反向挤压力计算公式分析

目前，用于计算反向挤压力的公式，都是根据相应的正向挤压力计算公式，直接令金属与挤压筒内壁间的摩擦为零得来的，其它参数的确定基本上与正向挤压时相同。在实践中发现，按照这些公式计算出的挤压力往往与其实测值有较大差异。本文结合对比实验，分析了造成这种差异的主要原因：只注意了反向挤压时挤压筒内壁上无摩擦，而忽略了反向挤压时金属的变形流动规律与正向挤压时不同；塑性变形区和死区的形状、位置与正向挤压不同，其体积远比正向挤压时小；变形区中的温升比正向挤压时小得多；加工硬化程度比正向挤压时大；制订工艺时锭坯的加热温度比正向挤压时低，挤压速度比正向挤压时快，等等。计算反向挤压的挤压力时，如果直接采用这些公式，应选用不同于正向挤压时的变形抗力值。     

铝合金线坯单孔模和多孔模挤压力问题的分析

根据И.Л.皮尔林挤压力公式,选用纯铝线坯挤压时,摩擦系数和挤压比对挤压力的影响进行了分析。     

И.Л.别尔林反向挤压管材挤压力公式修正

И．Л．别尔林挤压力公式是目前众多挤压力公式中应用最广的。本文分析了用于管材反向挤压的И．Л．别尔林挤压力计算公式，发现影响其计算精度的主要原因是反向挤压时变形区体积很难确定，因而无法确定金属在塑性变形区内的持续时间，也就无法确定金属材料的硬化系数，从而造成无法准确选择金属的变形抗力值；提出了无润滑反向挤压管材时的И．Л．别尔林挤压力公式的修正式，使计算过程大为简化，提高了计算精度。     

纯铝等径角挤压塑性流动的有限元模拟分析

本文采用DEFORM有限元软件模拟分析了ECAP过程中纯铝的塑性流动.通过模拟分析得出,可将ECAP过程中挤压力的变化分成四个阶段:A区:挤压起始阶段挤压力很低,随后挤压力接近线性增加;B区:挤压力先增加后减小,其中增加速率比A区缓慢;C区:挤压力基本趋于稳定;D区:随着挤压的进行挤压力开始回升.挤压过程中材料塑性流动的均匀部分大致可分为三个区域:内侧A区,变形体延伸方向与水平方向的夹角约为27.5(°);中间B区,变形体延伸方向与水平方向的夹角约为28.6(°);外侧C区,变形体延伸方向与水平方向的夹角约为56.6(°).同时,通过理论计算得到了变形体延伸方向与水平方向的夹角.结果表明:模拟结果与理论计算相符.     

冷挤压有限元分析

详细阐述了杯形反挤压成形的冷挤压过程。通过经典理论算法和ANSYS有限元算法，计算出了挤压力的大小。分析比较可以发现：有限元法能获得更高的计算精度。通过ANSYS的求解后处理，分析得出了挤压件的应力应变的分布情况。和挤压阶段时凸模的压力行程曲线。在此基础上，改用不同的材料特性、凸模的形式、润滑条件以及通过APDL参数化设计语言改变挤压件的尺寸大小进行反复求解。从而获得了这些因素对挤压力的影响规律。     

铜及铜合金反向挤压技术（续）

5棒材反向挤压力计算 正向挤压法和反向挤压法挤压时的挤压力曲线如图6^[3]所示。反挤压时铸锭与挤压筒内衬间基本不存在摩擦,在挤压过程中挤压力基本保持不变,挤压峰值压力出现在挤压终了阶段,反挤压所需挤压力在同一条件下比正挤压大约降低25—30％。影响反向挤压力的主要因素有金属变形抗力、变形程度、挤压速度、制品与模具接触表面摩擦条件、挤压模角、制品断面形状等。     

大口径无缝紫铜管挤压工艺研究

大口径紫铜结晶器是钛合金、镍基合金等贵重金属真空冶炼设备的重要部件,结晶器选用大口径无缝紫铜管寿命更长。挤压法相对于离心铸造法和锻造法等是最适合制造大口径无缝紫铜管的方法,挤压法制得的紫铜管组织均匀、力学性能更优。挤压工艺参数对紫铜管性能有显著影响,但目前尚无大口径紫铜挤压工艺参数的研究。文中研究了加热温度和挤压变形量对大口径紫铜管挤压力、晶粒尺寸和力学性能的影响。结果表明,大口径紫铜管的坯料加热温度越高,最大挤压力越低,但是降幅随着温度的升高逐渐减小;最大挤压力主要由紫铜的塑性变形力和与模具间的摩擦力构成,塑性变形力与挤压比的自然对数成正比;晶粒尺寸随加热温度提高和挤压比减小呈增大趋势;无缝紫铜管在挤压加热温度为780~860 ℃且挤压比为5.4~6.4时的力学性能相近,在该工艺窗口下挤压制造的无缝紫铜管均满足产品技术指标要求。     

凿岩钎头壳体温挤压精密成形力能分析

采用钎头壳体温挤压精密成形专利技术生产了小型凿岩钎头。从分析钎头壳体温挤压成形特点入手，将非轴对称正反复合挤压问题转化为轴对称锥孔反挤问题，再通过曲线的平移和拉伸变换，推导出钎头壳体温挤压力和变形功的近似计算公式，从理论上确定了挤压力的主要影响因素及其变化规律，为该项新工艺的模具设计和设备选择提供了理论依据。     

铜管的挤压成型和模具特点

铜管的挤压成型和模具特点江西省冶金工业厅文涛我们知道铜管挤压时大部分材料的表面被模具包围，坯料四周受很高的压缩应力产生塑性变形（图１）。挤压比（λ，即坯料断面积Ａｏ和挤成件断面积小的比值）越大和坯料长度（Ｈｏ）越长，则挤压力越高［１］，所以挤压用坯料...     

介绍几种新挤压方法

本文对几种新挤压方法进行综合介绍。它们包括棒材静液挤压法、双金属挤压法、Conform挤压法与Linex挤压法、Raflcw薄壁管挤压法、连续挤压法、壳层挤压法、粉末材料挤压法以及其它挤压方法。 一、静液挤压法 静液挤压可分非连续、半连续和连续挤压过程。棒材静液挤压是非连续过程。静液挤压可用来生产带色复层的半制品、小直径金属丝,难变形材料半制品,薄壁管以及截面形状复杂的型材。它可以对包复材料,脆性材料,铝及其合金,铜及其合金,钢及金属粉末和特殊钢进行挤压。     

挤压比对粉末包套热挤压致密W-40%Cu合金的影响

采用不同挤压比对W-40%Cu混合粉末进行粉末包套热挤压,获得了W-40%Cu合金。研究了模具总挤压比λ对热挤压坯料致密化以及组织性能的影响。结果表明,随着挤压比的增加,热挤压坯料的相对密度也增加,同时电导率和硬度值也随之提高。由于含铜量比较高(质量分数为40%),即便在挤压比为25时,挤压坯内部W相也不发生变形,主要是铜相产生变形。进一步将模具总挤压比λ细分为不考虑体积变形的坯料总挤压比α,除去体积变形因素的坯料塑性挤压比β以及包套挤压比γ三种实际挤压比,分析了不同挤压比对热挤压致密化过程的影响。     

高温合金617B管材热挤压特征及工艺优化控制

基于高温合金617B的组织演变模型，采用DEFORM-2D有限元软件构建了617B合金管材的热挤压模拟计算过程，对高温合金617B的热挤压特征进行了分析，并实现了管坯温度、晶粒尺寸等的定量预测.在结合生产实际的基础上，提出了包括温度准则、载荷准则、组织精确控制准则等在内的组织可控的可挤出性准则，对准则的控制原理和实施过程进行了阐述，并采用该类准则对617B合金的热挤压工艺参数范围进行优化，顺利得到了轴向形状尺寸均匀，表面质量较好的高温合金617B管材.该方法的提出和验证，为镍基高温合金无缝管材的生产提供了工艺优化的理论依据和研究方法.      

Thyroid hormone export regulates cellular hormone content and response

Actions of thyroid hormones (THs) are determined by intracellular free hormone concentration. Here we report that enhanced TH extrusion via a saturable, cold-sensitive mechanism lowers intracellular TH and causes TH resistance in hepatoma cells. Since these cells overexpress multidrug resistance P-glycoproteins and TH extrusion and resistance are blunted by verapamil, P-glycoproteins may mediate this resistance. Verapamil-inhibitable TH efflux was also found in primary hepatocytes, cardiocytes, and fibroblasts. These findings demonstrate that TH extrusion can modulate TH availability and action in mammalian cells.     

Structural changes in metals subjected to direct or twist extrusion: Mathematical simulation

The structural evolution of a material is calculated using a phenomenological grain-refinement and failure model based on the relation between these two processes. Direct extrusion and various schemes of twist extrusion are compared, and the effect of pressure is considered. The results obtained are used to draw conclusions regarding the advantages of certain deformation schemes.     

Influence of extrusion ratio and temperature on microstructure and mechanical properties of 2024 aluminium alloy consolidated from nanocrystalline alloy powders via hot hydrostatic extrusion

Abstract

Nanocrystalline 2024 aluminium alloy powders with an average grain size less than 50 nm, prepared by a unique technique which combines rapid solidification and mechanical milling, were consolidated into bulk material under various technical conditions via hot hydrostatic extrusion and the microstructure and mechanical properties of the consolidated alloy were experimentally investigated. The influence of the two main technical parameters, extrusion ratio and temperature, on the microstructure and mechanical properties of the as extruded alloy is made clear and the reasons why these two parameters had such an influence on the microstructure and mechanical properties of the alloy are also discussed. Furthermore, suggestions are given for rationalising the extrusion ratio and temperature for the consolidation of the nanocry stalline 2024 aluminium alloy powders via hot hydro static extrusion.     

TearSim: A two-phase model addressing hot tearing formation during aluminum direct chill casting

A two-phase mathematical model for the study of hot tearing formation is presented. The model accounts for the main phenomena associated with the formation of hot tears, i.e., the lack of feeding at the late stages of solidification and the localization of viscoplastic deformation. The model incorporates an advanced viscoplastic constitutive model for the coherent part of the mushy zone, allowing for the possibility of dilatation/densification of the semisolid skeleton under applied deformation. Based on quantities computed by the model, a hot tearing criterion is proposed where liquid feeding difficulties and viscoplastic deformation at the late stages of solidification are taken into account. The model is applied to study hot tearing formation during the start-up phase for direct-chill (DC) casting of extrusion ingots, and to discuss the effect of different phenomena and process parameters. The modeling results are also compared to experimentally measured hot tearing susceptibilities, and the model is able to reproduce known experimental trends such as the effect of the casting speed and the importance of the design of the starting block.     

大型工业铝合金型材的挤压生产工艺与关键技术

在综合分析国外先进技术的基础上,结合我国研究开发的成果,对工业用大型扁宽薄壁复杂实心和空心铝合金型材的特点、分类与应用,挤压生产工艺与设备,扁挤压筒与特种模具设计以及型材用铝合金的性能等进行了系统的分析讨论,以求加速这些材料的国产化.     

钼管靶材的挤压理论与组织性能分析

首先采用粉末冶金法制备了钼管坯或钼棒坯,然后通过挤压的加工方式得到满足溅射靶材密度要求的成品钼管靶。通过对管靶的挤压理论分析,得出钼管靶材的挤压工艺参数,包括挤压力（即挤压比）、挤压温度、挤压速度以及润滑剂等,并通过挤压前后组织和性能测试对比结果,得出挤压后的钼管靶材性能优异且能满足客户要求。     

Development of a model for the simulation of the transfer of surface structure in the temper-rolling process

In the temper rolling process the effect of transferring the roll-surface structure to the steel sheet is purposely used to adjust a defined sheet-surface structure required for further processing. At the moment four different texturing techniques (SBT, EDT, EBT, LT) are available for the production of specified roll-surface structures; these techniques are based on two fundamental mechanisms; plastic deformation and local melting. The objective of the investigation presented in this paper is to analyze the transfer behaviour specific to the texturing technique used and, in addition to that, to develop a model for the simulation of these transfer characteristics. For this purpose in the first part the results of a comparative study on the basis of rolling tests on an industrial temper mill are presented. These results do not only point out the basic transfer mechanisms – penetration processes and reverse extrusion phenomena – but beyond that also lead to an explanation of the transfer behaviour specific to the texturing systems by the application of similarity numbers (substitute profile model). Possible reasons for the different transfer behaviour are on the one hand wear effects and on the other hand process-induced characteristics of the structure itself (e.g. isolated lubrication pockets). On the basis of these results in the second part a model is developed to simulate the transfer characteristics by the application of the finite element method (FEM).     

核电主管道非对称双管嘴同时挤压成形工艺

针对AP1000核电主管道侧向双管嘴非对称分布的特点, 本文在单轴单向压力机平台上增加提升油缸的运动作用, 提出双管嘴同时挤压成形的新工艺.首先, 分析了双管嘴同时挤压成形的工艺原理并建立了可实现同时成形的上顶杆及提升油缸的速度与管嘴尺寸之间的解析关系.其次, 建立双管嘴同时挤压成形的有限元模型, 分析了同时挤压成形方案的可行性及在避免管嘴处材料撕裂缺陷方面的优势.最后, 从降低成形载荷和关键部位晶粒尺寸以及提高组织均匀性的角度, 分析了坯料温度、挤压速度和摩擦条件三个重要因素的影响规律, 为实施主管道挤压成形提供工艺参考.