弹塑性有限元法分析不同型线凹模静液挤压时的应力和应变状态

静液挤压时,如凹模的型线不同,变形区的应力和流动状态是不同的。目前,静液挤压时,广泛采用圆锥模,但在挤压脆性金属时,产品经常会出现缺陷。为了研究产生缺陷的原因,应用弹塑性有限元法计算和分析了等应变型线模、余弦型线模、最短流线模、椭圆型线模及圆锥模等五种不同型线凹模在静液挤压时的应力和应变状态。结果表明,等应变型线凹模挤压时的应力和应变分布最为均匀,挤压力和塑变区内的拉应力最小,适用于挤压脆性金属。计算结果与实验比较,符合很好。计算结果对设计挤压凹模有很大的参考价值。     

基于流函数法的铝型材挤压导流模合理设计

采用模拟试验法和理论分析法研究了导流模内型材挤压的流动机理;提出了确定导流腔最小深度的理论依据;用基于流函数的上限分析法确定了实心薄壁铝型材挤压变形的流线方程、动可容速度场、应变速率场及上限功率;讨论了变形程度等参数对导流模最小理论深度的影响,得出实心薄壁铝型材导流腔深度的理论最小值为导流腔半宽的0.7～0.8倍。理论结果得到了试验证实,为导流模合理设计提供了可靠的依据。     

压铸机压射头冷挤压成形工艺DEFORM-3D优化分析

为了获得高质量的压射头,采用冷挤压成形方式。基于压射头成形过程工艺的研究,设计了合理的工艺流程、冷挤压前处理工艺与边界条件,建立了正挤压和反挤压两种成形方式的有限元模型,以DEFORM-3D为平台,初步预测了冷挤压成形过程中材料应变场、应力场与流速场的分布情况。结果表明:采用正挤压成形,凹模径向负载比反挤压减小72.2%,模具寿命延长;等效应变增大了93.4%,材料变形更充分,性能有效提高。     

复合挤压变形规律的研究

利用光塑性方法模拟研究复合挤压变形,获得变形区的全场应变分布曲线;分析材料的流动规律,将变形体分为挤压型变形区,镦粗型变形区和刚性区３个特性区域。建立上限模型,分析模具几何参数对复合挤压变形的影响,证明凸模直径与正挤出口直径对复合挤压变形的影响最大。     

基于磨损正交试验的温挤压模具优化设计

以汽车转向螺杆的杯-杆件温热挤压凹模为例,通过对温挤压成形工序的分析,得到影响温挤压凹模磨损寿命的4个主要因素,即凹模入口处圆角大小、模具初始硬度、模具初始温度、摩擦因子。设计四因素四水平标准正交实验表,通过Deform-3D数值模拟软件,基于Archard磨损理论进行温挤压凹模型腔磨损正交试验。以凹模磨损量最小为目标获得凹模模具的最优四因素组合,并得出在温挤压内孔工序中模具初始硬度对凹模磨损影响最大,对实际生产中模具材料的选择和热处理有一定指导作用。在最优参数组合下,通过数值模拟计算得到凹模在温挤内孔中稳定阶段的磨损量,并预测出模具的使用寿命。     

基于正交试验的温挤压模具磨损优化设计

以汽车转向螺杆的杯-杆件温热挤压凹模为例,通过对温挤压成形工序的分析,得到影响温挤压凹模磨损寿命的4个主要因素,即凹模入口处圆角大小、模具初始硬度、模具初始温度、摩擦因子。设计四因素四水平标准正交实验表,通过Deform 3D数值模拟软件,基于Archard磨损理论进行温挤压凹模型腔磨损正交试验。以凹模磨损量最小为目标获得凹模模具的最优四因素组合,并得出在温挤压内孔工序中模具初始硬度对凹模磨损影响最大,对实际生产中模具材料的选择和热处理有一定指导作用。在最优参数组合下,通过数值模拟计算得到凹模在温挤内孔中稳定阶段的磨损量,并预测出模具的使用寿命。     

双杯形件温挤压成形数值模拟与分析

应用有限元法对双杯形件温挤压成形进行了数值模拟，着重分析了不同挤压温度、不同凹模圆角下的金属流变和应力应变分布，对模拟结果进行了对比分析，从而为优化模具设计，以及实验研究和生产提供了科学的依据。     

陶瓷浆料微流挤压成形关键问题研究

利用流体力学理论,针对基于微流挤压成形的陶瓷浆料挤出过程的关键部件挤压凹模的流道形状进行了设计,使用ANSYS软件对挤压凹模出口横截面的流速和流道内部压力场的分布情况进行模拟,分析了四种不同流道形状挤压凹模内部压力场和出口流速的分布规律。研究结果为解决陶瓷浆料挤压成形工艺的难点问题提供了理论依据,具有重要的参考价值。     

摩擦因数与模角对扭转挤压模具影响的研究

为了优化扭转挤压模具,基于刚塑性有限元理论,应用Deform-3D软件对T2纯铜坯料在扭转挤压下的成形过程进行数值模拟,对比分析了不同摩擦因数与模角情况下,载荷的挤压行程曲线、坯料的等效应变和模具的磨损。结果表明,增大摩擦因数与模角均可增大坯料的变形量,且增大模角效果更明显。     

筒形件颗粒或可压缩粉末软凹模拉深工艺的力学分析

提出了一种颗粒或可压缩粉末软凹模成形工艺。基于一定的基本假设,对筒形件颗粒或可压缩粉末软凹模的成形工艺进行了力学分析。将该工艺与刚性模具成形工艺进行了对比,分析了筒形件成形过程中各变形区域的应力应变状态及数值大小,推导出变形时与颗粒或可压缩粉末接触区域的应力和应变的计算公式。研究结果证明,颗粒或可压缩粉末软凹模成形工艺...     

Axi-symmetric tube extrusion through a smooth conical or cosine die and over a conical or ogival mandrel: numerical construction of axi-symmetric slip-line fields and associated velocity fields

The numerical method of construction of axi-symmetric slip-line fields and their associated velocity fields suggested earlier for rod extrusion (Chitkara NR, Butt MA. Axi-symmetric rod extrusion through smooth conical, cosine and lat-faced dies, International Journal of Mechanical Sciences, submitted) and tube extrusion (Chitkara NR, Butt MA. Axi-synnetric tube extrusion through a flat-faced circular die: International Journal of Mechanical Sciences, 1997;39(3);341–366) is employed to construct slip-line fields and their associated velocity fields for a few cases of forward tube extrusion through smooth, rigid conical and cosine dies and over a smooth rigid conical or ogival mandrel. The computographic plots of slip-line fields and associated velocity fields are given in the form of weighted and directed velocity vectors as are the normal pressure distribution on both the die and the mandrel surfaces. The values of the non-dimensionalised mean extrusion pressures, are compared in each case with a similar case of plane strin extrusion and the results commented upon.     

Axisymmetric extrusion through adaptable dies—Part 3: Minimum pressure streamlined die shapes

In Part 1 of this series of papers, six kinematically admissible velocity fields, as well as the power terms, were developed for use in upper bound models for arbitrarily shaped dies for axisymmetric extrusion. Part 2 compared the results obtained in upper bound models for the six velocity fields through a spherical die shape and demonstrated that the sine-based velocity field was the best. In this final part, the application of the sine-1 field to extrusion through streamlined dies is developed. By fixing the values of two additional constants in the radial flow flexibility function, the two surfaces of velocity discontinuity, which separate the deformation zone from the incoming and outgoing material, will have no shear. In effect, the analysis for streamlined dies can be modeled without the surface of velocity discontinuity power terms. The results for an arbitrarily curved streamlined die, as proposed by Yang and Han, using the sine-1 velocity field and the cylindrical velocity field from the work by Yang and Han are compared. It is found that the upper bound model using the sine-1 velocity field predicts lower values for the extrusion pressure. A method to determine a streamlined die shape is proposed. The method allows flexibility between the entrance and exit by the use of a Legendre polynomial series for representation of the die surface. The method is termed an adaptable die design. The adaptable die design method is used to determine streamlined die shapes, which will minimize the pressure required for the extrusion process.     

平面挤压变形的模拟研究

本文利用光塑性方法,以国产聚碳酸酯为模拟材料,研究了平面挤压变形,获得了平面挤压变形的全场应变分布。所得应变值的平均误差小于7%。利用光塑性的特性确定了变形区的范围和磨擦对变形区的影响。本文的研究揭示了平面挤压变形的特点及模具润滑等条件对变形流动的影响。     

An analytical solution for the spread extrusion of shaped sections

Spread extrusion could be used for manufacturing of wide profiles in the extrusion industry. In this paper a new method of design and analysis has been presented for such a problem. Special dies were designed for profiled sections such as square, rectangular, elliptical and cross shapes. These dies force the material to flow sideways and spread so as to extrude sections with wider dimensions than the initial billet or the maximum container diameter. The geometry of the deforming zone in the die was formulated and based upon that, a kinematically admissible velocity field was derived. Using this velocity, we estimated the field upper bound on extrusion power. Profile sections with different aspect ratios were investigated and the influence of other process parameters such as friction and reduction of area on the extrusion pressure were studied. Optimum die lengths for each die were calculated so as to minimize the extrusion pressure. Finite element analysis for the numerical simulation of the process was also carried out. The finite element results were also used as an aid to the design process of the extrusion dies. Dies were manufactured for different sections such as square, rectangle, and ellipse and cross shapes. Experiments were carried out to obtain data to verify the theory. Comparison of the results showed good agreement between the theoretical, numerical and experimental data. It was concluded the present method could be used to design dies for the spread extrusion of different shaped dies.     

Axisymmetric extrusion through adaptable dies—Part 1: Flexible velocity fields and power terms

An adaptable die is one that not only produces the correct geometrical shape, but also is designed through an adaptable method to impart other desirable properties to the product or process. In this first part of a series of papers, six kinematically admissible velocity fields are developed for use in upper bound models for axisymmetric extrusion through various dies, including extrusion through adaptable dies. Three base velocity fields are presented:

(1) assuming proportional angles in the deformation zone,

(2) assuming proportional areas in the deformation zone, or

(3) assuming proportional distances from the centerline in the deformation zone.

The base velocity is modified by an additional term comprised of two functions. One function allows extra flexibility in the radial direction, and the second function allows extra flexibility in the angular direction. There are two forms of the second function, which meet the required boundary conditions. The flexibility function in the radial direction is represented by a series of Legendre polynomials, which are orthogonal over the deformation region. The power terms derived for these velocity fields for use in upper bound models are also presented.Part 2 of this series compares the results obtained in upper bound models for the six velocity fields for a spherical extrusion die. In Part 3, the use of the best velocity field for extrusion through streamlined dies is developed to determine the adaptable die shape, which minimizes the required extrusion pressure. Additionally, the adaptable die shape is compared with results from Yang and Han for arbitrarily curved and streamlined dies.     

Extrusion of non-symmetric T-shaped sections, an analysis and some experiments

In the present study, previously developed analytical approach (Int. J. Mech. Sci. 42 (2000) 273), based on the upper-bound theory, for the design of three-dimensional off-centric extrusion of arbitrarily shaped dies was applied to the extrusion of T-shaped sections from initially round billets with the experimental verifications. Here, non-symmetric T-shaped sections as well as symmetric ones were considered. A computer program was written to obtain optimum die design which yield the lowest upper-bound for a given reduction in area, die length, its off-centric positioning and the frictional conditions. Computations were carried out both for the converging (ruled-surface) and the smooth curved (advanced-surface) dies. Curvature of the extruded product and simulated deforming grid pattern were also predicted. A sophisticated CAD/CAM package was used in conjunction with the CNC and EDM processes to manufacture the streamlined dies for the extrusion of T-shaped sections. The theoretical predictions were observed to be in good agreement with the experimental results.     

铝合金轴固定件热挤压成形的有限体积法模拟研究

由于变形剧烈，复杂铝型材挤压成形有限元模拟会因网格不断重划分而精度欠佳。文中基于可以有效避免网格重划分难题的有限体积法，对铝合金门轴固定产品的热挤压过程进行数值模拟，详细分析挤压成形中各个阶段金属流动情况以及应力、应变、温度、速度等场量的分布变化情况。棒料进人模口至完全流出工作带这段时间是型材挤压最为困难的阶段，材料在工作带处的应力、应变最大，温度最高，因而对模具工作带处造成的磨损也最为严重。进人到最终稳定挤压阶段时挤压方向金属流速计算值与理论挤出速度吻合很好。模拟结果表明所用有限体积法是有效的，可以为铝型材挤压的模具设计与工艺参数的选择提供理论指导。     

A generalized method for analysis of three-dimensional extrusion of arbitrarily-shaped sections

Despite increasing demand for and application of three-dimensional extrusion of various sections through continuous dies, so far very little work has been done by systematic and general analysis to predict the plastic flow properly. For effective die design, efficient design method and the related method of theoretical analysis are required for extrusion of complicated sections. In generalized three-dimensional extrusion of sections through continuous dies, a new method of die surface representation, using blending function and Fourier series expansion, is proposed by which smooth transitions of die contour from the die entrance to the die exit are obtained. The flow patterns as well as the upper-bound extrusion pressures are obtained on the basis of the derived velocity field. The effects of area reduction, product shape complexity, die length and frictional condition are discussed in relation to extrusion pressure, the distorted grid pattern and distribution of the final effective strain on the cross-section of the extruded billet. As computational examples for arbitrarily-shaped products rounded rectangles and ellipses are chosen for the extruded sections. Experiments are carried out for aluminum alloys at room temperature for a rounded square section and an elliptic section. In order to visualize the plastic flow, the grid-marking technique is employed. The theoretical predictions both in extrusion load and deformed pattern are in good agreement with the experimental results.