机床主轴热误差的累积法建模研究

为实现数控机床热误差的快速精确建模,提出一种基于累积法的机床热误差建模新方法。对一台立式加工中心,利用温度传感器与非接触式激光位移传感器同步测量主轴温度变化及热变形值,对获取的模型数据进行累积算子求和,构建累积矩阵及热误差正规方程来估计模型中的参数以实现热误差建模。利用该方法构建的热误差模型分别与最小二乘法(LS)、最小二乘支持向量机(LSSVM)模型进行对比,结果表明:累积法的建模精度要高于最小二乘法,且建模时间比最小二乘支持向量机法要少。     

多工况下数控机床主轴热误差建模

单一工况条件下数控机床主轴热误差模型无法准确预测其它工况下的热误差。通过研究分析支持向量机回归的算法和参数的关系,提出一种经过遗传算法(GA)在多工况条件下优化的支持向量机(SVM)的建模方法。以一台数控车床为研究对象,进行热误差测量实验,利用电涡流位移传感器和温度传感器同步测量机床主轴两个方向热误差和温度变化数值,获取两种工况的建模数据。运用遗传算法对SVM的惩罚函数、核函数参数和不敏感损失函数进行多工况条件下的优化选择,建立机床主轴热误差补偿模型。通过热误差建模实验验证,该方法在工况一的残差为0.838μm,工况二的残差为0.653μm,在保持较高预测精度的同时,能在两种工况下进行有效的热误差预测,使热误差补偿更适合实际加工环境。     

立式加工中心主轴系统热变形试验及误差补偿

立式加工中心经过长时间的运行之后,主轴箱及主轴系统组成的单元会产生热变形,这影响到被加工零件轴向尺寸的加工精度。以VMC750立式加工中心为试验对象,测量主轴箱多点温度及主轴变形伸长量,确定主轴变形的主要原因,建立误差补偿模型,通过对立式加工中心加工过程中的热误差进行了实时补偿实验,结果表明：通过热变形补偿,主轴系统热变形实测为0.28～0.33 mm,其误差可减少75％左右,验证了该模型的有效性。     

精密卧式加工中心主轴轴向热误差补偿方法

热误差是精密机床最主要的误差源之一。主轴是机床的关键部件,其热误差直接影响机床的加工精度。文章以某型号精密卧式加工中心主轴为对象,对其温度场和热变形进行了仿真分析。根据仿真结果发现主轴轴向热变形更严重,并结合机床结构确定温度传感器布置位置。在此基础上,对不同转速下主轴部分位置温度和轴向热误差进行现场测试。运用最小二乘法建立热误差补偿模型,直接结合机床FANUC数控系统实施主轴轴向热误差补偿。经实验验证,补偿后主轴轴向热误差减小了85%以上。     

基于GA-LSSVM的数控机床热误差建模方法研究

为减小数控机床热误差对加工精度的影响,实现对热误差的补偿控制,提出一种基于遗传算法(GA)优化的最小二乘支持向量机(LSSVM)数控机床热误差建模方法.利用遗传算法优化选择LSSVM惩罚因子C和核函数参数σ2,构建针对某卧式加工中心主轴热误差的GA-LSSVM模型.根据该模型得到热误差的模拟值和测量值对比曲线,通过分析...     

主轴动态精度测试与分析

主轴动态误差对加工精度有至关重要的影响,针对主轴动态误差进行了试验与分析。介绍了主轴动态误差的概念,采用主轴动态误差分析仪对主轴动态误差进行了采集,采集的数据包括主轴径向平均误差、径向异步误差、轴向平均误差、轴向异步误差以及轴向最小间隙。对某型号同类型三台立式加工中心分别进行了多转速情况下的测量,对比并分析了三台立式加工中心的测量结果。在转速为7 500 r/min时,三台立式加工中心径向异步误差分别为70、15、15μm;在转速升至6 000 r/min之后主轴最小径向间隙均有较大提升。试验结果表明:主轴动态精度受到机床工况和转速共同影响;在高速转动情况下,主轴径向最小间隙增大明显;加工时要根据工况合理安排转速,以保证加工质量。     

基于GA-SVR的数控机床热误差建模

为了提高数控机床加工精度,消除数控机床热误差对加工精度的影响,文章提出了基于GA-SVR(遗传算法-支持向量回归机)的数控机床热误差建模方法.为了构建机床的热误差模型,首先采用温度传感器与位置传感器测量机床的温度与对应的机床主轴变形量.其次把获得的数据进行支持向量回归机建模训练,同时使用遗传算法寻找支持向量回归机相关参数的最优值.最后建立机床热误差模型,并验证模型的准确度.结果表明,基于GA-SVR的数控机床热误差建模方法具有精度高和鲁棒性强的特点.     

模糊神经网络在精密卧式加工中心热误差的预测

为了提高精密数控机床的加工精度,减少精密机床的热误差,文章提出了模糊神经网络径向热误差的建模方法。以数控加工中心关键点的温度和主轴径向的热变形量的关系为基础,应用模糊神经网络建模法,采用精密卧式加工中心主轴径向热误差的数据,对机床主轴热误差进行建模与预报。从数控机床主轴建模试验结果分析表明,模糊神经网络预测模型能够较为精准的对机床主轴径向热误差的做出预测,在实际应用中有利于提高机床的补偿精度,对数控机床热误差补偿提供参照。     

基于SOM神经网络聚类以及支持向量机的数控机床热误差建模方法的研究

为了减小主轴季节性热误差影响,提高机床的加工精度,提出了基于针对机床热源进行SOM神经网络预聚类后的支持向量回归机的主轴热误差综合模型。针对一台型号为HTM40100h的车铣复合中心,对主轴的关键温度测点进行了内外热源的划分,并在冬夏两个季节对所有测温点温度和热误差数据进行采集,将外部热源温度数据作为SOM网络的输入变量进行季节性聚类,聚类后的外部热源温度数据连同同时刻的内部热源温度数据一起作为不同季节支持向量回归机模型的输入变量,得到热误差拟合值。将通过聚类预处理的方法与未经聚类的方法进行了对比试验,结果表明:该综合预测模型在冬夏两个季节均获得了较高的建模精度和鲁棒性。     

高速高精密立式加工中心主轴热态特性分析北大核心

主轴的热特性是影响机床加工精度的主要因素之一,文章针对某高速高精密立式加工中心主轴首先进行三维模型构建,分析其主要热源并确定热边界条件,然后采用有限元方法进行温度场和热—结构耦合分析,得到主轴温度场和热变形分布图,最后分析了冷却液流量对主轴热特性的影响。结果表明:主轴达到热平衡时,最高温升为7.9℃,总变形量为22.6μm,且当冷却液流量为4.5L/min时,主轴热特性最佳,该结果为后续的立式加工中心主轴结构优化设计及热误差补偿奠定了基础。     

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.     

电化学噪声数据处理方法概述

综述了常见的电化学噪声数据处理方法,介绍了直流趋势剔除、统计分析、快速傅立叶变换(FFT)法计算功率谱密度(PSD)以及小波变换处理电化学噪声信号的基本过程,并阐释了各种数学处理及所得参数的物理意义。