多向塑性成形数值模拟研究

金属在多向受力状态下产生的流动复杂多变,人工预测及一些简单解析法计算无法准确预测金属的实际流动规律.本文用MSC/superform软件对复杂形状零件分别进行了多向挤压成形数值模拟.通过模拟结果可以看出,体积成形过程中金属的流动主要与模具型腔的形状以及填充系数有很大的关系,适当的填充系数不仅方便装料,更能减小坯料与型腔内壁的摩擦从而减少变形抗力及变形不均匀现象.模拟分析了金属在多向挤压时的载荷-行程曲线和等效应变的分布,为后续模具的设计提供科学的依据.     

工艺参数对铝型材挤压变形规律的影响

通过引进一个反映金属流速不均衡性的参数———流速均方差 ,有效地控制型材挤压成形时金属流动的不均匀性。采用有限变形弹塑性有限元方法 ,对不同挤压参数 (挤压比、摩擦因子 )下铝型材挤压过程进行了数值模拟研究 ,获得了挤压压力、流速均方差和型材件内部应力应变场随挤压参数变化的规律 ,为铝型材挤压工艺参数优化提供了理论参考。     

热反挤压过程中金属不稳定流动状态的研究

利用有限元软件Deform-3D对厚壁钢管热反挤压制坯过程进行数值模拟,分析了摩擦系数和壁厚对金属流动状态的影响.结果表明:反挤压件管壁内侧的金属在向上平移的同时还伴有径向移动,摩擦系数越大、管壁越厚,径向移动的程度越大,越容易造成凸模抱模的现象.根据模拟结果,提出了一种新增径向塑性变形区的大型厚壁钢管热反挤制坯的变形...     

型材挤压模工作带长度设计计算的数学建模

本文采用有限元方法 ,以型材挤压过程的有限元模拟为基础 ,研究了局部挤压比、挤压带面积和模孔距离对金属流动速度的影响 ,获得了型材挤压过程的变形流动规律。并综合主要模具结构参数对金属流动速度的影响 ,建立了铝型材挤压模模孔工作带设计计算的数学模型。选择实际型材零件按本文推导的公式设计了工作带长度 ,并与实验进行了验证 ,结果表明挤压效果良好。该公式可用于铝型材挤压模工作带长度设计计算     

6061合金双向等通道挤压金属流动规律研究

摘 要: 采用数值模拟和实验验证的方法研究了双向等通道挤压过程金属流动规律,发现双向等通道技术能够在材料内部造成剧烈的剪切变形,具有晶粒细化和形变强化作用,可以通过调整摩擦系数对变形过程进行调控。6061合金A、B两种路径四道次双向等通道挤压发现,双向等通道具有强烈的形变强化作用,在相同道次下,B路径等效应变量大于A路径。     

用有限元法揭示钣材挤压工艺的成形特点

采用刚塑性有限元法、自编程序对钣材挤压工艺进行了模拟 ,从而获得了钣材挤压成形时的网格畸变图、金属流动图、速度场、等效应力场、等效应变场以及H M无量纲数分布场等结果 ,并进一步揭示了钣材挤压工艺的一些成形特点。此外 ,通过实验获得了钣材挤压成形时的网格畸变照片以及裂纹出现照片 ,其结果与采用有限元法所揭示的结果相一致。     

AZ80镁合金变形特性及管材挤压数值模拟研究

利用Gleeble热模拟机研究了AZ80合金的高温变形特性。结果表明,流变应力取决于变形温度和变形速率。当应变速率一定时,流变应力随变形温度的升高而降低;当温度一定时,流变应力随着应变速率的升高而增大。根据AZ80镁合金真应力-真应变曲线,建立了其流变应力模型。采用刚塑性有限元法对AZ80镁合金管材挤压过程进行热力耦合数值模拟,并分析了高温挤压成形过程中变形力及金属流动规律,着重探讨了变形温度和挤压速度等挤压工艺参数对挤压力、应变场以及应力场的分布及变化情况的影响。模拟的结果为AZ80镁合金管材挤压工艺参数的制定、优化提供了科学依据。     

钢结构镀锌涂层冲蚀磨损表面形貌及粗糙度

我国西北地区风沙特殊环境对该地区钢结构的耐久性和安全性影响严重。利用风沙环境侵蚀实验系统、扫描电子显微镜(SEM)和激光共聚焦显微镜(LSCM)研究钢结构镀锌涂层受风沙冲蚀磨损损伤行为和损伤形貌,并分析其表面粗糙度。结果表明:涂层材料的冲蚀损伤行为更加依赖于冲蚀角度,在不同冲蚀角度下风沙流对涂层材料的冲蚀磨损过程同时存在类似表面划伤和挤压变形剥落;涂层材料的冲蚀坑深度随着冲蚀速度的增大而增加,在90°时冲蚀坑深度大于45°时的冲蚀坑深度;在相同的冲蚀速度下,45°时表面平均粗糙度Sa和均方差Sq较90°时大,在相同的冲蚀角度下,Sa和Sq均随速度的增大而增大。在冲蚀中后期,粒子对凹凸不平的表面冲蚀磨损破坏严重,试件表面峰谷的形成和破坏导致冲蚀率增加。     

不同参数对铝合金枝杈类构件金属流线的影响及优化

通过有限元模拟软件,分析了不同参数对某铝合金枝杈类构件金属流线的影响,分析了该构件在成形过程中金属流线缺陷形成的原因。通过对坯料的高径比、挤压速度和摩擦因子3个参数进行优化,确定了最佳金属流线分布的成形方案。研究结果表明:适当增大坯料与模具之间的摩擦,可控制后期径向金属流动量和流动速度,从而有效地避免穿流缺陷的产生;较慢的挤压速度和合适的高径比,可有效降低金属的径向流动速度和向上反挤的速度差,从而避免产生穿流缺陷,使成形构件的金属流线分布合理。通过有限元模拟确定出金属流线分布的最佳成形方案为摩擦因子为0.3、挤压速度为0.3 mm·s^-1、坯料的高径比为1.285。     

平面变形侧向流动过程的上限分析

径向挤压是挤压技术中的一种新的挤压方法,近年来该方法正日益引起国内外学者的兴趣和重视,并逐渐得到发展。本文采用了极限分析理论中的上限原理较为详细地研究了平面变形状态侧向流动过程、平面变形状态侧向流动过程中金属流动特性、挤压力随变形过程和变形程度不同的变化规律,以及有关工艺参数对变形的影响等问题。理论分析结果与试验结果十分一致。     

Temperature effects on mechanical properties,deformation behavior and formability of Zr−Ti−Cu−Ni−Be−Nb bulk metallic glass composite

The deformation behavior and macroscopic formability of a Zr-based bulk metallic glass composite (BMGC) has been investigated in this study by performing a series of compression and laboratory-scale extrusion tests under various deformation rates within the supercooled liquid temperature region. The morphology of Zr−Ti−Nb-rich dendrite precipitates after warm deformation was first examined by using optical microscopy (OM) and a field emission scanning electron microscope (FE-SEM). The extrusion of this BMGC alloy within the supercooled liquid temperature region was found more difficult than the extrusion of other Zr-based monolithic BMG alloys, possibly due to the existence of dendrite phases hindering the characteristic viscous flow generated in the amorphous phase. A FEM simulation has also been carried out by utilizing the stress-strain behaviors obtained from high temperature compression tests, and the results have been compared with the experimental extrusion test results. The FEM simulation results for the extrusion process as well as a processing map based on a dynamic materials model (DMM) were found to agree relatively well with the actual macroscopic extrusion formability.     

Hot deformation behavior of Mg-7.22Gd-4.84Y-1.26Nd-0.58Zr magnesium alloy

The behavior evolvement of Mg-7.22Gd-4.84Y-1.26Nd-0.58Zr(GWN751K) magnesium alloy during the hot deformation process was discussed.The flow stress behavior of the magnesium alloy over the strain rate range of 0.002 to 2.000 s-1 and in the temperature range of 623 to 773 K was studied on a Gleeble-1500D hot simulator under the maximum deformation degree of 60%.The experimental results showed that the relationship between stress and strain was obviously affected by strain rate and deformation temperature.The flow stress of GWN751K magnesium alloy during high temperature deformation could be represented by the Zener-Hollomon parameter in the hyperbolic Arrhenius-type equation.The stress exponent n and deformation activation energy Q were evaluated by linear regression analysis.The stress exponent n was fitted to be 3.16.The hot deformation activation energy of the alloy during hot deformation was 230.03 kJ/mol.The microstructures of hot deformation were also influenced by strain rate and compression temperature strongly.It was found that the alloy could be extruded at 723 K with the mechanical properties of σ0.2 = 260 MPa,σb = 320 MPa,and δ = 18%.     

型材挤压过程金属变形流动的有限元仿真

采用大变形弹塑性有限元理论,对典型型材角铝零件的挤压成形过程进行了全面有限元仿真和分析。深入研究了了型材挤压变形过程中金属变形流动规律和力学特征,对挤压工艺参数合理选择和优化奠定了基础。     

316不锈钢异形Ⅰ截面型材挤压成形过程有限元模拟

以异形Ⅰ形截面不锈钢型材为研究对象,采用DEFORM-3D有限元软件系统对其热挤压成形过程进行数值模拟分析.研究了挤压稳态成形过程中挤压速度、摩擦系数、坯料预热温度等因素对不锈钢型材挤压过程的影响.计算结果表明,当挤压比为9、挤压速度为200mm/s、摩擦因子为0.3、模具预热温度为450℃、坯料预热温度为1050℃时,金属流动状况良好,材料的应力应交分布均匀,可有效提高模具的寿命,对指导实际生产具有积极的参考价值.     

挤压筒摩擦对正挤压成形影响的研究

在对正挤压摩擦特点分析的基础上,采用Deform-2D对挤压筒与坯料之间的摩擦在挤压成形中的影响进行了研究.结果表明:挤压筒不动的情况下两者之间的摩擦是成形的阻碍;但挤压筒随挤压杆同向运动且形成有效摩擦时,可以降低成形力,改善金属的流动,有利于提高挤压件的质量和模具的使用寿命.     

Zr41Ti14Cu12.5Ni10Be22.5非晶棒料摩擦焊接

设计了一种非晶合金摩擦焊装置,以Zr₄₁Ti₁₄Cu_12.5Ni₁₀Be_22.5非晶棒料为研究对象,进行了摩擦焊试验.焊接样品经SEM,XRD,维氏硬度、TEM等检测,结果显示焊接界面无明显未熔合,样品仍然保持非晶态,接头硬度总体增大,接头处出现了纳米晶.采用ANSYS软件对非晶合金摩擦焊的温度场进行仿真.结果表明,在摩擦时间t=0.25s时摩擦界面中心温度超过非晶棒料玻璃转变温度,接触面全部进入过冷液相区,应进行顶锻.仿真结果与摩擦焊试验结果基本吻合,有利于指导焊接试验.     

Die structure optimization of equal channel angular extrusion for AZ31 magnesium alloy based on finite element method

Three-dimensional(3D)geometric models with different corner angles(90°and 120°)and with or without inner round fillets in the bottom die were designed.Some important process parameters were regarded as the calculation conditions used in DEFORMT M-3D software,such as stress—strain data of compression test for AZ31 magnesium,temperatures of die and billet,and friction coefficient.Influence of friction coefficient on deformation process was discussed.The results show that reasonable lubrication condition is im...     

Evaluation of friction condition in cold forging by using T-shape compression test

Friction plays an important role in metal forming, and numerical simulation of forging processes requires precise informations about the material properties and the value of the friction factor m or coefficient μ. This paper describes the T-shape compression, a new friction testing method by combined compression and extrusion of a cylinder between a flat punch and a V-grooved die. It can realize actual cold forging condition and allows measuring the friction on the cylindrical surface of the billet during forging process. The results of experiments and simulations show that the stroke–load curve and the height of the extruded part are both sensitive to friction. In order to obtain the highest sensitivity to friction, a FE parametric study of this test has been performed: it indicates that small corner radius and V-groove angle in the die should be chosen. Two commercial FE codes, FORGE 3D and ABAQUS, were used and provided very similar results for a given friction condition. Low carbon steel drawn bar with phosphate and soap coating was chosen as specimens. Friction tests with three different lubrication conditions (solid coating, oil and oil + solid coating) were carried out, and then friction factor m and friction coefficient μ were determined by using experimental results and the calibration by numerical simulation of T-shape compression test.     

Determination of workpiece flow stress and friction at the chip–tool contact for high-speed cutting

This paper presents a methodology to determine simultaneously (a) the flow stress at high deformation rates and temperatures that are encountered in the cutting zone, and (b) the friction at the chip–tool interface. This information is necessary to simulate high-speed machining using FEM based programs. A flow stress model based on process dependent parameters such as strain, strain-rate and temperature was used together with a friction model based on shear flow stress of the workpiece at the chip–tool interface. High-speed cutting experiments and process simulations were utilized to determine the unknown parameters in flow stress and friction models. This technique was applied to obtain flow stress for P20 mold steel at hardness of 30 HRC and friction data when using uncoated carbide tooling at high-speed cutting conditions. The average strain, strain-rates and temperatures were computed both in primary (shear plane) and secondary (chip–tool contact) deformation zones. The friction conditions in sticking and sliding regions at the chip–tool interface are estimated using Zorev's stress distribution model. The shear flow stress (k_chip) was also determined using computed average strain, strain-rate, and temperatures in secondary deformation zone, while the friction coefficient (μ) was estimated by minimizing the difference between predicted and measured thrust forces. By matching the measured values of the cutting forces with the predicted results from FEM simulations, an expression for workpiece flow stress and the unknown friction parameters at the chip–tool contact were determined.     

连续等径角挤压及其成形过程的三维数值模拟

连续等径角挤压是一种制备大尺寸超细晶材料的新技术,它结合了等径角挤压和连续挤压技术的特点,解决了等径角挤压不能制备大尺寸超细晶材料的问题,该技术对超细晶材料的推广应用具有重要意义。利用DE-FORM3D软件对纯铜连续等径角挤压变形行为进行了数值模拟,分析了变形过程中材料的流动、应变和温度变化情况,并对不同变形速度、摩擦条件和模具结构下的变形过程进行了比较,为连续等径角挤压工艺提供了理论指导。