含间隙高速精密压力机机构动力学研究

铰间隙是影响高速精密压力机动态精度的重要因素,为研究间隙对其动态特性的影响,本文采用非线性弹簧阻尼模型描述间隙处的碰撞接触、修正的Coulomb摩擦模型描述间隙处的摩擦、无质量圆弧间的接触约束描述含间隙铰,建立周期性冲击工况下含间隙高速精密压力机机构的虚拟样机模型,通过动力学仿真,分析了有无间隙、间隙大小和打击力对机构...     

运动副间隙对高速精密压力机振动的影响

曲柄压力机高速化带来振动加剧问题,影响工件质量、模具和机床的使用寿命.为研究间隙对压力机振动的影响,以JF75G-200型曲柄压力机为例,在RecurDyn中建立曲柄滑块机构的刚柔耦合动力学模型.在理想模型的基础上,加入了接触碰撞模型,探讨运动副间隙对压力机激振力大小的影响.并通过RecurDyn与Matlab联合仿真,分析了间隙对振幅大小的影响,从而为高速压力机的动平衡设计提供参考.     

上三角肘杆式压力机构间隙动力学特性分析

压力机械的运动副常因受到反冲作用力而产生运动间隙,导致机械系统的冲击增大,冲压成形稳定性降低。优选三角肘杆式压力机构运动副间隙动力学的建模及仿真,依据其工作原理分析了上三角型与下三角型肘杆式压力机构执行连杆的运动特性变化规律,得出上三角型相对下三角型在位移、速度和加速度方面分别优化了30%、59%和390%;基于MLSD运动副间隙模型,运用ADMAS虚拟样机技术建立了含运动副间隙上三角型肘杆式压力机构的动力学仿真模型,分析了运动副间隙引起的碰撞和磨损对机构动态特性的影响。结果表明,运动副相对间隙值超20%时,机构运行将伴随较大的冲击,并伴随一定程度的振动和噪声,影响机构工作的稳定性。研究结果为肘杆式压力机构的结构设计提供了理论依据。     

考虑间隙和构件柔性的3-RRR机构运动精度分析

在考虑运动副间隙和构件柔性的情况下,对3-RRR并联机构的运动精度进行分析。计入能量损耗和摩擦力变化,构建了含间隙转动副的接触力模型,并利用ANSYS关于柔性体转化的方法描述构件的柔性,在ADAMS中建立该机构的虚拟样机模型。并利用该模型对比不同间隙值下动平台中心运动的位移及速度。引入量纲一参数对间隙尺寸、动平台转速和构件柔性的影响进行评估,对3-RRR机构运动精度进行定量分析。结果表明:在3-RRR机构中,间隙值越大,动平台的运动精度越低;相较刚性构件,采用柔化模型时动平台速度误差有所下降;输入转速的增大会使动平台速度误差显著增大。     

高速精密压力机动态精度影响因素分析

本文对影响高速、高精密压力机动态精度的主要因素——运动副间隙、机构的弹性变形、机床热变形进行了阐述.介绍了目前研究者针对运动副间隙和弹性变形采用的理论模型与研究方法,以及得出的一些初步结论.指出机床发热的主要热源,并罗列出现有的解决方案.     

含间隙铰的柔性机器人动力学研究

论文将多柔体动力学的建模方法引入柔性机器人的动力学分析中。应用Lagrange方程建立空间刚-柔耦合多体系统动力学方程，采用牛顿二状态模型，对含间隙机器人的副间接触和分离过程，建立了铰接间隙动力学方程。仿真分析结果表明，由于间隙铰的存在。间隙运动副反力呈现大幅度连续波动现象，使整个机器人的稳定性大大降低。而当记入大臂的柔性后，间隙副反力的波动减小，所以，机器人可以通过适当添加弹性补偿单元降低部分副间碰撞时的冲击效应，提高机构运转的稳定性。     

高速精密压力机动态精度影响因素分析

压力机作为锻压机床的代表．广泛应用于航空航天、汽车制造、交通运输、冶金化工等重要工业部门。近年来．大规模集成电路和电器元件、计算机和通讯设备以及微电机芯片的技术进步，进一步有力地推进了高速精密；中床的发展。高速、高精密；中床作为一种精密、高效的压力加工装备，在高速范围内的超精密加工方面，达到了前所未有的水平（下死点动态控制精度为±0.005mm）。影响压力机动态精度的因素包括．运动副间隙、机构的弹性变形、机床热变形等。     

考虑关节间隙的空间机械臂臂杆振动特性研究

基于ADAMS动力学仿真软件,建立含间隙关节空间机械臂的动力学仿真模型,改变关节间隙尺寸和刚度系数等相关参数,获取不同关节间隙尺寸下的空间机械臂动力学响应;通过搭建含间隙关节的空间机械臂实验台,采用改变臂杆端盖孔径的方法改变关节间隙尺寸,分析不同关节间隙尺寸下的空间机械臂臂杆的输出振动特性。仿真与实验结果表明:臂杆末端的加速度和关节的接触碰撞力会随着空间机械臂关节间隙的增大而逐渐增大,但增幅会逐渐减小;空间机械臂关节间隙的增大还会导致关节内碰撞加剧,引起更大的能量损失。这可为提高含间隙空间机械臂的控制精度提供参考。     

高速压力机传动系统对下死点精度影响的研究

下死点精度是高速压力机重要的动态精度,直接影响着冲压件的质量.从高速压力机传动系统入手,以转速、静平衡气压和运动副间隙等因素对下死点精度的影响为例,采用多体系统动力学建模仿真和田口法,分析了最优下死点精度的参数组合和影响因素的显著性关系,从而为提高高速压力机下死点精度和优化其传动系统设计提供参考.     

基于ADAMS的理想铰约束模型的局限性研究

针对在多体系统动力学分析中采用理想铰约束模型模拟关节轴承的铰接功能引起仿真结果出现偏差的问题,以基于虚拟样机技术的组合臂架式门座起重机变幅过程的动力学分析为例,将其中的两个主要铰接点视为含间隙的滑动轴承,运用含间隙矢量模型、非线性连续接触碰撞力的混合模型和修正的库仑摩擦模型,综合考虑铰链间隙、接触变形和摩擦等因素的影响,求解了系统在典型工况下的动力学响应,并与按照理想铰约束模型得到的响应结果进行对比,揭示了理想铰约束模型存在的局限性,为如何在工程机械动力学分析中合理使用理想铰约束模型提供了参考。     

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).     

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.     

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.     

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.