Solidified structure of thin-walled titanium parts by vertical centrifugal casting

The solidified structure of the thin-walled and complicated Ti-6AI-4V castings produced by the vertical centrifugal casting process was studied in the present work. The results show that the wall thickness of the section is featured with homogeneously distributed fine equiaxial grains, compared with the microstructure of the thick-walled section. The grain size of the castings has a tendency to decrease gradually with the increasing of the centrifugal radius. The inter-lamellar space in thick-walled casting parts is bigger than that of the thin-walled parts, and the profile of inter-lamellar space is not susceptible to the centrifugal radius.

Filling mode and regularity of vertical centrifugal casting process of titanium alloy in thin-walled cylinder cavity

The mold filling process of titanium alloy in a thin-walled cylinder cavity under vertical centrifugal casting process was studied by means of the hydraulic simulation experiments. Results show that the filling mode of the melt in the cylinder cavity varies with casting wall-thickness. When the casting wall-thickness is less than or equal to the thickness of the first layer during the filling process, the melts fill the cavity from the bottom to the top.When the casting wall-thickness is greater than the thickness of the first layer during the filling process, the melts first fill the largest radius parts of the cavity with a certain thickness of the first layer from the bottom to the top of the cavity, and then they fill the cavity from the larger radius part to the smaller radius part. The melt filling ability increases with the increment of the mold rotational speed and the pouring temperature. In another aspect, the melt filling ability rises with the decrement of the melt viscosity, and the melt with the better filling ability is prone to fill the cylinder cavity layer by layer.

Hot spinning of cylindrical workpieces of TA15 titanium alloy

In order to form large-diameter thin-wall cylindrical workpieces of TA15 titanium alloy,tube hot spinning experiments of the alloy were conducted on a CNC hot spinning machine.The causes of some forming defects occuring in hot spinning,such as crack,pileup,bulge and corrugation,were analyzed and the corresponding measures were put forward to avoid spinning defects,based on which a proper process scheme of hot spinning of TA15 alloy was obtained and the large-diameter and thin-walled cylindrical workpieces were formed with good quality.The results show that spinning temperature has distinct influence on forming quality of spun workpieces.The range of spinning temperature determines the spinnability of titanium alloy and the ununiformity of temperature distribution near the deformation zone leads to the formation of bulge.The reasonable heating method is that the deforming region is heated to the optimum temperature range of 600-700 ℃,the deformed region is heated continuously and a certain length of undeformed region is preheated.With the thickness-to-diameter ratio(t/D) of spun workpiece reducing to certain value(t/D<1%),surface bulge and corrugation is rather easier to come into being,which could be controlled through restraining diameter growth and employing smaller reduction rate and lower temperature in the optimum spinning temperature range.

High-efficiency forming processes for complex thin-walled titanium alloys components: state-of-the-art and perspectives

Complex thin-walled titanium alloy components play a key role in the aircraft,aerospace and marine industries,offering the advantages of reduced weight and increased thermal resistance.The geometrical complexity,dimensional accuracy and in-service properties are essential to fulfill the high-performance standards required in new transportation systems,which brings new challenges to titanium alloy forming technologies.Traditional forming processes,such as superplastic forming or hot pressing,cannot meet all demands of modern applications due to their limited properties,low productivity and high cost.This has encouraged industry and research groups to develop novel high-efficiency forming processes.Hot gas pressure forming and hot stamping-quenching technologies have been developed for the manufacture of tubular and panel components,and are believed to be the cut-edge processes guaranteeing dimensional accuracy,microstructure and mechanical properties.This article intends to provide a critical review of high-efficiency titanium alloy forming processes,concentrating on latest investigations of controlling dimensional accuracy,microstructure and properties.The advantages and limitations of individual forming process are comprehensively analyzed,through which,future research trends of high-efficiency forming are identified including trends in process integration,processing window design,full cycle and multi-objective optimization.This review aims to provide a guide for researchers and process designers on the manufacture of thin-walled titanium alloy components whilst achieving high dimensional accuracy and satisfying performance properties with high efficiency and low cost.

Elastic Buckling of Bionic Cylindrical Shells Based on Bamboo

High load-bearing efficiency is one of the advantages of biological structures after the evolution of billions of years. Biomimicking from nature may offer the potential for lightweight design. In the viewpoint ofrnechanics properties, the culm of bamboo comprises of two types of cells and the number of the vascular bundles takes a gradient of distribution. A three-point bending test was carried out to measure the elastic modulus. Results show that the elastic modulus of bamboo decreases gradually from the periphery towards the centre. Based on the structural characteristics of bamboo, a bionic cylindrical structure was designed to mimic the gradient distribution of vascular bundles and parenchyma cells. The buckling resistance of the bionic structure was compared with that of a traditional shell of equal mass under axial pressure by finite element simulations. Results show that the load-bearing capacity of bionic shell is increased by 124.8%. The buckling mode of bionic structure is global buckling while that of the conventional shell is local buckling.

Deformation Analysis and Fixture Design of Thin-walled Cylinder in Drilling Process Based on TRIZ Theory

Thin-walled cylindrical workpiece is easy to deform during machining and clamping processes due to the insufficient rigidi.Moreover,it’s also difficult to ensure the perpendicularity of flange holes during drilling process.In this paper,the element birth and death technique is used to obtain the axial deformation of the hole through finite element simulation.The measured value of the perpendicularity of the hole was compared with the simulated value to verify then the rationality of the simulation model.To reduce the perpendicularity error of the hole in the drilling process,the theory of inventive principle solution(TRIZ)was used to analyze the drilling process of thin-walled cylinder,and the corresponding fixture was developed to adjust the supporting surface height adaptively.Three different fixture supporting layout schemes were used for numerical simulation of drilling process,and the maximum,average and standard deviation of the axial deformation of the flange holes and their maximum hole perpendicularity errors were comparatively analyzed,and the optimal arrangement was optimized.The results show that the proposed deformation control strategy can effectively improve the drilling deformation of thin-walled cylindrical workpiece,thereby significantly improving the machining quality of the parts.

环肋布局对钛合金圆柱耐压壳内爆过程的影响研究

环肋圆柱壳是深潜器耐压结构的主要形式,但由于极限承载能力和振动特性的需求,存在不同的环肋布局形式。为探究环肋布局对钛合金圆柱耐压壳内爆的影响,基于任意拉格朗日欧拉方法开展数值研究。首先对比试验结果验证液-固-气三相流固耦合数值模型的准确性。然后分析3种环肋布局下圆柱耐压壳水下内爆过程中的结构动态响应、冲击波传播以及能量演化等特征。结果表明,环肋均布时,内爆中心由筒体中部向一端移动。而中部和端部加强时,内爆中心由环肋稀疏位置向密集位置移动,结构动能均存在显著的二次波峰现象。此外,中部加强能有效降低最大冲击波峰值。通过对环肋圆柱壳内爆响应特性的分析,对深海耐压结构的设计具有重要的工程意义。

钛合金环肋结构焊接应力变形与承载能力仿真分析

环肋圆柱壳结构抗压能力强,组焊过程方便。但焊接通常带有残余应力与变形,对该类结构的承载能力造成不利影响。本文采用有限元仿真方法,对钛合金环肋圆柱壳结构进行了纵缝焊接—环缝焊接—肋骨焊接—外压承载的全流程模拟。研究发现,焊接完成后焊后等效米塞斯应力接近材料屈服强度,对于大型结构而言,总变形相对较小,最大为17.23 mm。在承载压力从0加载到20 MPa的过程中,结构的变形呈现近似线性变化,结构均能够很好地承受载荷,但随着压力持续增大,应力水平随之升高,结构开始出现非线性的变形趋势。在无焊接缺陷存在的情况下,残余应力的存在对结构的承载影响不显著。研究结果为后续该类型结构的承载水平提供一定的技术参考。

Axisymmetric 3:1 internal resonance of thin-walled hyperelastic cylindrical shells under both axial and radial excitations

Nonlinear vibration with axisymmetric 3:1 internal resonance is investigated for an incompressible neo-Hookean hyperelastic cylindrical shell under both axial and radial harmonic excitations.A full nonlinear strain-displacement relation is derived from the large deflection theory of thin-walled shells.A set of nonlinear differential equations describing the large deflection vibration are formulated by the Lagrange equation and the assumption of small strains.Steady-state responses of the system are predicted via the harmonic balance method with the arc length continuation,and their stabilities are determined via the modified sorting method.The effects of excitations on the steady-state responses are analyzed.The results reveal a crucial role played by the phase difference in the structural response,and the phase difference can effectively control the amplitude of vibration.

TC21钛合金筒形件旋压演变模拟及分析

钛合金筒形件因其独特的性质及性能,在航空、航天领域得到广泛应用,在技术推动下,钛合金筒形件的制作工艺日益精湛。以TC21钛合金筒形件为研究对象,在概述筒形件旋压技术的基础上,列举TC21钛合金筒形件旋压中常见的模拟方法,着重探讨TC21钛合金筒形件旋压演变模拟过程,并提出相关结论及展望,为相关研究提供借鉴。

大尺寸薄壁钛合金筒体结构的离心精密铸造

采用离心精密铸造方法,初步研究了铸造大尺寸薄壁钛合金筒体(直径660 mm,高750 mm,壁厚4 mm)的可行性。结果表明:离心转速较小时,Ti-6Al-4V筒体无法完整充型,而较大的转速可实现完整充型。对于完整充型的筒体,其内部疏松缺陷数量随转速提高而减少。对于给定转速和具有均匀温度场的型壳,筒体中疏松缺陷数量随熔液路径增长而增加。采用Y2O3面层型壳可获得无α壳层的表面质量良好的精密铸件,其内部疏松可通过热等静压消除。铸件的晶粒度随铸件截面厚度变化改变较大,需通过微合金化和后续热处理等措施加以调整。

旋压参数对TC21钛合金筒形件旋压织构的影响

通过二次开发将晶体塑性滑移模型嵌入ABAQUS商业软件,对TC21钛合金筒形件旋压织构演变进行了有限元数值模拟,研究了旋压工艺参数对合金筒形件旋压织构组分和织构强度的影响。结果表明,实验与模拟结果对比显示出采用晶体塑性模型模拟织构演变时具有较高可靠性。减薄率显著影响旋压织构的组分和强度,当减薄率<25%时,织构组分主要为■,当减薄率>30%时,织构组分主要为■及■织构,且织构强度随减薄率增加而增大。主轴转速和进给速度不明显改变织构组分,主要为■及■纤维织构。随主轴转速和进给速度增加,■及■织构强度增大。

钛合金薄壁筒形件热强旋宏微观成形规律研究进展

钛合金薄壁筒形件是航空航天等重要领域迫切需要的高性能轻量化构件,强力旋压成形技术是实现该类构件整体化高性能精确成形的一种有效途径。然而,钛合金筒形件强旋是多场耦合、多参数作用下的多道次热成形过程,变形过程中极易产生隆起、喇叭口和破裂等宏观缺陷,且会诱发复杂的组织演化,改变组织形态与特征参数,进而影响筒形件的力学性能。为此,国内外学者针对钛合金薄壁筒形件热强旋宏微观成形规律开展了大量研究。本文从旋压变形规律与宏观缺陷的控制、强力旋压损伤破裂预测、钛合金筒形件热强旋的微观组织性能演变特征等方面综述了相关研究工作,最后总结了钛合金筒形件热强旋成形仍面临的关键难题与挑战。本文对认识和发展钛合金薄壁筒形件精确成形成性一体化制造技术具有重要指导意义和参考价值。

基于粒子群算法的钛合金高速外圆磨削参数优化

采用正交试验法研究砂轮线速度、工件转速、磨削深度对磨削后TC4钛合金表面粗糙度的影响规律,并采用粒子群算法对建立的表面粗糙度数学模型进行优化,最后用工艺试验法对优化结果进行验证。结果表明:工件表面粗糙度基本随砂轮线速度的增大而减小,随工件转速、磨削深度的增大而增加;磨削深度对表面粗糙度的影响最大,砂轮线速度次之,工件转速最小;当砂轮线速度为150 m/s、工件转速为60 r/min、磨削深度为0.005 mm时,工件表面粗糙度最小,其优化值为1.444μm,与工艺试验结果(1.468μm)的误差小于5%,表明采用粒子群算法对表面粗糙度数学模型进行优化是有效的。

TC4钛合金高速外圆磨削表面完整性实验

为充分发挥钛合金的优良性能,以TC4为研究对象进行高速外圆磨削实验,分析外圆磨削工艺参数对工件表面完整性的影响规律。结果表明:工件亚表面未出现变质层;随着砂轮线速度提高,表面质量提高;随着工件转速提高,表面划痕明显;随着磨削深度增加,出现表面烧伤现象,并且磨削深度对表面完整性的影响程度最大;磨削力与磨削温度对表面硬度的影响是正相关的,且磨削力对表面硬度的影响程度较大。因此可以通过选择合理的工艺参数来保证较大的材料去除率与较好的工件表面质量,为TC4钛合金高速外圆磨削提供指导。

钛合金筒形件真空热胀形壁厚效应的数值模拟

建立了钛合金筒形件真空热胀形的二维非线性热力耦合有限元模型。使用有限元软件MSC.Marc对钛合金筒形件真空热胀形过程进行数值模拟。计算了钛合金筒形件真空热胀形过程的温度场和变形场,并进行了相应的实验验证。模拟结果与实验结果吻合较好。用建立的模型对真空热胀形过程中钛合金筒形件壁厚效应进行数值模拟,讨论了一定工艺条件下钛合金筒形件壁厚与弯曲角度、胀形量和残余应力之间的关系,为实际生产中制定和优化钛合金筒形件真空热胀形工艺参数提供理论与实践依据。

钛合金筒形件真空热胀形过程热力耦合数值模拟

基于热弹塑性有限元理论,建立了钛合金筒形件真空热胀形过程的二维热力耦合有限元模型。采用MSC.Marc有限元分析软件,计算了钛合金筒形件真空热胀形过程的温度场和变形场,分析了温度对热胀形的影响规律。结果表明,随着温度的提高,工件胀形量增大,塑性应变增加。试验验证了模拟的可靠性和有效性,为确定合理的工艺参数提供理论依据。

多孔空心柱状TiO_2制备及其对Cr(Ⅵ)的吸附特性

以工业P25Ti O2为原料,采用水热法制备多孔空心柱状Ti O2,并对其进行结构、形貌表征。所得产物为多孔空心柱状结构,分散性较好,富含孔隙,比表面积为38.71 m2/g,平均孔直径为58.14 nm。以该Ti O2为吸附剂吸附处理含铬废水,结果表明:Ti O2对Cr(Ⅵ)具有良好的吸附性能,p H对Ti O2的吸附性能影响很大,在p H=2.15,Ti O2的质量浓度为2 g/L,Cr(Ⅵ)的质量浓度为10 mg/L时,Ti O2吸附率达84%。Ti O2吸附Cr(Ⅵ)后,使用碱液可将吸附的Cr(Ⅵ)离子脱附,表现出良好的再生性能。

肋骨焊接顺序对钛合金加筋壳体残余变形的影响

本文主要采用有限元软件对钛合金筒体与环形内肋骨熔焊所引入的残余变形进行了数值仿真,系统分析了肋骨装焊顺序对残余变形的影响规律。结果表明:肋骨与筒体装焊角焊缝所引入的焊接变形主要表现为径向收缩;在内肋骨的约束作用下,环肋圆柱壳焊接残余变形量较小,且主要集中在肋骨之间的跨中位置;肋骨垂直度会受到焊接变形的影响,发生一定程度的偏差,需要采用工装进行约束;采用从中间至两端的肋骨装焊顺序可得到更小的焊接变形和更高的变形均匀度。

TC21钛合金筒形旋压有限元模拟和工艺优化

应用有限元分析软件ABAQUS对TC21钛合金筒形热旋压工艺进行有限元数值模拟,分析了钛合金在热旋压过程中的受力及变形特性,探讨了旋压温度、主轴转速、进给速度及减薄率对筒形热旋压成形性能的影响。结果表明,随旋压温度升高,最大等效应力减小,等效应变峰值增大,过高(>890℃)或过低(<860℃)旋压温度均不利于筒形件的外径圆度精度。主轴转速对等效应力应变变化影响不显著,但会影响坯料起皱和外径圆度精度,主轴转速4 r/s时最为适宜。旋压进给速度或减薄率增加,最大应力区域面积和应变峰值增大,进给速度2.5 mm/s和减薄率35%时旋压件隆起缺陷最为严重。从旋压成形质量考虑,TC21钛合金筒形旋压应以旋压温度860℃、进给速度1 mm/s、主轴转速4 r/s及减薄率20%为宜。