相变诱发塑性钢板的时效回弹行为

在对冷轧相变诱发塑性钢TRIP780和烘烤硬化钢BH180两种钢板基本力学性能分析的基础上,通过U形件冲压成形试验分析这两种钢板的回弹对压边力和模具圆角半径变化的敏感性。对U形件冲压成形卸载后1 min至零件放置12周期间的回弹进行监测,重点对随时间变化的回弹即时效回弹进行详细的分析和讨论。采用X射线衍射对TRIP780钢中奥氏体体积分数随时效时间的变化趋势进行研究。结果表明,TRIP780钢不仅具有高强度、良好塑性和回弹大的特点,而且有显著的时效回弹,BH180基本没有时效回弹。TRIP780钢U形件卸载后1天内时效回弹最大,然后趋于稳定,卸载12周后时效回弹相对初始回弹的最大比例达到20%。X射线衍射结果表明时效回弹与相变诱发塑性效应有内在联系。TRIP780钢对压边力的变化更为敏感,可利用这个规律进行回弹控制。     

TRIP600钢板成形汽车前纵梁冲压工艺研究

TRIP高强度钢板具有高强度、高应变率变形时的高动态吸能特性,符合现代汽车用钢材料的发展趋势。基于有限元法对TRIP600的汽车前纵梁冲压成形过程进行数值模拟,通过调整坯料外形,改善了成形质量;采用多元非线性回归模型分别拟合成形工艺参数(压边力、摩擦因数和拉深筋阻力)与破裂目标函数及回弹目标函数间的非线性关系,并基于NSGA-II多目标遗传算法,进行了成形工艺参数的优化,进一步提高了成形质量。     

用数值模拟TRIP600汽车前翼子板成形研究

对使用新型高强度相变诱导塑性(TRIP)钢板拉深成形的某轿车翼子板进行研究,针对零件的拉深成形工艺,采用有限元模拟对成形过程进行仿真,通过分析定性地判断成形件的危险区域,并通过调整压边力、拉深筋的布置以及板料的形状等,定量地获得拉深成形过程中的工艺参数,实现了拉深成形工艺的优化,并最终得到合格的拉深件制品,为实际生产提供指导。     

汽车油底壳成形工艺数值模拟

采用Dynaform软件对某汽车油底壳的拉深成形过程进行了数值模拟.研究了压边力、凹模圆角半径以及有无拉延筋时对零件冲压成形的影响,通过FLD,厚薄图和成形结果对比,调整成形时压边力和凹模圆角半径,得到了优化的压边力和凹模圆角半径,为同类零件以及模具的设计提供参考.     

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。     

两种先进高强度钢板冷冲压成形的数值模拟

根据GB/T 15825.3-2008规定的极限拉深试验方法和HAT回弹测试试验方法,运用Dynaform软件对SZBS600和SPFH590两种先进高强度钢板的冷冲压成形过程进行了数值模拟,分析了压边力、摩擦因数对回弹的影响,探讨了试验钢的极限拉深性能,并进行了试验验证。结果表明:在相同的压边力下,试验得到的两种试验钢的回弹角基本相当,且均随压边力的增大而减小;模拟和试验得到的回弹角最大相差1.03°;当压边力为200kN时,随着摩擦因数从0.03增加到0.06后,模拟得到的SZBS600钢的回弹角从13.769°降至0.676°;试验得到的SPFH590钢和SZBS600钢的极限拉深比分别为2.150和2.175,模拟得到的在2.02.2之间,与试验结果基本吻合,证明了所建模型的正确性;两种钢的回弹和极限拉深性能相当。     

半球底直筒形拉深件成形极限实验研究

以半球底直筒形拉深件为研究对象,用实验的方法,从压边力、摩擦系数、凹模圆角半径等几个方面对半球底直筒形件进行成形研究,得到了各工艺参数对其成形极限的影响.即压边力、摩擦系数在一定范围内的增大,半球底直筒形拉深件的胀形区域减小,成形极限有降低的趋势.     

汽车行李箱内板拉深过程的数值模拟

行李箱内板是汽车覆盖件中的重要零件,生产中为了减轻汽车重量,可采用高强度钢板来成形。在板料成形基本理论的基础上,以高强度钢TRIP600为材料模型,采用有限元软件DYNAFORM对汽车行李箱内板拉深过程进行了模拟,获得了成形后的零件壁厚变薄率分布图、成形极限图和对称面的回弹值。结果表明,汽车行李箱内板在拉深过程中不易破裂,但容易出现起皱和回弹缺陷,形状冻结性差。该结果对提高汽车行李箱内板拉深件的成形质量具有重要的指导意义。     

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。     

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。     

双重拉深筋力能特性的实验研究

以双重拉深筋中最常见的双圆筋为对象，设计了专门的实验装置。通过大量实验，对拉深筋的阻力、压筋力和夹持力与其高度及各圆角半径间的关系进行了系统的研究。研究表明，拉深筋的阻力、压筋力和夹持力主要受其高度的影响，而拉深筋圆角半径的影响相对较弱；内侧拉深筋高度对拉深筋阻力的影响大于对压筋力与夹持力的影响，外侧拉深筋则相反，对压筋力与夹持力的影响较大。同时对双拉深筋与单拉深筋的力能特点进行了对比，指出双拉深筋的阻力可达到单筋的2倍以上，而压筋力和夹持力则明显大于单筋的2倍。提出了双拉深筋的设计调整原则。给出了双拉深筋的高度和圆角半径的合理取值范围。     

Semi-implicit numerical integration of Yoshida-Uemori two-surface plasticity model

A semi-implicit integration scheme was used to implement the Yoshida-Uemori two-surface model into the finite element method. Hill’s quadratic yield function was employed to account for the orthotropic behaviour of the metal sheet. The model was used to predict the cyclic simple shear response of DP-600. In order to evaluate the capability of the model for sheet metal forming, the model was used to simulate both the forming stage of a channel draw process in the presence of drawbeads and the subsequent springback stage. The results show that the model predicts the springback profile very well, especially at deeper drawbead penetrations.     

Electromagnetic blank restrainer in sheet metal forming processes

Electromagnetic blank restrainer (EMBR) is a new technology that was recently developed to control material movement in sheet metal forming processes. Magnetic attraction on the ferrous sheet metal is the intrinsic property of EMBR. Such magnetic force is quantified using Maxwell's stress tensor to assess the feasibility of EMBR in the sheet metal forming process. The 3D finite element analysis (FEA) of an electromagnetic system is conducted to determine the distribution of magnetic flux density on contacting surfaces of the sheet metal. The distribution is then used to estimate the magnetic force. Experiments have been conducted to measure the magnetic force and compare with results from the FEA. Biaxial-loading apparatus has been built to measure restraining forces on the sheet metal with blankholder, drawbead, and EMBR. All the restraining forces are put together in a chart to see where each method stands with respect to one another. In order to evaluate the quality of forming with each method, an experimental die has been built. The die forms a channel in a single stroke and provides a direct indication of how each restraining method controls blank movement in the die. The real advantage of EMBR lies in the effectiveness of force control and its flexible location in a sheet metal forming die. To prove this, a prototype has been built in a tryout die where house appliance panel is formed with blankholder and EMBR. EMBRs are locally installed in the die and actively controlled during the forming process. The part formed with EMBR shows a significant improvement in the forming quality. At the end of this paper, two immediate impacts that EMBR can bring to the sheet metal forming industry are also discussed.     

铝型材多点三维拉压复合弯曲成形工艺

轻量化薄壁型材三维弯曲结构件是高端装备制造业中一种难成形加工的关键零部件。针对此类制件的高精度、低成本的成形需求,提出一种拉弯-压弯相结合的铝合金型材三维弯曲成形工艺,设计多点联动的拉压复合成形单元体结构,通过水平方向由夹钳带动拉弯,垂直方向由各单元体上液压执行机构压弯,实现"W"形三维弯曲零件的成形,并研制成形装备样机。建立分析成形过程及回弹预测的数值仿真模型,通过试验对模型的有效性进行验证,仿真结果与试验结果回弹变形一致,回弹预测最大误差小于15%。此外,研究拉力对矩形截面型材拉压复合成形件回弹变形的影响规律,预拉伸力较补拉伸力对成形件的回弹减小趋势更为明显,当预拉伸力从零达到临界塑性应力Aσ_s时,总回弹减少了26.81%,为保证成形件不发生截面畸变和破裂等成形缺陷,确定了预拉伸力为Aσ_s、补拉伸力为0.3Aσ_s的最优工艺参数。所提出的多点三维拉压复合弯曲成形工艺解决了W形一类型材传统三维拉弯无法实现的多向曲率半径复杂弯曲成形的技术难题,为实现镜面对称结构件的成对一次成形提供了一种新方法。     

拉延筋对回弹的影响机理研究

采用拉延筋影响试验、平板拉伸试验,研究了板料过拉延筋后几何参数和材料参数的变化情况,结合翻边回弹试验和回弹一维分析方法,研究了拉延筋对回弹的影响机理。研究表明,板料过拉延筋后板内的残余应力和材料的硬化是影响回弹的关键因素;等效拉延筋模型即使能提供准确的拉延阻力,一般也难以满足精确计算回弹的要求。     

差厚激光拼焊板的拉延切边回弹特性

采用数值模拟和试验的方法,对厚度组合为1.2 mm/0.8 mm的激光拼焊板进行拉延切边工艺分析,重点就压边力大小、摩擦因数、凹模圆角等参数对回弹的影响进行研究,测量各工艺参数下拼焊板拉延切边的凸凹模圆角处的回弹角、总的回弹角和侧壁曲率,还测量出拼焊板成形中的焊缝移动和应力分布情况和分析相互联系,并与拼焊板拉延弯曲回弹进行比较。分析认为,与拉延弯曲回弹相似,压边力、摩擦因数、凹模圆角等工艺参数对拼焊板拉延切边回弹有着明显的影响,而压边力是关键因素;拼焊板拉延切边回弹和拉弯回弹都与焊缝移动有密切的关系,控制焊缝移动将有利于回弹的降低;相比之下,拼焊板拉延切边回弹比拉弯回弹要小。     

Effects of variable blank holder forces and a controllable drawbead on the springback of shallow-drawn TA2M titanium alloy boxes

Springback, which occurs during stamping of shallow-drawn titanium alloy sheets, can negatively influence the stamping accuracy and reliability of follow-up assembly and welding of parts and restrict the application of titanium alloy sheets when high precision is a requirement. Therefore, accurate prediction and control of springback in titanium alloy sheets is an industrial problem that requires urgent attention. In this paper, a TA2M titanium alloy box formed via shallow drawing is used as the research object and springback control during stamping is attempted by varying the magnitude and mode of the blank holder force (VBHF) and height of a controllable drawbead. The influences of drawbead height, VBHF magnitude, and loading mode on the resulting sheet springback are determined by means of finite element simulation and experimentation to determine the best combination yielding the minimum springback. The results of this research provide a reliable reference for future efforts to form tough materials.     

One-step FEM-based evaluation of weld line movement and development of blank in sheet metal stamping with tailor-welded blanks

Currently, more and more tailor-welded blanks (TWBs) are used in the automobile industry. It is very important to locate the weld line and predict its movement during the forming process. The initial weld line can be predicted by one-step finite-element analysis according to the desired weld line in the final workpiece. Meanwhile, weld line movement during the deformation process can be evaluated in advance. In this paper, the procedures of finite-element analysis of one-step FEM with TWBs are established. The contact between tool and blank and the effect of restraining forces under the blankholder due to drawbead and blankholder pressure are considered as well. Forming limit diagram (FLD) is used to show not only the tendency of reduction in thickness and fracture but also of increase in thickness and wrinkle. Hydraulic controlled pads used to clamp the weld line during the deep drawing process are simplified as static external force to eliminate the movement of the weld line. In order to speed up and ensure the convergence of Newton-Raphson iterations, energy-based 3D mesh mapping algorithm is introduced to obtain the initial solution. The above-mentioned methods have been implemented in the authors’ in-house one-step FEM code InverStamp. A rectangular cup drawing case demonstrates that this approach can be easily implemented to evaluate weld line movement and develop initial blank in sheet metal stamping with tailor-welded blanks.     

Finite element simulation of springback for a channel draw process with drawbead using different hardening models

The objective of this work is to predict the springback of Numisheet’05 Benchmark#3 with different material models using the commercial finite element code ABAQUS. This Benchmark consisted of drawing straight channel sections using different sheet materials and four different drawbead penetrations. Numerical simulations were performed using Hill's 1948 anisotropic yield function and two types of hardening models: isotropic hardening (IH) and combined isotropic-nonlinear kinematic hardening (NKH). A user-defined material subroutine was developed based on Hill's quadratic yield function and mixed isotropic-nonlinear kinematic hardening models for both ABAQUS-Explicit (VUMAT) and ABAQUS-Standard (UMAT). The work hardening behavior of the AA6022-T43 aluminum alloy was described with the Voce model and that of the DP600, HSLA and AKDQ steels with Hollomon's power law. Kinematic hardening was modeled using the Armstrong-Frederick nonlinear kinematic hardening model with the purpose of accounting for cyclic deformation phenomena such as the Bauschinger effect and yield stress saturation which are important for springback prediction. The effect of drawbead penetration or restraining force on the springback has also been studied. Experimental cyclic shear tests were carried out in order to determine the cyclic stress-strain behavior. Comparisons between simulation results and experimental data showed that the IH model generally overestimated the predicted amount of springback due to higher stresses derived by this model. On the other hand, the NKH model was able to predict the springback significantly more accurately than the IH model.     

基于流变学理论的TRIP600钢本构模型研究

相变诱发塑性(Transformation induced plasticity,TRIP)钢在成形过程中容易发生开裂,主要是由于发生残余奥氏体向马氏体的转变,导致外力与变形不协调。其力学行为不仅有传统的弹性变形和塑性变形,还表现出与时间相关的黏性性质,因此在对其进行本构建模时有必要考虑时间因素对变形行为的影响作用。利用流变模型既可以通过不同构件的组合准确、合理地描述TRIP钢的软、硬相性质,还可以通过各个构件弹性、塑形及黏性系数的变化与组合描述TRIP钢在变形过程中残余奥氏体向马氏体转变的行为特性,即TRIP效应。本文基于流变学理论,对TRIP600的流变学本构模型进行研究和探讨,并最终建立TRIP600分别在蠕变和松弛试验条件下统一的本构方程。