Because magnets fabricated using Nd-Fe-B exhibit excellent magnetic properties, this novel material is used in various high-tech industries. However, because of the brittleness and low formability of Nd-Fe-B magnets, the design freedom of shapes for improving the performance is limited based on conventional tooling and postprocessing. Laserpowder bed fusion (L-PBF), the most famous additive manufacturing (AM) technique, has recently emerged as a novel process for producing geometrically complex shapes of Nd-Fe-B parts owing to its high precision and good spatial resolution. However, because of the repeated thermal shock applied to the materials during L-PBF, it is difficult to fabricate a dense Nd-Fe-B magnet. In this study, a high-density (>96%) Nd-Fe-B magnet is successfully fabricated by minimizing the thermal residual stress caused by substrate heating during L-PBF.

본 연구는 MRI 검사 시 임플란트 자석 틀니의 자기 유지력 변화와 구조물 간의 금속 인공물을 분석하였다. 연구 방법으론 자기 유지력 변화의 평가를 위해 자석 구조체를 고속스핀에코 시퀀스로 검사하며 자력을 30분 간격으로 최대 90분까지 측정하였고, 금속 인공물 평가를 위해 자석 구조체와 임플란트 팬텀의 축상면 이미지에서 금속 인공물 크기를 측정하였다. 자석 구조체의 자력은 1.5T 검사에선 1.11 ∼ 5.29G의 차이를, 3.0T 검사에선 0.78 ∼ 2.97G의 차이를 보였으나 검사 시간과는 유의미한 상관관계를 보이지 않았다(p>0.05). 금속 인공물의 크기는 1.5T 장비에서 임플란트 팬텀은 15.02mm ∼ 21.97mm, 자석 구조체 팬텀은 87.86mm ∼ 102.54mm, 3.0T 장비에서 임플란트 팬텀은 19.15mm ∼ 25.81mm, 자석 구조체 팬텀은 94.18mm ∼ 125.56mm로 나타났다. 이로 인해 자석 구조체의 자력은 MRI 검사 시간에 따른 유의미 한 변화를 보이지 않으며, 자력을 가진 구조물이 일반적인 구조물보다 더 큰 금속 인공물을 보인다는 것을 알 수 있었다. 따라서 MRI 검사는 임플란트 자석 틀니의 자기 유지력에 영향을 미치지 않으며, 금속 인공물을 줄이기 위해 검사 전 자력을 가지는 삽입물은 제거되어야 한다.

Magnetic 0-D Nd2Fe14B powders are successfully fabricated using 1-D Nd2Fe14B nanowire formed by an efficient and facile electrospinning process approach. The synthesized Nd-Fe-B fibers and powders are investigated for their microstructural, crystallographic, and magnetic properties according to a series of subsequent heat treatments. Each heat-treatment process leads to the removal of organic impurities and the formation of the respective oxides/composites of Nd, Fe, and B, resulting in the formation of Nd2Fe14B powders. Nd-Fe-B fibers exhibit the following magnetic properties: The coercivity (Hci) of 3260 Oe, a maximum magnetization at 3T of 109.44 emu/g, and a magnetization remanence (Mr) of 44.11 emu/g. This process easily mass produces hard magnetic Nd2Fe14B powders using a 1-D synthesis process and can be extended to the experimental design of other magnetic materials.

In this research, the magnetic abrasive finishing process using (Nd-Fe-B) permanent magnet was applied to confirm the performance and to find the optimum conditions. The STS304 bar was used as the specimen in this experiment. In order to confirm the performance of magnetic abrasive finishing process, the surface roughness (Ra) and diameter reduction were measured when the specimens were processed under the conditions of rotational speeds, frequencies, and magnetic pole shapes. The rotational speeds were varied at 8000rpm, 15000rpm, 20000rpm, and 25000rpm. And the frequencies were changed to 0Hz, 4Hz and 10Hz. Also the shapes of the magnetic pole were changed to flat edge, sharp edge and round edge. It can be concluded that the surface roughness (Ra) and diameter reduction were found to be the best at 25000rpm, 4Hz, flat edge.

Rare earth magnets are the strongest type of permanent magnets and are integral to the high tech industry, particularly in clean energies, such as electric vehicle motors and wind turbine generators. However, the cost of rare earth materials and the imbalance in supply and demand still remain big problems to solve for permanent magnet related industries. Thus, a magnet with abundant elements and moderate magnetic performance is required to replace rare-earth magnets. Recently, a”-Fe16N2 has attracted considerable attention as a promising candidate for next-generation non-rare-earth permanent magnets due to its gigantic magnetization (3.23 T). Also, metastable a”-Fe16N2 exhibits high tetragonality (c/a = 1.1) by interstitial introduction of N atoms, leading to a high magnetocrystalline anisotropy constant (K1 = 1.0MJ/m3). In addition, Fe has a large amount of reserves on the Earth compared to other magnetic materials, leading to low cost of raw materials and manufacturing for industrial production. In this paper, we review the synthetic methods of metastable a”-Fe16N2 with film, powder and bulk form and discuss the approaches to enhance magnetocrystalline anisotropy of a”-Fe16N2. Future research prospects are also offered with patent trends observed thus far.

Since the encoder and resolver are expensive, it is difficult to apply it as a position sensor of a motor in a real industrial field. Optical position sensors, such as encoders and resolvers, are also difficult to mount because of their size and durability. Therefore, in order to solve these problems, we propose a system that uses a linear motor as a stator and a magnet plate as a mover, and a system that excludes a separate linear scale and uses two linear Hall sensors and permanent magnets to generate a conventional sine wave, A linear motor capable of detecting an absolute position and a movement position of a magnet, a control method thereof, and a technology development that can reduce a production cost by developing a position control system using a magnet mover that can improve stability and reliability.

Neodymium-iron-boron (Nd-Fe-B) sintered magnets have excellent magnetic properties such as the remanence, coercive force, and the maximum energy product compared to other hard magnetic materials. The coercive force of Nd-Fe-B sintered magnets is improved by the addition of heavy rare earth elements such as dysprosium and terbium instead of neodymium. Then, the magnetocrystalline anisotropy of Nd-Fe-B sintered magnets increases. However, additional elements have increased the production cost of Nd-Fe-B sintered magnets. Hence, a study on the control of the microstructure of Nd-Fe-B magnets is being conducted. As the coercive force of magnets improves, the grain size of the Nd2Fe14B grain is close to 300 nm because they are nucleation-type magnets. In this study, fine particles of Nd-Fe-B are prepared with various grinding energies in the pulverization process used for preparing sintered magnets, and the microstructure and magnetic properties of the magnets are investigated.

Recently, the grain boundary diffusion process (GBDP), involving heavy rare-earth elements such as Dy and Tb, has been widely used to enhance the coercivity of Nd-Fe-B permanent magnets. For example, a Dy compound is coated onto the surface of Nd-Fe-B sintered magnets, and then the magnets are heat treated. Subsequently, Dy diffuses into the grain boundaries of Nd-Fe-B magnets, forming Dy-Fe-B or Nd-Dy-Fe-B. The dip-coating process is also used widely instead of the GBDP. However, it is quite hard to control the thickness uniformity using dip coating. In this study, first, a DyF3 paste is fabricated using DyF3 powder. Subsequently, the fabricated DyF3 paste is homogeneously coated onto the surface of a Nd-Fe-B sintered magnet. The magnet is then subjected to GBDP to enhance its coercivity. The weight ratio of binder and DyF3 powder is controlled, and we find that the coercivity enhances with decreasing binder content. In addition, the maximum coercivity is obtained with the paste containing 70 wt% of DyF3 powder.

We investigate the microstructural and magnetic property changes of DyH2, Cu + DyH2, and Al + DyH2 diffusion-treated NdFeB sintered magnets with the post annealing (PA) temperature. The coercivity of all the diffusiontreated magnets increases with increasing heat treatment temperature except at 910oC, where it decreases slightly. Moreover, at 880oC, the coercivity increases by 3.8 kOe in Cu and 4.7 kOe in Al-mixed DyH2-coated magnets, whereas this increase is relatively low (3.0 kOe) in the magnet coated with only DyH2. Both Cu and Al have an almost similar effect on the coercivity improvement, particularly over the heat treatment temperature range of 790-880oC. The diffusivity and diffusion depth of Dy increases in those magnets that are treated with Cu or Al-mixed DyH2, mainly because of the comparatively easy diffusion path provided by Cu and Al owing to their solubility in the Nd-rich grain boundary phase. The formation of a highly anisotropic (Nd, Dy)2Fe14B phase layer, which acts as the shell in the core-shell-type structure so as to prevent the reverse domain movement, is the cause of enhanced coercivity of diffusion-treated Nd-Fe-B magnets.

자전거의 안장 지주에 영구자석의 척력을 이용하여 완충장치를 설치하고자 자기 해석용 상용프로그램을 이용하였다. 유한요소법으로 구한 해석치를 실험치와 비교하여 유한요소 해석치의 신뢰성을 확보하였다. 그 후에 3 자유도계의 자전거 동역학 모델을 완성하고 자석의 크기에 상응하는 등가 스프링 강성값을 모델에 이식하였다. 자전거의 동역학 모델에서 전륜과 후륜은 주행면의 비평탄도에 의한 입력을 부담하도록 하였다. 전륜과 후륜이 독립적으로, 또는 동시에 반삼각 범프(halftriangular bump)와 정현파 굴곡로(sinusoidal road)를 통과할 때의 동적 거동을 살펴보았다. 운전자와 프레임의 수직거동, 주행방향의 피칭 거동을 관찰하였으며 자전거의 완충 시스템을 보다 구체화할 수 있는 기반을 마련하였다.

This paper studies the repulsion occurring between the permanent magnet by the simulation analysis. Nowadays, there are many cases such as magnetic levitation, safety bumper device and so on using the properties of the permanent magnet. As the neodymium magnet of the powerful ferromagnetic material is less expensive by comparing with the strong magnetic force for industrial, medical areas and etc., it can be used at the various applications. The prediction of the magnetic force is becoming increasingly important in order to be used effectively permanent magnet in various fields. Therefore, the results of the magnetostatics by Ansys and the MAXWELL of commercial electromagnetic analysis software are analyzed and compared. Magnetic force is inversely proportional to the distance and power. In this paper, the permanent magnet was simulated and compared by the two permanent magnets of the small sizes with the diameter of 4mm and the length of 8mm. In addition, the forces between the ferromagnetic iron and permanent magnets are simulated.

Many automotive components for power generation such as motors and alternators have been widely using ferrite magnets. To ensure a high level of efficiency could be achieved in an alternator, the assembled magnets must be in good enough durability. Recently, some hairline cracks have been found on the magnet produced by manufacturers in Korea. Thus, there is an increasing concern that some of the magnets produced could cause further problems after being assembled in the alternator. Based on the standard alternator test (RS0008 : 2006), this paper has developed an accelerated failure-free test for magnets in alternator to demonstrate that assembled magnets will meet durability objective specified by the manufacturer. This guarantees the target life of the magnet with 90 percent reliability and 90 percent confidence level (R90C90). Temperature and rotation speed were selected as accelerated stress factors.