磁流体研磨装置中磁场加工区的设计

针对特定的加工要求 ,设计磁流体研磨装置中磁场加工区的重要参数 ,并分析验算设计的合理性     

基于DSP控制的交变磁场装置的研究

本文研制一套以DSP为控制核心的变频电源装置,采用新型单相SVPWM调制技术,激励铁氧体线圈可产生频率、场强均可独立调节的交流磁场。主电路部分采用桥式拓扑电路结构,磁场输出部分采用带气隙的回形磁芯,在气隙中产生交变磁场,用于研究磁场对细胞的生物效应。实验效果比较理想,测量结果较精确,系统稳定可靠,数字化界面操作简洁方便。     

Design and fabrication of a novel polishing tool for finishing freeform surfaces in magnetic field assisted finishing (MFAF) process

Surface finish is a critical requirement for different applications in industries and research areas. Freeform surfaces are widely used in medical, aerospace, and automobile sectors. Magnetic field assisted finishing process can be used very efficiently to finish freeform surfaces. In this process, magnetorheological fluid is used as the polishing medium and permanent magnet is used to control its rheological properties to generate finishing force during polishing. To avail sufficient magnetic field in the finishing zone, it is necessary to design an optimum polishing tool. In the present study, a specially designed polishing tool is designed using a finite element based software package (Ansys Maxwell^®) based on Maxwell equations. At first, dimension of the permanent magnet is determined for designing optimum tool geometry. After that, dimension and configuration of the magnet fixture are optimized. A special type of metal named mu-metal which is a nickel-iron based alloy is selected for magnet fixture due to its magnetic-field shielding property. Mu-metal directs the magnetic flux lines in such a way that in the finishing zone the magnetic flux can be concentrated on the workpiece surface required for finishing. Also, the Mu-metal magnet fixture shields the magnetic field from outside environment so that MR fluid as well as any surrounding magnetic materials do not stick to the polishing tool. Experiments are carried out to validate the Maxwell simulation results to compare the magnetic flux distribution on the workpiece surface which shows good agreement between them. Also, finishing of flat titanium workpieces are carried out and it is found that the novel polishing tool has the capability to finish the workpieces in the nanometer range.     

Dynamic stability of ferromagnetic plate under transverse magnetic field and in-plane periodic compression

The dynamic stability of a soft ferromagnetic rectangular and simply supported plate immersed in an applied transverse magnetic field, as well as subjected to an in-plane periodic compression is presented in this paper. The fundamental equations involving magnetoelastic interaction and magnetic damping effect for the ferromagnetic plate are developed. In the theoretical model, the expression of induced magnetic force is based on a generalized magnetoelastic variational model, and the magnetic damping is due to the Lorentz body force arising from eddy current in the ferromagnetic material. By means of a linearized magnetoelastic theory and perturbation technique, the motion equation of the ferromagnetic plate is reduced to a damped Mathieu's equation and solved. The dynamic stability of the magnetoelastic system without in-plane compression is theoretically analyzed first, to show that there exist two stable states: magnetic damped stable oscillation, and over-damped asymptotically stable motion before static divergence instability of the ferromagnetic plate occurs. The dynamic instability and stability regions for the parametric excitation of the ferromagnetic plate due to the harmonically excited in-plane compression are obtained next. The effects of magnetic damping and excitation frequency of the in-plane periodic compression on the stability regions are discussed in detail.     

Tribological behavior and surface analysis of magnetized sliding contact XC 48 steel/XC 48 steel

We have studied the tribological behavior of a XC 48 steel/XC 48 steel sliding couple in the presence of an A.C. magnetic field. Experiments were conducted on a pin-on-disc tribometer in ambient atmosphere under an applied normal load P=62.85 N and sliding speed v=0.38 m/s. The magnetic field was applied to the pin and remained constant during each test. Experimental results showed that the presence of a magnetic field around the tribocontact modifies the tribological behavior through changes of the mechanical properties of the subsurface. The surface microhardness increases in magnetic field and modifies the tribocontact rheology. The modifications induced in the contact surface and subsurface of XC 48 steel, by the magnetic field H=0 to 8 kA/m after 30 min of sliding, were analyzed by Vickers microhardness measurement, scratch testing with acoustic emission detector, scanning electron microscopy (SEM) and energy dispersive spectroscopy (EDS).     

Effects of magnetic field distributions on wire sawing performance

To transport more abrasive grains into the cutting zone, the method of magnetic-induction free-abrasive wire sawing is proposed. A uniform magnetic field is used to magnetize a steel wire and forms a high gradient magnetic field around the wire. The magnetic abrasive grains are adsorbed on the magnetized wire and are transported into the cutting zone, which improves the wire sawing performance. The adsorption of the magnetic abrasive grains is observed using an experimental setup along the wire cross-sectional direction. The results suggest that magnetic abrasive grains are increasingly adsorbed in the paramagnetic region of the wire with increasing magnetic field intensity. Single-wire sawing experiments are conducted on a WXD170 reciprocating wire sawing machine at variable magnetic field intensity and distribution. The results suggest that the change in magnetic field intensity strongly affects the cutting efficiency, kerf loss, and surface roughness. The performance of the magnetic-induction free-abrasive wire sawing under different magnetic field intensities and distributions are compared. The wire sawing performance improves when the uniform magnetic field is evenly distributed in the cutting zone and at the top of cutting zone.     

Influence of magnetic field on wear in high frequency reciprocating sliding contacts

Results of experimental studies concerning the influence of permanent magnetic field on wear of dry sliding contact operating at short stroke and high frequency are presented. It was found that horizontal magnetic field with different orientations relative to the sliding direction is affecting performance of the contact. The increase in frequency of sliding reduces accumulated mass loss and lowers the surface roughness of the wear track in the presence of magnetic field. Enhanced chemisorptions of oxygen by a ferromagnetic material due to the influence of external magnetic field is postulated.     

对磁流变抛光技术中磁场的分析

本文对磁流变抛光(magnetorheological finishing)过程中所采用的梯度磁场,以及磁流变抛光液（MRP fluid）中的磁性颗粒在磁场中的受力情况进行了分析,进而证明了该磁场满足磁流变抛光的要求。最后以实验对其进行了验证。     

Cosserat continuum theory to simulate microscopic rotation of magnetic powder in applied magnetic field

Numerical method based on the Cosserat continuum theory is proposed for simulating behavior of a magnetic powder in an applied magnetic field. The Maxwell stress is induced in the magnetic powder. During powder forming process in the magnetic field, the magnetic particles are thus rotated and transferred by both mechanical and magnetic interaction. To simulate such powder behavior, we formulate a finite element equation considering Maxwell stress based on the Cosserat continuum theory of compressible plasticity. The powder behavior with magnetic alignment during compaction in magnetic field is simulated by the proposed method and the effect of couple-stress on the powder behavior is discussed.     

旋转磁场在微小工件磁力研磨加工中的应用

微小工件在工业产品中的应用日益增多,相对于其他工件的加工,微小工件由于在加工过程中装夹困难,至今缺少高效的加工手段。磁力研磨加工中使用旋转磁场被认为是解决微小工件加工困难的有效手段。介绍了磁力研磨技术在应用领域的最新成果,总结了产生旋转磁场几种的方法,分析了磁力研磨加工的加工原理和技术特点。讨论了影响磁力研磨加工质量的几个因素,解释了影响因素的作用原理。最后指出了在磁力研磨加工存在的问题,展望了旋转磁场在微小工件磁力研磨加工中的发展前景。     

A 2D micro-fluxgate earth magnetic field measurement systems with fully automated acquisition setup

In this paper we present an Earth magnetic field measurement system and an automated acquisition setup to characterize it. The measurement system consists of a fluxgate sensor and an integrated front-end circuit, both realized in CMOS technology. The couple of orthogonal axes of the sensor makes the system suitable for realizing an electronic compass device. Indeed, we can measure not only the amplitude of the Earth magnetic field (whose full-scale value is of the order of 60 μT), but also its direction. The complete measurement system achieves a maximum angular error of 1.5° in the measurement of the Earth magnetic field direction. Furthermore, an acquisition setup was developed to evaluate the measurement system performance. It consists of a precision mechanical plastic structure, in tower form, a microcontroller-based interface circuit, that provides a digital output through an RS232 serial interface, a PC software suitably developed to post-process the data from the acquisition system and a couple of Helmholtz coils to evaluate the linearity of the system. This setup allows us to perform a completely automated and numerically controlled characterization of the measurement system.     

永磁齿轮传动特性研究

计算分析了新型传动机构永磁齿轮传动机构的磁场，研究了永磁齿轮传动中从动轮的转矩。从恒定负载出发，得出从动轮在运动中的位置变化曲线并进行了实验验证。研究表明，该传动机构转速波动很小，具有优异的传动性能。     

两相开关磁阻电机磁场二维有限元分析

开关磁阻电机电磁场分析对电机的性能计算具有重要意义,利用ANSYS有限元软件对电机转子的四个特殊位置进行了二维磁场分析,得到了相应的磁力线分布图和磁通密度值,为电机重要磁化曲线的解析计算提供了相应的依据。     

磁场对工艺系统影响的试验

研究了磁场作用于工艺系统时对工艺系统的静刚度和工艺系统振动的影响,研究表明,磁场的作用在很大程度上提高工艺系统的静刚度,并且增加系统阻尼,减小工艺系统振动。此外也进行了带磁车削细长轴时圆柱度和加工表面粗糙度的研究。     

磁场分布不均匀性对磁流变液剪切传力的影响

通过对磁流变液剪切传力机理的研究 ,充分考虑磁场饱和情况以及磁场各要素间的非线性关系 ,分析磁场分布不均匀性导致磁流变液中剪切力分布的变化 ,并对最具代表性的两平板间磁流变液传递剪切力的情况进行有限元分析 ,得出比较符合实际的结果。     

Quantitative measurements of magnetic stray field dynamics of Permalloy particles in a photoemission electron microscopy

By example of a Permalloy particle (40 × 40 μm(2) size, 30 nm thickness) we demonstrate a procedure to quantitatively investigate the dynamics of magnetic stray fields during ultrafast magnetization reversal. The measurements have been performed in a time-resolving photoemission electron microscope using the X-ray magnetic circular dichroism. In the particle under investigation, we have observed a flux-closure-dominated magnetic ground structure, minimizing the magnetic stray field outside the sample. A fast magnetic field pulse introduced changes in the micromagnetic structure accompanied with an incomplete flux closure. As a result, stray fields arise along the edges of domains, which cause a change of contrast and an image deformation of the particles geometry (curvature of its edge). The magnetic stray fields are calculated from a deformation of the X-ray magnetic circular dichroism (XMCD) images taken after the magnetic field pulse in a 1 ns interval. These measurements reveal a decrease of magnetic stray fields with time. An estimate of the lower limit of the domain wall velocity yields about 2 × 10(3) m s(-1).     

Magnetic field detection for current evaluation by magnetic force microscopy

A current measurement method through magnetic field detection by magnetic force microscopy was proposed and demonstrated. We observed the magnetic field induced by an AC below 2.2 μA around a GaAs/AlGaAs mesa stripe. To achieve high sensitivity in magnetic field detection, we tuned the AC bias frequency to the torsional resonant frequency of the cantilever. As a result, the sensitivity of the magnetic field detection was much improved and specific features of the magnetic field around the mesa stripe were clearly observed at a current in sub-μA range.     

太钢为核电工业攻克了世界性的技术难题

太钢不锈钢钢管公司成功攻克了一项世界性技术难题,研发出全球第一支使用挤压机生产的W型钢,产品主要用于核电裂变反应堆的管道支架。为全面提高不锈钢管市场占有率和应用范围,W型钢作为AP1000第三代核电站汽轮机发电余热排出换热系统的支撑件用钢,一直是由热轧加焊接工艺最终成W型钢,一方面热轧成本较高,另一方面对厚壁材料也增大了焊接难度,且所承担的风险远远大于无缝件。     

一种磁悬浮平台的电磁场分析

利用ANSYS分析软件,对这种新型磁悬浮平台进行了电磁场分析,得出了磁力线分布图、磁通量密度矢量图及磁通量密度等值线。并进一步分析了磁悬浮平台载体间隙对磁力线分布的影响,载体受力与电流之间的关系以及载体受力与间隙大小之间的关系,所得结果与物理特性相符,对磁悬浮平台的控制起到关键作用。     

Modeling and analysis of magnetic dipoles in weak magnetic field

The magnetic leakage field distribution resulting from linear defects of a tube sample in the geomagnetic field is modeled according to the magnetic dipole theory. The formula to compute the normal component of the weak magnetic field is deduced based on the spatial distribution of the magnetic dipole. The shape and characteristics of the zero line (an important criterion for magnetic memory testing) of the normal field is analyzed under different longitudinal magnetizations. Results show that the characteristics of the zero line should be considered when the metal magnetic memory testing method is used to find and locate the defect. __________ Translated from Transactions of Beijing Institute of Technology, 2007, 27(147): 395–398 [译自: 北京理工大学学报]