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.     

考虑磁场区影响的电控永磁压边方法

电控永磁压边方法具有独立加载、传动链短、节能、易于控制等优点。针对铁磁性板材成形,提出了一种新的成形区和磁场区重合的电控永磁压边方法。以圆筒形件的拉深成形为例,采用新设计的压边装置对不同压边力加载条件下的结构变形进行了磁-力耦合有限元模拟,分析了板坯磁性对磁场和压边力分布的影响。由分析结果可知,新设计的压边力加载装置的刚度明显提高,新压边方法具有更好的压边效果,模具结构更紧凑。根据模拟和理论分析结果设计制作了拉深试验装置。实验结果表明,将成形区和磁场区重合的电控永磁压边方法是完全可行的。     

薄板成形中变压边力优化设计方法

变压边力的最大优点是可以根据成形过程不同阶段的变形特点来设置不同压边力 ,从而可以充分利用板料的成形性能 ,然而如何设计变压边力的形式及大小一直未成定论。T Ohata提出的基于网格法和单纯形法的混合算法在求解约束问题时存在解的可行性和有效性问题 ,针对这种不足提出一种改进的混合优化算法 ,使之适合求解非线性约束优化问题 ,并将这种改进的优化算法与薄板成形数值仿真软件相结合 ,提出应用优化理论和数值仿真来确定薄板成形中的变压边力设计方法。将这种方法应用到一球头柱形杯零件的变压边力方案设计时 ,大大减小了零件局部最大减薄量 ,改善了零件的总体质量     

电磁力作用下平板变形的实验研究

通过平板件的电磁无底凹模成形、有底凹模成形的实验研究，发现不同形式的压边圈可以导致不同的工件变形高度。有底凹模成形时，在设备能量足以使工件变形达到凹模底部的情况下，工件的最大变形高度小于凹模深度，并且电压越大，工件的变形高度越小，而且在较大电压的情况下，工件底部还会出现反向变形。对实验现象进行了分析，认为不同形式的压边圈，板料所受径向拉深力不同，导致不同的工件变形高度；板料受撞击产生的反向运动是导致工件最大变形高度小于凹模深度的主要原因。     

拉深工艺中脉动压边力控制方法

压边力是板料拉深成形过程的重要工艺参数之一 ,合理控制压边力的大小可避免起皱或破裂缺陷。采用脉动变化的压边力控制拉深工艺 ,可提高成形极限及拉深件的表面质量。本文采用数值模拟方法研究了脉动变化压边力的振幅、振频对成形的影响。     

圆锥形件拉深过程中变压边力的研究

起皱和断裂是板料成形过程的主要失效模式，合理控制成形过程中的压边力，可以消除这些缺陷，提高成形性能。本文以圆锥形件的成形为例，采用Dynaform软件对变压边力控制的成形工艺进行了数值模拟计算，得到了最佳压边力变化曲线。本文还对模拟结果进行了实验验证。结果表明，变压边力拉深工艺能够极大提高板料的极限拉深高度。     

压边力控制技术研究现状及伺服数控压边方法可行性探讨

对压边力控制技术研究现状进行了分析。现有的压边方法多数采用弹性介质传递力和运动。在拉深过程中，压料板和被压板坯的相对位移很小，压边所需能耗很小。实际压边过程中的大部分功耗都转变为弹性介质的势能或动能。采用数控伺服驱动方式压边，更符合拉深过程中的压边力、瞬时功耗、速度等要求。利用伺服电机良好的速度可控性，可以通过压边力调节装置调整作用在板坯上的压边力的大小，更容易实施变压边力控制。给出了最大设计压边力与压边装置结构参数、伺服电机参数的匹配关系，探讨了数控压边的软硬件系统的实现方法。可以以数控压边为手段对拉深过程中的成形极限、理想压边力行程曲线等问题进行深入研究。数控压边对改善生产环境、节约能耗以及完善和改进冲压成形的实验技术等方面有重要的实际意义，还将对冲压成形的自动化、柔性化和智能化等相关技术的发展产生积极的推动作用。     

The effect of nanoparticulate loading on the fabrication and characterization of multi-doped Zn-Al2O3-Cr2O3 hybrid coatings on mild steel

In this paper, an improved approach is proposed to determine the optimal profiles of two controllable process parameters (hydraulic pressure and blank holder force), which improve the forming condition and/or make better use of forming limits in hydromechanical deep drawing (HMD) process. A method based on adaptive finite element analysis coupled with fuzzy control algorithm (aFEA-FCA) was developed using LS-DYNA to determine the optimal loading profiles and thus to maximize the limiting drawing ratio (LDR). Maximum thickness reduction, maximum wrinkle height in the flange region of the sheet metal blank, and position of the nodes in the unsupported portion of the sheet metal blank between punch and die were used as criteria in the fuzzy control algorithm. Different rule-based matrices were compared by considering the maximum thinning occurred in the sheet metal blank, and thus, the most accurate matrices were determined for the control algorithm. The optimal loading profiles could be determined in a single FEA, thus reducing the computation time. The proposed approach enables determining the optimal loading profiles and also could be applied to complex parts easily. In addition, effects of initial blank diameter and coefficient of friction between the sheet-blank holder and sheet-die on the optimal loading profiles were investigated. An attainable LDR of 2.75 for AA 5754-O sheet material in hydromechanical deep drawing process was proven experimentally using the optimal loading profiles determined by adaptive FEA.     

矩形盒分块变压料力拉深的有限元分析

作为薄板非回转对称拉深成形系统研究的一部分,针对矩形盒拉深中压料力对成形性和成形极限的影响进行相应的实验和有限元模拟分析。研究表明,矩形盒分块变压料力拉深有助于提高拉深成形性和成形极限。但如何对压料板正确分块、分块衔接方式以及实现变压料力实时控制还需要做大量深入的基础研究工作。     

CAE仿真技术在空调冲压件的模具设计和制造中的应用

采用板料成形有限元分析软件Dynaform5.7对某空调器钣金件的冲压成形过程进行了数值模拟,预测工艺参数如压边力、拉延筋对成形质量的影响。结果表明调整压边力可控制材料的总体流动,有效改善起皱和成形不足等成形缺陷。设置拉延筋直接影响材料的局部流动,增加压料面上相应部位的进料阻力,但如何设置拉延筋的位置、根数和形状是取决能否得到满意的成形质量的关键。通过数值模拟技术调整压边力大小和拉延筋以得到合理的设计方案,改进后方案的成形质量好,无起皱和破裂等缺陷,变形均匀,产品精度符合要求。     

Numerical and experimental investigation of pulsating blankholder effect on drawing of cylindrical part of aluminum alloy in deep drawing process

In this study, the effect of a new pulsating blankholder system has been investigated on improving the formability of aluminum 1050 alloy. By using this system, during each pulsating cycle, first, the metal was easily flowed into the die through removing the blankholder force, and then the blankholder force applied by springs was employed to prevent excessive metal flow and wrinkling. Deep drawing of cylindrical cup was simulated by ABAQUS6.7 software. Cup depth, tearing, and thickness distribution of the experimental and numerical analyses were then compared. The results indicated that by using the pulsating blankholder system coupled with proper frequency and gap, the cup depth can be increased and thickness distribution can be improved. Further, good agreement was observed between simulation and experimental results.     

基于径向基神经网络杯形件拉深成形变压边力预测技术研究

分析了RBF神经网络的预测策略和方法,并建立了板料拉深成形的变压边力预测神经网络模型.采用正交设计法进行样本参数的制定,利用板材成形CAE软件Dynaform获得训练数据,利用被训练好的神经网络对薄板成形过程中变压边力的预测技术进行了研究.数值模拟结果表明,此方法对拉深成形变压边力的预测是可行的.     

确定拉延筋约束阻力的一种数值模拟方法

利用率形式的虚功原理和考虑弯曲影响的 Mindlin曲壳单元 ,根据塑性变形体积不可压缩的假设 ,将大变形弹塑性有限元应用于板料成形过程中 ,建立了接触摩擦模型。在此基础上 ,利用自行开发的软件 Sheet Form模拟板料流经拉延筋的过程 ,确定板料成形数值模拟中建立等效拉延筋模型需要的拉延筋约束阻力、塑性厚向应变和最小压边力 3个边界条件 ,并与Nine等人的实验结果进行对比 ,证明了该方法的有效性     

面向设计的板料成形快速仿真系统FASTAMP

FASTAMP是基于改进的有限元逆算法和动力显式算法的板料成形快速仿真软件。改进的逆算法求解器采用了考虑弯曲效应的DKQ四边形单元及方程组快速求解算法,真实考虑了摩擦、压边力、背压力和曲压料面等实际工艺条件,在模拟精度和速度上均有较大的提高。系统结合了两种算法的优势,将产品设计、选材和工艺设计三个独立的过程紧密结合起来,可快速分析产品设计中的潜在缺陷,为工艺设计人员提供有效的工艺设计参考和强有力的设计辅助分析工具。     

Numerical simulation of the electromagnetic sheet metal bulging process

Electromagnetic forming (EMF) is an uncommon metal working process that relies on the use of electromagnetic forces to deform metallic workpieces at high speeds. It is expected to overcome some formability barriers of materials. EMF process analysis is the foundation of theoretical analysis. However, the electromagnetic sheet metal process is very difficult to describe, because of the complexity of magnetic pressure distribution. In this paper, a numerical modeling of the electromagnetic sheet metal process is performed using a finite element method, and a series of simulations on free bulging are carried out using the FEA program ADINA. The dynamic deformation process of sheet metal is investigated. At last, some experiments are made and those simulations agree well with the experimental results.     

An approach to eliminate stepped features in multistage incremental sheet forming process: Experimental and FEA analysis

Incremental sheet forming (ISF) is a recently developed manufacturing technique. In ISF, forming is done by applying deformation force through the motion of Numerically controlled (NC) single point forming tool on the clamped sheet metal blank. Single Point Incremental sheet forming (SPISF) is also known as a die-less forming process because no die is required to fabricate any component by using this process. Now a day it is widely accepted for rapid manufacturing of sheet metal components. The formability of SPISF process improves by adding some intermediate stages into it, which is known as Multi-stage SPISF (MSPISF) process. However during forming in MSPISF process because of intermediate stages stepped features are generated. This paper investigates the generation of stepped features with simulation and experimental results. An effective MSPISF strategy is proposed to remove or eliminate this generated undesirable stepped features.     

金属塑性成形的摩擦力学模型探讨

对金属板料在塑性变形过程中摩擦力的形成原因进行了分析,运用塑性成形理论和摩擦学原理建立了力学模型,并通过实验得出了当压力改变时摩擦力各分量的变化趋势。可以为数值模拟及工艺分析提供理论依据。     

基于多目标遗传算法优化板料拉深成形工艺参数

利用人工神经网络构建了板料拉深成形的目标函数模型,建立了板料拉深成形工艺参数和性能评价指标之间的映射关系.以多种工艺参数(压边力、摩擦因数等)作为优化变量,多种成形缺陷(起皱、破裂等)作为优化目标,结合多目标遗传算法和数值模拟,建立了板料拉深成形工艺参数的优化设计模型,大大提高了优化的效率.以油底壳下盖为例,对其拉深成形工艺参数进行了优化,通过对优化结果进行数值模拟可以看出,该优化参数完全避免了各种缺陷的产生,这说明该优化算法具有较好的优化结果.     

Modified membrane finite element formulation for sheet metal forming analysis of planar anisotropic materials

A finite element formulation is derived for sheet metal forming analysis of planar anisotropic materials. The formulation incorporates membrane elements whereas it takes the bending effect into account explicitly. The strain energy term in the formulation is decomposed into the membrane energy term for mean stretching and the bending energy term for pure bending. This procedure needs careful evaluation for the orientation of the anisotropic axes. The formulation is then combined with an effective algorithm to calculate distribution of the blank holding force in each step according to the thickness in the flange region. The calculation employs a special relation between the thickness and the blank holding force. The simulation examples demonstrate the validity and versatility of the developed computer code by showing that the thickness variation in the flange region redistributes the blank holding force during the deformation. The present algorithm can predict accurate deformed shapes and thickness strain distribution with the anisotropy of materials and the variable blank holding force.     

Optimization of drawbead restraining forces and drawbead design in sheet metal forming process

This paper presents an optimization procedure of drawbead restraining forces in order to improve the sheet metal formability in deep drawing process. A simplified finite element method called inverse approach (IA) has been developed for sheet forming analysis with the consideration of the drawbead restraining forces. This IA is combined with a mathematical programming algorithm to optimize the restraining forces and then to design the drawbeads. The obtained optimization procedure is very efficient due to the simplified assumptions of the IA and the analytical sensitivity analysis. The Square cup of Numisheet’93 and the Renault Twingo dashpot cup are presented to demonstrate the usefulness of the proposed optimization procedure for industrial applications. Verifications of the obtained results have been carried out using a precise incremental commercial code OPTRIS^TM based on explicit dynamic approach to show the effectiveness of our approach.