导流角对挤压变形流动的影响机理分析

针对平模挤压时常因金属流速不均匀而易产生缺陷,本文采用了带导流角结构的芯模进行挤压研究.通过数值模拟和实验,深入分析了挤压过程中金属变形流动行为的机理,结果表明:带导流角芯模挤压时筒底不出现分流的现象,"死区"显著地缩小;处于塑性区内材料的应变类型由三种变为均一的拉伸类,显著地提高了金属变形流动的均匀性,利于金属的挤出成形及制品质量的提高.     

搅拌针端部挤压区内塑性金属的流动行为

以0.02 mm厚的铜箔作为标示材料、1 mm和2 mm厚的2024铝合金薄板作为基材,采用不同的叠加方式组成叠层并进行搅拌摩擦焊接(Friction stir welding, FSW)试验,分析搅拌针端部挤压区塑性金属的流动行为及其对焊缝成形的影响。结果表明,在FSW焊接过程中,焊缝上部被塑化的金属不断地沿着搅拌针螺纹旋向往搅拌针端部迁移、长大,形成挤压区。此挤压区由位于搅拌针两侧的扩展区和位于搅拌针端面下方的变形区组成。其中,变形区的金属一部分来自从焊缝上部迁移而来的塑性金属;另一部分来自搅拌针端面下方母材经旋转摩擦作用而发生塑性变形的金属。挤压区塑性金属的流动方式分为轴向挤压迁移、水平摩擦迁移和绕流迁移三种。对厚板进行FSW焊接时,挤压区的塑性金属倾向以绕流迁移方式为主,导致焊缝内部形成疏松区或孔洞型缺陷。     

工艺参数对辊弯成形金属流动的影响规律

目的提高辊弯成形工艺中工件的最终成形尺寸精度,并为辊弯成形工艺参数的制定提供理论依据。方法以非能动空气导流板辊弯成形为研究对象,对不同参数下金属的流动规律进行研究。建立非能动空气导流板辊弯成形实验和仿真模型,根据模型,分析不同结构参数对金属成形流动规律的影响。结果较大摩擦不利于板材成形,摩擦因数为0.06~0.2之间时成形较好,建议采用塑料润滑;随着板材成形速度的增大,金属的变形抗力增大,板材与轧辊之间出现打滑现象,成形速度为5~10 m/min时成形结果较好;随着轧辊间距的增大,板材刚度降低,不利于板材成形,故其间距取为450~560 mm之间。结论实验结果与仿真结果基本一致,结果表明采用控制成形参数可以有效控制板材的金属流动,从而控制板材辊弯成形以得到更高精度。     

连续挤压铜扁排的阻流角设计及物理场分布

基于Deform-3D平台,建立了Conform连续挤压生产大宽厚比铜扁排有限元模型,研究了连续挤压过程中阻流角变化对模具出口处金属流动及相应应力场分布的影响规律,并结合方差分析法获得了模具出口处的流速均方差,观察模具阻流角对扁排成型的影响.研究表明:模具阻流角从3°~15°变化时,随着阻流角的增加,金属流速均方差先增大后减小,其阻流角区域等效应力值以及模具入口处沿挤压方向应力也逐渐增加;在定径带长度一定以及模具载荷允许的情况下,选择3°、5°、15°的阻流角可使模具出口处金属流速相对稳定,扁排成形性较好;当模具容易损坏时,选择3°和5°阻流角既可降低模具载荷又可获得板形均匀的扁排.     

等通道角挤压AZ91D镁合金热压缩变形行为

在应变速率为0.005~1 s~(-1)、温度200~275℃条件下,利用Instron-5500热模拟机,对经过等通道角挤压(Equal Channel Angular Extrusion,ECAE)后的AZ91D镁合金的高温压缩特性进行了研究,得到了ECAE-ed态AZ91D镁合金真实应力-应变曲线,分析了挤压温度、应变速率等对其的影响,得出本构方程的一系列常量,建立了ECAE-ed态AZ91D镁合金在高温压缩中的本构方程关系式,并与铸态AZ91D镁合金进行了对比。结果表明:热压缩过程中,ECAE-ed态AZ91D镁合金与铸态一样,流动应力随温度的升高而降低,随应变速率的升高而升高;流动应力也可以用双曲正弦函数来描述,且双曲正弦值随Zener-Hollomon参数的自然对数的升高呈线性升高;两者同为正应变速率敏感材料,但ECAE-ed态AZ91D镁合金要比铸态应变速率敏感性小,其指数从铸态的m=0.14下降为0.096,变形激活能从182.65 kJ/mol上升为227.14 kJ/mol。研究结果对AZ91D镁合金进一步塑性成形和应用具有指导意义。     

导流介质对真空导入模塑工艺树脂流动行为的影响

采用可视化流动实验方法研究了高渗透率导流介质对真空导入模塑工艺中树脂流动行为的影响。结果表明: 导流介质能较大幅度地减少树脂的充模流动时间, 且充模时间随着导流介质使用比例的增加而呈线性减少的关系; 导流介质的提速作用随着预成型体厚度的增加而逐渐减弱; 预成型体上下表面树脂流动前沿位置差距与预成型体厚度呈良好的线性增加关系, 说明导流介质的影响作用具有明显的厚度效应。厚度效应原理为真空导入模塑工艺过程的参数优化和保证制品质量提供了理论依据。      

等径角挤压过程中材料的流变行为研究

分析了等径角挤压过程中材料流变的原因和特征,认为每道次挤压材料内部发生的剪切变形量与时间的函数曲线呈近似正态分布,适当升高温度和增加背压能有效减小难变形区,降低通道与试样接触面之间的摩擦能减小材料内部的滞变区.通过实验证明,随着挤压道次的增加,材料内部的滞变区将减小,均匀化程度会逐步提高.     

金属挤压成形技术研究与应用进展

针对传统挤压方法存在的材料利用率低、所需能耗大及制品均匀性差等不足,通过采用模具结构改进或变换作用方式等途径,可实现特殊形状及性能要求制品的加工成形,进而涌现出了一些"非"常规挤压工艺方法,丰富了现有挤压工艺的技术手段及应用领域。重点介绍了金属特种挤压成形的工艺原理、技术特点及应用情况,在挤压工艺技术附加值的提升和拓展性应用的开发等方面,具有重要的现实意义。     

三孔双芯模挤压方管型材的金属流动行为分析

为了分析双芯模挤压铝型材时造成的流动不均匀以及模具结构对该类型材焊合质量的影响,采用DEFORM-3D有限元分析软件,对三孔双芯模挤压6005A铝合金方管型材的金属流动行为进行了分析.模拟结果表明,分流孔面积分布不均易造成方管型材镰刀弯缺陷,当中间分流孔与一侧分流孔的面积比值为0.93～1.03时,型材出口流速均匀、焊缝居中.焊合室高度为13～16mm时焊合良好、成形质量好.挤压力在坯料与焊合室底面碰触后急速上升,在突破模孔时达到最高值.型材出口温度受分流孔面积和焊合室高度影响较小,当坯料温度为480℃时,型材出口温度为546～548℃.在650吨卧式挤压机上进行了挤压实验,实验结果与仿真结果吻合.     

等径角挤压对Al-Cu-Mg-Ag合金组织性能的影响

为研究大塑形变形对耐热铝合金的作用,采用铸冶金工艺制备了新型的Al-Cu-Mg-Ag耐热铝合金,通过显微组织观察、差热分析及硬度测试等方法,研究了等径角挤压对耐热铝合金显微组织与力学性能的影响.结果表明:通过对挤压态的Al-Cu-Mg-Ag耐热铝合金在固溶淬火后时效前进行等径角挤压变形,可获得晶粒尺寸低于2μm的块体超...     

球面挤压成形金属流动规律的数值模拟研究

为实现以挤压方法代替传统的钻锪工艺来成形球面定位孔,利用刚塑性有限元方法对圆孔的球面挤压成形过程进行数值模拟研究,分析了球面挤压过程中金属的流动规律,并研究了不同预冲孔直径板料挤压后孔径的变化.结果表明:整个成形过程金属的流动规律是先扩孔后缩孔;合理选择预冲孔尺寸是控制挤压成形后孔径尺寸精度的关键.     

Die shape optimal design in three-dimensional shape metal extrusion by the finite element method

A new approach to die shape optimal design in shape extrusion is presented. In this approach, the design problem is formulated as an optimization problem incorporating the three-dimensional finite element analysis model, and optimization of the die shape is conducted on the basis of the design sensitivities. The approach is applied to the determination of the die shapes for extrusion of parts with various cross sections including polygons and T sections. © 1998 John Wiley & Sons, Ltd.     

异形管材分流模挤压焊合过程金属流变及模具受力的模拟分析

针对采用有限元模拟时焊合面不能设置为刚性对称面的空心型材,其焊合过程不能模拟计算的问题,提出了基于有限元法结合逆向工程技术的焊合面网格重构技术的解决方法,并采用该方法对异形管材分流模挤压的焊合过程进行了模拟分析.研究结果表明:当挤压行程为33.1 mm时完成了焊合,焊合温度范围477~496℃,焊合室内静水压力为169~3 463 MPa,满足焊合要求;分流桥的焊合角部位所受应力最大,约为205 MPa.模具结构设计合理.     

Effect of die design parameters on the deformation behavior in pure shear extrusion

Influences of die design parameters in terms of diameter ratio and length of the deformation zone on the distribution of effective strain, filling fraction of the die exit channel and pressing load in pure shear extrusion (PSE) are studied using finite element method (FEM). Dimensional stability, pressing load and hardness measurements are used to validate the predictions of the simulation. Acceptable agreements between the predictions of simulation and experimental results are observed. It is found that strain is inhomogeneously distributed which increases from the center to the corners. Effective strain, inhomogeneity of strain, filling fraction of the die exit channel and pressing load are increased with increasing diameter ratio. In addition, the work-piece is deformed more homogeneously at lower pressing load by increasing the length of deformation zone. However, filling fraction of the die exit channel initially increases by the length of the deformation zone up to 60 mm after which it reduces. The optimum die design parameters covering a range of acceptable effective strain and strain homogeneity, filling fraction of the die exit channel and pressing load are proposed as being 60 mm and 2 for length of the deformation zone and diameter ratio, respectively.     

正挤压对SiCw/6061Al晶须形貌的影响

为了研究正挤压加工对SiCw/6061Al复合材料晶须形貌的影响规律,通过改变挤压温度、挤压比等工艺条件正挤压成形了挤压铸造法制备的15vol.%SiCw/6061Al复合材料,利用SEM技术观察和分析了正挤压加工前后复合材料的微观组织形貌.研究表明:正挤压加工导致SiC晶须沿着复合材料的塑性流动方向呈现出一定程度的定向排列趋势,并伴随有比较明显的折断现象;挤压温度、挤压比等工艺参数都是影响SiC晶须形貌的主要因素.     

Finite element analysis of the plastic deformation in tandem process of simple shear extrusion and twist extrusion

Recently, simple shear extrusion (SSE) and twist extrusion (TE) are introduced to fabricate ultrafine grained bulk rod metallic materials. The SSE and TE processes generate significant deformation inhomogeneity, with higher and lower strains in the center, respectively, which easily causes mechanical instability of the materials. In this study, to overcome this deformation inhomogeneity problem in SSE and TE, a tandem process of SSE and TE (TST) is suggested. The finite element method is applied for plastic deformation behavior during the TST process. The results demonstrate that the TST process can produce relatively homogeneously deformed materials. In particular, the effects of back pressure and processing order on the plastic deformation behaviors in the TST process are systematically analyzed.     

Experimental characterization of the crack-tip-opening angle in fibre metal laminates

Although the crack-tip-opening angle (CTOA) has been shown to be well suited for modelling stable crack growth in monolithic sheet aluminium alloys, its applicability for fibre metal laminates has not been fully analyzed yet. Fracture test were performed on M(T) panels made of Glare 2-3/2-0.4, Glare 3-3/2-0.4 and laminated 2024-T3 3/2-0.4. Different fatigue pre-crack lengths were created to study the effect of bridging fibres on the CTOA measured on the external layer. The effect of bridging fibres resulted in small deviations of the CTOA vs. crack extension curve with respect to the reference panel made of metal laminate. The CTOA criterion could be successfully used for predicting the residual strength in fibre metal laminates.