覆盖件冲压仿真参数化建模方法

针对在覆盖件冲压成形领域对快速、自动化的有限元网格建模方法的迫切需求,提出一种快速的汽车覆盖件冲压仿真建模的思路与方法.将覆盖件冲压工艺设计与冲压成形仿真前处理集成,使用散乱三角面片模型,在自主开发的CAE前处理软件中,进行参数化的工艺补充面和压料面设计.模型的网格剖分与冲压工艺设计同时进行,自动生成整套模具的网格模型供冲压仿真计算.为了真实地模拟板料网格的流动,提出了参数化的真实拉深筋的模型建模方法和板料网格的预细分方法.完成了相关软件的开发.多个汽车覆盖件冲压工艺设计和冲压仿真计算实例说明了该方法的有效性.     

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.     

冲压成形中凹模入口角曲线优化

冲压成形时,凹模入口角的形状对模具与工件之间的摩擦、冲压件表面质量以及模具使用寿命均有着重要的影响。为能获得最优的凹模入口角,提出了采用三次样条曲线作为凹模入口角曲线的新工艺方法。以板料与凹模入口角处的摩擦力做功为研究对象,基于响应面和试验设计方法,在满足成形质量前提下,优化凹模入口角曲线。结果表明:采用优化后的三次样条曲线进行凹模入口角设计,可以减小凹模入口角处的摩擦力做功,且摩擦力做功分布较均匀;可延长模具使用寿命,并可以提高工件表面质量。     

Optimization of sheet metal forming processes by the use of space mapping based metamodeling method

In this study, an adaptive space mapping technique based on response of objective was suggested for solving practical engineering problems. Response surface methodology was engaged in approximation of objective and constraint functions based on coarser model. The fine simulation model is not only used for correction of the coarser simulation model and validation of final solution but also for applied construction of space mapping expression. Finally, genetic algorithm (GA) was used to optimize updated metamodel according to coarse model. The proposed method combines the space mapping technology based on response of coarse model and modification of design of experiment. It guarantees that metamodel based coarser model is stepwise updated in the right searching direction. For demonstrating practicability of developed method, it was applied for optimization of geometric parameters of addendum surface, blank holder force and drawbead restraining force in sheet forming problems. It was confirmed that the corresponding problem can be optimized successfully in remarkably short computing time by proposed optimization method.     

考虑接触演变的板材回弹过程建模与优化

回弹是由工件在卸载后的弹性变形引起的。板料成形过程中为了控制成形件的最终形状,必须进行回弹设计优化。准确预测回弹对于板料成形过程的模具设计非常重要。降低回弹模拟结果与试验结果的偏差是设计过程中的难题。基于NUMISHEET’02的自由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回弹。采用一个常规的优化方法对有限元分析中的材料和单元模型进行了分析,研究发现不同模型对回弹结果有较大影响。模拟结果与参考文献中的试验结果比较表明了模型的正确性和可行性。     

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.     

板料拉深成形数值模拟中动态边界条件的处理

针对板料拉深成形过程中工件与模具接触边界的动态变化,将模具表面离散为若干个三角形单元,并用参数方程来描述工件节点及模具三角形单元的运动情况,将工件与模具的接触问题转化为空间直线与平面的动态求交问题。在此基础上,通过实际的模拟分析,证明该处理方法的可行性。     

基于扫描面的汽车覆盖件工艺补充设计

工艺补充面与压料面是覆盖件模具冲压成形的重要技术。大量试验及CAE仿真结果已经充分证明:补偿面和压料面的形状和形态对板材的成形性影响很大。在以往的覆盖件模具设计过程中,用户都是凭借设计经验,在三维CAD软件中手工地构造和生成这种补充面与压料面,其设计效率很低。针对曲面生成的难点,提出了基于B 样条扫描曲面的工艺补充设计方法,论述了扫描曲面的生成原理及实现方法。根据覆盖件成形特点,给出了基于扫描面的工艺补充和压料面生成算法。并结合实例编制了相应的程序,论证了其可行性。与在有限元网格意义下的生成方法比较,最大的优点是:提出的生成方法可以直接用于进行数控加工,同时,许多自动化和自适应的设计过程又能够明显提高设计效率。     

金属薄板开槽弯曲成形技术与设备

V形弯曲成形前，对金属薄板折弯处进行一定深度的V形开槽，然后在V形开槽处进行弯制成形，此种加工方法称之为V形开槽弯曲成形技术。用V形开槽弯曲成形技术弯制的工件弯曲圆角半径小，色泽变化不明显，弯制成形力小，且减少了窄长工件弯曲棱边直线度误差。并在普通折弯机上用通用模具就能弯制断面形状复杂的工件。V形开槽弯曲成形技术的关键设备是薄板开槽机，有多种结构形式和控制方式供选择。     

Optimization of drawbead design in sheet forming using one step finite element method coupled with response surface methodology

In a sheet forming process, drawbead plays an important role on the control of the material flow. In this paper, a numerical procedure for the design of forming processes is described. It is based on the coupling of an optimization technique and the simplified one step finite element method (also called inverse approach). The optimization technique allows adjustment of the process parameters so that specified criteria are fulfilled. Response surface methodology (RSM) is a global approximation method, which is ideally suited for solving highly nonlinear optimization problems. The finite element method, in addition to predicting the response of the process to certain parameters, allows assessment of the effect of a variation in these parameters on this response. The authors utilize the one step method at the preliminary design stage to supply stress or strain information for the following optimization using RSM. The procedure for this optimization process is fully described. The front fender for Numisheet 2002 is presented and the real defect free workpiece is produced to demonstrate the usefulness of the proposed optimization procedure. A comparison between the two forming limit curves (FLC) before and after optimization and results obtained using the precise incremental commercial software DYNAFORM based on the explicit dynamic approach verify that the optimization design method of drawbead could be successfully applied in designing actual tools of auto body cover panels.     

基于CAE技术的汽车覆盖件拉延模具设计

介绍了在CAE技术基础上进行的汽车覆盖件模具设计过程,利用板料成形有限元分析软件Autoform实现了模具压料面、工艺补充面以及拉伸筋设计和覆盖件成形过程模拟。实现了在有限元软件内部进行模具的参数化设计,既缩短了模具设计时间,又提高了模具设计可靠性。     

Blank shape design for a planar anisotropic sheet based on ideal forming design theory and FEM analysis

A sequential design procedure to optimize sheet forming processes was developed utilizing ideal forming design theory, FEM analysis and experimental trials. For demonstration purposes, this procedure was used to design a blank shape for a highly anisotropic aluminum alloy sheet (2090-T3) that results in a deep-drawn, circular cup with minimal earing. All blank shape design methods require a certain number of iterations. However, the sequential procedure can be more effective than the other iterative methods based on FEM analysis in conjunction with experimental trials or on experimental trials alone. For this design demonstration, the anisotropic constitutive behavior of the 2090-T3 sheet was expressed using plastic potentials previously proposed by Barlat et al. The implementation of the anisotropic strain-rate potential in the ideal forming design code is also briefly summarized.     

曲面修改在逆向工程中的应用研究

针对汽车A—class特征曲线高精度、高光顺性的基本要求,提出了基于控制顶点规范的Bezier曲面迭代微调方法,用曲面反算变换为NURBS曲面,经过基于最小弯曲能曲面修改以后,对进行外形优化。该法核心是控制顶点的微调计算和基于最小弯曲能曲面修改,实现对空间型值点的光顺拟合,实现迭代拟合过程的快速收敛,同时实现了曲面微调和曲面修改的自动化,使基于逆向工程得到的复杂曲面不仅满足精度要求,更可以进行美学设计。结合某汽车的A级曲面的点云数据实例,应用迭代微调有效地提高了生成CAD数据的效率和准确性。     

On finishing of pressing die surfaces using machine hammer peening

Machine hammer peening (MHP) is a new method for finishing of surfaces. With this method, the workpiece surface is hammered with a spherical carbide tool. The main objective of the study was to evaluate whether the MHP method could become a plausible substitute for manual polishing in pressing die manufacturing where nodular cast iron is a common workpiece material. To do this, sample nodular cast iron surfaces were hammered and evaluated. Changes to the surfaces were evaluated using surface roughness measurements, hardness measurements and optical images. First of all, the workpiece surface was smoothened. Secondly, the surface hardness was increased significantly. Thirdly, the nodules on the workpiece surface were affected. They appeared to be smaller and not as visible. This effect would likely create a die surface less prone to galling since the cavities would not be filled with sheet metal to the same extent in a forming operation. In addition, with MHP, the amount of polishing needed to manufacture a die surface can be reduced because of the smoothening effect.     

数值模拟技术及其在冲压加工中的应用

应用Autoform数值模拟软件的板料成形仿真技术,以某筒形件为例,探讨了从CAD造形到CAE拉深成形数值模拟的全过程,预测了板料在成形过程中可能出现的缺陷,为模具制造过程中及时修改和优化冲压工艺方案以及有效解决模具形状参数化调整问题节省了大量时间,同时为模具设计提供了可靠性保证。     

Generation and suppression of local severe plastic deformation in sectional multi-point forming

Sectional multi-point forming (SMPF) technology provides a new solution for forming large-size sheet metal. With this technique, large-size parts of sheet metal can be manufactured on a smaller multi-point forming press. But the force status and deformation of the workpiece are complicated in SMPF; the local severe plastic deformation will be produced easily in the transition region, and strain-hardening will be commonly produced subsequently. The hardening is difficult to eliminate in subsequent processes, which will largely affect the final deformation quality. In this paper, the generation of local severe plastic deformation was discussed; NURBS-based modeling method was used to construct the shape of the assortative region to suppress the defect. Experiments proved that the method is fairly effective. Finally, a plan was suggested to raise further the forming limit of materials and enhance the work efficiency by combining multi-point press forming with assortative region method.     

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。     

Study of multi-point forming for polycarbonate sheet

The multi-point forming (MPF) process of polycarbonate (PC) sheet is introduced briefly, geometrical relationship between objective surface and punch element is determined, and a simple calculation scheme of punch height is developed. Numerical simulations of spherical and saddle-shaped parts are carried out by dynamic explicit finite element analysis; the effects of forming temperature, forming pressure, punch matrix, and punch radius on the forming quality are investigated, and the suitable forming parameters are determined. Then, the MPF experiments of PC sheet for spherical and saddle-shaped parts based on the forming parameters are done, and the comparisons of shape error between experimental parts and object surfaces are carried out. Consequently, the PC products have good shape accuracy, which confirms that MPF used for forming PC sheet is feasible and the forming parameters obtained by numerical simulation are sensible.     

大型U形板材工件渐进滚弯成形数值模拟

利用ABAQUS有限元分析平台,对大型U形板材工件渐进滚弯成形及其回弹过程进行数值模拟,其中工件材料类型选择普通低碳钢。针对半椭圆形工件形状,提出用半径不同的五段圆弧逼近的几何规划。在此基础上,根据加工过程可能出现的缺陷,合理设计滚弯道次,调整ABAQUS参数设置。用模拟优化的工艺参数成形加工半椭圆形板材工件,经origin8拟合配准,其各段曲率半径最大误差小于5%。模拟结果表明,用渐进滚弯方法成形加工半椭圆形工件是可行的,且模拟过程满足准静态响应的要求。     

基于CATIA的某钣金件参数化逆向设计

介绍了CAD开发平台CATIA V5在钣金类零部件设计中的运用,通过采用自定义的CATIA V5参数化设计模板,对某钣金件进行了实例设计,利用其参数化的建模过程,便于优化和改进设计,提高了零件设计质量,缩短了设计时间。