On the prediction of the effect of process parameters upon forming limit strains in sheet metals

Plasticity analysis of sheet metal forming requires a detailed knowledge of the influence of process parameters on the stress–strain relationships from yielding up to localized necking, for accurate prediction of forming limits. Achievable strain and stress–strain relationships are sensitive to modulations in process parameters, chiefly temperature and strain rate. However, the effects of changes in strain rate and temperature are often complex as they also depend on the levels of strain, strain rate and the temperature employed. Such variations could be either triggered by the process dynamics of the forming operation or imposed for optimal exploitation of the material ductility. In this study, the influence of such process parameter modulations upon formability has been theoretically modelled, following the Sing–Rao prediction approach. The limit strains thus predicted compare favourably with experimental results for a drawing steel, thus validating the present formalism. This approach can also be adopted to accommodate non-linear straining conditions. Thus, theoretical modelling of strain-path-dependent forming limits, which has not been explored adequately so far, now becomes feasible.     

A theoretical and experimental investigation of limit strains in sheet metal forming

The paper deals with an analytical technique for predicting FLDs based on linear, bilinear and trilinear straining paths—although any general curvilinear strain path can be handled by the method. The analytical procedure was based on the work of Marciniak and Kuczynski (known as the M-K model). The influence of material properties, such as anisotropy, strain hardening and strain rate sensitivity, as well as the effect of strain path, on the shape and level of the FLD were investigated. Material property data were determined from tests on Interstitial Free (IF) steel sheet.An experimental FLD was constructed for the IF steel sheet in the as-received condition. Additional FLDs were also produced following pre-straining of the as-received sheet. Comparison between the experimentally determined FLDs and those predicted from the theoretical model was favourable.Conventional FLDs are constructed in strain space with the principal surface strains as coordinate axes. However, they can be plotted in principal stress space, and some investigators have claimed this is a better representation. By knowing the strain path the stress state at the limit strain can be determined, and these limit stresses were plotted in principal stress space in order to construct a Forming Limit Stress Diagram (FLSD). It turned out that regardless of the shape of the FLD and the type of pre-strain imposed, all the FLSDs were almost identical. In contrast when plotted in strain space the FLD was very sensitive to the type of straining path.     

模具温控成形技术及其应用于凝固过程数值模拟的研究进展

首先介绍了模具温控成形技术的方法和工艺.然后具体到凝固成形,分析了其数值模拟的研究现状.最后指出了模具温控成形技术是一种新的工艺优化和质量控制方法,有重要的研究意义.并将其应用于凝固成形,提出了进一步研究设想,可提供新的解决收缩缺陷及其他缺陷的有效途径.     

等效拉延筋模型及其在板料成形数值模拟中的应用

讨论等效拉延筋的建模方法、常用模型及其在板料成形数值模拟中的应用情况,并指出研究中仍存在的问题及今后的发展方向。     

板料屈服行为及强化规律的研究进展

研究板料塑性成形的理论基础是屈服准则、强化规律以及本构模型。随着新材料、新工艺的不断出现,温度和应变速率对塑性成形过程中的影响也不容忽视,原有的塑性理论已无法满足研究和工程应用的需求。从板料屈服准则研究、包辛格效应与强化模型研究、屈服强化规律试验方法研究以及涉及应变速率和温度的板料屈服强化研究4个方面阐述板料屈服行为及强化规律的研究进展,指出常用屈服准则的特点和不足,说明各种强化模型中组合强化模型仍然是研究重点。试验方法主要从研究屈服轨迹的双向拉伸试验及确定强化模型参数试验的2个方面进行介绍。此外,指出针对板料在复杂应力状态下应力张量与应变张量之间的涉及应变率和温度的屈服准则和相应的流动准则的本构关系还有待研究。提出随着新材料、新工艺的不断出现,涉及应变速率和温度的屈服准则和强化规律、试验方法以及在有限元模拟中的应用等研究将是未来的研究热点。     

An anisotropic damage-based plastic yield criterion and its application to analysis of metal forming process

Based on the continuum damage mechanics (CDM), both the total damage growth force and the damage equivalent stress has been firstly derived. Material and damage are considered to be anisotropic in this theoretical model. A new damage-based plastic yield criterion, where the damage equivalent stress is taken as the yield function, and the corresponding damage evolution equation has been established. A relation between the damage variable and the plastic deformation has been proposed. This relation can be applied to obtain the damage history in terms of Moiré photo-mechanics technology in this work. In addition, from the anisotropic damage-based plastic yield criterion presented, the large-scale finite element codes ABAQUS/Explicit in conjunction with the damage experimental results has been then used to calculate some mechanical variable fields in metal forming process. It has finally been verified that the position corresponding to the maximum value in damage equivalent stress field accurately coincides with the initial place of macro-crack given by Erichsen cupping tests carried out by authors.     

Effects of plastic anisotropy and yield criteria on prediction of forming limit curves

The effects of yield criteria on predictions of the right-hand side of forming limit diagrams (FLDs) are investigated. Predictions of limit strains are determined from an initial imperfection model based on the early work of Marciniak and Kuczynski (1967). Particular attention is placed on the effect of normal plastic anisotropy on limit strains during biaxial sheet stretching. The anisotropic yield criteria investigated in this paper include Hill’s (1948) quadratic criterion, Hosford’s (1979) higher-order criterion, and case 4 of Hill’s (1979) non-quadratic criterion. Several important characteristics of the yield surface shape are discussed and a new parameter that quantifies some of these aspects is introduced. Similar to the work of Barlat (1987), this parameter is based on the relative position of plane strain on the yield surface and can be used to predict the various effects of yield criteria on limit strains. Results indicate that predictions of FLD are very sensitive to selection of yield criteria.     

Predicting of plastic instability and forming limit diagrams

An analytical method is presented for predicting forming limit diagrams achieved during sheet metal forming operations for sheets having planar isotropy. This method is based on the three-phase deformation idealization developed by Johns and Gillis. The Johns–Gillis and Pishbin–Gillis model were restricted to the Hill yield criterion which is not suitable for aluminum alloys (R<1). The present work used the Hosford criterion that is widely used for materials with R<1, in conjunction with the power-law, the Tian–Zhang and the Vocé hardening equations. Results from this analysis are compared with the experimental data for AA3105 and AA8011 aluminum alloys. The results indicate good prediction of limit strains for the two alloys when the Vocé and the Tian–Zhang equations are applied.     

玻璃成形数值模拟技术研究概述

玻璃成形模拟技术的研究既具有重要的理论意义又具有广阔的应用前景,经过长期的研究和探索,人们对它的认识不断加深,研究范围不断扩大。但总体来说,目前对玻璃成形模拟技术的研究还较为薄弱,不够系统和深入,还需作更进一步的研究。这里对玻璃成形模拟技术的研究现状进行了综述。     

An evaluation of some recent yield criteria for industrial simulations of sheet forming processes

The present paper deals with material modeling in connection with sheet metal forming analyses. One purpose of the report is to discuss the special needs and demands of industrial analysts. With this in mind, in particular, the demands put on the yield condition are analyzed. Two recent yield criteria for anisotropic metal sheets, in the literature denoted Yld2000 and BBC2000, respectively, are found to be very well suited for industrial use. They do both belong to a group of yield criteria called the “Hosford family”. Practical issues with regard to these yield criteria, such as procedures for determining the parameters being part of the models, implementation issues, and numerical efficiency, are thoroughly discussed. A version of the above criteria, using a reduced set of parameters, is proposed, and is shown to offer a significantly reduced computing time at the cost of some loss of accuracy.     

基于数值模拟技术的吸塑模成型工艺优化

介绍了吸塑成型工艺过程,对吸塑成型的关键技术进行了阐述,包括运动函数的建立和成型时间的预测。基于Polyflow软件平台,以冰箱门体内胆吸塑模为例,通过对吸塑模成型过程的分析,对吸塑成型工艺过程进行了数值模拟分析。模拟结果表明:在整个真空吸塑成型过程中,吹泡时间的长短是控制制件成型质量的关键。吹泡时间过短会导致制件厚度局部变薄不均匀;而吹泡时间过长,则会出现局部折皱和折叠。结合数值模拟技术和运动函数,实现了吸塑成型工艺参数的优化。     

空心工字钢冷弯成型过程的数值模拟

空心工字钢是一种新型断面型材,它由铜板经冷弯成型机组在室温下冷弯成两块近似M形型钢后再焊接在一起而成.设计了一种冷弯成型孔型系统,并利用Pro/E软件建立了空心工字钢冷弯成型机的虚拟样机.采用三维有限元方法,利用ANSYS-LS/DYNA软件对冷弯成型过程中的弹塑性变形过程进行了数值模拟,系统地分析了成型过程中的应力变化规律.研究结果对于冷弯型钢产品的开发、孔型系统的设计具有参考价值.     

马鞍面件多道次多点模具成形数值模拟

通过对马鞍面件多道次多点模具成形的有限元数值模拟,阐述了多道次多点模具成形数值模拟的关键技术,并与单工步多点模具成形进行比较,分析了马鞍面件的成形过程,研究了不同曲率半径步长对成形结果的影响.结果表明:多道次多点模具成形与单工步多点模具成形相比改善了板材的受力状况,达到了消除变形集中的目的;多道次多点模具成形时,随着曲率半径步长的减小,板料厚度分布越来越均匀,不易形成集中失稳.     

铝合金汽车覆盖件冲压成形回弹的仿真研究

简要介绍了用于冲压成形回弹的有限元基本理论,提出了复杂汽车覆盖件成形仿真的模式,并以汽车底座横梁外板为例,利用DYNAFORM软件,对其拉延、切边、冲孔和回弹的过程进行了仿真,通过仿真结果与实验结果的比较,证明了所得到的数值参数和仿真方法能获得比较可靠的仿真结果,对实际生产有一定的指导意义。     

Experimental and theoretical study on the hot forming limit of 22MnB5 steel

To reveal the effects of forming temperature and blank thickness on the formability of boron steel 22MnB5, which is represented by forming limit diagram, the hot forming limit experiments and B-pillar hot stamping simulations are conducted. Combined with air cooling test, the forming limit diagrams of boron steels with different blank thicknesses of 1.8, 1.6, and 1.4 mm and forming temperatures of 800, 700, and 600 °C are established. The relationships between the formability and the crystal structure of steel, the forming limit diagram, and the effect of blank thickness and forming temperature on the formability of boron steel are extensively investigated. A model for prediction of hot forming limit of 22MnB5 steel before the occurrence of phase transformation induced by cooling based on Oh's ductile fracture criterion and Logan–Hosford yield criterion is derived and verified by experiments. The research thus provides an in-depth understanding of the formability of 22MnB5 steel for its process determination and process parameter configuration in industries.     

螺旋焊管机组中成型机的设计及调型

介绍了螺旋焊管机组的组成和特点及成型机的结构及原理,并对成型机的调型进行了分析。     

多次冲压工序的数值模拟研究

通过对多次冲压件冲压过程的初步计算和动态仿真,直观地了解了整个冲压过程的各道工序的变形情况,包括应力、应变和厚度分布等,从而知道哪些位置是危险区,并对冲压工艺进行调整。根据模拟结果,设计模具、确定冲压参数,确保了模具设计的成功。     

板料成形中单元大小对回弹的影响研究

板料成形数值模拟的准确性在很大程度上取决于回弹模拟的精度。本文就 DYNAFORM软件中单元尺寸与回弹模拟计算的关系进行了研究 ,得出了相应的结论。     

自由风扇的数值模拟与实验研究

以某型强力扇为例,采用数值模拟与实验相结合的方法对其进行优化设计工作.实验结果与数值模拟计算结果对比表明,采用该方法进行自由风扇的设计是有效缩短自由风扇研制周期、降低研制成本的方法之一.     

钣制带轮近净成形技术及应用前景

钣制带轮以其精度高、节能、节材、动平衡好、无环境污染等特点,逐步淘汰铸/锻造后经机加工生产的其他形式的传统带轮,具有良好的社会效益和经济效益.钣制带轮是以金属板料为毛坯,经过落料、拉深等冲压工序制成圆筒状,然后将其装夹在带有顶压座的芯模上,使其随主轴一起旋转,通过若干不同齿形的旋压成形轮分别沿径向施加压力而成形.分析钣制带轮近净成形技术的研究现状,阐述应用近净成形技术生产带轮的优点,介绍带轮数控旋压设备的发展趋势,最后论述钣制带轮近净成形技术的发展以及应用情况.