数控机床进给系统产生爬行的机理分析

数控机床在低速进给时,产生非匀速爬行,对加工精度和零件表面质量非常不利.本文应用控制理论对机床进给系统的爬行现象进行了理论分析,建立了进给系统的数学模型,用有限差分法对模型进行了求解,在此基础上,系统地研究了产生爬行的各种条件及影响爬行的主要因素,提出了解决爬行问题的几种措施,指出降低导轨摩擦系数是克服爬行的最直接有效的方法.     

机床进给爬行时的运动模型与振动方程

本文讨论了机床进给系统中因运动部件移动速度较低，因而产生爬行现象的自激振动机理。并通过对进给系统建立运动模型、导出振动方程从而对爬行现象进行了理论分析。     

重型数控卧式车床进给系统动力学分析

重型数控卧式机床进给系统在低速运行时,易产生爬行现象,严重影响机床的加工精度、表面粗糙度和定位精度。应用齿轮系统动力学理论分析进给系统的爬行机理,建立进给系统动力学模型,利用Newmark数值方法求解该动力学模型,并采用LMS Virtual.Lab Motion软件模拟进给系统拖板箱的进给位移,为爬行问题的解决奠定基础。     

基于西门子802D数控系统的机床进给爬行的模型分析及改进措施

数控机床爬行问题是提高机床加工精度的重要研究课题之一,本文基于产生数控机床爬行现象的原理对机床产生爬行原因进行了理论分析,并建立了爬行的数学模型。在对爬行原因进行合理分析的同时提出了解决数控机床爬行现象的有效措施,并以市场上较为流行的西门子802D数控系统为例,阐述了如何通过相关的机床参数改善进给爬行现象。该项研究对数控机床的设计、制造和维修具有重要意义。     

数控磨料水射流切割机伺服进给系统的振动爬行现象分析

提出数控磨料水射流切割机伺服进给系统存在振动爬行现象,并对其危害、影响因素、爬行机理进行分析,通过建立物理模型和分析临界速度找到解决爬行的措施和对策,对提高系统稳定性具有实际意义.     

高精度工作台速度反向时摩擦补偿研究

在消除了丝杠导程、间隙等误差之后,进给系统中存在的摩擦是影响工作台运动控制精度的主要因素。由于摩擦的影响,导致工作台速度反向时产生爬行现象,从而使得误差突然增大。文章对摩擦误差产生机理和补偿方法进行了研究,从瞬态响应的视角揭示了摩擦误差产生的机理,通过数学推导精确计算出爬行现象的持续时间,以及由此导致的最大跟随误差。提出了一种零速对称式摩擦补偿方法,该方法在工作台的爬行时间内进行补偿,使工作台尽快脱离爬行状态,仿真结果表明该方法能够显著的减小爬行时间。     

基于爬行理论的滚珠丝杆进给系统加工波纹度成因的研究

文章根据爬行理论对滚珠丝杠进给系统进行了分析,讨论了滚珠丝杠摩擦力矩的波动以及滚动导轨的摩擦阻力波动现象,认为滚珠进出滚道是引起滚珠丝杠及滚动导轨摩擦力(矩)波动的主要原因,丝杠系统的轴向作用力使得丝杠摩擦力矩的波动加剧,由于轴向作用力下丝杠接触刚度的下降将引起整体刚度的不足,在波动摩擦力(矩)的作用下丝杠进给系统将产生不平稳运动,而造成加工系统表面波纹度的产生。     

气缸运动建模及爬行现象判别

由于爬行现象的影响,气缸在低速驱动时不能保持平滑的运动状态,降低了气动系统的控制精度。本文对气动系统进行理论分析,建立系统的动力学方程,引入无量纲参数,并对爬行现象判别式进行理论推导。     

电源故障引发的加工中心失控现象

在各种数控机床和加工中心的电气控制系统中,都设有断相、相序错误的故障检测及报警功能.当发生电源引线接触不良,或其它原因引起一相电源电压下降很多时,因此会使机床产生一些错误动作,使系统对机床的动作失去控制.表现在驱动部分主要是轴的移动不按位置及速度指令执行,出现突然快速进给、冲击、爬行等现象,当速度较快时常与机械部分发生相撞而导致驱动控制器上过流检测报警,空气开关跳闸或其它保护装置动作而停机.     

控制静压轴承间隙实现精密定位机构的研制(研制报告之一)

1.前言对磨床来说,精密切入机构的定位精度是决定加工精度的重要因素。可是在以往的机械式定位机构中,由于产生弹性变形和爬行等现象,很难得到0.1μm量级的精密进给和定位精度。本报告是研究用控制轴承间隙来实现具有高精度和高刚度的精密定位、微进给机构的。     

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.     

新型的治疗阿尔茨海默氏症药物(1-二甲基磷酰基-2,2,2-三氯)-乙基-1-醇烟酸醋对体外神经细胞的作用

目的: 观察本实验室合成的一种治疗阿尔茨海默氏症(AD)的药物(1-二甲基磷酰基-2, 2, 2 -三氯)-乙基^-1-醇烟酸醋(NMF),对体外培养的皮层神经细胞活性的影响以及对海人藻酸(KA)所致的神经损伤的保护作用。方法: 采用体外培养皮层神经元的方法,解剖分离 15 d胚胎小鼠皮层神经细胞, 接种于 96孔板,48 h 后加药并培养 72 h,以 MIT 法 观察 NMF 对小鼠皮层神经细胞活性的影响;同时将接种于 24 孔板的细胞预先给予 NMF,d 3 时加或不加KA处理后,以台盼蓝染色鉴别并计数死、活细胞,可得出细胞的存活率。结果: NMF 明显促进胎鼠皮层神经元活性,其中 NMF1、0. 1、10nmol·L^-1促进神经元活性增殖率分别高达 34.7%、37.4%、36. 7%, NMF 明显促进正常胎鼠皮层神经元存活卒,与对照组比较,10nmol·L^-1 NMF 对皮层神经元的存活率分别提高 39.3%、73.5%。 NMF能显著 对抗 KA 所致的神经元损伤,与 KA 损伤组相比, NMF0.1、10、10nmol·L^-1对损伤皮层神经元的保护率分别为 77.30%、80.10%、84.15%。结论: NMF 明 显促进胎鼠皮层神经元的洁性、提高正常皮层神经元,的存活卒,并能有效地保护KA所致的神经元损伤,提示 NMF 是一种很有潜力的治疗 AD 的药物。     

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).     

Three-Dimensional Growth of Coherent Ferrite in Austenite: A Molecular Dynamics Study

Coherent second phase often exhibits anisotropic morphology with specifi c orientations with respect to both the second and the matrix phases. As a key feature of microstructure, the morphology of the coherent particles is essential for understanding the second-phase strengthening eff ect in various industrial alloys. This letter reports anisotropic growth of coherent ferrite from austenite matrix in pure iron based on molecular dynamics simulation. We found that the ferrite grain tends to grow into an elongated plate-like shape, independent of its initial confi guration. The fi nal shape of the ferrite is closely related to the misfi t between the two phases, with the longest direction and the broad facet of the plate being, respectively, consistent with the best matching direction and the best matching plane calculated via the Burgers vector content(BVC) method. The strain energy calculation in the framework of Eshelby's inclusion theory verifi es that the simulated orientation of the coherent ferrite is energetically favorable. It is anticipated that the BVC method will be applicable in analysis of anisotropic growth and morphology of coherent second phase in other phase transformation systems.     

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.