹仿真与工艺参数优化

板料冲压成形过程中易出现起皱、破裂、回弹缺陷,其中高强度钢冲压件的回弹问题更为严重,通过采用板料成形仿真软件Dynaform对某汽车结构件的回弹过程进行模拟分析,结合均匀实验设计方法,用二次多项式拟合了该件扭曲回弹角与冲压速度、压边力、凸凹模间隙和摩擦系数的回归模型,得出控制扭曲回弹最优的工艺参数组合,并对回归模型进行了瞬态的灵敏度分析,结果表明,采用优化后的工艺参数使零件扭曲回弹控制良好,为预测和控制该类零件的冲压成形质量提供了良好的指     

基于近似模型的板料成形稳健优化方法研究

为了控制板料成形的回弹量,同时提高板料成形优化效率,提出一种基于Kriging替代模型的板料成形稳健优化方法。首先通过灵敏度分析挑选出对板料成形质量影响较大的参数作为设计参数;然后利用BoxBehnken设计获取局部较少且分布合理的试验样本点,通过Kriging插值理论完成对设计变量与设计响应之间全局映射关系的拟合;最后结合Kriging近似模型对板料成形回弹进行稳健优化。以包容式节点为例,对本文方法进行应用,并与常规优化方法比较,验证所提方法的可行性。     

基于试验设计和灰色关联度的橡皮囊成形回弹影响因素显著性分析

橡皮囊成形是飞机钣金零件的一种重要成形工艺方法,回弹问题是橡皮囊成形的难点,对其影响因素进行显著性分析可有效控制回弹。基于橡皮囊成形有限元数值模拟,将正交试验设计方法与灰色关联度相结合用于分析橡皮囊成形回弹影响因素的显著性,以某实际长直U形件为例分析压力、最大充液速率、最大节点速度、保压时间、弯曲半径、板料厚度以及轧制方向等因素对回弹的影响程度,结果表明,模具圆角半径、压力、板料厚度、保压时间是橡皮囊成形回弹的主要影响因素,而最大充液速度、最大节点速度、轧制方向对回弹的影响较小。分析结果与工艺试验结果相吻合,从而验证了该方法的有效性。     

TA2M钛合金板材U形件弯曲回弹研究

应用PAM—STAMP冲压模拟软件,对TA2M钛合金板材U形弯曲成形及回弹过程进行了数值模拟预测,并对模拟结果进行了工艺试验验证,得到了板料厚度、轧制方向以及相对弯曲半径等参数对回弹影响的数值结果,并对结果进行了分析。     

Analytical modeling and numerical simulation for three-roll bending forming of sheet metal

The three-roll bending forming of sheet metal is an important and flexible manufacturing process due to simple configuration. It is suitable for forming large sheet parts with complex, curved faces. Most researches on roll bending forming of large workpiece are mainly based on experiments and explain the process through macroscopic metal deformation. An analytical model and ABAQUS finite element model (FEM) are proposed in this paper for investigating the three-roll bending forming process. A reasonably accurate relationship between the downward inner roller displacement and the desired springback radius (unloaded curvature radius) of the bent plate is yielded by both analytical and finite element approaches, which all agree well with experiments. Then, the three-roll bending forming process of a semi-circle-shaped workpiece with 3,105 mm (length)?×?714 mm (width)?×?545 mm (height) is simulated with FEM established by the optimum tool and process parameters. Manifested by the experiment for three-roll bending forming of this workpiece, the numerical simulation method proposed yields satisfactory performance in tool and process parameters optimization and workpiece forming. It can be taken as a valuable mathematical tool used for three-roll bending forming of large area sheet metal.     

Study on multiple-step incremental air-bending forming of sheet metal with springback model and FEM simulation

A mathematical model of springback radius was developed with dimensional analysis and orthogonal test. With this model, the punch radius could be solved for forming high-precision semiellipse-shaped workpieces. With the punch radius and other geometrical parameters of a tool, a 2D ABAQUS finite-element model (FEM) was established. Then, the forming process of sheet metal multiple-step incremental air bending was simulated with the FEM. The result showed that average errors of the simulated workpiece were +0.68/?0.65 mm, and provided the process data consisting of sheet feed rate, punch displacement and springback angle in each step. A semiellipse-shaped workpiece, whose average errors are +0.68/?0.69 mm, was made with the simulation data. These results indicate that the punch design method is feasible with the mathematical model, and the means of FEM simulation is effective. It can be taken as a new approach for sheet metal multiple-step incremental air-bending forming and tool design.     

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.     

Contact simulation for predicting surface topography in metal forming

A surface contact model that takes account of flattening, roughening and tool elastic microwedge effects on workpiece surface is developed. The model can be implemented in FEM codes to predict the final surface qualities of the products in metal forming. As an example, the proposed model has been combined with a membrane finite element code of sheet metal forming process to predict the contact area ratio, surface roughness and mean asperity spacing. Numerical results showed good agreement with the experiments.     

Smoothing Parametric Design of Addendum Surfaces for Sheet Metal Forming

The manual design of addendum surfaces on common CAD platforms is very tedious which requires many trialscorrections, which will certainly a ect the construction e ciency and quality of addendum surfaces, and then a ect the formability and quality of the workpiece in the process of sheet forming. In this paper, an automatic procedure based on parametric design method is proposed for the rapid construction of the addendum surfaces. The kernel of the parametric method is constructing boundary curves based on the shape of surfaces of workpiece and designing guide curves based on Hermite curve interpolation. By some simple parameters, the shape of the addendum surfaces could be controlled and adjusted easily. In addition, a minimum energy optimization method is employed to further optimize the constructed addendum surface. A finite element analysis for the sheet forming process is performed to evaluate the forming quality of constructed addendum surfaces. The instance illustrates that the addendum surface constructed by the proposed method could ensure both the overall smoothing of surfaces and the final forming quality, and it has a good e ect on springback after forming. This research proposes a smoothing parametric design method for addendum surfaces construction which could construct and optimize addendum surfaces rapidly.     

Study on design of progressive dies for manufacture of automobile structural member using DP980 advanced high strength steel

Advanced high-strength steel (AHSS) is widely used in automobile manufacturing to reduce the weight of vehicles, thereby improving fuel efficiency. However, the high yield and tensile strength of AHSS leads to a serious springback problem in the cold sheet metal forming process. This phenomenon has delayed the implementation of AHSS in vehicle parts due to the resulting negative impact on part accuracy. In this study, parameter optimization and multi-stage die compensation were conducted with Finite element (FE) analysis to develop a progressive forming process for automobile structural members using DP980. The FE simulation used the Yoshida-Uemori model to predict the springback phenomenon accurately. The key parameters that significantly influence the springback behavior were optimized using FE simulation and the Taguchi method. The simulation results were used to determine the die and mold compensation. After the parameter optimization and multi-stage die compensation, the final part was obtained with acceptable dimensional accuracy.

     

有限元逆算法与板料成形工艺的评价

依据理想形变理论，研究开发了冲压成形过程模拟的有限元逆算法，根据变形体的整体塑性功取相对极值的条件，导出了塑算法有限元方程。提出了求逆算法初始解以及求解与给定形状的毛坯相对应的冲压件形状的迭代计算方法。采用有限元塑算法预测了与冲压件形状相对应的冲压件毛坯的展开形状，根据给定的板坯形状计算了冲压件最终构形及应变分布。分析计算实例表明，逆算法可用于对板料成形工艺方案进行快速评价，对冲压工艺参数进行优化。     

汽车覆盖件冲压成形仿真研究进展

汽车覆盖件冲压成形仿真技术的发展,突破了原有汽车冲压件模具及工艺设计的设计方法,对保证工件质量、减少材料消耗、缩短产品开发周期、降低制造成本具有重要意义.概述了目前汽车覆盖件冲压成形仿真所涉及到的热点领域,如摩擦与接触、回弹分析、模具系统和工艺参数、材料屈服模型和板料形状设计,讨论了这些领域的研究进展和进一步研究的发展方向.     

The study for stability of closed-loop control system based on multiple-step incremental air-bending forming of sheet metal

To solve the springback problem for sheet metal forming, feedback control idea in automatic control theory is introduced to incremental air-bending forming process. The advanced control techniques are used to solve precision forming for workpiece of sheet metal. However, stability, accuracy, and rapidity of closed-loop control can directly affect system normal operation. Aiming to analyze the effect of stability on the quality of the formed workpiece, a closed-loop control system model for incremental air-bending forming is established. The transfer function and characteristic equation of the closed-loop system are solved through theory deduction and minor incremental linearization method. Both simulations with Matlab/Simulink and root locus results show that, as the overall gain is equal to one, the shape of formed part could converge to the target shape at the fastest rate. Finally, a semiellipse-shape workpiece is manufactured with the corrected mold obtained by the closed-loop forming method. The experimental results show that the closed-loop forming way is feasible and the means of correcting the mold parameters by iterative compensation of the stable closed-loop control system is effective. It can be taken as a new approach for sheet metal incremental air-bending forming and mold design.     

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。