影响闭挤式精冲成形表面质量的因素分析（英文）

首先分析了成形面撕裂与变形区应力状态的关系,然后用塑性有限元数值仿真和物理实验的方法,分析了材料塑性、凸凹模间隙、外环填充率、反顶力对成形表面质量的影响。研究表明:主、副凹模闭合时,变形区材料所受的压应力越大,所得精冲件成形面质量越好;材料塑性越好,剪切面撕裂带宽度越小;凸、凹模间隙越大,工件轮廓面光亮带的比例越小;材料剪切面光亮带比例随着外环填充率的增加而增加;随着反顶力的增加,工件轮廓面光亮带的比例明显增大。研究成果为闭挤式精冲新工艺的应用奠定了基础。     

闭挤式精冲成形直齿轮的齿顶撕裂问题

运用有限元分析软件分析了闭挤式精冲直齿轮齿顶端和齿根端剪切变形区材料的应力应变状态,以及凸凹模间隙、反顶力和外环填充率对齿顶撕裂的影响。结果表明:随着凸模下行,齿顶处静水压应力逐渐下降,齿顶附近侧面由于三面受摩擦力出现拉应力,导致静水压应力不足进而出现裂纹,另外加工硬化也会导致齿顶裂纹的出现;齿顶裂纹出现的几率与凸凹模间隙大小成正向关系,与反顶力和外环填充率大小成反向关系。研究发现,随着反顶力和外环填充率的增加以及凸凹模间隙的减小,可以有效控制裂纹的出现。     

基于数值模拟的厚板精冲件剪切面缺陷研究

借助有限元分析软件Deform-2D,以材料为AISI1020钢、直径为Φ30 mm、厚度为7 mm的精冲落料件的剪切面缺陷作为研究对象,以齿圈压边精冲工艺为精冲成形方法对厚板的精冲成形展开模拟研究。从精冲成形过程和力学角度描述了厚板精冲件剪切面撕裂带和塌角的形成过程,并得到影响剪切面缺陷的因素有:凹模圆角半径、精冲材料弹性模量、凹模摩擦系数、反压板摩擦系数、反顶力等;以上述各因素作为参考变量建立有限元模型,进行单因素影响的模拟研究,得到各因素对厚板精冲件剪切面缺陷的影响规律;最后利用正交试验方法进行多因素影响研究,得出上述各因素对厚板精冲件剪切面缺陷影响的主次关系,取得剪切面缺陷最小的优化参数组合。     

基于有限元分析的精冲凸模的变形及其对成形质量的影响

采用DEFORM-2D有限元分析软件模拟了精冲过程中凸模的变形,研究了凸模材料、凸凹模间隙和凹模圆角等对精冲凸模应力、应变及成形件质量的影响.结果表明:采用弹性模量较大的凸模材料可以降低精冲过程中凸模的变形量,提高成形工件的质量;精冲间隙对模具的应力、应变和工件的成形质量有很大的影响;一定的凹模圆角可以降低凸模的应力,减小凸模的变形,对提高模具寿命和改善零件质量有着重要的作用.     

基于正交方案的闭挤式精冲工艺参数优化

将模具结构各工艺参数(相对冲裁间隙、主凹模圆角半径等)作为优化变量,工件轮廓面光亮带比例作为优化目标,结合正交试验和有限元仿真技术,以AL2024材料的圆形落料件为例,研究了模具各工艺变量对优化目标的影响规律和影响程度大小.其次,在确定最佳模具参数的基础上,研究了反顶力大小与轮廓面光亮带比例的关系.最后,通过相关物理实...     

基于物理实验的平面压边精冲工艺研究

论述了平面压边精冲的机理和工艺方法,设计制造了实验模具,并对不同塑性和厚度的坯料进行了物理实验;分析了精冲过程中的冲裁力,研究了平面压边精冲工艺中材料塑性、模具的相对间隙、压边力和反顶力与剪切面光亮部位在剪切面中所占比值大小的相互关系。实验表明,平面压边精冲技术是一种有效提高工件冲裁剪切面质量而成本较低的工艺。通过对制件的流线分析和变形区硬度的检测,得出平面压边精冲工艺对工件的外周有很明显的加工硬化作用,而心部强度不变的结论。     

闭挤式精冲工艺及其成形规律

针对存在的低塑性和高厚度零件难以精冲成形问题,提出了闭挤式精冲的概念和工艺方法,并阐述了该工艺的过程、原理和特点;设计了该闭挤式精冲工艺实验模具并用该工艺在低塑性材料YL12上精冲出了φ15 mm、高13 mm的高尺寸精度和低粗糙度的圆柱形零件.最后分析了变形区材料的流动规律和产品品质与坯料的关系.结果表明:精冲件外表面的光亮带大小随外环填充率增大而增大;内表面比外表面容易形成100%光亮带;试件表面的光亮带大小还与坯料厚度和模具主、副凹模凹坑深度的匹配有较大关系.     

基于物理实验的闭挤式精冲工艺研究

针对闭挤式精冲的机理和工艺方法,设计制造了闭挤式精冲工艺实验模具,并采用不同厚度和直径的坯料进行实验;分析了闭挤式精冲工艺中外环填充率与剪切面光亮比例的关系以及外环填充率与工件增厚之间的关系,得出模具工作部分尺寸的计算方法。实验表明,闭挤式精冲是一种有效的冲裁低塑性材料和厚板的工艺。     

间隙与精冲质量的关系研究

建立了精密冲裁有限元模型,对相对间隙分别为0.1%t、0.7%t、1.3%t,材料为45钢,板厚为2.9mm,直径为φ16 mm的圆形零件精冲过程进行了模拟,通过数值模拟获得了材料在精冲过程中静水应力场的分布情况,分析了静水压应力与剪切面裂纹产生的关系,通过分析得到相对间隙越小,光亮带越大的结论。     

离合器星轮精冲挤压工艺分析与模具设计

介绍了离合器星轮精冲挤压成形原理,零件成形过程中工件产生纯剪切变形与挤压变形,以获得形状与尺寸精度较高的零件。设计了双面齿形压边圈与组合凹模的精冲挤压模,提高了模具强度。     

A new pore closure concept for the manufacturing of heavy rings

In order to avoid pores in heavy rings, a new forming concept is presented. The proposed manufacturing route is based on an analysis regarding the current manufacturing of a ring associated with serious pore closure problems. It is concluded that the present method results in small strains close to the outer surface of the ring. Thus, the likelihood for remaining pores in this region is considered to be high. This apprehension was confirmed both by ultrasonic testing and metallographic analysis. The forming route starts with heavy upsetting of a cylindrical billet followed by piercing in a closed die. The penetrating punch is furnished with an upper flat part that is used for upsetting at the end of the process, forcing the material to fill the cavity between the die and the upper tool. The remaining bottom disk is then sheared off in a separate tool. The new concept starts with a lighter upsetting, resulting in a higher “pan cake” of smaller diameter. This workpiece is then moved to a closed die of the same diameter as that of the material. The diameter of the piercing punch is not changed. Because of the small die diameter, the workpiece is, after piercing, considerably higher than in today’s production. The so-obtained workpiece is placed into a die equal to the original one with the exception of a bottom hole. A new mandrel, with a flat upper part and a lower part meant for shearing off the thin bottom disk, will be inserted to fit the recently generated cylindrical hole. At the beginning of the operation, the bottom disk is cut away as the punch moves through the bottom hole and after that, during the same stroke, the high ring will be heavily upset to its final geometry. During the upsetting the ring is supported by the mandrel. If the ring is too high during upsetting, there is a risk for the material to loose contact with the punch, which might result in instability and a fold. Applying the new concept, the strains close to the envelope surface became approximately 160% larger. The present analysis is carried out with an FE-code Q-form making it possible to trace different material elements of the initial billet throughout the different manufacturing steps. The results are presented in form of hydrostatic pressure as a function of the effective strain. Theoretically determined workpiece shapes, based on the conditions of today’s production are in good agreement with those obtained from full-scale experiments. The present work also includes comparisons with another analysis of similar character, published by the authors. In that work, the manufacturing of two other types of rings were analysed, one with pore closure problems and one without.     

齿坯冲孔切边模设计

介绍在凸模端面加设锥度 ,在侧面加设刃带的方法 ,消除了凸模被镦粗而卡料的可能 ,同时减少了凸模侧面与冲件的接触面积 ,减少了卸料力 ,从而改善凸模受力 ,提高模具寿命     

Analysis of Pick-Up Development in Punching

The development of pick-up of workpiece material on the punch surface with increasing number of strokes during punching of stainless steel sheet is investigated applying Scanning Electron Microscopy (SEM), 3D roughness mapping and measurements of the backstroke force. It is found that pick-up on the punch stem develops gradually backwards from the tip of the punch with increasing number of strokes saturating at a certain level while the radial build-up in the case of dry friction conditions continues until the clearance between the punch and die has been filled up. The rate of pick-up is significantly smaller in case of lubrication and may be very low if an efficient boundary lubricant is applied. Good correlation between the pick-up development and the backstroke force is found.     

Cold piercing of magnesium alloy billet with high aspect ratio

Cylindrical billet of a magnesium alloy AZ31B (Mg–3%Al–1%Zn) is pierced at room temperature by applying counter pressure to make a hole of an aspect ratio (initial billet height/piercing punch diameter) greater than 1.0. During piercing, the billet is kept in a container and the counter pressure is applied to the billet by a counter punch from the opposite side of the piercing punch. The effects of die clearance and counter pressure on the quality of the created hole surface are examined. In the case of piercing without counter pressure, the hole surface is very rough due to fracture irrespective of the clearance between the punch and the die. When a high counter pressure is applied, a hole with good shear surface quality is obtained. By applying the counter pressure, the height of the pierced billet becomes slightly higher and the height of the slug ejected from the hole becomes lower because of the change of the deformation mode from pure shear deformation to combined forward–backward extrusion.     

A study of high-rate shearing of commercially pure aluminum sheet

The effect of shearing speed on the quality of shape and edge-face of the sheared-off products is studied. The tested material is a commercially pure aluminum. The maximum shearing speed is 10 m/s. It is evidenced that the shape quality of the sheared-off parts is better when a smaller clearance and a higher rate of shearing are applied. A thin ring of almost complete rectangular cross-section, i.e. 1.5 mm in width and 10 mm in height, whose edge-face is glossy, is successfully produced by the high-rate shearing process using a constraint tool set at the outer periphery of the sheet blank. It is demonstrated clearly by the pictures of microstructure that the material flow is concentrated within a very narrow band, showing even a recrystallized structure. A theoretical analysis proves that the band is the so-called adiabatic shear band (ASB), and that even melting of material takes place within it. In the shearing process, first an ASB evolves, followed by melting in the early stage of shearing. The major stroke of the punch is occupied by an easy simple shearing in a melted state.     

Factors influencing fill-out of a closed die during cold forging

Closed die cold forging is an important industrial metal forming process used extensively in the manufacture of headed fasteners. In this paper an upper bound solution is presented based on observed velocity fields resulting from the deformation of initially cylindrical workpieces within hexagonal and square dies. The influence of workpiece aspect ratio, forging loads and friction conditions on the fill-out of the hexagonal and square dies is examined. It is shown that at high die fill-out, friction conditions and workpiece aspect ratio have little influence on the forging pressure ratio. The surface stress state, produced by relative movement between workpiece and punch/die, is examined with the aid of microhardness measurements.     

制动毂挡尘盖拉深成形过程的应力应变分析

在大型CAD软件Pro/E中建立了汽车车轴制动毂挡尘盖拉深成形的凸凹模模型,运用大型商用有限元软件MSC.Marc,对其拉深成形过程进行了数值模拟.分析金属材料在拉深时的流动情况及挡尘盖在拉深后的应力应变分布规律,重点研究了压边力和凸凹模间隙对板材成形性能的影响,分析了起皱和破裂产生的原因、特点、影响因素以及预防措施等.模拟及试验结果表明,工件在拉深时,凸缘部分材料易产生失稳起皱现象;凸、凹模之间的间隙是影响盒形部分产生破裂的主要原因.当刚性压边圈与凹模之间的间隙减小到1.2倍的料厚时,能获得表面质量光滑的合格件;当凸凹模及浮动凸凹模之间的间隙大于料厚时,能确保拉深过程顺利进行.     

筒形件冲压缩口成形工艺的数值模拟研究

应用有限元分析软件中的显式动力学求解器模拟筒形零件缩口成形工艺过程中应力、应变和位移流向的分布云图,分析了工件成形时的塑性变形特点及其对成形质量的影响关系.研究表明:筒形件冲压缩口成形工艺主要失效形式是缩径区的裂纹、定径区的起皱和传力区部分的失稳等;工件失效的主要原因是塑性变形区材料流动速度不均匀导致的应力集中;冲压缩口力随着摩擦系数和模具锥角的增大而增大,但是会随着模具型腔内圆角半径的增大而减小.     

Ductile damage and simulation of fine-blanking process by FEM

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Shear behavior of AZ80 Mg alloy using experimental,theoretical and numerical techniques

The shear punch test (SPT) is a suitable experiment for characterizing the shear behavior of various materials, especially where there are volume limitations. In the present investigation, the relations among various parameters such as clearance, die diameter and sample thickness, and the yield and ultimate shear strengths of AZ80 Mg alloy were studied. Moreover, based on the Mohr?Coulomb theory, relatively optimum conditions were introduced for the shear punch test. With this regard, a range of 2%?10% is found to be suitable for the clearance/sheet thickness ratio. To provide a simple shear stress state during a shear punch test, it is also necessary to select the die diameter/sheet thickness ratio between 2:1 and 10:1. Based on the predictions of the Mohr?Coulomb theory, it is better to conduct a room-temperature shear punch test with a sample thickness of 0.5 mm, a clearance of 25 µm and a die diameter of 2 mm. Finally, the mean conversion factors to gain the tensile and compressive yield strengths of the cast AZ80 from its shear one are found to be 1.70 and 3.09, respectively.