助推式翻管方法的模拟分析与试验研究

针对现有薄壁管材翻转方式存在的问题,提出了一种新的助推式翻管结构。利用塑性有限元模拟,确定了相应外翻管模具的下模圆角半径r、助推块内径D、助推块速度v等工艺参数的数值,在此基础上设计并制造了一套助推式外翻管模具进行试验验证。有限元模拟和物理试验均证明,该助推式翻管方法可以得到比传统翻管方式质量更高的翻管件,且成品率更高。     

自由外翻式组合吸能装置的设计及优化

本文设计了一种三节直圆管翻卷吸能装置,该装置基于金属圆管外翻吸收冲击能的原理,受到冲击时通过上部圆管及下部圆管的外翻卷变形,中部波纹管与多胞管的轴向压缩缓冲碰撞带来的冲击,经过仿真得出,该装置具有较高的比吸能及冲击效率。     

基于非线性有限元的钣金件成形极限研究

用非线性有限元软件包 SHEET- FORMING研究橡皮成形工艺的模具圆角半径和板料厚度对钣金件凹凸翻边成形极限的影响 ,建立了用于预测橡皮成形工艺成败和分析其原因的极限翻边高度 h、模具圆角半径 r凹 / r凸 、板料厚度 t的曲面关系 ,用非线性有限元法有效地取代了坐标网应变法。文中主要论述 ,以圆框为对象 (L Y12 M)和用试验得到的成形极限曲线作判据 ,选取合适参数范围作正交设计 ,用动力显式算法对凹翻边破裂数值模拟并与生产型试验结果进行对比基本吻合。     

数值模拟在摩托车油箱外壳体冲压成形中的应用研究

应用DYNAFORM软件对摩托车油箱外壳体冲压成形过程进行有限元数值模拟。针对实际生产中油箱外壳体材料厚度不均匀、局部变薄严重的现象，分析其变形特点及主要工艺参数对板料厚度变化的影响，确定了油箱外壳体冲压成形的三个主要工艺参数及模具调整过程中的修整原则。指出应先修整模具拉延筋高度，然后修整凹模圆角半径，再修整凸模圆角半径。生产实践表明，与传统设计的试模方法相比，采用有限元数值模拟方法，模具调试时间缩短75％，且得到的产品板料厚度均匀，刚性好，精度高。     

液压成形不锈钢波节换热管外压失稳与其尺寸关系的研究

将液压成形过程和外压失稳过程相结合,通过试验和数值模拟,研究液压成形不锈钢换热管的外压稳定性。结果表明,波节管的外压稳定性比原始直管高;通过试验和数值模拟分别得到的波节管失稳压力与波节高度的关系曲线数值和变化趋势相近,证明了数值模拟的合理性;初始间隙和过渡圆角半径对波节管的失稳压力有一定的影响,而过渡圆角半径对波节管失稳压力的影响程度取决于初始间隙的大小;为使成形后的波节管具有良好的综合性能,应尽量保证管件与模具之间的初始间隙足够小,并采用较大的过渡圆角半径。     

基于ANSYS的曲轴应力及变形敏感度分析

建立了494柴油机曲轴有限元模型,采用试验的方法验证了模型的准确性。选择轴颈直径、过渡圆角半径、油孔直径等参数,模拟了最大爆发压力为15MPa时,曲轴过渡圆角应力和曲柄臂变形的变化规律,分析了曲轴结构参数与应力、变形敏感度系数的关系。结果表明,过渡圆角应力随轴颈直径、过渡圆角半径、重叠度的增加而减小,随油孔直径的增加而增加;曲柄臂变形随轴颈直径、曲柄销过渡圆角半径、重叠度的增加而减小,随主轴颈过渡圆角半径、油孔直径的增加而增加。曲柄销直径对过渡圆角应力最敏感,应力敏感度系数为-0.46;主轴颈直径对曲柄臂变形敏感度系数为-0.497,对变形最敏感。     

T2紫铜箔材的U型弯曲变形

设计了箔板U型弯曲试验方案,使用不同凹模槽宽尺寸和圆角半径的微型模具,在三思微型试验机上完成了试验,分析了模具几何尺寸、箔板厚度等对箔板U型弯曲变形中冲头载荷、回弹以及表面质量的影响。研究结果表明,槽宽尺寸或圆角半径减小时,最大冲头载荷显著增加,且冲头载荷上升和下降速率都明显增大;对比两种不同厚度箔板的冲头载荷显示,冲头载荷减小速率明显快于横截面面积的减小速率,说明产生了明显的尺寸效应;另外,圆角半径或板厚减小,导致回弹角度增大,成形件精度降低;虽然成形件表面比较平整,但侧面出现划痕提示需要提高模具表面质量和采取润滑措施。以上研究结果对指导箔板微成形工艺设计具有重要意义。     

有限元网格的圆角过渡特征提取及网格修改

根据过渡曲面的曲率特性，提出了一种有限元网格的圆角过渡特征提取及网格局部修改算法。通过曲率估算、过渡区域圆弧识别和圆弧分组等步骤，计算出一系列截面轮廓线来描述圆角过渡特征，同时将过渡区域网格从模型中提取出来。直接调整圆弧半径，快捷、准确地修改网格模型中等半径及变半径过渡区域网格。应用该算法，能够在有限元网格模型中直接修改零件或模具的过渡圆角形状，提高设计与CAE分析的效率。     

板材在模具圆角处的接触状态研究

以数值模拟为手段对板材在拉力下通过模具团角时的接触状态进行了研究，分析了板材与模具圆角间的接触特点，通过大量对比计算给出了接触状态与圆角大小及受力状态间的关系。指出一般情况下，板材与模具圆角间的接触压力呈两端高、中间低的分布趋势；两者间依拉力及圆角半径的不同存在4种典型的接触状态。并在此基础上对欧拉公式进行了误差分析及修正。     

冲裁模具间隙及凹模圆角对凸模应力应变影响的有限元分析

冲裁模具的间隙和凹模圆角,对凸模的应力、应变有重要的影响。运用有限元分析了冲裁模具在不同间隙与圆角下凸模的应力、应变特性。分析结果表明,应力、应变随着间隙和凹模圆角的增加而减小。模拟分析的结果为模具间隙和圆角半径的选择提供了依据。     

Mechanics of static and dynamic inversion processes

The paper presents an experimental and theoretical analysis of tube inversion process under quasi-static and dynamic loading conditions. The aim of the work is to propose a method of predicting the dynamic inversion load based on the quasi-static data. The method employs the principle of conservation of energy of the body in collision which is totally dissipated through plastic deformation of the tube under an inversion process. A dynamic inversion test was performed by means of drop hammer against the tube—die assembly. The hammer was coupled to an accelerometer to permit dynamic load readings. The results demonstrated that for a given impact velocity, the axial shortening as well as the dynamic inversion load compare very well to those predicted from the theoretical quasi-static results. The quasi-static and dynamic experiments were carried out on copper and brass tubes. Different inversion die radii were also used. In addition other relevant parameters will be discussed.     

Finite element analysis of tube inversion process with radiused dies

The extended r_min technique has been incorporated in the incremental updated Lagrangian formulation (ULF) of an elasto-plastic finite element computer code in order to handle the contact boundary condition when analyzing the axisymmetric tube inversion process with a quarter fillet die radius. A fillet die applies an axial compressional load onto a thin tube so that the inside or outside of the tube inverts totally making the central axis of the original tube the same as a new double-walled tube. This is called an inside-out or outside-in inversion process. This study employs an elasto-plastic finite element method to simulate and analyze inside-out inversion. The objective is to examine how different process factors, such as the geometry and material modulus, influence metal tube inversion. This study also simulates a quarter fillet radius of the die to analyze the tube forming condition and range that can be applied in engineering under these requirements. In addition, the axial compressional load under inside-out inversion stability to be suitable for a personal computer, so it can be effectively analyzed and evaluated on line instantaneously.     

Transient effects in the quasi-static and dynamic internal inversion and nosing of metal tubes

The plastic deformation mechanisms of metal tubes during quasi-static nosing and internal inversion are analysed. Rigid-plastic analyses which incorporate an assumption of full conformity between the deforming tube and the forming die predict accurately the nosing load-displacement curve. Details of the deformation processes during internal inversion are examined using the non-linear facilities of the finiteelement code ABAQUS. The early stages of the forced inversion characteristic are more complex than for nosing, with different deformation modes dominating the behaviour at different times. Each of these is also examined using rigid, perfectly plastic models.The quasi-static behaviour is used to provide insight into features of the load pulses generated during dynamic/impact loading of the tubes. The peak impact loads can only be assessed through a full dynamic analysis since inertial effects strongly influence the magnitude of the dynamic loads. It is shown that measured dynamic force pulses for both nosing and internal inversion can be accurately predicted fusing appropriate finite element models and the source of the high dynamic force peaks in inversion is discussed. It has been found both experimentally and numerically that the steady-state inversion force is lower under dynamic loading conditions than under quasi-static loading. A simple analytical model provides an explanation for this and highlights the importance of the ratio of the mass of the striker to that of the inverted portion of the tube in this phenomenon.     

On the axial splitting and curling of circular metal tubes

The present paper investigates the axial splitting and curling behaviour of circular metal tubes. Mild steel and aluminum circular tubes were pressed axially onto a series of conical dies each with different semi-angle. By pre-cutting eight 5 mm slits which were distributed evenly at the lower end of each tube, the tube split axially and the strips curled outward. Experiments showed that this mechanism results in a long stroke and a steady load. An approximate analysis is presented which successfully predicts the number of propagated cracks, the curling radius and the force applied. This analysis takes into account ductile tearing of the cracks, plastic bending/stretching and friction. Effects of tube dimensions, semi-angle of the die and friction are discussed in detail.     

Effect of die corner radius on the formability and dimensional accuracy of tube shear bending

Tube shear bending is a beneficial technique to realize considerable small bending radii. The authors have investigated the tube shear bending process of circular tubes experimentally. Moreover, an elastoplastic 3D finite element simulation has been conducted, aimed at clarifying the forming mechanism. Both the experiment and simulation results indicate that, in order to perform successful forming, the value of the applied pushing force on the tube must be appropriate. In this paper, the mechanism of defect generation was clarified. Two failure criteria were introduced and employed to recognize the occurrence of defects in the simulation. The effects of the die corner radius, as the main parameter, on the defect generation of circular A1050 aluminum tubes were investigated both by experiments and numerical simulation. From the results, the formability of tube on dies with different corner radii applying various pushing pressures was clarified. Moreover, the influence of the die radius on the dimensional accuracy of the deformed tube regarding cross-section ovality and thickness changes of the deformed tube was evaluated. The results of this study indicate that, whilst a small bending radius results in high cross-section ovality, increasing the die corner radius raises the wrinkling tendency of the tube. However, the die radius has a small effect on the suitable values of pushing pressure required for a successful shear bending deformation. Moreover, the effect of the die corner radius on the thickness strain of the deformed tube is insignificant.     

Axial splitting of circular metal tubes

A novel mode of deformation of circular tubes axially compressed on to a die is examined experimentally with regard to its energy absorbing capacity. The tube splits as a number of axial cracks are produced and the strips so formed are bent into curls. The major part of the deformation takes place at a nearly constant load which can be increased by preventing the formation of the curls. A simple upper bound approach is used to estimate this operating load. Compared with axial buckling and the inversion mode, the operating load for a splitting tube is somewhat lower. However, the fact that the stroke is of the order of 90% of the tube length means that the performance as measured by the total energy absorbed is often as good as these two efficient modes of deformation.     

Effects of process variables on V-die bending process of steel sheet

This investigation aims to clarify the process conditions of the V-die bending operation of steel sheet. It provides a model which predicts the correct punch load for bending and the precise final shape of products after unloading, in relation to the tensile properties of the material and the geometry of tools. The process variables are punch radius (R_p), die radius (R_d), punch width (W_p), punch speed (V_p), friction coefficient (μ), strain hardening exponent (n) and normal anisotropy (R).This investigation is carried out by performing some experiments and by finite-element simulation. Experiments determine the punch for bending for various process variables, such as punch radius, punch speed and lubrication, were carried out. As a result it was found that punch load increases as punch radius and punch speed increase or lubrication decreases.An elasto-plastic incremental finite-element computer code based on an updated Lagrangian formulation was developed to simulate the V-die bending process of sheet metal under the plane-strain condition. Isotropic and normal anisotropic material behavior was considered including nonlinear work hardening. A modified Coulomb’s friction law was introduced to treat the alternation of sliding–sticking state of friction at the contact interface. Simulation results, such as the punch load of bending and the bend angle of the bent part after unloading, are compared with experimental data; satisfactory agreement was observed. The simulation clearly demonstrates that the code to simulate V-die bending process was efficient.Simulations were made to evaluate the effects of die radius, punch width, strain hardening exponent and normal anisotropy on punch load of bending. The punch load for bending is smaller for materials with a larger strain hardening exponent. The effect of punch width on punch load is limited. The punch load decreases in the early stage and increases in the final stage of the bending process as the die radius increases. The influences of all of the process variables on the final bend angle of the bent parts of sheet after unloading were also evaluated. The effects of process variables except die radius on the bend angle after unloading are also limited. The angle of spring-back is greater for tools with larger die radius.     

Energy absorption of expansion tubes using a conical-cylindrical die: Experiments and numerical simulation

This paper is concerned with the plastic energy absorption behavior of expansion tubes under axial compression by a conical-cylindrical die. The experiments and numerical simulation using FEM are presented in this paper. Experiments were conducted on circular 5A06 aluminum tubes with an internal radius fixed at 22.5 mm and different thicknesses between 1 and 5 mm; the tubes were pressed axially onto a series of conical-cylindrical dies each with a different semi-angle from 5° to 20°, where the radius of the cylindrical part was 24 mm. A numerical analysis was performed to investigate the tube deformation and the friction between the tube and die. A good fit of the experimental data was obtained by taking the value of the friction coefficient μ=0.05. Based on these experimental and numerical results, characteristics of driving force-stroke curves in different deformation modes are discussed in detail. Effects of tube dimensions and semi-angle of the die on steady-state force and energy absorption efficiency are also presented. Based on these experimental studies, a theoretical analysis to explain the deformation mechanisms of the tube expanded by a die is carried out and will be given in a subsequent paper [1].     

Guist and marble revisited—On the natural knuckle radius in tube inversion

An attempt has been made to resolve an apparent anomaly between theoretical predictions and experimental observations on the natural knuckle radius during external inversion of tubes. A rigid, linear strain-hardening material model is used. The Tresca yield condition and associated flow rules along with a kinematic hardening law are employed. Analytical results show good agreement between predicted and experimentally observed values of the critical knuckle radius. It is found that the strain-hardening parameter which provides the best agreement with the experimental data depends on the magnitude of the strain and hence the geometry of the tube. The calculated inversion loads are seen to agree better with the observed values than those from an earlier analysis.     

管材胀形中的圆角成形

提出考虑管材和模具间滑动摩擦的力学模型,来研究在方形模具中的管材胀形的塑性变形行为。通过对无摩擦条件下的滑动模型的研究,在理论上首次证明成形圆角半径存在最小极限值,并给出理论计算公式。采用提出的方法确定的最小极限半径可用于确定管材成形工件形状及其成形压力。最后采用自行设计的胀形装置进行管材在方形模具中的胀形试验,并与滑动模型计算结果进行比较。试验结果与计算结果对比表明,试验结果介于摩擦滑动模型和无摩擦滑动模型之间,这说明无摩擦滑动模型和滑动摩擦滑动模型的分析是正确的。