DEFORMATION ANALYSIS OF SHEET METAL SINGLE-POINT INCREMENTAL FORMING BY FINITE ELEMENT METHOD SIMULATION

Single-point incremental forming （SPIF） is an innovational sheet metal forming method without dedicated dies, which belongs to rapid prototyping technology. In generalizing the SPIF of sheet metal, the deformation analysis on forming process becomes an important and useful method for the planning of shell products, the choice of material, the design of the forming process and the planning of the forming tool. Using solid brick elements, the finite element method（FEM） model of truncated pyramid was established. Based on the theory of anisotropy and assumed strain formulation, the SPIF processes with different parameters were simulated. The resulted comparison between the simulations and the experiments shows that the FEM model is feasible and effective. Then, according to the simulated forming process, the deformation pattern of SPIF can be summarized as the combination of plane-stretching deformation and bending deformation. And the study about the process parameters＇ impact on deformation shows that the process parameter of interlayer spacing is a dominant factor on the deformation. Decreasing interlayer spacing, the strain of one step decreases and the formability of blank will be improved. With bigger interlayer spacing, the plastic deformation zone increases and the forming force will be bigger.

Treatment of discontinuous interface in liquid-solid forming with extended finite element method

Extended finite element method(XFEM) is proposed to simulate the discontinuous interface in the liquid-solid forming process.The discontinuous interface is an important phenomenon happening in the liquid-solid forming processes and it is difficult to be simulated accurately with conventional finite element method(CFEM) because it involves solid phase and liquid phase simultaneously.XFEM is becoming more and more popular with the need of solving the discontinuous problem happening in engineering field.The implementation method of XFEM is proposed on Abaqus code by using UEL(user element) with the flowchart.The key is to modify the element stiffness in the proposed method by using UEL on the platform of Abaqus code.In contrast to XFEM used in the simulation of solidification,the geometrical and physical properties of elements were modified at the same time in our method that is beneficial to getting smooth interface transition and precise analysis results.The analysis is simplified significantly with XFEM.

Simulation of bulk metal forming processes using one-step finite element approach based on deformation theory of plasticity

The bulk metal forming processes were simulated by using a one-step finite element(FE)approach based on deformation theory of plasticity,which enables rapid prediction of final workpiece configurations and stress/strain distributions.This approach was implemented to minimize the approximated plastic potential energy derived from the total plastic work and the equivalent external work in static equilibrium,for incompressibly rigid-plastic materials,by FE calculation based on the extremum work principle.The one-step forward simulations of compression and rolling processes were presented as examples,and the results were compared with those obtained by classical incremental FE simulation to verify the feasibility and validity of the proposed method.

Sintering zone prediction in direct metal laser sintering by finite element method

A three-dimensional finite element thermal model in direct metal laser sintering(DMLS) including the effect of powder-to-solid transition were established to predict sintering zone, which benefited the determination of suitable process parameters in DMLS. The nonlinear transient model of the metals thermal conductivity for powder-to-solid transition was developed. The model uses solid thermal properties of material in liquid-phase zone, transitional ones in sintering or sintered zone and powder ones in unsintered zones of powder bed to predict, respectively. Sintering zone boundary was estimated by maximum temperature history profile. Experiments were carried out using multi-component Cu-based metal powder. Compared experimental and predicted results, the mean error of sintering depth and width are 7.8% and 14.4%, respectively, which confirms the accuracy of the FEM prediction.

Numerical Simulation of Mechanical Characteristics of a Metal Net for Deep-Sea Aquaculture

The investigation on hydrodynamic characteristics of a cage is important for its application in the deep-sea aquaculture in our country.With finite element method,the beam element is used to simulate a three-dimensional metal chain net,and the connector element is introduced as the interaction between metal net lines.A mechanical model for the metal net is constructed to simulate the hydrodynamic characteristics of a metal net subjected to fluid current forces.The static simulation results show that the relative errors of the displacements are 2.13%,4.19%,6.64%,and 11.35% compared with static concentrated load tests under concentrated forces of 20,40,60,and 80 N,respectively.Both the transient hydrodynamic deformations and drag forces of the netting structures under different current velocities are obtained by solving the hydrodynamic equation of the netting structure.The average relative error of the current forces obtained by numerical simulations shows an 8.13%deviation from the drag tests of the metal nets in the tank under five current velocities.The effectiveness and precision of the simulation approach are verified by static and dynamic tests.The proposed simulation approach will provide a good foundation for the further investigation of the hydrodynamic characteristics of deep-sea aquaculture metal cages and the parameter design for the safety of such cage systems.

Numerical simulation and experimental investigation of incremental sheet forming process

In order to investigate the process of incremental sheet forming (ISF) through both experimental and numerical approaches, a three-dimensional elasto-plastic finite element model (FEM) was developed to simulate the process and the simulated results were compared with those of experiment. The results of numerical simulations, such as the strain history and distribution, the stress state and distribution, sheet thickness distribution, etc, were discussed in details, and the influences of process parameters on these results were also analyzed. The simulated results of the radial strain and the thickness distribution are in good agreement with experimental results. The simulations reveal that the deformation is localized around the tool and constantly remains close to a plane strain state. With decreasing depth step, increasing tool diameter and wall inclination angle, the axial stress reduces, leading to less thinning and more homogeneous plastic strain and thickness distribution. During ISF, the plastic strain increases stepwise under the action of the tool. Each increase in plastic strain is accompanied by hydrostatic pressure, which explains why obtainable deformation using ISF exceeds the forming limits of conventional sheet forming.

Adaptive finite element-element-free Galerkin coupling method for bulk metal forming processes

An adaptive finite element-element-free Galerkin (FE-EFG) coupling method is proposed and developed for the numerical simulation of bulk metal forming processes. This approach is able to adaptively convert distorted FE elements to EFG domain in analysis. A new scheme to implement adaptive conversion and coupling is presented. The coupling method takes both advantages of finite element method (FEM) and meshless methods. It is capable of handling large deformations with no need of remeshing procedures, while it is computationally more efficient than those full meshless methods. The effectiveness of the proposed method is demonstrated with the numerical simulations of the bulk metal forming processes including forging and extrusion.

Simulation of local effect of reinforcement on temperature field during solidification of aluminum metal matrix composite

The effect of reinforcement on the solidification of pure metal matrix composites (MMCs) was simulated using a two-dimensional solidification temperature field model by the finite element method. The concept of the character length was proposed to describe the size of reinforcement local heat influential zone in MMCs solidification according to the change of the morphologies of solid-liquid interface. The relationship between the character length and the geometrical conditions, the boundary condition and physical properties of the reinforcement were studied, respectively. The results show that the width of the unit and the cold boundary temperature have no effect on the character lengths but have effect on the distance between cold boundary and reinforcement (l) and the thermal parameters of the reinforcement. An experimental rule to predict the value of the character length was derived and applied.

Rapid Finite Element Analysis of Bulk Metal Forming Process Based on Deformation Theory

The one-step finite element method （FEM）, based on plastic deformation theory, has been widely used to simulate sheet metal forming processes, but its application in bulk metal forming simulation has been seldom investigated, because of the complexity involved. Thus, a bulk metal forming process was analyzed using a rapid FEM based on deformation theory. The material was assumed to be rigid-plastic and strain-hardened. The constitutive relationship between stress and total strain was adopted, whereas the incompressible condition was enforced by penalty function. The geometrical non-linearity in large plastic deformation was taken into consideration. Furthermore, the force boundary condition was treated by a simplified equivalent approach, considering the contact history. Based on constraint variational principle, the deformation FEM was proposed. The one-step forward simulation of axisymmettic upsetting process was performed using this method. The results were compared with those obtained by the traditional incremental FEM to verify the feasibility of the proposed method.

采用向量式有限元的拉索参数振动模拟

拉索的参数振动主要是由连接拉索端部的结构振动引起的,当端部振动频率与拉索的自振频率满足一定倍数关系时,拉索端部激励容易激发较大拉索参数振动。由于参数振动存在复杂的非线性振动特征,传统的解析方法难以应用于实际工程。本文发展了模拟拉索参数振动的向量式有限元方法,对斜拉索在动边界条件下的振动进行分析,对比控制方程的数值解以验证结果的准确性。并基于向量式有限元模型对端部支座轴向运动激励下产生的主共振区和主参数共振区特性进行讨论,分别研究了拉索倾角、阻尼比以及风荷载协同作用对参数振动的影响。研究结果表明向量式有限元可以有效模拟复杂工况下的拉索参数振动,有利于实际工程应用。

板料成形数值模拟进展

在给出板料成形的典型成形过程、物理过程与力学模型的基础上，评述了板料成形数值模拟的发展历史和最新进展，包括成形过程与成形缺陷模拟发展，常用材料模型与壳体模型，接触摩擦处理及汽车覆盖件成形应用，文末指出了该领域的发展趋势。

金属塑性成形过程再生核质点无网格方法数值模拟

应用微可压缩材料的流动法则,采用再生核函数无网格方法,自行开发了求解方棒压缩、圆棒压缩、反向挤压和轧制等金属塑性成形过程应用程序。应用再生核质点无网格方法计算得到纯铝和铝合金材料金属塑性成形过程的速度场和应力场解析结果,并与自行开发的I-Form有限元程序得到的计算结果以及试验数据进行了分析比较,结果符合良好。再生核质点无网格方法具有求解金属大变形特点,解决了有限元法中的网格重划问题,为复杂金属变形分析提供了良好的研究手段。

金属塑性成形过程CSPH无网格法数值模拟

应用微可压缩刚塑性材料的流动法则,采用修正的光滑粒子力学(Corrected smooth particle hydrodynamics, CSPH)无网格法,自行开发了求解金属方棒压缩和圆棒压缩等金属塑性成形过程应用程序。提出一种简单的求解体积应变速率的光滑技术,该技术使应力场计算结果能得到较好的改善。采用CSPH无网格法求解纯铝和Al6060铝合金材料压缩过程得到的速度场和应力场结果与有限元法计算结果以及试验数据进行了分析比较。结果表明, CSPH法能够较好地求解金属大变形过程,为今后进一步分析复杂金属变形问题提供了良好的研究手段。

基于FEM与SPH耦合算法的金属切削仿真研究

采用FEM与SPH耦合算法进行了金属切削加工仿真研究,模拟了切削过程中材料的本构行为.模拟结果表明,切削过程是切削层材料受到刀具的推挤后而产生的以剪切滑移为主的塑性变形过程;在切削过程中,切削力从零开始迅速增大,然后又减小,最后在一定范围内变动;稳定切削后,前刀面上的最大等效应力在距离切削刃一定距离处上下波动。与有限元仿真结果相比较,材料的变形情况与应力分布基本相符,验证了FEM与SPH耦合算法应用于金属切削仿真研究的可靠性。

二维金属切削过程的数值模拟

本文基于数值模拟技术,借助于有限元软件成功地模拟了二维金属切削过程中切屑形成及切削区应力、应变变化的过程,计算出了剪切角及切削起始阶段切削力的变化,并通过实验验证了这一规律的正确性。该方法新颖、独特,从而为金属切削理论研究和刀具产品开发领域中提出一种更为有效、更为可靠的研究方法。

用动态显式有限元法对板材成形进行计算机模拟

介绍了动态显式有限元法的原理和特点 ,总结讨论了国际现有各种商用有限元软件的情况。采用显式有限元软件 L S- DYNA3D对板材零件冲压过程进行计算机模拟分析 ,预测冲压过程中可能出现的各种工艺缺陷 ,例如坯料的起皱、局部减薄和破裂 ,并以模拟结果为依据提出改进模具和工艺参数的办法 ,优化工艺参数 ,可以减少调试和修模的次数 ,以此实现降低模具费用、缩短制模时间、提高产品成品率和材料利用率 ,最终达到减少产品成本的目的。

有限体积法仿真金属塑性成形的基本理论

基于有限体积和塑性成形基本理论 ,推导出金属塑性成形的有限体积质量方程、动量方程、能量方程等控制方程 ,给出有限体积单元的速度分量和温度关于时间的微分方程 ,并提出了求解成形体的速度、温度、应变速率和应力等物理场量的计算方法 .

塑性成形三维数值模拟中的模具几何描述技术

详细讨论了塑性成形有限元三维数值模拟中主要几种模具几何描述技术的优缺点，对塑性成形三维数值模拟中的模具几何描述方法的选取具有重要的参考价值。本文还总结了塑性成形有限元三维数值模拟中模具几何描述技术的发展趋势。

金属体积成形三维数值仿真的研究进展

金属体积成形是一个具有几何非线性和物理非线性的复杂的塑性大变形问题，采用基于刚塑性／刚粘塑性有限元法的ＣＡＥ仿真技术对其分析，则可掌握其详细的变形规律．本文对体积成形三维有限元仿真技术的发展作了全面的回顾，并详细总结了其中的关键技术、存在的技术难点和发展趋势．

基于ABAQUS的金属板料激光冲击成形数值模拟

在激光冲击波加载转换模型的基础上,以有限元分析软件ABAQUS/CAE为平台,对圆形板料进行了直线形轨迹和圆形轨迹多点冲击成形的数值模拟,探索了冲击轨迹、应力分布和板料变形之间的相互关系。数值模拟分析表明,对圆形板料进行多点冲击成形时,选择圆形轨迹是最佳的。根据模拟结果对铝合金板料试样进行了无间隔冲击成形的实验,获得了和数值模拟相同的成形结果,模拟和实验结果一致性较好。