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...     

钛合金实心锭穿孔挤压穿孔过程有限元分析

探明实心锭穿孔过程的材料流动和穿透断裂行为对高性能优质无缝管材的实心锭穿孔挤压推广应用具有重要意义。以直径200 mm实心锭为原料,穿孔挤压成直径80 mm、壁厚10 mm的钛合金管材为研究对象,基于DEFORM-2D软件环境,建立了能够描述材料流动和穿透断裂行为的实心锭穿孔挤压穿孔过程的热力耦合有限元模型。研究分析了2种形状穿孔冲头的穿孔过程。结果表明:穿孔初始阶段变形行为类似正挤压,随后材料反向流动,堵头去掉前都是反挤压变形;正挤压变形下穿孔力迅速上升,上升至稳定值后开始反挤变形,去掉堵头后的穿透断裂阶段穿孔力迅速下降;采用圆柱形穿孔冲头情况下反挤时穿孔力变化幅度不大,而采用瓶形穿孔冲头情况下的穿孔力稳定一段时间后再次显著增加,瓶形穿孔冲头的穿孔力远大于圆柱形穿孔冲头的穿孔力;穿透断裂阶段,圆柱形穿孔冲头下的断裂行为类似于冲裁断裂,而瓶形穿孔冲头下的约束增强,其断裂面近似呈L型。     

十字轴套筒精密热挤压新型模具结构

分析了一般的开口式反挤压模挤压杯形件时 ,锻件存在孔口高低不平和壁厚不匀的缺陷 ,提出了一种精密挤压杯形件的新型模具 ,挤压时 ,锻件杯口由背压套施压 ,且依靠背压套限制凸模偏移 ,解决了孔口高低不平和壁厚不匀的问题     

核电主蒸汽超级管道管嘴成形有限元分析

针对核电主蒸汽超级管道管嘴的成形工艺难点:加热工艺、管嘴挤压成形工艺,采用有限元软件ABAQUS分析了影响核电主蒸汽超级管道管嘴成形的主要因素:凸模形状、凸模高度、接触摩擦力和材料温降等。分析结果表明,凸模轮廓直接影响材料的等效塑性应变和管嘴成形尺寸;凸模高度、表面摩擦条件影响管嘴壁厚和高度变化。优化这些影响因素后,进行管嘴一次挤压成形试验,试验结果表明,采用凸形凸模、调整凸模高度、增加润滑条件和降低坯料温降,可以成形出合格的管嘴零件。     

铝质软管冷挤压成形工艺及模具

通过对铝质软管挤压工艺的分析,得到了适合于冷挤压成形的软管深度、壁厚和内孔带阶梯的杯形件的小孔长径比等方面的参数;确定了坯料的形状尺寸、坯料成形前的软化处理和表面处理方式、挤压过程中的润滑,设计了挤压模具结构,并在模具工作部分结构上采用组合式凸模、芯轴冲头兼做辅助导向、模杆的紧固和自定心等方面进行了创新设计,满足了工艺需要.     

On the conventional simple spinning of cylindrical aluminium cups

In this work, a study into the conventional simple spinning of cylindrical aluminium cups was carried out. The effects of roller face angle, feed rate and roller nose radius on each of wall thickness variation, cup inner diameter uniformity, spinning ratio, roundness uniformity, surface roughness, and spinning forces during simple spinning under dry conditions were investigated. Theoretical relationships for axial and radial components of the spinning force are determined and their validity is experimentally examined. The results show that decreasing both roller angle and feed rate, and increasing roller nose radius improve most of the spinning characteristics of the spun cup for the range of parameters considered. The results could be interpreted in terms of temperature rise in the deformation zone, over-rolling and spring-back phenomena, spinning forces, and the variations of contact area between the roller and the spun metal.     

反挤压凸模形状对挤压成形工艺的影响

通过数值模拟分析,比较了不同形状反挤压凸模对挤压过程中金属流动、挤压力以及凸模温升等方面的影响,进而得出凸模形状对反挤压成形工艺的影响,为挤压凸模及挤压件形状的优化设计提供一定的参考依据。     

Influence of punch geometries on the divided material flow in a double cup extrusion process

This paper provides an analysis of the deformation patterns in a backward can extrusion combined simultaneously with a forward can extrusion process, which is known as a double cup extrusion process. The main objective of this study is to examine the divided material flow characteristics in DCEP. Analyses were conducted in a numerical manner by employing a rigid-plastic finite element method. Among many process parameters, the major design factors chosen for analysis include the reduction in area (RAB), the wall thickness ratio (TR), the punch nose radius (R), and the friction condition. The simulation results were summarized in terms of relationships between the process parameters and the ratios of extruded length and volume, and between the process parameters and force requirements, respectively. Comparisons between a multi-stage forming process in sequential operations and one-stage combined operation were also made in terms of the forming load and pressure exerted on the tool. The force requirement and self-regulating characteristics were more greatly influenced by the wall thickness ratio among the selected major design factors. And more severe load to form the same shape is expected in sequential operations than in a combined extrusion process.     

深孔变壁厚锥形件冷挤压工艺与模具设计

深孔变壁厚锥形件需要3次挤压成形,给出了该零件冷挤压工艺和实用的模具结构,论述了反挤压工序件与成品正挤压模腔的关系,以及凸模和凹模设计。该模具采用伸缩式双级卸料装置,实现较大行程的卸料。     

圆筒形件充液拉深成形精度

本文系统地研究了平底和球面圆筒形件充液拉深成形精度。充液拉深成形中，由于高压液体紧紧将毛坯贴向凸模表面，因而零件具有良好的贴模性并能获得很高的内径精度。同样，由于液压的施加在凸模圆角和压边圈之间产生与凸模运动方向相反的局部胀形，减小了凸模圆角处的弹复，提高了侧壁及球面件底部的形状冻结性。但是，平底零件的底面形状因液压的施加而使形状冻结性不好，平面度降低。     

7B04铝合金板材圆孔翻边成形性能试验研究

室温下用预制圆孔的1．5mm厚7B04铝合金坯料进行一系列圆孔翻边成形工艺试验。结果表明，翻边制件卸载后没有发生形状非对称化，但口部直径有弹性收缩。采用圆角半径5．0mm的平底圆柱形凸模和相同直径尺寸的半球形翻边凸模所得极限翻边系数相同，而采用直径30mm和40mm两种不同的凸模时，极限翻边系数却存在明显差异。给出了不同工艺条件下的极限翻边系数，并对试验结果作了必要的解释。     

Deep drawing of cylindrical cups with friction-actuated blank holding

The draw force and the blank-holder variations that are obtained when drawing with friction-actuated blank holding are determined theoretically for a urethane pad of particular dimensions. A prototype tooling for blanking and drawing of sheet metal of thickness 1 mm and less to cups of diameter 100 mm at draw ratio of 1.85 with such a blank holder has been designed, fabricated and tested. Experimental results from the above tooling are presented, these including the punch and blank-holder force variations with stroke and the thickness strains in the cup wall. The experimentally-measured punch force variations are compared with the theoretical predictions. The theoretical and the experimentally-measured blank-holding force variations are presented, together with the variation of critical blank-holding force that is needed to suppress wrinkling. The differences between the theoretical and the experimental force variations are discussed.     

轴向冲头和移动推块共同进给成形三通管新工艺

运用ABAQUS显式算法模拟仿真轴向位移变量和内压变量对成形支管的高度、最大和最小壁厚的影响,分析壁厚分布情况,探究支管补料原理。模拟仿真结果表明:在一定位移变量和内压变量范围内,大位移量和高内压对增加支管高度的贡献率分别为330%和84.2%,对最大壁厚值的影响分别为39.4%和13.5%,对最小壁厚值的影响分别为5.1%和33.8%;双侧移动型成形工艺的支管壁厚呈现出两侧对称的4个峰值和3个谷值分布规律;移动推块和轴向挤压冲头的补料原理是将两端的管料推挤送进到支管根部实现补料过程。     

Determination of optimal loading profiles in warm hydroforming of lightweight materials

In this study, a methodology is developed to determine proper profiles of the hydraulic pressure and the blank holder force under warm hydroforming conditions at different punch speeds. First, finite element models (2-D and 3-D) are developed and validated through comparisons with the experimental results from the literature. To determine the optimal hydraulic pressure and blank holder force profiles simultaneously, an adaptive FE analysis with fuzzy control algorithm was developed. Thinning, wrinkling, punch wall contact, die corner floating and conduction were used as criteria in the fuzzy control algorithm. The effects of the determined loading profiles are then presented in terms of thickness, strain and stress, and temperature distributions as well as success/failure of the forming process. The effect of punch speed was also investigated to reveal its impact on part formability. It was found that the optimal process conditions can be rapidly and accurately obtained with the developed adaptive FEA method coupled with fuzzy control algorithm.     

Axial crush of hollow cylindrical structures with various polygonal cross-sections: Numerical simulation and experiment

The crush behaviors of hollow cylindrical structures with various regular polygonal cross-sections are numerically investigated under axial compression using the FEM program code of the public domain version of DYNA3D. The effects of wall thickness and plastic hardening rate of material on the crush behavior are also investigated. Crush strength increases as the number of corners of the cross-section increases, though it almost saturates for the number of corners beyond 11. Cross-sectional shape with less than six corners should be avoided to take a regulated collapse pattern. The effect of number of polygonal corners on enhancement in crush strength becomes more prominent as the initial wall thickness decreases. Higher plastic hardening rate stabilizes the collapse pattern, where it is a symmetric accordion mode in circular cross-section, otherwise asymmetric diamond one occurs. Further, for hollow cylindrical structures with circular or square cross-section which are aluminum alloy extrusions, quasi-static and impact axial compression tests and the corresponding computations are carried out. As for the circular cross-section, the number of corners induced during collapse increases as the initial wall thickness decreases both in the experiment and the numerical simulation. Crush strength is lower for square cross-section than that for circular one. This tendency agrees with the computational result.     

提高挤压筒内壁耐磨性的WC-12Co涂层有限元优化

目的获得WC-12Co涂层厚度的优化方案,以提高挤压筒内壁的耐磨性。方法基于ANSYS软件,以两层套圆挤压筒为研究对象,进行挤压筒内壁有无WC-12Co涂层及涂层厚度对挤压筒应力分布影响的有限元模拟。结果施加涂层后,在装配、挤压-装配和热-挤压-装配情况下,涂层的应力分布合理且都小于该温度下涂层的屈服强度;而在热-装配条件下,由于热应力和过盈量引起的预应力相互抵消,使得总体应力较小;同时,等效应力在涂层与挤压筒的结合处发生剧烈变化,而在其他位置的应力相较于不施加涂层时变化较小。在各种工况下,挤压筒内出现的最大等效应力均随着涂层厚度的增加而降低,且热-挤压-装配下涂层厚度对最大应力影响最大。结论在所选涂层厚度范围内,涂层厚度越大,挤压筒所受的最大应力越小,越有利于挤压筒使用。当涂层厚度为6.4 mm时,各种工况下的最大等效应力最小,此时在热-挤压-装配工况下的最大等效应力为760.61 MPa,已经远低于H13钢的屈服强度,可以满足实际使用要求。     

Microstructure Evolution and Deformation Behavior of AZ31 Magnesium Alloy During Alternate Forward Extrusion

The paper presents a new extrusion method,alternate forward extrusion,in which the punch was replaced with double-split structures so as to achieve the grain refinement for material near the interface of double-split structures.The results showed that the unique loading mode made metal flow sequence and behavior significantly changed during alternate forward extrusion.The additional shear deformation produced by the double-split punch structures resulted in a refining effect on the microstructure of the blank,which was then further refined during flow through the die orifice owing to shear deformation.Compared with the conventional extrusion,the recrystallization process in the alternate forward extrusion process produced grains that were smaller and more homogeneous in size.The recrystallization process was more abundant,and the dislocation density was significantly increased.It can be concluded that the alternate forward extrusion process could achieve fine-grained strengthening,which provided technical support and scientific guidance for the engineering application of magnesium alloy extrusion forming technology.     

平板导体上方倾斜圆形线圈的瞬态涡流场

研究了有限厚导电平板上方的倾斜圆形线圈在脉冲电流激励下产生的电磁场。推导了倾斜圆形通电线圈的电流密度表达式,解析求解了导体内部的涡流密度,并提出了一种计算时域响应的有效方法。结合算例,分析了瞬态涡流的时空特点,讨论了线圈倾角、板厚与响应的关系。计算结果显示,提出的方法可用于分析倾斜圆形线圈的线性瞬态涡流场问题。与软件仿真结果的对比验证了所提模型和方法。所得结果有助于了解在倾斜条件下所获得的脉冲涡流检测信号。     

组合形活塞销冷镦挤成形工艺

针对组合形活塞销结构特征和工艺要求,分析该零件的成形难点为:两端圆锥孔的挤压成形和深径比大于2. 5的中心圆孔反挤压。为此,应用DEFORM-2D有限元分析软件对组合形活塞销7工位冷镦挤成形工艺进行数值模拟分析。通过数值模拟分析和工艺方案修订,确定最终的成形工艺方案为:下料-整形-压凹-反挤压-冲孔-第1次挤锥-第2次挤锥,并采用硬质合金YG15制造反挤压凸模,以避免一次反挤压成形时凸模横截面变化处的折断。采用该方案进行工艺实验,实验结果表明:组合形活塞销尺寸满足零件设计要求,无折叠、开裂等锻造缺陷,深孔反挤压凸模使用寿命大于8万件。     

基于正交试验的圆柱电极参数对电火花沉积质量影响分析

在圆柱电极与基体线接触情况下,设计并进行了电火花沉积正交试验,分析了电极直径、电极厚度和电极转速对质量转移效率、沉积效率和沉积层表面粗糙度的影响,并优化了圆柱电极参数.结果表明,在一定试验条件下,采用圆柱电极能够获得较均匀致密的沉积层,随着电极直径与电极转速的增大,间隙放电数量增加,火花和飞溅增多,沉积层表面粗糙度增加...