基于动态仿真的多道冲压工序研究

通过对复杂多次冲压件冲压工艺的分析,初步确定工件各道工序的形状与尺寸。利用DYNAFORM软件对冲压工序进行动态模拟,分析冲压工序的合理性。通过修改参数,确定切实可行的冲压方案。再根据确定的方案设计制造模具,冲压出符合要求的工件。对冲压工序的设计方法和多道成形的动态模拟方法进行了说明,确保模具设计的成功,缩短生产周期,降低生产成本。     

多次冲压工序的数值模拟研究

通过对多次冲压件冲压过程的初步计算和动态仿真,直观地了解了整个冲压过程的各道工序的变形情况,包括应力、应变和厚度分布等,从而知道哪些位置是危险区,并对冲压工艺进行调整。根据模拟结果,设计模具、确定冲压参数,确保了模具设计的成功。     

Analysis of superplastic blow-forming in a conical closed die

A mathematical model using the finite-difference method has been proposed in this work to examine the plastic deformation behavior of the sheet during blow-forming in a conical closed die. In the formulation of this mathematical model, nonuniform thinning in the free bulged region and the contact condition including the sticking and sliding friction modes between the sheet and die are considered. Effects of various forming parameters such as the die entry radius, friction coefficient, inclined angle of the die, etc., upon the optimized pressurization profile, forming time and the thickness distribution of products were discussed systematically. Furthermore, experiments on superplastic blow-forming in a conical closed die were carried out using 8090 Al-Li sheets. It is found that the theoretical predictions agree with experimental results. The thickness distributions of the SPF-ed product obtained with different friction coefficients along the die entry, sidewall and bottom are closer to the experimental data than those obtained with a constant friction coefficient.     

Hydro-rim deep-drawing processes of hardening and rate-sensitive materials

The conventional deep drawing process is limited to a certain limit drawing ratio (LDR) beyond which rupture will ensue. An asymptotic solution of the complete governing equations of this process indicates that this relatively low LDR results from the steep build-up of radial tensile stress with maximum value at the die lip. This tensile stress is significantly enhanced by interfacial friction along the die/flange and by high speed of the operating load and thus holds responsible for premature ruptures. The intention of this work is to examine the possibilities of relaxing the above limitation, aiming towards a process with an ‘unlimited drawing ratio’. The ideas which may lead to this goal are:(a) exerting an external fluid pressure on the outside rim of the blank (“Hydro-rim process”) to reduce radial stress and to decrease, in parallel, the interfacial friction,(b) increasing the blank temperature to a level at which the material is more rate sensitive, and thus less prone to early failure. The benefits of these ideas are examined via parametric analysis of the solution and with experiments in deep drawing processes.A clear outcome from the solution is that if changes in the material properties (strain hardening, strain-rate sensitivity, yield stress, etc.) can be controlled, say, by controlling the temperature and/or the operating speed, the process can reach higher drawing ratios with substantially less assisted fluid pressure.     

Large deformation compression–torsion behaviour of a titanium alloy and its modelling

A range of sequential and compound compression-torsion tests has been carried out on titanium alloy IMI834 at 1000°C and nominal true strain rate 5 × 10⁻³ s⁻¹, typical of forging conditions. The tests were used to investigate initial and subsequent yield and flow behaviour, the nature of the material hardening and the effect of flow softening on subsequent deformation. In addition, a material model with isotropic or directional hardening has been used to predict the material behaviour.The results show that the material behaviour at large strains is reasonably isotropic, although a directional hardening model provides slightly better quantitative agreement with the experimental results. Large pre-strains (0.4), either axial or torsional, are found not to change significantly subsequent material behaviour. A stress state dependence of flow softening is observed to exist.The material model presented is shown to give good quantitative agreement of predicted and experimental results.     

Determination of friction coefficient encountered in large deformation processes

A new technique, namely, the open-die backward extrusion test technique, was developed as an alternative method to the ring compression test in order to quantitatively evaluate the coefficient of friction, μ, at the die/workpiece interface. This technique relates the percentage deformation in height of the specimen to the percentage increase in extruded height of the specimen. In this study, the open-die backward extrusion tests (ODBET) were simulated for different aspect ratios, (H/D), and different die geometries, (d/D), by utilizing an elastic-plastic finite element code (ANSYS) in order to obtain the friction calibration curves (FCCs). The results indicated that the extruded height is related to the friction conditions at the die/workpiece interface. Therefore, ODBET can be used to generate FCCs to determine the coefficient of friction at the die/workpiece interface in large deformation processes.     

塑料注塑的CAD／CAE／CAM（Ⅱ）注塑保压过程分析与应用

借助计算机辅助工程技术模拟注塑保压过程，以优化注塑模具设计和注塑工艺条件设定，是当今改善注塑制品质量和提高生产效率的有效途径．本文介绍了注塑保压过程的一种数学模型与数值解法，并就分析结果介绍了工程应用方法．     

轴对称拉深成形凸缘变形区应力的解析求解

在一定的假设条件下,对轴对称拉深成形凸缘变形区的应力进行解析分析,得到以积分形式表示的应力表达式.进行恰当的变量代换后,根据积分函数符合线性变化的规律,分别利用积分中值定理和泰勒级数展开公式,简化得到径向应力的解析表达式.根据简化公式可直接计算得到任一变形瞬间凸缘变形区的应力分布,以及不同变形瞬间的凹模入口处的径向应力.采用两种简化方法计算与以积分计算得到的结果非常接近,给出的算例表明,在拉深过程中,凹模入口处的径向应力最大相对误差小于0.6％,最大应力相对误差小于0.15％.以圆筒形件的拉深成形为例,在考虑板坯在凸缘区和凹模圆角区的摩擦、及板坯在凹模圆角区的弯曲等条件下,采用简化解析公式,计算极限拉深系数,计算结果与试验值吻合较好.     

The application of abductive networks and FEM to predict the limiting drawing ratio in sheet metal forming processes

The deep drawing process, one of the sheet metal forming methods, is very useful in the industrial field because of its efficiency. The limiting drawing ratio (LDR) is affected by many material and process parameters, such as the strain-hardening exponent, the plastic strain ratio, friction and lubrication, the blank holder force, the presence of drawbeads, the profile radius of the die and punch, etc. In order to verify the finite element method (FEM) simulation results of the LDR, the experimental data are compared with the results of the current simulation. The influences of the process parameters such as the blank holder force, the profile radius of the die, the clearance between the punch and the die, and the friction coefficient on the LDR are also examined. The abductive network was then applied to synthesize the data sets obtained from the numerical simulation. The predicted results of the LDR from the prediction model are in good agreement with the results obtained from the FEM simulation. By employing the predictive model, it can provide valuable references to the prediction of the LDR under a suitable range of process parameters.     

方盒件拉深摩擦状况的分析与研究

摩擦状况是评定拉深成形难易甚至成功与否的重要指标之一,而法兰部分又是拉深时的主要变形区域.通过探针法来获取各种情况下不同部位的摩擦系数,进而分析出方盒件的成形特点,并分析出各种工艺参数与材料参数对成形时摩擦的影响规律,以便在实际生产中能对摩擦状况进行控制.     

Modelling the evolution of residual stresses during tensile testing of elastoplastic wires subjected to a previous bending operation

During coiling operations high residual stresses are frequently developed in steel wire. In this paper the stress distribution in wires during coiling, unwinding and subsequent tensile testing is modelled for numerous bending degrees, assuming perfect Voce plastic deformation and linear elastic behaviour. The influence of such residual stresses on the observed tensile test data can be deduced. It is shown that coiling with spool radii as used today industrially can lead to measurement of wire properties deviating significantly from the “true” properties of a properly coiled wire. Also, a method is proposed to deduce the original flow behaviour of coiled samples from tensile test curves, hence filtering the effect of the residual stresses.     

基于DYNAFORM的筒形件拉深成形数值模拟技术

应用数值模拟技术对金属板料成形规律进行研究越来越受到重视。对影响筒形件拉深成形的主要因素压边力、凹模圆角半径、凸模圆角半径、摩擦系数进行了分析,并研究了单元技术、求解格式、本构关系等金属板料成形模拟中的关键技术。应用DYNAFORM数值模拟软件,对筒形件的两道次拉深成形四种主要因素的工艺参数进行了模拟优化。模拟结果分析表明,各因素对金属板料拉深系数影响的主次顺序在不同拉深道次下是不相同的,不能一概而论,与实验结果基本吻合。     

Analysis of nonlinear vibrations in metal cutting

A nonlinear model of wave cutting is presented. Orthogonal cutting conditions are assumed. Effects of the cutting velocity on the mean friction coefficient are accounted for. An approximate analytical solution of the nonlinear problem is obtained. It is shown that for some supercritical conditions, corresponding to linear instability, the amplitude of vibrations saturates and decreases in the nonlinear analysis. A study of the influence of different parameters (friction, ploughing force, cutting velocity, etc.) on the linear and nonlinear stability results is developed.     

基于时间描述的批处理短期调度方法综述

回顾了近二十年来批处理过程的短期调度研究已经取得的显著进步,对批处理调度方法进行了简要介绍。从基于时间描述的方式出发,将现有的调度方法分为离散时间表示法和连续时间表示法两大类,然后分别分析了这两大类方法的优点和局限性,最后进行了总结及展望,指出了批处理调度研究的重点将是调度理论的基础方面。     

Analysis of annular Reissner/Mindlin plates using differential quadrature method

The axisymmetric flexure responses of moderately thick annular plates under static loading are investigated. The shear deformation is considered using the first-order Reissner/Mindlin plate theory and the solutions are obtained using the differential quadrature (DQ) method. In the solution process, the governing differential equations and boundary conditions for the problem are initially discretized by the DQ algorithm into a set of linear algebraic equations. The solutions of the problem are then determined by solving the set of algebraic equations. This study considers the plate subjected to various combinations of clamped, simply-supported, free and guided boundary conditions and different loading manners. The accuracy of the method is demonstrated through direct comparison of the present results with the corresponding exact solutions available in the literature.     

Experimental methodology to study tribological aspects of deep drawing — application to aluminium alloy sheets and tool coatings

To optimise the contact between aluminium alloy sheets and coated HSS steel tools during deep drawing operation, we present an experimental methodology to decompose an extended slippage by using a strip drawing test with cylindrical tools in multipassing mode. We show in this paper the role of transfer films formed on the tool surface on the evolution of both friction coefficient and surface topography of the metal sheet.     

Numerical modelling of cold compaction of metal powder

A finite element programme has been developed for the analysis of porosity and stress distributions in a powder compact, based on rate-independent finite strain plasticity theory. The strain hardening versions of the Gurson model (J. Engng. Mater. Technol., 1977, 99, 2-15), the more recent FKM model (J. Mech. Phys. Solids, 1992, 40(5), 1139-1162), developed by Fleck, Kuhn and McMeeking, and a combination of the two models are used. The friction between the mould wall and the metal powder is modelled by a combination of Coulomb friction and a constant friction shear stress, since Coulomb friction is not realistic at high normal pressures. The finite element programme has been used to study the effects of friction, compaction method, and material parameters. Analyses for powder compacts of various geometries are presented to illustrate the method.     

Improved design of constrained model predictive tracking control for batch processes against unknown uncertainties

In this paper, an improved constrained tracking control design is proposed for batch processes under uncertainties. A new process model that facilitates process state and tracking error augmentation with further additional tuning is first proposed. Then a subsequent controller design is formulated using robust stable constrained MPC optimization. Unlike conventional robust model predictive control (MPC), the proposed method enables the controller design to bear more degrees of tuning so that improved tracking control can be acquired, which is very important since uncertainties exist inevitably in practice and cause model/plant mismatches. An injection molding process is introduced to illustrate the effectiveness of the proposed MPC approach in comparison with conventional robust MPC.     

Further evaluation of boric acid vis-à-vis other lubricants for cold forming applications

The effectiveness of boric acid as lubricant has been evaluated in ring forging and deep drawing operations. The elapsed lay-by time between boric acid coating preparation and forming operation has significant influence on the friction factor. Fresh surfaces provide least friction since longer lay-by time permits absorption of moisture from the environment and tend to increase friction. Forging speed has no effect on the performance of boric acid lubricant. The average of peak forces obtained with tools having different surface coatings indicated that the hardness of the coating also has no effect on the effectiveness of the boric acid lubricant.