Industrial applications of sheet stamping simulation using new finite element models

The paper is aimed to present industrial applications of sheet stamping simulation using new finite element formulations developed in the International Center for Numerical Methods in Engineering in Barcelona. Theoretical formulation is briefly reviewed. Both continuum and shell elements have been considered. The new shell elements developed are based on a geometrically exact shell model treating the shell as one-director Cosserat surface. The formulation of the continuum elements employs the multiplicative decomposition of the deformation gradient tensor into its elastic and plastic parts. The new finite element models have been implemented in the in-house explicit dynamic code STAMPACK. A number of practical problems of sheet metalforming have been solved with the program. Some of the problems, namely stamping of a kitchen sink, hydraulic forming of an aeronautical part and stamping of a food can, have been presented in the paper. The examples give an idea of practical information that can be obtained from the computer simulation of a forming process. The results confirm a good behaviour of the formulation and program used in the industrial applications.     

环件轧制过程的显式有限元模拟分析

用于金属成形模拟的有限元方程的求解方法 ,主要有隐式和显式积分两种方法。对于复杂的三维变形分析 ,如环件轧制 ,隐式方法需要很长的运行时间。而利用显式方法 ,可以达到很好的效果。本文利用Abaqus /Ex plicit通用有限元程序对径向环轧进行了模拟。     

Studying grain fragmentation in ECAE by simulating simple shear

A crystal plasticity based finite element model is developed to simulate grain fragmentation during equal-channel angular extrusion (ECAE). Route C multiple passes are approximated by repetitive planar simple shears. Results are presented in terms of plastic strain distribution, texture and grain size evolution. Numerical results are found to be in qualitative agreement with experimental observations associated with the grain refinement in ECAE.     

半球形凸模拉深过程的动力显式有限元分析

本文基于连续介质力学及有限变形理论 ,建立了用于三维板料成形过程分析的有限元模型 ,开发了动力显式算法的板料成形过程模拟的有限元分析程序DESSFORM3D。采取集中质量矩阵 ,用动力显式积分的方法 ,使位移计算显式化 ,避免了由材料、几何、边界条件等高度非线性因素引起的计算收敛问题。对半球形凸模拉深过程进行模拟计算 ,并把模拟结果与实验结果进行对比 ,验证了软件的计算结果     

The determination of initial blank shape by using the one-step finite element method and experimental verification

Many process parameters have an effect on the sheet metal forming process. A well-designed blank shape causes the material to flow smoothly, reduces the punch force, and yields a product with a uniform thickness distribution. Therefore, the determination of an initial blank shape plays the important role of saving time and cost in the sheet metal forming process. For these reasons, some approaches to estimate the initial blank shape have been implemented. In this paper, the one-step approach using a finite element inverse method will be introduced to predict the initial blank shape. The developed program is applied to several sheet metal forming examples for the demonstration of its validity. Moreover, the usefulness of the developed one-step approach program is investigated as compared with the FAST-3D program, which is a commercial package that is commonly used. Finally, the verification will be performed by comparing the predicted and experimental results.     

基于有限元分析的汽车覆盖件模具设计及优化

介绍了静力隐式弹塑性有限元板料成形软件AutoForm的基本理论和关键技术。利用AutoForm软件实现了汽车覆盖件模具设计,包括模具压料面、工艺补充面以及拉延筋设计,完成了覆盖件成形过程模拟及优化,改变了传统的在有限元模拟后依靠CAD软件频繁进行模具修改的方法。在有限元软件内部实现了模具的参数化设计,既缩短了模具设计时间,又提高了模具设计可靠性。     

Finite element analysis of tailored sheet forming processes considering laser welding zone

The finite element formulation for predicting strain distributions and weld line movements in the forming processes of tailored sheet metals is developed. The material properties of the welding zone such as strength coefficient, work-hardening exponent, and plastic anisotropic parameter are analytically obtained from those of base metals based on the tensile tests. The welding zone is modelled with the several, narrow finite elements called by weld elements. To verify the finite element formulation for tailored blanks, the forming processes of autobody door inner panel section and hemispherical dome are simulated. FEM predictions are compared and showed good agreements with experimental measurements.     

Simulation of grinding processes using finite element analysis and geometric simulation of individual grains

The wear-resistance of sheet metal forming tools can be increased by thermally sprayed coatings. However, without further treatment, the high roughness of the coatings leads to poor qualities of the deep drawn sheet surfaces. In order to increase the surface quality of deep drawing tools, grinding on machining centers is a suitable solution. Due to the varying engagement situations of the grinding tools on free-formed surfaces, the process forces vary as well, resulting in inaccuracies of the ground surface shape. The grinding process can be optimized by means of a simulative prediction of the occurring forces. In this paper, a geometric-kinematic simulation coupled with a finite element analysis is presented. Considering the influence of individual grains, an additional approximation to the resulting topography of the ground surface is possible. By using constructive solid geometry and dexel modeling techniques, multiple grains can be simulated with the geometric-kinematic approach simultaneously. The process forces are predicted with the finite element method based on an elasto-plastic material model. Single grain engagement experiments were conducted to validate the simulation results.     

Predictive modeling of grain refinement during multi-pass cold rolling

Recently, grain refinement and grain misorientation have been experimentally studied for various materials with ultra-fine grained microstructures, which are achieved by the multi-pass cold rolling process. In this paper, a numerical framework is developed to model the evolution of grain size and grain misorientation based on a dislocation density-based material model. Novel finite element models embedded with the dislocation density-based material subroutine are developed to model the plastic deformation and microstructural evolution during the multi-pass cold rolling process. The multi-pass cold rolling processes of commercially pure titanium (CP Ti) and aluminum (AA 1200) are simulated in order to assess the validity of the numerical solution through comparison with experiments. The dislocation density-based material models are developed for CP Ti and AA 1200, which reproduce the observed material constitutive mechanical behavior under various strains, strain rates and temperatures occurring in the cold rolling process. It is shown that the developed model captures the essential features of the material mechanical behaviors and predicts a minimum grain size of below 100 nm after five-pass cold rolling of CP Ti with equivalent strains up to 2.07 and the average incidental dislocation boundary (IDB) misorientation angle increased to 4.6° after six-pass cold rolling of AA 1200 with equivalent strains accumulated to 5.77.     

Modified looping technique for remeshing of forming simulations with free surface folding

In finite element simulations of forming processes with a complex geometry, free surface folding phenomenon is likely during simulations when die design or the size of initial billet is inappropriately determined. In such cases, free surface geometry becomes so acute that mesh generation may be impossible with a conventional looping technique automatically. In order to solve this kind of problem, looping technique was modified to generate boundary elements for the acute geometry with a better mesh quality. The developed technique was implemented to the in-house bulk metal forming simulation program CAMPform and applied for forming simulations of ring gear forging and nosing in which surface folding defects occur. It was found that folding phenomenon was successfully handled with the currently developed algorithm and suitable process conditions to eliminate the free surface folding were determined through numerical simulations.     

单曲率板材激光弯曲成形过程的有限元模拟

利用有限元软件MSC.Marc建立了单曲率板激光弯曲成形过程的热力耦合有限元模型。计算并分析了激光弯曲成形过程中板材内部的温度场、应力场和位移场。此外,还研究了扫描线的长度和单曲率板的初始形状对激光弯曲成形的影响。结果表明:随着扫描线长度的增加,板材的弯曲变形量增大;随着单曲率板曲率的增加,板材的弯曲变形量减小。实验结果验证了模型的可靠性。     

连轴体成形工艺模拟分析

根据连轴体件凸缘较宽、凸台较高且直径较小、壁厚不均匀等结构特点及成形难点,制定了拉深和挤压2种工艺方案。采用有限元数值模拟,对2种成形工艺的模拟结果分析表明：采用拉深工艺时,成形力小,成形质量差;采用挤压工艺时,成形力大,成形质量好。通过对挤压工艺坯料形状的改进,降低了成形载荷并提高成形质量。     

热成形TA32钛合金薄壁件的形状控制与性能优化

为了优化TA32钛合金薄壁件的热成形工艺,对其热流动行为、显微组织演变和断口形貌进行研究.根据实验数据建立一套基于合金显微组织的本构方程,描述高温流动应力与相体积分数、位错密度、晶粒尺寸和损伤演化之间的关系.将本构模型嵌入ABAQUS 6.14中模拟典型薄壁件的热成形过程,预测不同工艺参数下成形件的等效应变、位错密度、...     

超声波加工硬脆材料机理的有限元分析

通过非线性有限元程序LS-DYNA,模拟金刚石磨粒冲击玻璃材料过程中裂纹的产生和材料去除情况,分析超声加工硬脆材料的去除机理.     

T型管接头挤压胀形过程的有限元分析

根据T形管挤压胀形双重非线性的变形特点，建立了动力分析有限元方程。开发了在HP715／50工作站上运行的程序软件SFMP。对T形管挤压胀形过程及主要因素的影响进行模拟分析，总结归纳了分析结果。     

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。     

Finite element simulation of aluminum alloy cross valve forming by multi-way loading

Deformation behavior, temperature evolution and coupled effects have a significant influence on forming process and quality of component formed, which are very complex in forming process of aluminum alloy 7075 cross valve under multi-way loading due to the complexity of loading path and the multiplicity of associated processing parameters. A model of the process was developed under DFEORM-3D environment based on the coupled thermo-mechanical finite element method. The comparison between two process models, the conventional isothermal process model and the non-isothermal process model developed in this study, was carried out, and the results indicate that the thermal events play an important role in the aluminum alloy forming process under multi-way loading. The distributions and evolutions of the temperature field and strain filed are obtained by non-isothermal process simulation. The plastic zone and its extension in forming process of cross valve were analyzed. The results may provide guidelines for the determination of multi-way loading forming scheme and loading conditions of the forming cross valve components.     

Through-process macro–micro finite element modeling of local loading forming of large-scale complex titanium alloy component for microstructure prediction

The intrinsic multi-heat unequal deformation behavior of the local loading forming requires a through-process macro–micro model to characterize the microstructure evolution during the forming process. In the present work, the phenomena and mechanisms of microstructural developments in local loading forming of titanium alloys are summarized. Mechanism-based unified material models, which characterize the through process microstructure evolution, are developed for integrated prediction of constitutive behavior and microstructure. A through-process macro–micro finite element model is established for the local loading forming of large scale complex titanium alloy component. The model can predict the microstructure evolution as well as macroscopic deformation in multi-step local loading forming process. Model predictions are in good agreement with experimental results. The microstructure evolution in local loading forming is investigated by the established finite element model. It is found that the thermo-mechanical processing route greatly affects the volume fraction of primary alpha but has little influence on the grain size in local loading forming     

弹塑性大变形有限元分析槽钢成型过程的位移场和速度场

应用弹塑性有限元方法, 同时考虑材料和几何双重非线性, 研究槽钢辊弯成型的位移场和速度场。文中有效的处理了动态位移加载模型, 采用三维实体单元基于 Ｐｒａｎｄｔｌ Ｒｅｕｓｓ 流动规律和 Ｍｉｓｅｓ 屈服准则及 Ｕｐｄａｔｅｄ ｌａｇｒａｎｇｉａｎ 增量迭加法分析槽钢由非稳态到稳态成型过程中金属的流动规律, 然后通过有限元程序实现了计算机冷弯成型过程的真实模拟。     

一种耦合晶粒长大的超塑性本构及数值模拟

本文基于弹粘塑性有限元技术 ,将经过修正的晶粒长大模型耦合到材料粘塑模型中 ,得到一个考虑晶粒行为的超塑材料本构模型。利用所建立的考虑晶粒效应的本构模型和经典的Backofen本构模型 ,分别对Ti 6Al 4V圆杯进行超塑性成形模拟 ,其厚度分布结果表明 ,新本构能很好地描述晶粒敏感型材料的超塑性能。