Expansion and reduction of thin-walled tubes using a die: Experimental and theoretical investigation

The production of sound thin-walled tubular parts by expansion and reduction using a die is generally limited to components having geometrical features within a compact range. Basic design rules, providing the geometrical and material parameters that govern the process, are mainly derived from the accumulated experience of both manufacturers of tubular parts and suppliers of machine-tools. However, no information is generally available on the influence of interface friction on material flow and on the effect of material damage and strain path on the occurrence of fracture, wrinkling and local buckling. The aim of this paper is to refresh and extend the fundamentals of tube expansion and reduction using a die by means of a comprehensive theoretical and experimental investigation. The emphasis is focused on understanding modes of deformation and on establishing formability principles for the benefit of those who design tubular parts in daily practice. The theoretical investigation is accomplished by the utilization of virtual prototyping modelling techniques based on the finite element method and the experimental work is mainly utilized for supporting and validating the theoretical investigation.     

External inversion of thin-walled tubes using a die: experimental and theoretical investigation

External inversion of thin-walled tubes using a die is used for producing double-walled parts that are difficult to manufacture by any other technique. Previously published works in the field generally provide the main geometrical and material parameters that govern the process. However, insufficient knowledge can still be found in understanding the influence of interface friction on the material flow and of the strain path and material damage on the occurrence of fracture. Moreover, although the analytical conditions for the occurrence of buckling are easily available in the literature its numerical modelization is usually not commonly available.This paper presents a comprehensive numerical and experimental modelling of the external inversion of thin-walled tubes with the purpose of reexamining the process mechanics and obtaining a better understanding of the deformation modes associated with its formability limits. Fundamental research is undertaken by using virtual prototyping modelling techniques based on the finite element method. The experimental work is performed on Aluminium Al6060 industrial tubes and it is mainly utilized for supporting and validating the theoretical investigation.     

Internal inversion of thin-walled tubes using a die: experimental and theoretical investigation

The design of sound double-walled tubular parts by external inversion using a die is presently well established. Major parameters are identified, the influence of lubrication is sufficiently well understood and the typical modes of deformation that may occur during the forming process are fully characterized. In contrast to external inversion, there are almost no published works that comprehensively cover the conception of double-walled tubular parts by internal inversion using a die.This paper draws from fundamental research on the internal inversion of thin-walled tubes using a die to the establishment of formability diagrams in terms of the major process parameters. Fundamental research is based on a comprehensive theoretical and experimental investigation of a wide range of subjects, such as: development of plastic instability modes (local buckling), thickening of the tube-wall and occurrence of wrinkling phenomena at the free curved end of the inwardly inverted tubes. The influence of the frictional conditions prevailing at the contact interface between the tube and the die is also examined. The theoretical investigation is supported by numerical predictions based on the finite element flow formulation and the overall methodology is assessed by means of experimental tests on industrial Al6060 Aluminium alloy tubes (annealed and naturally aged) under laboratory-controlled conditions.     

Forming of thin-walled tubes into toroidal shells

The purpose of this paper is to introduce a new forming process that is capable of shaping thin-walled industrial tubes into toroidal shells in a single-stage operation.The methodology draws from the existing know-how on conventional end forming of tubes to aspects of deformation mechanics that are necessary to identify the typical modes of deformation and to establish the formability limits in terms of the major process variables. The approach is illustrated and enriched with selected test cases obtained from finite element modelling and experimentation and the overall presentation is expected to effectively contribute to transferable of original technological knowledge.The new proposed process is a fast and low-cost manufacturing alternative to existing solutions for producing toroidal shells that are based on incremental forming and hydroforming. However, it is shown that the overall feasibility of the process is limited to toroidal shells having slenderness ratios within a compact range in order to avoid superposition of material along the equatorial plane and to prevent fracture during forming.     

薄壁管管端成形的有限元分析

针对管端成形过程中金属塑性流动引起的轴向伸缩及卸载回弹导致的成形精度问题,研究金属的塑性流动和回弹对管端成形的影响。以不锈钢卡压式直通管件为研究对象,运用LS-DYNA的有限元显式算法和隐式算法对薄壁管管端成形进行数值模拟,得到管材的金属流动分布和卸载后的回弹结果,并进行了实验验证。研究表明,管端扩孔和缩孔中,在变形急剧处,金属出现一定程度的累积,壁厚有较明显地增加。金属的流动对管端的径向尺寸影响可以忽略,但是对管端的轴向尺寸影响较大,需对坯料进行补偿;管端卸载后的回弹尺寸影响成形的精度,需通过模具进行补偿。对金属塑性流动和回弹进行有限元分析,能有效地指导管端成形的模具设计及优化加工工艺,极大缩短产品开发和模具设计周期。     

薄壁零件成形工艺与模具设计

简述了复杂薄壁零件的结构特点及成形工艺,介绍了拉深模、翻孔模和压凸包模的结构、工作过程及设计要点,利用这些模具生产薄壁零件能显著提高生产效率,保证零件质量,对类似复杂薄壁零件的成形有一定参考作用。     

内压对薄壁管充液压弯时的影响

失稳起皱和截面畸变是薄壁管弯曲成形过程中的主要缺陷,通过数值模拟和实验的方法,研究了液压支承下管材的弯曲变形行为,进行了从无内压到内压为18MPa的管材充液弯曲成形,分析了充液弯曲成形过程中的内压值对成形的影响,给出了成形后的不圆度和典型点壁厚减薄率的变化规律,结果显示,随着充液压力的增加,管材的截面不圆度逐渐减小,管材内侧壁厚增厚趋势减小,外侧壁厚减薄趋势增大。并根据模拟结果给出了成形后的典型点的应力状态。     

不同材料薄壁圆管准静态轴压变形特性

材料选取是缓冲吸能结构耐撞性及轻量化设计的重要环节,该文采用LS-DYAN软件对低碳钢、铝合金和不锈钢等不同材料薄壁圆管的变形模式、比载荷、平均比载荷及比吸能等轴压变形特性进行数值模拟分析。研究结果显示,几组圆管试样均发生了轴向渐进叠缩变形,分别形成了周向折叠凸角数目不同的非轴对称和轴对称变形模式,其中铝合金圆管发生了较为特殊的横截面呈"椭圆形"的非轴对称变形模式,对比研究发现,铝合金的比吸能远高于不锈钢和低碳钢,更适用于缓冲吸能结构的轻量化设计。     

大口径薄壁纯钛管数控热弯内外侧的塑性变形机制

为了发展大直径薄壁纯钛管数控加热弯曲技术,实验研究了大口径薄壁CP-3管材在不同温度下数控弯曲后的内外侧塑性变形机制。通过EBSD分析和维氏显微硬度测试方法,对数控弯曲温度293、423和573 K下弯管件试样弯曲外侧受拉区域以及弯曲内侧受压区域进行显微组织变化和维氏硬度分析。结果表明：1）在不同温度下数控弯曲变形后,弯管外侧塑性变形机制主要为滑移,孪生变形微弱,择优取向类似于初始管材的;弯管内侧塑性变形机制主要以{1 012}孪晶为主,滑移为辅助机制,且孪晶使管壁材料择优取向产生剧烈转变。2）维氏硬度的变化与塑性变形机制及织构有关。弯曲变形后,管材试样内外侧轴向与周向的维氏硬度值均显著得到提高,且管材试样内侧的维氏硬度值要明显高于外侧的,周向的维氏硬度值高于轴向的。     

薄壁卡圈精冲级进模设计

分析了薄壁卡圈的成形工艺,设计了精冲级进模,介绍了模具结构及模具关键零件的设计。实际生产证明:模具结构合理,能保证产品质量,生产效率较高。     

焊点数量对薄壁帽型截面管吸能特性的影响

研究汽车车身吸能结构焊点的数量对碰撞安全的影响。在不改变吸能结构本身及生产工艺的前提下,通过焊点数量提高结构的吸能特性。针对上述问题,采用试验和有限元方法研究单帽、双帽管的轴向吸能特性,仿真结果与试验结果较好吻合,验证了有限元模型的准确性。通过有限元方法,研究不同数量的焊点对帽型截面管轴向和弯曲吸能特性的影响。结果表明,一定范围内增加焊点数量能够提高帽型截面管的轴向吸能特性,但对弯曲吸能特性的影响并不明显。     

扩展组合模连续铸挤铝管材的挤压力分析(英文)

为了确定管材扩展组合模连续铸挤过程的变形力,将金属扩展组合模的模腔划分为导流区、扩展区、分流区、焊合区和定径区,分析各区金属的受力状态;用切块法建立各区应力计算公式。将金属连续铸挤型腔划分为液相区与半固态区、固态初始夹紧区和固态夹紧区,建立管材连续铸挤挤压力计算公式。在自行设计的连续铸挤机上进行铝管扩展组合模连续铸挤实验并测量其挤压力,获得的径向挤压力实验结果与理论计算结果吻合。     

热电厂薄壁小径管的相控阵超声检测

通过在薄壁小径管上预制模拟缺陷,采用数字射线检测和相控阵超声检测技术对其进行检测比对,验证了相控阵超声检测工艺的有效性.结果表明:相控阵超声检测技术操作简便,缺陷检出率高,且可以通过积累图谱,为缺陷的定性提供参考依据.     

推件板—推杆二次推出薄壁壳体压铸模设计

介绍了推件板—推杆二次推出薄壁壳体压铸模结构,模具设有特殊的定距拉板,定距拉板除了起模具分型的定距作用外,还在第2次分型结束时旋转一定角度,解除第1次分型的定距约束,实现分型面Ⅰ的再次分型。分型面Ⅱ分型时推件板带动动模镶块将铸件推离型芯,实现铸件的第1次推出。分型面Ⅰ再次分型到位后,推杆将铸件推离动模型腔,实现铸件的第2次推出。模具结构紧凑,工作可靠,操作方便。     

冷镦模具的冷挤压加工

介绍了利用冷挤压技术生产冷镦模具的优点和方法 ,以及典型冷镦模具的制造过程。     

薄壁钢管内胀推弯成形数值模拟及实验研究

针对薄壁管材弯曲成形过程中内壁起皱、外壁拉裂等成形缺陷,采用内胀推弯工艺成形规格为Φ30mm×0.3mm的1Cr18Ni9Ti薄壁管材。有限元模拟了不同内胀压力下,薄壁管成形性能和壁厚分布,并进行了实验研究。结果表明,该工艺可以很好的解决内壁起皱、外壁拉裂等成形缺陷,对生产实践具有一定的指导意义。     

Analytical model for the expansion of tubes under tension

This paper focuses on the expansion of metallic tubes subjected to large radial and circumferential plastic deformations. This process can be achieved by driving rigid conical mandrels of various diameters through them either mechanically or hydraulically in order to obtain desirable expansion ratios. A mathematical model was developed to predict the stress field in the expanded zone, the drawing force required for expansion, and the resulting dissipated energy from which optimum mandrel shapes were obtained. A finite element analysis was used to validate the theoretical results. A good agreement was obtained in terms of drawing force and dissipated energy for different geometric constraints and friction coefficients. The study showed that the optimum mandrel angle ranges between 22 and 25 degrees for low friction and increases non-linearly when friction increases.     

膨胀套筒级进模设计

介绍了膨胀套筒的级进模设计,分析了圆筒状冲压件的成形工艺,阐述了载体设计、卷圆成形设计、不同长度零件的共模设计、排样设计等,重点说明了级进模结构设计中的卷圆成形结构和搭料切断结构。     

三维非轴对称薄壁管件旋压成形机床液压系统的研究

在分析三维非轴对称薄壁管件旋压成形机床工作过程的基础上,利用MATLAB软件中SIMULINK模块对该机床的液压系统进行了建模与仿真。仿真结果与实验结果相吻合,结果表明,由比例流量阀、位移传感器和放大器共同构成的闭环控制系统能较好地满足三维非轴对称零件旋压成形工艺要求,从而为进一步进行系统的液压和机械系统的协同仿真,提供了客观可靠的理论基础。