Round-to-square section drawing through flat idle rolls

Cold drawn metal bars of regular polygonal section are industrially produced by direct drawing from round stock using either a round-to-polygonal section converging die or a drawing head comprising an adjustable set of symmetrically arranged flat idle rolls. In the present work a solution is obtained to determine the roll load and drawing force for steady state direct cold drawing of square section from round stock through flat idle rolls. The results obtained have shown that the drawing force in a case of fair lubrication condition amounts to about 40% of that required for drawing through converging dies, which allows using a drawbench of lower load capacity. The drawing stress is highly influenced by the friction conditions at the roll surface and to a lesser extent by the area reduction ratio and roll diameter, indicating the need for good quality finish and adequate lubrication for the rolls contact surface. The ratio of the drawing stress to the roll mean pressure is independent of friction and increases almost linearly with the increase of area reduction ratio.     

Analysis of flow and stresses in a tube stretch-reducing hot rolling schedule

Analytical expressions for the roll-pass geometry, velocity, strain, strain rate and stress components are obtained for steady-state tube stretch-reducing hot rolling. From these expressions the reduction in tube diameter and wall thickness, inter-stand tensions, roll load and rolling torque have been determined in relation to the roll gap opening and the inter-stand velocity increase ratio. The results have shown that increasing the interstand velocity increase ratio will increase the inter-stand tension while the roll load remains almost unchanged. The rolling torque increases with the increase of the back inter-stand velocity increase ratio and decreases with the increase of the ratio at the front. There is a limiting value for the inter-stand velocity increase ratio at which the rolling process will tend to become unstable. The analysis has been validated by comparing the theoretical results with on-line power measurements on an industrial tube stretch-reducing hot rolling mill.     

Flow and stresses in round–oval–round roll pass sequence

Analysis of flow and stresses in isothermal steady-state round–oval–round pass sequence for the production of round bars has been obtained from a flowline field solution. The velocity, strain-rate and stress components are derived from kinematic and static considerations together with the material constitutive law and friction boundary conditions. The results obtained show that the roll pressure and friction shear traction at the roll interface are fairly uniform and the normalized average roll pressure and friction shear factor have lower values than those for flat bar rolling at the same rolling conditions. Small variations in the rolls clearance gap have no appreciable effect on the roll load and torque. Increasing friction causes a significant increase in the roll load and torque. The analysis predicts pass grooves’ dimensions, roll load and torque for different values of height reductions.     

基于ANSYS技术的铜管空拔过程数值模拟分析

为优化铜管空拔工艺参数和提高工件加工质量,应用大型有限元分析软件ANSYS中的LS-DYNA求解器模拟了某规格铜管的空拔成形过程,得到了管件成形过程中任一时刻主要场量的分布云图,分析了成形过程中管件的变形和应力的特点,研究了摩擦力和模具锥角等因素对空拔力与管件伸长率的影响规律。数值模拟分析表明:在应变分布上,管件轴向和周向的最大塑性变形主要发生在管件与模具初始接触处与减径区;在应力分布上,轴向应力和径向应力随管件在模具中的位置不同而有较大差异,在壁厚方向上由管件的外表面到内表面其应力依次为拉应力和压应力,且最大压应力出现在减径区,而最大拉应力则出现在定径区连接处。在管件拉拔力的变化规律上,降低摩擦力和合理的模具锥角能使拉拔力控制在最小范围内。在管件伸长率的变化规律上,较大的摩擦力和模具锥角能使管件的伸长率增大。     

An upper bound analysis for the reshaping of thick tubes with experimental verification

Reshaping process based on the cold roll forming technology is a process in which noncircular pipes can be produced from circular pipes. A generalized upper bound solution for the deformation of thick tubes between four flat rolls has been formulated. The deforming zone has been divided into two areas namely the “contact region” and the “free region”. Owing to the different physical character of these deforming zones two different kinds of admissible velocity fields have been obtained for each of the deforming zones. To formulate the stream lines and stream surfaces in the deforming zones use has been made of the Bezier curves which have been utilized to define stream lines in such a way that could be manipulated easily to obtain the optimum shape for the upper bound solution to be optimized. This new formulation was used to predict the upper bound on power. Using the theory presented here, the influence of process parameters such as radius of rolls, initial pipe dimensions; amount of roll gap reduction and the roll speed on the final rolled product were investigated. In order to verify the theoretical results, an experimental rolling rig was designed and built which comprised of four flat rolls. Using this rig Al 6101 round pipes were rolled and the variations in the above-mentioned parameters were investigated. Quantities such as energy, wall thickness, and corner radius of the tube were observed and measured. Comparison of theoretical and experimental results showed good agreement and hence demonstrated the capabilities of the new formulation presented here.     

基于熵权综合评价法的动力电池壳首道次拉深成形参数优化

针对某动力电池壳首道次拉深成形过程中的起皱、破裂、厚度不均匀和模具接触力大的问题,提出了一种基于熵权的综合评价法对其进行多目标工艺参数优化来提高首道次成形质量。选取压边力、凹模圆角半径、凸模圆角半径、模具间隙、摩擦因数为影响因素,以最大减薄率、最大增厚率、最大凸模接触力、最大厚度差为评价指标,进行正交试验仿真。在此基础上应用熵值法和综合评价法,获得了最优的工艺参数组合,提高了动力电池壳首道次成形质量。     

圆筒件拉深过程中压边力的研究

利用恒定压边力经验公式计算得到的压边力值进行模拟时,圆筒件质量存在明显的缺陷。采用变压边力优化曲线作为圆筒件拉深成形的压边力加载模式,研究了临界防皱变压边力曲线的确定方法,应用Dynaform软件对恒定压边力、优化压边力下圆筒件的拉深成形进行了数值模拟,得出了成形极限图(FLD)和材料厚度变化图。将模拟结果进行对比分析,发现在后者作用下的圆筒件平面外缘厚度变化较小,筒壁等其他部分的材料厚度变化率也较小,采用优化压边力可有效防止圆筒件起皱、拉裂现象,提高圆筒件成形质量。     

镀层薄板拉深过程中镀层厚度变化影响因素分析

对镀层板料拉深成圆筒件的过程进行模拟及试验研究,得到了圆筒件各部分镀层厚度的变化规律。选取镀层最薄处厚度为镀层质量评价因素,利用LS-DYNA软件,基于正交法分析了拉深过程中的主要工艺参数（压边力、凹模圆角半径、凸模入口圆角半径和摩擦因数）对镀层厚度变化的影响规律,并结合拉深机理对其进行了深入研究,得到了所选工艺参数的最优组合。     

圆管凸缘整体成形技术的研究

对圆管凸缘一步及多步整体成形工艺进行了研究,采用有限元数值模拟方法分析了圆管坯料尺寸、摩擦等因素对成形过程中金属流动的影响及缺陷产生的原因。给出了2种内径、3种壁厚情况下,成形凸缘宽度－极限摩擦因数关系曲线,提出了圆管镦锻凸缘成形极限图的概念。并依据数值模拟结果进行了圆管镦锻凸缘一步整体成形试验,试验结果显示所成形的圆管凸缘符合数值模拟预测的结果,说明所提出的成形极限概念对圆管凸缘整体成形技术有指导意义。     

Collapse mode transitions of thin tubes with wall thickness, end condition and shape eccentricity

Transition of deformation mode shapes of round aluminum tubes from axisymmetric concertina to non-axisymmetric diamond mode have been studied with varying tube wall thickness, boundary conditions and tube shape eccentricities. Quasi-static axial compression experiments were carried out on as received aluminum tubes and tubes with wall thickness eccentricity, incorporated by off center machining. Tubes were of D/t=29 and L/D=1.4. The numerical simulation of the collapse phenomenon has been undertaken using a static non-linear finite element analysis in ANSYS with a fine mesh discretization of the tube domain and small incremental displacements as load steps. Convergence studies for the finite element model with respect to load step size and mesh density have also been established. The numerical results are found to compare well with the experimental load compression and energy absorption responses both for the axisymmetric concertina and non-axisymmetric diamond collapse modes. Having validated the numerical model with experiments, it has been used to undertake a systematic study of the load–deformation characteristics, energy absorption response and collapse mode transition of the tubes in varying configurations of wall thickness, shape and inplane boundary condition eccentricities. Dependence of tube collapse characteristics and collapse mode transitions on such eccentricities have been discussed.     

非回转对称拉深成形中压料面上摩擦的研究

在大量拉深试验的基础上,结合法兰、矩形盒底部产生的应力应变状态以及载荷的变化情况,分析了相对凸模半径较大的薄板非回转对称成形过程中,压料力对拉深载荷以致断裂载荷所产生的复杂影响。指出法兰曲边部的滑动摩擦因数对于成形过程中的压料力相当敏感,并且对法兰部和断裂危险部材料的应力应变状态产生直接影响。特别是在面压较高的成形后期,由于法兰部润滑效果恶化,导致拉深载荷增大、成形极限降低。     

半球底直筒形拉深件成形极限实验研究

以半球底直筒形拉深件为研究对象,用实验的方法,从压边力、摩擦系数、凹模圆角半径等几个方面对半球底直筒形件进行成形研究,得到了各工艺参数对其成形极限的影响.即压边力、摩擦系数在一定范围内的增大,半球底直筒形拉深件的胀形区域减小,成形极限有降低的趋势.     

数值模拟分析工艺参数与拉深件壁厚变化的关系

在分析板料拉深成形有限元理论的基础上建立数值模拟的分析模型,利用数值模拟技术系统地对拉深过程进行模拟。主要研究模具圆角半径、摩擦因数、压边力与模具间隙等工艺参数与拉深件壁厚最大变薄率的内在关系。     

Finite element analysis of tube flaring process with a conical tool

The extended r_min technique is incorporated into an incrementally updated Lagrangian formulation (ULF) of an elasto-plastic finite element computer code in order to handle contact boundary conditions to analyse the axisymmetric tube flaring process with a conical tool. A modified Coulomb friction law was adopted to calculate the influence of the friction coefficient on the tube flaring process. The effects of size and mechanical properties of tubes, as well as lubricants and tool semi-angle on flaring load were studied. It was found that good lubrication is effective in reducing flaring load. An optimum tool semi-angle (tool load is lower) in flaring is determined by frictional and bending activity at the tool inlet. In addition, the forming behaviour of the tube end is investigated to understand whether outward curling takes place and how much influence the tool semi-angle and tube size (initial thickness/initial mean diameter of tube) have on outward curling mode.     

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.     

Three dimensional thermal mechanical coupled simulation during hot rolling of aluminium alloy 3003

Rolling passes of a pass schedule supplied by an aluminium company and containing reliable measured data of roll load and torque is considered. Percentage reductions range from 6% to 20% and are analysed by a commercial thermo-mechanical coupled FEM program FORGE3 V5.3. An inverse analysis method is adopted to match the calculated rolling force and torque with the measured rolling force and torque by treating the friction law and the friction coefficient as free parameters. Three widely accepted friction laws are investigated; Tresca friction, Coulomb friction and viscoplastic friction. The use of viscoplastic friction is shown to yield both more reliable and more accurate results than other models. Significantly the friction coefficient can be traced to remain constant throughout the pass schedule of the breakdown rolling. The contact pressure distribution is then studied with different thickness reductions and compared with published experimental results. The predicted and experimental agreement is such that the load calculation can be regarded as satisfactory. Acceptable agreement is also obtained with the measured torque values. The distribution of equivalent strain, temperature and the stress in the roll gap and the lateral profile are discussed.     

Effects of film thickness and contact load on nanotribological properties of sputtered amorphous carbon thin films

The nanotribological properties of amorphous carbon (a-C) films of thickness in the range of 5-85 nm sputtered on Si(1 0 0) substrates were investigated with a surface force microscope (SFM), using a Berkovich diamond tip of nominal radius of curvature approximately equal to 200 nm and contact (normal) loads between 10 and 1200 μN. The dependence of the friction and wear behaviors of the a-C films on normal load and film thickness was studied in terms of nanomechanical properties, images of scratched surfaces, and numerical results obtained from a previous analytical friction model. The increase of the contact load caused the coefficient of friction to decrease initially to a minimum value and, subsequently, to increase to a maximum value, after which, it either remained constant or decreased slightly. The dominant friction mechanism in the low-load range was adhesion, while both adhesion and plowing mechanisms contributed to the friction behavior in the intermediate- and high-load ranges. Thinner (thicker) a-C films yielded higher (lower) friction coefficients for normal loads less than 50 μN (low-load range) and lower (higher) friction coefficients for normal loads greater than 150 μN (high-load range). Elastic and plastic deformation, microcracking, and delamination of the a-C films occurred, depending on the contact load and film thickness ranges. The reduced load-carrying capacity, relatively low effective hardness (strength) obtained with thinner films, and dominant friction and wear mechanisms at each load range illustrate the film thickness and contact load dependence of the nanotribological properties of the sputtered a-C films.     

基于径压胀形确定管材的摩擦因数

摩擦对管材液压成形有极大的影响,管材摩擦因数的确定是一项极其重要的工作。在分析比较现有测试方法的基础上,基于径压胀形原理及其变形规律提出确定管材液压成形胀形区摩擦因数的新模型。该模型以恒定内压力下圆形管材径压胀形成方形断面后,以断面对角线长度差作为确定摩擦因数的测量指标。对比对角线长度差的有限元数值模拟结果及实测结果,以此确定管材液压成形时胀形区的摩擦因数。对低碳钢及不锈钢管的有限元数值模拟分析表明：对角线长度差与摩擦因数及内压力均成指数关系,该长度差对摩擦力很敏感且可方便测量,也可作为针对管材液压成形胀形区润滑剂特性的评定指标。所提出的新模型具有简单、实用等优点。     

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.     

游动芯头拉拔模具锥角优化的数值模拟

采用非线性有限元软件对铜管游动芯头拉拔工艺中不同配合锥角的模具受力情况和铜管表面的受力情况进行了数值模拟和分析，推断企业目前使用的模具锥角配合是否合理，以分析当前模具锥角配合是否为影响模具寿命的主要原因。