TA2管材平锥模热挤压成形过程的有限元模拟

为了优化TA2钛管挤压模具结构,本文建立了TA2管材的平锥模热挤压有限元模型,分别对挤压温度为600℃、650℃、700℃,挤压速度为50mm/s、100mm/s、150mm/s,平模长度为7%D、9%D和11%D,模角为55°、60°、65°、70°的挤压模型进行了模拟,研究了诸参数对金属钛流动及挤压力的影响.以切头率、压余比和挤压力系数最小为评判标准,得出平锥模的平模长度为9%D,模角为60°时结构最优的结论.     

5052铝合金薄板数控渐进成形制件表面质量分析

为研究影响5052铝合金薄板数控渐进成形制件表面质量的因素,分别制备了成形角为60°的圆锥台件、成形角为45°的圆锥台件和成形角为45°的方锥台件。首先在金相显微镜下对试样表面进行观察,然后使用三维表面轮廓仪对试样表面进行定量测量;基于小波分析对测量数据进行预处理,提取试样表面的粗糙度成分;采用功率谱和表面三维表征参数分析影响表面质量的因素。研究发现,由于受到成形工具的碾压和拖动的影响,渐进成形制件表面的磨粒磨损、划痕现象比较严重;成形角是影响制件表面质量的重要因素,成形角越小,制件表面粗糙度越大;几何形状对制件表面粗糙度没有显著影响;功率谱和表面的三维表征参数能很好的表征渐进成形制件表面质量。     

液室压力加载路径对5A06铝合金锥形件充液拉深成形的影响北大核心CSCD

为提高5A06铝合金锥形件的拉深成形极限,采用数值模拟与实验相结合的方法进行了锥形件充液拉深成形的研究,分析了不同锥角的锥形件充液拉深变形过程中的缺陷形成机制及工艺参数的影响规律。锥形件成形的典型缺陷为悬空区起皱,分析了不同液室压力加载路径对锥角分别为5°、10°、15°及20°的5A06铝合金锥形件的典型缺陷的影响,获得了避免缺陷的加载路径以及不同锥角的锥形件的壁厚分布规律,实验确定了不同锥角的锥形件的拉深成形极限。结果表明:随着锥形件锥角的增大,锥面悬空区增大,充液拉深成形过程中的第1阶段液室压力加载路径的斜率减小,可避免为克服悬空区起皱而导致的破裂缺陷;锥角越大,锥形件壁厚减薄率越大,拉深成形极限越小。     

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。     

基于Simufact多道次变薄拉深筒形件尺寸精度研究

为了探究多道次变薄拉深冷成形加工工艺参数与筒形件尺寸精度之间的关系,采用Simufact. forming有限元仿真软件,选取C15-c低碳钢为试验材料进行多道次变薄拉深冷成形模拟试验,采用正交试验设计方案,探究了多道次变薄拉深冷成形过程中工艺参数(减薄率、凹模锥角与摩擦系数)对筒形件尺寸精度(内径扩径量、外圆度误差与壁厚偏差)的影响规律,并进行了试验验证。结果表明:在C15-c低碳钢材料筒形件的多道次变薄拉深冷成形工艺中,当减薄率为40%、凹模锥角为12°、摩擦系数为0. 10时,筒形件的尺寸精度较高。加工工艺参数对内径扩径量的影响顺序为:减薄率凹模锥角摩擦系数;对外圆度误差的影响顺序为:摩擦系数凹模锥角减薄率;对壁厚偏差的影响顺序为:减薄率凹模锥角摩擦系数。     

棒料几何参数对其预制表面V型槽槽底应力集中系数的影响规律

针对研究新型低应力精密下料系统时,需要获得不同直径的带V型槽棒料几何参数对槽底应力集中水平的影响规律的问题,利用ANSYS软件,建立了系统棒料下料时的三维有限元模型。采用正交法设计了实验方案,通过有限元法的数值模拟实验,确定了使V型槽尖端应力集中系数最大的棒料几何参数的最佳取值条件,即槽外形夹角为90°,槽底圆角半径与棒料直径的比为0.005,槽深与棒料的直径比为0.15。实验研究表明,槽底圆角半径对应力集中系数的影响最大,棒料的直径与槽深对应力集中系数的影响较小,而槽外形夹角对槽底应力集中系数的影响程度最小。     

基于灰色关联度的筒形件变薄拉深工艺参数优化

利用Simufact. forming有限元仿真软件,以变薄拉深工艺中第1道次减薄比、凹模锥角和拉深速度3个工艺参数为自变量,以筒形件的外圆度误差与壁厚偏差为优化目标进行数值模拟,设计3水平3因素的正交试验。基于灰色关联分析法,计算各工艺参数对筒形件尺寸精度的关联系数与关联度,进行多目标优化得到最优工艺参数组合。结果表明,变薄拉深冷成形工艺中,当第1道次减薄比为70%、凹模锥角为10°、拉深速度为10 mm·s~(-1)时,筒形件的尺寸精度较高。变薄拉深工艺参数对筒形件尺寸精度的影响顺序为:第1道次减薄比凹模锥角拉深速度。经过试验验证,仿真结果与试验结果的相对误差小于10%,证明了有限元仿真有良好的可靠性,可为实际生产做出指导。     

基于DEFORM-3D对AZ31镁合金往复挤压变形均匀性有限元分析

通过DEFORM-3D对不同的模具进行往复挤压变形有限元模拟,研究了不同挤压比λ、挤压角度θ和变形区长度l对AZ31镁合金等效应变分布的影响。结果表明:模具挤压角度在45°～60°时,有助于改善等效应变分布的均匀性,挤压角度由30°增大至60°时,线性拟合后斜率从0. 85降至0. 53。减小挤压比λ和变形区长度l对改善等效应变分布均匀性效果显著,挤压比λ由4. 69减小至2. 64时,线性拟合后斜率从0. 53降低至0. 2。变形区长度l由5. 4 mm变为圆弧过渡(圆角半径r=5 mm),等效应变不均匀程度参数Ci从0. 4减小至0. 258。当模具挤压角度为45°,颈缩区直径为Φ16 mm (λ=2. 64),变形区长度l改为r=5 mm圆弧过渡时,试样等效应变不均匀程度参数Ci=0. 102,在模拟结果中数值最小,表明等效应变分布最均匀。     

空心钨极TIG焊电弧特性数值模拟

基于磁流体动力学理论,建立钨极半径为0.8 mm,尖端锥角分别为15°,30°,45°和60°的微TIG点焊电弧数值模型;使用Fluent软件UDF功能加载保护气体物性参数、动量方程和能量方程源项,探究钨极尖端锥角对微TIG点焊电弧温度场、流场、压力场和电势场的影响规律。结果表明,微TIG电弧呈钟罩形状,随着锥角由60°减至30°,钨极导电截面半径减小,导致电流密度增加,电弧温度增高;随着锥角继续减小,电弧上爬现象严重,钨极导电面积增大,平均电流密度减小,电弧温度随之下降。钨极锥角变化显著影响等离子体流力和电磁收缩力对电弧等离子体动量作用,进而影响电弧等离子体运动速度和阳极表面压力分布。数值模拟结果与微TIG点焊试验结果吻合良好,模拟结果对调控钨极锥角,改善电弧形貌及焊接质量具有重要意义。

     

结合齿冷锻工艺分析及参数优化

利用Deform-3D软件对结合齿的冷锻成形过程进行了模拟,应用正交模拟试验以及工程试验相结合的方法,对某汽车变速箱结合齿冷锻工艺及参数优化进行研究,对预成形制件主要几何参数进行优化。研究结果表明:采用制定的冷锻预成形加精整倒锥工艺是可行的;凸台直径是影响成形力大小的最主要因素,其次是圆角半径,而齿形长度、内孔直径及凸台长度对成形力的影响较小;优化结果是当齿形长度A=6.5mm、内孔直径B=45mm、凸台直径C=62mm、凸台长度D=11mm、圆角半径E=2mm时,成形载荷最小。以优化结果为依据,成功实现了该类零件的冷锻成形。     

Effects of Post-weld Heat Treatment on Microstructure,Mechanical Properties and the Role of Weld Reinforcement in 2219 Aluminum Alloy TIG-Welded Joints

In as-welded state, each region of 2219 aluminum alloy TIG-welded joint shows diff erent microstructure and microhardness due to the diff erent welding heat cycles and the resulting evolution of second phases. After the post-weld heat treatment, both the amount and the size of the eutectic structure or θ phases decreased. Correspondingly, both the Cu content in α-Al matrix and the microhardness increased to a similar level in each region of the joint, and the tensile strength of the entire joint was greatly improved. Post-weld heat treatment played the role of solid solution strengthening and aging strengthening. After the post-weld heat treatment, the weld performance became similar to other regions, but weld reinforcements lost their reinforcing eff ect on the weld and their existence was more of an adverse eff ect. The joint without weld reinforcements after the post-weld heat treatment had the optimal tensile properties, and the specimens randomly crack in the weld zone.     

The First Phase of the SRIF Industrialized Base in ＂West Area＂ Has Been Put into Operation

After nearly two years＇ tense construction, the first phase of industrialized base of Shenyang Research Institute of Foundry （SRIF）, located at the Tiexi Casting and Forging Industrial Park in the west of Tiexi District, has now been completed and formally put into operation.     

Thermodynamics Study on the Decomposition of Chromite with KOH

Institute of Process Engineering, Chinese Academy of Sciences, China, has proposed a method for oxidative leaching of chromite with potassium hydroxide. Understanding the mechanism of chromite decomposition, especially in the potassium hydroxide fusion, is important for the optimization of the operating parameters of the oxidative leaching process. A traditional thermodynamic method is proposed and the thermal decomposition and the reaction decomposition during the oxidative leaching of chromite with KOH and oxygen is discussed, which suggests that chromite is mainly destroyed by reactions with KOH and oxygen. Meanwhile, equilibrium of the main reactions of the above process was calculated at different temperatures and oxygen partial pressures. The stable zones of productions, namely, K2CrO4 and Fe2O3, increase with the decrease of temperature, which indicates that higher temperature is not beneficial to thermodynamic reactions. In addition, a comparison of the general alkali methods is carried out, and it is concluded that the KOH leaching process is thermodynamically superior to the conventional chromate production process.     

Influence of Heat Treatment on Damping Behaviour of the Magnesium Wrought Alloy AZ61

The effect of isochronal heat treatments for 1h on variation of damping, hardness and microstructural change of the magnesium wrought alloy AZ61 was investigated. Damping and hardness behaviour could be attributed to the evolution of precipitation process. The influence of precipitation on damping behaviour was explained in the framework of the dislocation string model of Granato and Lücke.     

Effect of Rare Earth Doping on Impedance,Modulus and Conductivity Properties of Multiferroic Composites:0.5(BiLa_xFe_(1-x)O_3)–0.5(PbTiO_3)

The Lanthanum-doped bismuth ferrite–lead titanate compositions of 0.5(Bi LaxFe1-xO3)–0.5(Pb Ti O3)(x = 0.05,0.10,0.15,0.20)(BLxF1-x-PT) were prepared by mixed oxide method.Structural characterization was performed by X-ray diffraction and shows a tetragonal structure at room temperature.The lattice parameter c/a ratio decreases with increasing of La(x = 0.05–0.20) concentration of the composites.The effect of charge carrier/ion hopping mechanism,conductivity,relaxation process and impedance parameters was studied using an impedance analyzer in a wide frequency range(102–106Hz) at different temperatures.The nature of Nyquist plot confirms the presence of bulk effects only,and non-Debye type of relaxation processes occurs in the composites.The electrical modulus exhibits an important role of the hopping mechanism in the electrical transport process of the materials.The ac conductivity and dc conductivity of the materials were studied,and the activation energy found to be 0.81,0.77,0.76 and 0.74 e V for all compositions of x = 0.05–0.20 at different temperatures(200–300 °C).     

Quantitative Analysis of the Crystallographic Orientation Relationship Between the Martensite and Austenite in Quenching–Partitioning–Tempering Steels

The orientation relationships(ORs)between the martensite and the retained austenite in low-and medium-carbon steels after quenching–partitioning–tempering process were studied in this work.The ORs in the studied steels are identified by selected-area electron diffraction(SAED)as either K–S or N–W ORs.Meanwhile,the ORs were also studied based on numerical fitting of electron backscatter diffraction data method suggested by Miyamoto.The simulated K–S and N–W ORs in the low-index directions generally do not well coincide with the experimental pole figure,which may be attributed to both the orientation spread from the ideal variant orientations and high symmetry of the low-index directions.However,the simulated results coincide well with experimental pole figures in the high-index directions{123}_(bcc).A modified method with simplicity based on Miyamoto’s work was proposed.The results indicate that the ORs determined by modified method are similar to those determined by Miyamoto’method,that is,the OR is near K–S OR for the low-carbon Q–P–T steel,and with the increase of carbon content,the OR is closer to N–W OR in medium-carbon Q–P–T steel.     

Using Finite Element and Contour Method to Evaluate Residual Stress in Thick Ti-6Al-4V Alloy Welded by Electron Beam Welding

This work was to reveal the residual stress profile in electron beam welded Ti-6Al-4V alloy plates(50 mm thick) by using finite element and contour measurement methods.A three-dimensional finite element model of 50-mmthick titanium component was proposed,in which a column–cone combined heat source model was used to simulate the temperature field and a thermo-elastic–plastic model to analyze residual stress in a weld joint based on ABAQUS software.Considering the uncertainty of welding simulation,the computation was calibrated by experimental data of contour measurement method.Both test and simulated results show that residual stresses on the surface and inside the weld zone are significantly different and present a narrow and large gradient feature in the weld joint.The peak tensile stress exceeds the yield strength of base materials inside weld,which are distinctly different from residual stress of the thin Ti-6Al-4V alloy plates presented in references before.     

Microstructures and Tensile Properties of Ultrafine-Grained Ni–(1–3.5) wt% SiC_(NP) Composites Prepared by a Powder Metallurgy Route

Silicon carbide nanoparticle-reinforced nickel-based composites(Ni–Si CNP),with a Si CNPcontent ranged from1 to 3.5 wt%,were prepared using mechanical alloying and spark plasma sintering.In addition,unreinforced pure nickel samples were also prepared for comparative purposes.To characterize the microstructural properties of both the unreinforced pure nickel and the Ni–Si CNPcomposites transmission electron microscopy(TEM) was used,while their mechanical behavior was investigated using the Vickers pyramid method for hardness measurements and a universal tensile testing machine for tensile tests.TEM results showed an array of dislocation lines decorated in the sintered pure nickel sample,whereas,for the Ni–Si CNPcomposites,the presence of nano-dispersed Si CNPand twinning crystals was observed.These homogeneously distributed Si CNPwere found located either within the matrix,between twins or on grain boundaries.For the Ni–Si CNPcomposites,coerced coarsening of the Si CNPassembly occurred with increasing Si CNPcontent.Furthermore,the grain sizes of the Ni–Si CNPcomposites were much finer than that of the unreinforced pure nickel,which was considered to be due to the composite ball milling process.In all cases,the Ni–Si CNPcomposites showed higher strengths and hardness values than the unreinforced pure nickel,likely due to a combination of dispersion strengthening(Orowan effects) and particle strengthening(Hall–Petch effects).For the Ni–Si CNPcomposites,the strength increased initially and then decreased as a function of Si CNPcontent,whereas their elongation percentages decreased linearly.Compared to all materials tested,the Ni–Si CNPcomposite containing 1.5% Si C was found more superior considering both their strength and plastic properties.     

Directional Growth of Tin Crystals Controlled by Combined Solute Concentration Gradient Field and Static Magnetic Field

A new method was introduced to achieve directional growth of Sn crystals. Microstructures in liquid(Pb)/liquid(Sn) diffusion couples were investigated under various static magnetic fields. Results show that the β-Sn crystals mainly reveal an irregular dendritic morphology without or with a relatively low static magnetic field(B0.3 T). When the magnetic field is increased to 0.5 T, the β-Sn dendrites close to the final stage of growth begin to show some directional character. With a further increase in the magnetic field to a higher level(0.8–5 T), the β-Sn dendrites have an enhanced directional growth character, but the dendrites show a certain deflection. As the magnetic field is increased to 12 T, the directional growth of the β-Sn dendrites in the center of the couple is severely destroyed. The mechanism of the directional growth of the β-Sn crystals and the deflection of the β-Sn crystals with the application of static magnetic field was tentatively discussed.     

Growth Kinetics of Single Inclusion Particle in Molten Melts

On the basis of the single-particle framework, a new theory on inclusion growth in metallurgical melts is developed to study the kinetics of inclusion growth on account of reaction and collision. The studies show that the early growth of inclusion depends on reaction growth and Brawnian motion collision, and where the former is decisive, the late growth depends on turbulence collision and Stokes＇ collision, and where the former is dominant; collision growth is very quick during the smelting process, lessened in the refining process, but nearly negligible in the continuous casting process.