钛合金弯管动态流量控制法挤压成形的模拟与实验研究

通过有限元分析和实验研究动态流量控制法挤压钛合金弯管件。实验验证弯管的尺寸精度和挤压载荷。分析调控量对弯曲曲率的影响、速度场和温度场。结果表明:挤压载荷的峰值误差为14.51%,挤出的管材弯曲曲率误差为3.47%;在模具结构中,调控通道Ⅱ截面面积不变时,弯管曲率半径随调控通道Ⅰ有效截面面积的增大而增大;在定径带处的合金呈非均匀流动,弯管件内外弧面存在流速差是挤出弯曲件的原因;合金的流速在通过定径带时发生分流补偿,由调控通道Ⅱ进入定径带的合金流速反超辅助通道内的流速,在焊合腔内边缘处存在金属流动死区。在定径带区域温升明显,最大温升为134℃。     

方管铝型材自弯曲挤压工艺

提出一种方管自弯曲挤压新工艺,通过设计倾斜分流桥结构,使金属在型腔内产生不均匀流动,从而直接挤出弯曲方管型材。利用外部网格重构方法,实现金属在型腔内分流焊合过程的模拟分析,得到自弯曲挤压过程金属流动规律、等效应力应变场分布;研究分流桥倾斜角和挤压速度对方管型材自弯曲成形性的影响,并通过挤压实验制备出自弯曲方管。结果表明:自弯曲模具结构可挤出形状规则、曲率一致的弯曲方管件,型材应力应变分布均匀,随分流桥倾斜角或挤压速度的增加,型材曲率半径呈非线性递减,挤压后弯曲方管的上表面、侧面和下表面的晶粒均匀且为等轴晶,晶粒尺寸分别为64.3、61.7和58.3μm。     

滚弯过程的三维动态仿真模拟

用大型工程有限元分析软件MSC.Marc,成功地实现了对船用大尺寸钢板滚弯及其回弹过程的三维动态仿真模拟,模拟结果表明,滚弯时间越长,获得的板材各个部分的塑性变形和曲率半径越均匀且趋于一定值;回弹后弹性能释放,等效Mises应力的峰值变小,但在板材的起始滚弯位置仍有一个较小的残余应力集中。文章对于有限元模拟过程中实体单元离散的板材曲率计算问题进行了研究,提出了计算曲率的方法。计算结果和测量结果对比表明,相同的滚弯工艺下,获得的板材整体曲率半径误差不超过7%,最大曲率半径误差不超过8%;厚度方向上x方向的应力分布趋势和实测结果一致。     

筒形件挤压翻边的数值模拟

利用有限元分析软件DEFORM-3D,对筒形件内孔挤压翻边成形过程进行了数值模拟,得出了挤压翻边成形过程中的行程载荷曲线、板料厚度以及翻边高度随挤压行程变化的规律。分析了挤压翻边与传统翻边应力状态的不同之处,以及翻边凸模的冲头曲率半径对翻边效果的影响。     

7050高强铝合金孔板的挤压强化与拉伸试验研究

针对航空用7050高强铝合金的孔板件拉伸性能进行试验研究与模拟分析,并对不同过盈量 (0%～11.11%) 的孔挤压强化效果进行了对比分析。研究表明:孔板的表观强度、延伸率和弹性模量均降低,但塑性失稳点应变却有很大程度的提高;孔挤压强化提高了孔壁处材料的屈服强度,改善了孔表面的受力状态,使得应力峰值得到钝化,并扩大了孔壁沿厚度方向的平面应变范围,因此拉伸断口随孔挤压量的变化呈规律性的变化;孔挤压强化后残余拉、压应力峰值随挤压量的增加而增加,且其峰值出现的部位随挤压量的增加而向远离于孔壁的深处转移。     

新型等通道球形转角膨胀挤压过程模拟与实验验证

将"球形分流"和"膨胀挤压"概念引入传统ECAP技术,提出一种新型等通道球形转角膨胀挤压(ECAEE-SC)工艺。采用有限元模拟和实验验证的方法研究ECAEE-SC过程中工业纯铝的塑性变形行为。结果表明:ECAEE-SC工艺具有复合剧烈塑性变形的效果,球形转角和膨胀通道为两个主要变形区域;挤压过程中材料处于理想的压应力状态,坯料单道次ECAEE-SC变形累积等效应变量约为3.5,整体变形均匀性良好,挤压效率大幅提高。挤压实验与有限元模拟结果相一致,挤出坯料外形完整且宏观无裂纹,坯料显微硬度平均值从初始36.6HV增加至70.2 HV,力学性能得到显著改善。     

300M超高强度钢孔挤压强化残余应力场的三维模拟分析

利用ANSYS有限元软件模拟计算了300M超高强度钢构件的孔挤压强化残余应力,建立了材料不同厚度构件的孔挤压残余应力场三维有限元模型,分析研究了构件厚度对残余应力场的影响,确定了最大残余压应力出现的位置,比较了孔挤压入口、中部和出口处残余应力场的变化情况。结果表明,残余压应力沿孔壁厚度方向的分布是不均匀的,入口处残余压应力最小,出口处次之,而中部的残余压应力最大。     

辊弯拱型波纹板的回弹问题

通过辊弯拱型波纹板的回弹公式计算和有限元模拟计算 ,探讨了辊弯拱型波纹板的回弹问题。研究得出 ,辊弯拱型波纹板的回弹过程是一个应力释放过程 ,回弹后的最大变形量降低 ;带有侧边板的拱型波纹板回弹前后曲率半径变化不大 ,而无侧边板的拱型波纹板曲率半径变化较大 ;理论曲率半径值与实测结果基本符合。     

钛合金面内弯曲板挤压成形的数值模拟与实验研究

通过有限元分析和实验研究了钛合金面内弯曲板挤压成形。实验验证了挤压力和工件的尺寸精度。分析了调控量对工件曲率半径的影响和速度分布。结果表明,面内弯曲板的曲率误差为0.86%,挤压力的峰值误差为10.49%;在模具结构中,工件曲率半径随调控量的增大而减小;在定径带处变形体呈非均匀性流动,工件的内外弧存在流速差是形成弯曲件的原因;在工作带横截面上,自内弧侧至外弧侧,流速呈线性增长,在焊合腔两端存在流动死区。     

基于有限元法的空心铝型材挤压过程瞬态分析

采用有限元软件,对一非对称截面列车上侧梁型材挤压分流、焊合直至稳态挤出的整个非稳态过程进行了数值模拟。着重研究了挤压成形过程中变形体的速度、温度、应变速率等物理场量的分布与变化情况,以及模具应力分布情况。针对模拟过程中出现的挤出物前端存在严重变形的问题,对模具的二级焊合室尺寸、阻流块高度以及工作带尺寸作出优化。模具结构优化后模孔出口截面速度均匀性得到明显改善,其速度差从22 mm·s-1减小到7 mm·s-1。通过分析等效应变速率与温度分布的关系,发现坯料温度升高所需的热量主要来源于坯料变形产生的塑性变形能。通过模具应力分析得知模具在各挤压阶段的应力分布情况。     

Effect of extrusion wheel angular velocity on continuous extrusion forming process of copper concave bus bar

The continuous extrusion forming process for producing large section copper concave bus bar under different extrusion wheel angular velocities was studied by three-dimensional finite element technology based on software DEFORM-3D. The rigid-viscoplastic constitutive equation was employed in the model. The numerical simulation results show that the deformation body flow velocity in the die orifice increases gradually with the increase of the extrusion wheel angular velocity. But slippage between the rod and extrusion wheel occurs when the extrusion wheel angular velocity is high. The effective stress near the die orifice enhances gradually with increasing extrusion wheel angular velocity. High stress is concentrated in adjacent regions of the flash gap. The effective strain gradient is greater near the abutment than that near the die orifice. The effective strain of the product increases gradually with increasing extrusion wheel angular velocity. In the deformation process, the deformation body temperature increases remarkably due to friction and deformation. So the cooling is necessary in the region of the die and tools.     

双凸模差速挤压方形弯曲管件工艺过程有限元模拟

提出通过控制不同凸模的压下速度并调节挤压管件的弯曲曲率,实现弯曲管件一次性挤压成形的新方法。采用有限元法模拟了弯曲管件双凸模差速挤出过程,分析了双凸模挤压过程速度场分布、材料流动规律、挤压力、应力场和应变场的分布。     

四辊连续滚弯侧辊位移计算与数值模拟

在四辊卷板过程中,卷制工件的曲率主要取决于侧辊的位移量。以塑性弯曲理论为基础,对四辊连续滚弯过程中板材各阶段的变形情况进行了理论分析。根据卸载定理推导出双线性硬化模型板材的回弹曲率计算公式,建立了四辊连续滚弯侧辊位移的数学模型。利用ABAQUS有限元软件对四辊连续滚弯过程进行三维动态模拟,对仿真值和理论值进行了比较,分析了不同板厚下侧辊进给量、相对弯曲半径与成形曲率半径之间的关系。结果表明:有限元仿真误差较小,可以用来指导实践;随着侧辊进给量的增加,板厚对成形曲率半径的影响逐渐减小;成形曲率半径随着相对弯曲半径的增加基本呈线性关系变化。     

Determination of forming limit of a structural aluminum tube in rubber pad bending

Rubber pad bending is a novel technique for producing space frame to reduce the weight of automobiles because it can produce bent profiles with various curvatures in a single production set-up. As in other bending processes, cross-section of the aluminum tube deforms during the process. Such a deformed geometry diminishes bending rigidity, making it inappropriate for a structural use in some cases. Thus, it is important to determine a minimum radius of curvature with sufficient bending resistance. In this study, experimental set-up was developed to investigate deformation characteristics of an extruded rectangular aluminum tube in rubber pad bending. For better understanding of the effect of process parameters such as the material property of rubber and roller diameter, finite element (FE) analyses were also conducted. The ratio of the second moment of inertia of the initial and deformed cross-sections of the tube was introduced as a measure of cross-sectional deformation to represent the variation of bending rigidity of the bent tube. In result, a critical value of sectional deformation and minimum formable radius of curvature with maintaining suitable sectional bending rigidity were, respectively, determined under the present process conditions investigated.     

基于有限元模拟的数控弯管过程轴力和弯矩的分析计算

获取管材数控弯曲过程中的轴力和弯矩,有助于对成形机理的了解和后续的回弹分析,以及为选择设备和设计模具提供重要依据。提出了基于三维有限元模拟的数控弯管过程中轴力和弯矩的求解方法,详细阐述了其实现过程。采用该方法,分析了轴力和弯矩随弯曲角的变化特征以及工艺和材料参数对轴力和弯矩的影响规律:随着弯曲过程的进行,塑性变形区的轴力变化不大,弯矩呈指数关系变化,而弯曲变形区刚性端的轴力几乎线性递增,弯矩类似于阻尼正弦曲线变化;弯曲速度和材料强度系数的增大以及弯曲半径和硬化指数的减小会引起轴力和弯矩的增加。文中提出的方法也可推广应用于板材、其他型材和管材的弯曲。     

不同工艺参数对大口径厚壁无缝钢管垂直挤压过程的影响

针对火电、核电设备使用的基础构件大口径厚壁无缝钢管,利用有限元模拟软件Deform-3D对钢管的垂直挤压过程进行数值模拟,通过改变挤压比、凹模锥角等参数对其等效应力、等效应变、温度场及载荷进行分析。结果表明:随着挤压的进行,坯料等效应力、等效应变及载荷都是先逐渐增加后趋于平稳;随着挤压比以及凹模锥角的变化,等效应力、等效应变及载荷也发生不同程度的变化;并且当挤压比为6、凹模锥角为30°时最有利于坯料的成形。     

Analysis of axisymmetric tube extrusion

A comprehensive investigation of an axisymmetric steady-state tube extrusion through a streamlined die is carried out by the finite element method (FEM) to study the influence of process variables on tool design and final product quality for a strain hardening material. The process variables considered are: the reduction in area; coefficient of friction; mandrel radius; die-length; the hardening capacity of the material. The extrusion parameters studied are: the extrusion pressure; die pressure; mandrel pressure; hydrostatic stress distribution; strain-rate distribution; strain distribution. The mixed (pressure-velocity) formulation is used along with the Householder method to solve the resulting ill-conditioned algebraic equations. The extrusion pressure predicted by the present model is in reasonably good agreement with the published experimental results. The trends predicted for other parameters also conform with the published results.     

An extrusion−shear−expanding process for manufacturing AZ31 magnesium alloy tube

A new severe plastic deformation method for manufacturing tubes made of AZ31 magnesium alloy with a large diameter was developed, which is called the TCESE (tube continuous extrusion?shear?expanding) process. The process combines direct extrusion with a two-step shear?expanding process. The influences of expanding ratios, extrusion temperatures on the deformation of finite element meshes, strain evolution and flow velocity of tube blanks during the TCESE process were researched based on numerical simulations by using DEFORM-3D software. Simulation results show that the maximum expanding ratio is 3.0 in the TCESE process. The deformation of finite element meshes of tube blanks is inhomogeneous in the shear?expanding zone, and the equivalent strains increase significantly during the TCESE process of the AZ31 magnesium alloy. A extrusion temperature of 380 °C and expanding ratio of 2.0 were selected as the optimized process parameters from the numerical simulation results. The average grain size of tubes fabricated by the TCESE process is approximately 10 µm. The TCESE process can refine grains of magnesium alloy tubes with the occurrence of dynamic recrystallization. The (0001) basal texture intensities of the magnesium alloy tube blanks decrease due to continuous plastic deformation during the TCESE process. The average hardness of the extruded tubes is approximately HV 75, which is obviously improved.     

AZ80镁合金变形特性及管材挤压数值模拟研究

利用Gleeble热模拟机研究了AZ80合金的高温变形特性。结果表明,流变应力取决于变形温度和变形速率。当应变速率一定时,流变应力随变形温度的升高而降低;当温度一定时,流变应力随着应变速率的升高而增大。根据AZ80镁合金真应力-真应变曲线,建立了其流变应力模型。采用刚塑性有限元法对AZ80镁合金管材挤压过程进行热力耦合数值模拟,并分析了高温挤压成形过程中变形力及金属流动规律,着重探讨了变形温度和挤压速度等挤压工艺参数对挤压力、应变场以及应力场的分布及变化情况的影响。模拟的结果为AZ80镁合金管材挤压工艺参数的制定、优化提供了科学依据。     

Effect of geometric shape of plate on residual stress and deformation distribution for butt-weld joint

This paper presents a numerical simulation of deformation and residual stress in butt-weld joint for different shaped plates.Within the framework of numerical investigation,3 types of models and a double ellipsoidal heat source were implemented in finite element simulation. As for an effect of geometric shape,the weld-induced deformation and residual stress should be taken into account during designing the welded structure. And for U-shape plates,the effect of curvature radius on the mechanical properties was also obtained,which is a significant factor affecting its service life. The simulation results revealed that the plate processed into U-shape could reduce the deformation and residual stress near the weld. And the deformation and residual stress in U-shape plate with circular arc transition were further reduced. Furthermore,the effect of curvature radius on the mechanical properties of plates was not general considered as the bigger curvature radius the better mechanical properties. The results concluded that the geometric shape significantly affects the mechanical properties,which provides prediction for structural design.