铝合金板材磁脉冲辅助U形弯曲过程回弹数值模拟分析

目的揭示铝合金板材磁脉冲辅助弯曲成形对回弹的影响机理。方法基于两种磁脉冲辅助成形方案,采用数值模拟软件LS-DYNA,建立磁脉冲辅助U形弯曲的有限元模型。结果与准静态成形相比,磁脉冲辅助U形弯曲成形能减小板料圆角区的残余应力,方案Ⅰ板料圆角区等效塑性应变大于方案Ⅱ板料圆角区的等效塑性应变;电磁体积力能有效减小回弹,且放电能量越大,回弹角越小;磁脉冲辅助U形弯曲成形能减小板料的弹性应变能。结论相同放电电压下,方案Ⅰ的回弹控制效果好于方案Ⅱ的回弹控制效果。磁脉冲辅助U形弯曲减小回弹的主要原因是板料圆角区残余应力的减小和弹性应变能的降低。     

铝合金双曲率薄壁件电磁渐进辅助拉伸成形工艺方案设计与开发

目的 针对铝合金双曲率薄壁件传统拉伸成形工艺成形均匀性差的问题,提出一种采用电磁渐进辅助拉伸成形的高精度成形工艺。方法 设计电磁渐进辅助拉伸成形工艺方案,基于有限元仿真软件LS-DYNA R13.0,建立拉伸成形和电磁成形有限元模型。通过数值仿真研究线圈移动路径和放电电压组合对成形质量的影响以及薄壁件的整体贴模成形过程和等效塑性应变。结果 与单程放电相比,双程放电能够大幅度提高板材变形均匀性。与以中间值电压连续放电以及先大电压后小电压的放电电压组合相比,在先小电压后大电压的放电电压组合下,板材的成形质量更高。选择线圈双程顺序移动路径和7 kV-10 kV放电电压组合,通过10次拉伸和9层54次放电,得到了减薄率仅为3%的贴模性良好的双曲率薄壁件。变形量基本呈现随着放电层数的增加而不断降低的趋势。电磁放电仅扩展更大的塑性应变区域,不改变已贴模区板材的塑性应变值。结论 与拉伸成形相比,电磁渐进辅助拉伸成形工艺有效提高了板材的塑性变形程度并极大控制了回弹的发生。     

铝合金板阵列微结构零件电磁冲击液压成形研究

目的 解决室温条件下因铝合金塑性流动不均而导致的零件开裂和尺寸偏差等问题。方法 利用高速冲击提高材料成形极限以及流体均匀载荷精确控形的优势,提出了电磁冲击液压工艺并实现了铝合金阵列结构零件的成形,采用实验手段研究了放电电压和放电次数对零件贴模精度和厚度分布的影响。结果 随着放电电压的增大,零件的成形深度增大。在单次放电8 kV下,板料最大成形深度达到模具深度的97%,连续3次放电8 kV后,零件通道填充率达到89.7%。建立了与物理实验模型一致的电磁-流体-结构的多物理场耦合仿真模型,发现冲击液体对板料施加的瞬态压强超过200 MPa,板料最大变形速度达到40.5 m/s。模拟得到的板料变形轮廓与实验结果一致,证明了多物理场耦合仿真模型的准确性。结论 电磁冲击液压成形是一种新型的高速成形方法,能够实现铝合金阵列微结构零件的精确制造,为提高复杂薄壁难变形构件的成形性能和精度提供了新的技术手段。     

大型铝合金曲面件在电磁渐进成形首次放电条件下的起皱行为研究

针对大型铝合金曲面件电磁渐进成形技术,采用整体压边和分块变压边力压边的方式,研究了电磁渐进成形工艺中首次放电后板料的起皱现象和规律,揭示了压边力对电磁渐进成形首次放电过程中板料起皱和材料塑性流动行为的影响。结果表明:数值模拟结果预测出的首次放电后易起皱区域为板料的法兰区和悬空侧壁区,与实验结果一致;整体压边方式下法兰区域和悬空侧壁区域无起皱的临界压边力分别为8.4 kN和21.6 kN;分块变压边力方式下,最靠近局部塑性变形区的压边分块上的法兰区域无起皱临界压边力为8.4 kN,最靠近悬空区的对称的两个压边分块上的悬空侧壁区域无起皱临界压边力为23.8 kN,且相比于整体压边方式的无起皱临界条件下,在分块压边方式的无起皱临界条件下板料的变形流动能力得以明显提高。     

UOE焊管成形三维有限元模拟

建立了UOE焊管成形过程的三维有限元模型,模拟具有大变形和复杂接触的成形过程,分析板料各个成形段的回弹,获得了不同成形段板料的变形构形、等效塑性应变分布以及成形载荷的变化。研究结果可为UOE工艺设计以及评估成形机组制管能力提供指导。     

电磁成形放电频率对板料变形的影响

目的研究电磁成形放电频率对板料变形的影响规律。方法以商用有限元软件ANSYS为平台,建立板料电磁成形有限元模型。通过数值模拟方法,研究不同厚度的1040铝合金板在不同放电频率下的变形过程,得到不同板厚对应的最优放电频率。对比板料自由胀形试验结果,验证数值模拟的可靠性。结果放电频率对线圈放电电流、板料内电流分布、磁场力分布以及变形影响较大,并且存在最优放电频率使得板料的变形量最大。结论最优相对放电频率随着板厚的增加而减小,其变化规律呈幂指数函数变化。     

镁合金板料温冲压成形数值模拟技术

用板料成形的方法对变形镁合金进行加工可以制造更薄更轻的零件,符合轻质化的发展趋势.利用有限元数值模拟的方法可以对实际的冲压过程进行模拟,达到改进工艺与模具的目的.对于板料加热状态下的数值模拟,为了使结果准确,最重要的就是要建立正确的材料本构关系模型,这一材料模型需给出应变、应变率、应力与温度之间的关系.在经典的塑性成型计算中,材料模型包含两方面的内容:①初始屈服表面的确定,②流动法则和加工硬化模型的建立.总结了经典屈服模型和材料本构关系模型以及国内外学者在经典理论基础上建立起来的镁合金材料模型;探讨了板料成形有限元数值模拟技术以及目前常用的模拟软件;并在此基础上综述了镁合金冲压变形的热-机耦合的数值模拟的研究进展.     

大口径铝合金波纹管电磁胀形数值模拟

目的研究大口径铝合金波纹管电磁成形过程及工艺参数对成形效果的影响规律。方法针对波纹管现有制造工艺——压弯和焊接复合成形存在压痕严重、焊缝多和可靠性不高等问题,提出采用电磁成形波纹管的方法,并基于ANSYS建立了波纹管电磁胀形的三维有限元分析模型。结果揭示了波纹管电磁胀形过程中的应力应变分布规律,发现波纹区域和过渡圆角区域是应力和应变集中区。采用单因素实验方法,获得了放电电压和线圈匝数对成形质量的影响规律。结论在波纹管电磁胀形过程中,波纹区域的应力和应变均呈圆环带状分布,波纹管的壁厚在波纹的波峰处达到最小,最大减薄率为10.67%。放电电压和线圈匝数都存在一个最佳值。放电电压过小时,成形不足,放电电压过大时,工件高速碰撞模具,引起较大反弹,导致最终贴模性较差;线圈匝数也对成形质量有一定的影响,在本次模拟实验中,11匝线圈作用下的工件贴模性最佳。     

轿车后围板成形过程数值模拟及参数优化

为提高轿车后围板零件的成形质量和设计效率,采用单向拉伸试验,测定了板料的力学性能参数,并对测量参数的有效性进行了验证;基于测量的参数,对该零件的冲压成形过程进行了数值模拟,改进了拉延筋的受力并优化了工艺和模具参数;对零件成形之后的回弹进行了研究,并对回弹变形进行了补偿.研究结果表明:采用测定的参数能有效地提高数值模拟的精度;优化拉延筋的受力及成形参数,可以提高成形件的质量;利用补偿法可以有效的补偿零件的回弹变形;经验知识与数值模拟相结合的优化方法是提高产品质量及工艺设计效率的有效途径.     

铝合金板料电磁成形工艺与理论的研究进展

将电磁成形与现有板料成形工艺相结合,能够有效拓宽电磁成形应用领域,可为汽车、航空、航天等高端装备中铝合金零件高性能精确成形带来新的突破.主要综述了电磁复合成形工艺、多物理场耦合数值模拟与本构建模、铝合金板料电磁成形性能与组织演变等3个方面的研究进展,并结合笔者的研究工作对电磁成形工艺与理论研究中存在的问题进行了简要分析...     

Finite Element Analysis of sheet metal bending process to predict the springback

Springback remains a major concern in sheet metal forming process. Springback, shape discrepancy between fully loaded and unloaded configuration due to elastic recovery of material, is mainly affected by geometrical parameters, material properties of sheet and lubrication condition between the blank and the tool. A total-elastic–incremental-plastic (TEIP) algorithm, for large deformation and large rotational problems, was incorporated in indigenous Finite Element software. This software was used to predict the springback in a typical sheet metal bending process and to investigate the influence of these parameters on springback. The results of simulation are validated with own experiments and published experimental results.     

A new anisotropic elasto-plastic model with degradation of elastic modulus for accurate springback simulations

Springback, a phenomenon that is governed by elastic strain recovery after the removal of forming loads, is of great concern in sheet metal forming. There is no doubt that in this regard, physically reliable numerical modelling of the forming process and predictions of springback obtained by respective computer simulations are crucial for controlling this problem. Unfortunately, by currently available approaches, springback still cannot be adequately predicted in general. In this paper, a new constitutive model is proposed which considers simultaneously sheet anisotropy, damage evolution and strain path-dependent stiffness degradation during sheet metal forming. For parameter identification of the built constitutive model, a particular experimental procedure is developed and an optimization procedure is employed to solve the inverse problem that arises. The proposed approach to constitutive modelling is validated in the end by a simulation of the springback in the formed HSS steel sheet. The simulation results, which prove to be in good agreement with the experimental ones, lead to the conclusion that accurate modelling only of anisotropic yielding is not enough to accurately predict the springback phenomenon; the constitutive model should also include the strain path-dependent change of the elastic moduli.     

电磁成形技术在钛合金板材成形中的应用

钛合金是航空航天领域主要的轻质结构材料,强度高,但不易成形且回弹大,而电磁成形技术的发展为钛合金零件的精密高效成形提供了新的有效途径.从高速增塑、成形工艺、数值仿真3个方面综述了电磁成形技术在钛合金板材成形的应用研究情况,并结合笔者的研究经历对钛合金电磁成形中存在的问题进行了简要分析.在此基础上,着重综述了电磁成形技术下材料的成形性能与变形机理,进而综述了钛合金电磁胀形、电磁翻边工艺研究进展,并介绍了钛合金电磁成形多物理场耦合仿真技术,最后对未来钛合金板材电磁成形技术的发展进行了展望.电磁成形技术可以提高钛合金板材的成形性能;厚度接近集肤深度的高导电性低强度板材是优质的驱动片.为了进一步促进电磁成形技术在钛合金板材成形中的应用,需要开发更高强度的磁体线圈以及更优的驱动方式.     

Modeling of the elastic modulus evolution in unloading-reloading stages

It was already stated that springback in sheet metal forming strongly depends on the elastic properties. Several experimental investigations have revealed that the elastic modulus decreases as the plastic strain increases. Two approaches have been separately employed to explain this phenomenon: dislocations rearrangements and damage. These approaches are considered in a proposed elastoplastic model coupled with damage based on Lemaitre type isotropic ductile damage law. In addition, a hysteresis aspect, which is experimentally observed during unloading-reloading stages, is also considered. Uniaxial tension tests have been used and the predicted results agree well with published experimental data. The proposed model is intended to be implemented in FEM codes for reliable results in forming processes including springback.     

航空发动机钣金件多工序连续工艺链式仿真方法研究及实验验证

目的 针对航空发动机上挡溅盘钣金件的多工序成形过程,进行有限元仿真分析与实验验证。方法 以ABAQUS和DEFORM为仿真平台,先采用ABAQUS对钣金件第一道次的拉深回弹过程进行仿真,在此基础上,将第一道次仿真结果导入DEFORM中,作为初始状态进行退火热处理;然后将仿真结果导入ABAQUS中作为初始状态进行第二道次的拉深回弹仿真,重复上一道次的数据传递过程,再进行热处理与第三道次整形模拟,在每一道次拉深成形后对比模拟与实验结果。结果 实现了钣金件在同一软件和不同软件之间几何形状及物理场的数据传递,完成了钣金件的多工序连续工艺仿真成形。第一道次拉深卸载后零件回弹较小,模拟得到的零件几何尺寸与实验结果误差较小,但卸载后零件中有较大残余应力,通过热处理可以很大程度地消除残余应力,增强高温合金后续的成形性能,经过多工序成形仿真后,几何特征尺寸累计误差值略有增大,但仍在可接受范围内。结论 包含中间退火热处理的多工序成形仿真可以较好地描述实验结果,证明了仿真结果的准确性与有效性,可以为改进和优化钣金件的设计及成形过程提供科学指导。     

Reduction of springback using simultaneous stretch-bending processes

Springback due to the elastic material behaviour can lead to shape errors that cause geometrical and dimensional inaccuracies in sheet metal forming processes, especially in bending operations. In order to reduce springback, the technique of integrating stretching with bending in sheet metal forming processes has been investigated. The object of this paper is to explain how to reduce the effect of the elastic component in the material behaviour using simultaneous stretching and bending so that a method is established for applying plastic forming during the main process, without changing the tool design. This study focuses on three main points: the stretching method, the stretching direction and the stretching length. In regard to swing- and v-bending processes, the springback factor is used as the standard evaluation to investigate these effects using Finite Element simulation. The springback factors are compared for four processes: Bending process without stretching (WS), pre-stretching and bending process (PB), pre-stretching plus simultaneous stretching and bending (PSB) and simultaneous stretching and bending (SB). The simulation results are then verified through experimentation. Based on the validated results, simultaneous stretching can then be subsequently applied to the existing stretch-forming process, which consists of pre-stretching and bending. Using this process, springback was successfully reduced which confirms the efficiency of SB process.     

材料硬化模式对弯曲回弹模拟精度的影响

回弹的模拟精度低，是几乎所有软件在计算大型复杂件的回弹时都存在的缺点，因此提高回弹模拟精度成为回弹仿真研究的重点和难点，利用自主开发的二维弹塑性有限元程序，分别采用线性硬化模型和弹塑性幂次硬化模型对V型自由弯曲的回弹进行模拟，探讨材料硬化模式对回弹模拟精度的影响，特别对于硬化模型中代表弹性变形阶段的重要参数一弹性模量，考虑了其随塑性变形进行而发生的变化，结果表明：材料的硬化模式直接影响回弹模拟精度，而采用的硬化模式越能真实地反映材料变形规律，回弹模拟的精度就越高，尤其是采用随塑性变形而发生变化的弹性模量，使模拟精度进一步提高。     

An analytical model for bending and springback of bimetallic sheets

Springback is an inevitable phenomenon due to elastic redistribution of internal stresses occurring in sheet metal forming operations. Most of the research reported in this area has been concerned with the components formed from single metal. This article deals with the analytical solution for prediction of springback in bending of bimetallic sheets. A mathematical model is derived based on Woo and Marshall's constitutive equation, considering logarithmic strain (nonlinear) distribution across the thickness and thickness change during bending. Analytical modeling, based on logarithmic strain distribution across the thickness, can be used for accurate springback predictions in the case of smaller bend radius to the thickness ratio. The results of the springback and thickness change are validated using experimental results for the aluminum sheet layered with steel. Further, springback variation in bimetallic sheets is studied, with a change in material properties and thickness of each layer.