板料冲压成形和回弹分析过程的三维动态模拟

利用ANSYS/LS DYNA非线性动力有限元程序的显式 隐式连续求解功能 ,模拟了板料成形过程与卸载后板料回弹变形的全过程 ,得到了成形过程中任一时刻各处的应力和应变值及卸载后板料的回弹结果     

薄板深拉延成形有限元仿真

板材成形有限元仿真采用虚拟制造技术反映模具与板材之间的相互作用以及板材实际变形的全过程,有助于推动生产的快速化和设计的智能化。汽车企业通过对板材成形过程的有限元仿真可确定钢板性能参数范围和冲压工艺参数范围,以保证生产的稳定性。采用动力显式有限元软件LS-DYNA,对上海宝钢St14-T冷轧薄板的深拉延成形过程进行了仿真计算,分析了变形过程的金属流动规律。     

External force-assisted laser forming process for gaining high bending angles

Laser forming process is used in forming and bending of metallic and non-metallic sheets. Laser beam irradiation causes a localized temperature increase and a localized mechanical strength decrease. In this article, an external mechanical force is added to a laser beam irradiation, which is called external force-assisted laser forming process, to gain a 90-degree bending angle. Furthermore, Numerical simulation of the process is performed to achieve a good understanding of the process. Simulation results show that more than two-third of the final forming is due to the laser beam irradiation. Equivalent plastic strain values during laser forming and external force-assisted laser forming processes are compared. Results show that equivalent plastic strain in laser forming process increases in a step pattern, with increasing in scan pass numbers. This occurs because when the laser beam irradiates on the sheet surface, it reduces the yield strength of the sheet. Equivalent plastic strain in external force-assisted laser forming process has an oscillatory step nature. This attributes to simultaneous effects of strain hardening and thermal induced reduction of yield strength of the sheet. Simulations were in good accordance with experiments.     

Application of CGP-cross route process for microstructure refinement and mechanical properties improvement in steel sheets

A modified method of severe plastic deformation (SPD) entitled constrained groove pressing-cross route (CGP-CR) was introduced for imposing a high magnitude of equivalent strain of about 2.32 per pass on the sheet form samples. The major benefit of this improved route compared to previous common route was the more homogeneity of strain in the rolling (RD) and transverse (TD) directions of sheets. In this study, low carbon steel samples were used for examination of evolutions in microstructure and mechanical properties during SPD via CGP-CR process. Mechanical properties improvement were measured by tensile and macro hardness tests. The results indicate that CGP-CR process can effectively improve tensile strength; and also, yield stress and hardness of as-received low carbon steel samples were improved up to about 100% after two deformation passes. Also, high magnitude of inhomogeneity can be observed in hardness distribution through first pass of the process which diminishes in the subsequent passes. Microstructural evolutions during process were monitored by optical microscopy observations and X-ray diffraction analysis. The results demonstrate that initial ferritic microstructure with grain size of about 30 μm was refined to a 225 nm cell structure after two passes of CGP-CR process.     

多通管塑挤胀形关键技术的研究

多通管是工业上应用量大面广的一种基础件,但其传统的制造工艺目前还只限于铸造、焊接和机加工等,从经济或技术的角度讲都显得比较落后.此文讨论了利用聚氨酯橡胶棒为胀形介质,采用塑挤胀形的复合工艺把无缝管坯一次成形为成品的加工方法,分析了多通管塑挤胀形的过程,讨论了冲头作用于管坯的压力、聚氨酯橡胶棒产生的内压和平衡缸应提供的背压三者间应具备的合理的关系.以使变形区处于最有利于变形的强烈的三向压应力和合适的偏应力状态,获得尽可能长的支管.     

基于能量中值等效原理的液压鼓胀毫微测试技术研究

目的 基于液压鼓胀毫微测试技术获取材料单轴拉伸力学性能参数.方法 借助能量中值等效原理和有限元辅助测试方法,提出了获取材料单轴拉伸力学性能的液压鼓胀毫微测试理论.结合小圆片试样液压鼓胀试验,获取了压水反应堆机组蒸汽发生器接管材料20MND5的屈服应力和应变强化指数.将其输入有限元,进而模拟小圆片试样液压鼓胀加载的全过程...     

Prediction of flange wrinkling in deep drawing process using bifurcation criterion

Surface distortions in the form of wrinkles are often observed in sheet metals during stamping and other forming operations. Because of the trend in recent years towards thinner, higher-strength sheet metals, wrinkling is increasingly becoming a more common and troublesome mode of failure in sheet metal forming. The prediction and prevention of wrinkling during a sheet forming process are important issues for the design of part geometry and processing parameters. This paper treats the phenomenon of flange wrinkling as a bifurcated solution of the equations governing the deep drawing problem when the flat position of the flange becomes unstable. Hill’s bifurcation criterion is used to predict the onset of flange wrinkling in circular and square cup drawing. In particular, the maximum cup height that can be drawn without the onset of flange wrinkling is predicted for the given set of process parameters. A parametric study of the maximum cup height is also carried out with respect to various geometric, material and process parameters. Finite element formulation, based on the updated Lagrangian approach, is employed for the analysis. The incremental logarithmic strain measure, which allows the use of a large incremental deformation, is used. The stresses are updated in a material frame. The material is assumed to be elastic–plastic, strain hardening, yielding according to an anisotropic yield criterion of Barlat et al. (2005) [23] (named as Yld2004-18p). Isotropic power law hardening is assumed. Inertia forces are neglected due to small accelerations. Modified Newton–Raphson iterative technique is used to solve the nonlinear incremental equations.     

Bending of Titanium Sheet Using Laser Forming

Laser forming, a novel manufacturing method for bending sheet metal first reported in 1985, has been investigated as an alternative to hot brake forming (industry standard) of titanium sheet parts for the aircraft industry. Laser forming involves scanning a focused or partially defocused laser beam over the surface of a titanium workpiece to cause localized heating along the bend line and angular deflection toward the beam. The main advantage that laser forming has over conventional brake forming is increased process flexibility. An experimental investigation of this process (primarily designed experiments) met the following objectives: identified the response variables related to change in geometry (bend angle) and material microstructure; characterized the influence of process variables (scanning speed, beam diameter, laser power) on these response variables; determined the degree of controllability over the process variables; and evaluated the suitability of laser forming for the aircraft industry (most important), all with respect to titanium sheet. It has been determined that laser forming with an Nd:YAG laser is a controllable, flexible manufacturing process for titanium sheet bending. Unfortunately, these advantages over traditional hot brake forming are overshadowed by the fact that, with regard to forming with titanium, laser forming is significantly slower and more labor and energy intensive, and results in unacceptable material properties at the bend line according to aircraft industry standards. These findings cast doubt over the assertions of some researchers that laser forming may be a viable manufacturing process for parts made in small batches. Instead, it appears that it may be best suited for rapid prototyping of sheet metal parts.     

金属板材成形的静力隐式有限元分析与程序设计

阐述了用于板材成形过程静力隐式数值模拟的弹塑性大变形有限元方法 ,基于给出的方法编制了板材成形过程数值模拟软件 ,并对矩形板的液压胀形进行了有限元分析 ,计算结果与典型的实验结果吻合很好。对球形模具拉伸成形过程进行了数值模拟 ,给出了计算结果     

Numerical modelling of electrohydraulic free-forming and die-forming of DP590 steel

Electrohydraulic forming (EHF) is a high energy rate forming process in which the strain rate in the sheet metal can vary from 5 × 10² to 10⁵ s⁻¹ depending on various factors. Several mechanisms have been reported to cause an improvement in formability in EHF such as material deformation mechanisms, inertial effects and the dynamic impact of the sheet against the die. EHF is a complex high speed forming process and experimental work alone is not sufficient to properly understand this process. To understand the variation of some influential variables in EHF, electrohydraulic die-forming (EHDF) and free-forming (EHFF) of DP590 dual phase steel were simulated in ABAQUS/Explicit by considering the fluid/structure interactions. Three-dimensional finite element simulations were conducted by modelling the water with Eulerian elements with a view to investigating the effect of released energy on the sheet deformation profile history, strain distribution, loading path and damage accumulation type. The Johnson–Cook constitutive material model was used to predict the sheet behaviour and the parameters in this model were calibrated based on experimental test results available for DP590 at various strain rates. The Johnson–Cook phenomenological damage model was also used to predict the ductile failure (damage accumulation) in both EHDF and EHFF. Predicted final strain values and damage accumulation type showed good agreement with the experimental observations.     

采用薄膜模型模拟三维板料成形过程

此文基于有限变形理论建立了三维金属板料成形过程的弹塑性有限元数学模型。数学模型采用物质坐标系中的Total Lagrange描述、J_2型本构方程、等向强化假设,考虑了板料的厚向异性,对于金属板料与模具的摩擦采用近似的库仑摩擦定律以改善计算的收敛性。为简化计算采用薄膜单元。采用根据此模型编制的程序模拟了机油收集器基本件的成形过程,并与实验结果进行了对比。     

Deformation inhomogeneity in roll drawing process

The deformation inhomogeneity of flat wires produced with roll drawing process is analyzed. The effect of main process parameters, i.e., initial wire diameter, forming roll dimension and thickness reduction on deformation inhomogeneity is established by means of experimental tests and a developed FE model. Vickers microhardness–strain relationship is developed for the analyzed material (low carbon steel AISI-1010) by correlating the microhardness measurements and effective strain fields as predicted by an axisymmetric numerical model of a compression test. A non-linear finite element model of roll drawing process is developed for a thorough understanding of process parameters effect on deformation inhomogeneity. Thus, in order to encompass the wide range of process conditions, an inhomogeneity index, calculated as the coefficient of variation of effective strain, is used. The numerical results showed that the inhomogeneity factor of flat wires produced with roll drawing is highly dependent on area reduction.     

LY12超塑性成形有限元分析

基于LY12铝合金超塑性材料属性建立了弹-粘塑性本构模型。利用该本构模型并结合最大等效应变速率控制压力变化算法对LY12铝合金板超塑性圆杯成形进行数值模拟,得到圆杯变形过程中的应力应变分布、板料厚度变化及所需成形时间。根据模拟获得的优化压力时间曲线对圆杯进行超塑性气压胀形加载实验,制件厚度分布与模拟结果非常接近。     

金属板料成形摩擦机理研究

对不锈钢板料和碳钢在金属塑性成形时 (高接触压力 )的摩擦机理进行了实验研究 ,分析了压力对滑动阻力和摩擦系数的影响 ,得出了随压力增大摩擦系数逐渐变小的结论 ,从而为应用有限元法进行板料成形过程中塑性变形的计算机模拟提供真实的边界条件打下了基础。     

LYl2半球形件拉深成形过程的动力显式有限元模拟

基于连续介质力学及有限变形理论 ,建立了用于三维板料成形过程模拟的有限元模型 ,开发了动力显式算法的板料成形过程模拟的有限元分析程序DESSFORMM3D。最后 ,用笔者新开发的动力显式弹粘塑性有限元程序对不同压边情况下半球形件的拉深过程进行分析 ,并把数值结果与实验进行对比 ,验证了软件的计算结果。     

Warm forming die design,part I: Experimental validation of a novel thermal finite element modeling code

Finite element analysis (FEA) has become an invaluable tool in the design of sheet metal stamping dies and processes. FEA has gained widespread acceptance as the best method of optimizing dies for conventional stamping processes. More recently, FEA has been shown to be an effective method of designing tooling for sheet forming processes. In this work, an FEA based approach is applied to the warm stamping (warm forming) process. This work introduces a new thermal finite element analysis software called PASSAGE®/Forming (PASSAGE) that enables the up-front design of the thermal management of warm forming dies. This thermal finite element analysis software is designed to specifically handle the forming and optimization scenarios related to the heating of a stamping die while minimizing user interface time. In this work, PASSAGE has been applied to a simple block of steel embedded with cartridge heaters to validate the prediction capability of this software under two different heating conditions. The results show that PASSAGE is capable of predicting the actual steady-state temperature distribution within the block with an acceptable level of accuracy while yielding notable information to the user with respect to specifying power requirements. A finite element software package like PASSAGE is a valuable tool that will aid greatly in the implementation of warm forming as a manufacturing process beyond the scope of the laboratory and into production.     

板材超塑性拉延过程的数值模拟

板料超塑性成形是一种全新的成形方法。用刚塑性有限元法对Zn 2 2Al合金U形拉延过程进行了数值模拟 ,分析了变形过程中工件的应力、应变、摩擦和厚度分布 ,揭示了成形过程中金属的塑性变形规律 ,为成形工艺设计提供了有效的分析工具。     

Influence of displacement constraints in thermomechanical analysis of laser micro-spot welding process

The evolution of mechanical components into smaller size generating a need for microwelding of these components using laser which offers better control as compared to arc and plasma processing. The present article describes the numerical simulation of laser micro-spot welding using finite element method. A two dimensional Gaussian distributed surface heat flux as a function of time is used to perform a sequentially coupled thermal and mechanical analysis. The model is used for simulating laser micro-spot welding of stainless steel sheet under different power conditions and configurations of mechanical constraints. The temperature dependent physical properties of SS304 have been considered for the simulation and an isotropic strain hardening model has been used. The simulated weld bead dimensions have been compared with experimental results and temperature profiles have been calculated. The maximum deformation of 0.02 mm is obtained with maximum laser power of 75 W. The thermal stress is more inducing factor to temperature induced residual stresses and plastic strain as compared to mechanical constraints. The plastic strain changes significantly by displacement constraints as compared to residual stress.     

An Analytical Prediction of Flange Wrinkling in Sheet Metal Forming

Wrinkling is one of the major defects in sheet metal forming. The ability to accurately predict the occurrence of wrinkling is critical to the design of tooling and processing parameters. An analytical approach for predicting the onset of flange wrinkling is presented. This method is based on the wrinkling criterion proposed by Cao and Boyce for predicting the buckling behavior of sheet metal under normal constraint. Using a combination of energy conservation and plastic bending theory, the analysis provides the critical buckling stress and wavelength as functions of normal pressure. The results are in excellent agreement with those obtained from Cao and Boyce's numerical approach, and also match well with the experimental results of a square cup forming. In addition, the effects of material properties on the wrinkling behavior are also discussed. The analytical method significantly reduces computational time and is suitable for direct engineering application.     

半球形件粘性介质压力成形的数值模拟研究

粘性压力成形技术是金属板材成形领域里新近出现的一种先进的加工工艺。对双面施放粘性介质的板材胀形进行了模拟研究 ,在双面施放介质的板材粘性介质胀形时 ,排放孔位置分布对毛坯成形过程有明显的影响。排放孔位置分布的不同造成模腔内介质的速度场不同 ,进而导致板材不同部位的流动速度的方向大小发生变化 ,最终使成形件的厚度分布不同