• Nuclear Engineering and Technology
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• v.52 no.8
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• pp.1714-1723
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• 2020

This study aims at characterizing the rheological properties of uranium oxide powders for nuclear fuel pellets manufacturing. The flowability of these powders must be compatible with a reproducible filling of press molds. The particle size distribution is known to have an impact on the rheological properties and fine particles (<100 ㎛) are suspected to have a detrimental effect. In this study, the impact of the particle size distribution on the rheological properties of UO₂ powders was quantified, focusing on the influence of fine particles. Two complementary approaches were used. The first approach involved characterizing the powder in a static state: density, compressibility and shear test measurements were used to understand the behavior of the powder when it is transitioned from a static to a dynamic state (i.e., incipient flow conditions). The second approach involved characterizing the behavior of the powder in a dynamic state. Two zones, corresponding to two characteristic behaviors, were demonstrated for both types of measurements. The obtained results showed the amount of fines should be kept below 10 % wt to ensure a robust mold filling operation (i.e., constant mass and production rate).

• Journal of Korea Foundry Society
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• v.5 no.3
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• pp.47-51
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• 1985

FMC(FULL MOLD CASTING)법(法)이란 발포 polystyrene모형을 사용하여 조형후, 주형으로부터 모형을 발형치 않은채, 용탕을 주입하여 주물을 제조하는 방법을 말한다. 합성수지 발포체를 주조용(用) 모형의 재료로써 사용하는 방법은 1956년 미국의 슈로이어(H. F. Shroyer)에 의하여 발명되었으나 이것은 실제 주조에 응용하기에는 여러 곤란한 문제가 있어, 단순히 착상에 그치고 공업적으로 적용할 수 있는 기술을 확립치는 못하였다. 그후 서독 아헨대학교수로서 당시 발포폴리스티렌을 포함하는 각종단열재 제조회사 G+H 사(社)의 A. Wittmoser에 의하여 1962년에 처음으로 공업적으로 이용되어, 현재 서독, 미국, 일본등 유럽전역에서 응용되고 있다. 당사(當社)는 1977년6월 5일 첫 가동된 이후, 동(同)그룹 사(社)인 현대자동차로부터 자동차금형 (Press Die)주조를 FMC법(法)으로 생산하여 달라는 요구를 받고, 그해 12月부터 개발시험에 착수하여 이듬해 6월(月)부터 본(本) FM주조를 적용하여왔다. 그러나 1) 폴리스티렌 모형의 주입시(時) 부(不)기화 잔유물에 의한 주물표면결함 2) 도형제 박리 현상에 의한 표면결함 3) 주입시(時) 다량의 매연발생 및 4) 조형시(時) 모형의 변형에 의한 칫수결함 등의 문제가 대두되어 품질면에서는 1982년6월(月)에 와서야 어느정도 정상궤도에 도달하여 본격적인 FM 생산을 해오고 있는 중이다. 여기서 그동안 당사가 경험한 대형주물 (자동차금형:$1{\sim}10$톤/개)에 있어서의 FM 주조법의 적용사례를 본지(本誌)를 통하여 간단히 소개하고자 한다.

• 한국금형공학회:학술대회논문집
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• 2008.06a
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• pp.61-66
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• 2008

The hydraulic system have been used much in a heavy machine which high power source is desired. In the case of the heavy press machine and the injection molding machine, the use of the hydraulic power is essential especially for increasing productivity and getting the good products. Because the hydraulic circuit is very complex and the system parameters are uncertain, the development of the simulation model for hydraulic system is not easy in the heavy machine. In this case, Many researchers have used a commercial program for analysis and development in a major field of study. In this paper, the aim is to develop the simulation model of the hydraulic system with various commercial program for trajectory tracking. And adaptive control method is applied to the simulation model for the trajectory tracking of a cylinder motion. Load on the cylinder is modeled in ADAMS program, the hydraulic circuit including pump, spool valve and cylinder is modeled in AMESim program and a controller is designed in MatLab/simulink program. The suggested model is applied for the tracking of a cylinder motion, and through computer simulation, its trajectory tracking performance is illustrated.

• Steel and Composite Structures
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• v.10 no.3
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• pp.245-260
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• 2010

In this paper, experimental and theoretical investigations on the response and collapse of 310 stainless steel tubes with different diameter-to-thickness ratios subjected to cyclic bending are discussed. The tube-bending device and curvature-ovalization measurement apparatus were used to conduct the experiment. The endochronic theory combined with the principle of virtual work and finite element software, ANSYS, were used to simulate the moment-curvature and ovalization-curvature relationships. It is shown that although the two methods lead to good simulation of the moment-curvature relationship, the endochronic theory combined with the principle of virtual work has the better simulation of the ovalization-curvature response when compared with experimental data and the simulation by ANSYS. In addition, the theoretical formulations proposed by Kyriakides and Shaw (1987) and Lee et al. (2001) were used to simulate the controlled curvature-number of cycles to produce buckling relationship. It is shown that the theoretical formulations effectively simulate the experimental data.

• Transactions of Materials Processing
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• v.31 no.4
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• pp.186-193
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• 2022

The application of UHSS sheet is being expanded up to 50% to reduce the weight of automobiles and improve safety. However, due to the high strength and low elongation of the ultra-high tensile strength steel sheet, product defects such as spring back and mold defects such as cracks and chippings also occur. In this study, Pin/Ring on Disc and Spiral wear tests were conducted to evaluate the durability of Ti/Cr-coated molds for forming 1.2GPa grade UHSS sheets. Component analysis and thickness were measured for each coating layer, and hardness and adhesion were investigated to determine mechanical properties. Combining the results of various wear tests, it was found that the TiAlN coating had the best wear and sticking resistance.

• Design & Manufacturing
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• v.13 no.4
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• pp.10-16
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• 2019

Semiconductor chip is bonded to the substrate by melting solder bumps. In general, the chip bonding is applied by a Reflow process or a Thermo-Compression(TC) bonding process. In this paper, we introduce a Laser Assisted Thermo-Compression bonding (LATCB) process to improve the anxiety of the existing process(Reflow, TC bonding). In the LATCB process, the chip is bonded to the substrate by irradiating a laser with a uniform energy density in the same area as the chip to melt only the solder bumps and press the chip with a Transparent Compression Module (TCM). The TCM consists of a fused silica header for penetrating the laser and pressurizing the chip, and a piezoelectric actuator (P.A.) coupled to both ends of the header for micro displacement control of the header. In addition, TCM is a structure that can pressurize the chip and deliver it to the chip and solder bumps without losing the energy of the laser. Fused silica, which is brittle, is vulnerable to deformation, so the header may be damaged when an external force is applied for pressurization or a displacement differenced is caused by piezoelectric actuators at both ends. On the other hand, in order to avoid interference between the header and the adjacent chip when pressing the chip using the TCM, the header has a notch at the bottom, and breakage due to stress concentration of the notch is expected. In this study, the thickness and notch length that the header does not break when the external force (500 N) is applied to both ends of the header are optimized using structural analysis and Coulomb-Mohr failure theory. In addition, the maximum displacement difference of the P.A.s at both ends where no break occurred in the header was derived. As a result, the thickness of the header is 11 mm, and the maximum displacement difference between both ends is 8 um.

• Tribology and Lubricants
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• v.31 no.4
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• pp.157-162
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• 2015

In this study, an ultrasonic nanocrystalline surface modification (UNSM) technique is applied to tungsten carbide-cobalt (WC-Co) to extend the service life of carbide parts used in press mold. The UNSM technique modifies the structure, reduces the surface roughness, increases the surface hardness, induces the compressive residual stress, and increases the wear resistance of materials by introducing severe plastic deformation. The surface roughness, hardness, and compressive residual stress of WC after UNSM treatment improve by about 42, 10, and 71%, respectively. A wear test under dry conditions is used to assess the effectiveness of the UNSM technique on the friction and wear behavior of WC. The UNSM technique is found to reduce the WC friction coefficient by approximately 21% and enhance the wear resistance by approximately 85%. The improved friction and wear behavior of WC may be mainly attributed to the increased hardness and compressive residual stress. Moreover, the WC specimen is treated by UNSM technique using three different WC, silicon nitride (Si₃N₄) and stainless steel (STS304) balls. The surface treated by WC balls shows the highest hardness when compared with treatment by stainless steel and silicon nitride balls. According to the obtained results, the UNSM technique is believed to increase the durability of the carbide component by improving the friction and wear behavior.

• Journal of Ocean Engineering and Technology
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• v.32 no.6
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• pp.502-510
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• 2018

In order to accumulate data to lower the friction coefficient of a press mold, tribological tests were performed before and after coating SM45C with a PVC/PO film and plasma coating (CrN, concept). The ultrasonic nanocrystal surface modification (UNSM)-treated material had a nano-size surface texture, high surface hardness, and large and deep compressive residual stress formation. Even when the load was doubled, the small amount of abrasion, small weight of the abrasion, and width and depth of the abrasion did not increase as much as those of untreated materials. A comparison of the weight change before and after the tribological test with the CrN and the concept coating material and that of the untreated material showed that the wear loss of the concept coating material and P-UNSM treated material (that is, the UNSM treated material treated with the concept coating) showed a tendency to decrease by approximately 55-75%. Concept 100N had a lower friction coefficient of about 0.6, and P-UNSM-30-100N showed almost the same curve as concept 100N and had a low coefficient of friction of about 0.6. The concept multilayer coating had a thickness of $5.32{\mu}m$. In the beginning, the coefficient of friction decreased because of the plasma coating, but it started to increase from about 250-300 s. After about 350 s, the coefficient of friction tended to approach the friction coefficient of the SM45C base metal. The SGV-280F film-attached test specimen was slightly pushed back and forth, but the SM45C base material was not exposed due to abrasion. The friction coefficient was 0.22, which was the lowest, and the tribological property was the best in this study.

• Journal of Surface Science and Engineering
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• v.38 no.3
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• pp.126-135
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• 2005

SKD 11 steel has been widely used for tools, metallic mold and die for press working because of its favorable mechanical properties such as high toughness and creep strength as well as excellent oxidation resistance. The ion nitrided tool steel containing Mo results in improvement of corrosion resistance, strength at high temperature and pitting resistance, especially in $Cl^-$ contained environment. But the Mo addition causes a disadvantage such as lower oxidation resistance at elevated temperature. In this study, several effects of ion-disadvantage on the oxidation characteristics for SKD 11 steel with various oxidation temperature were investigated. SKD 11 steels were manufactured by using vacuum furnace and solutionized for 1 hr at $1,050^{\circ}C$. Steel surface was ion nitrided at $500^{\circ}C$ for 1 hr and 5 hr by ion nitriding equipment. ion nitrided specimen were investigated by SEM, OM and hardness tester. Oxidation was carried out by using muffle furnace in air at $500^{\circ}C,\;700^{\circ}C\;and\;900^{\circ}C$ for 1hr, respectively. Oxidation behavior of the ion nitrided specimen was investigated by SEM, EDX and surface roughness tester. The conclusions of this study are as follows: It was found that plasma nitriding for 5 hr at $500^{\circ}C$, compared with ion nitriding for 1 hr at $500^{\circ}C$, had a thick nitrided layer and produced a layer with good wear, corrosion resistance and hardness as nitriding time increased. Nitrided SKD 11 alloy for 1hr showed that wear resistance and hardness decreased, whereas surface roughness increased, compared with nitrided SKD 11 alloy for 5 hr. The oxidation surface at $900^{\circ}C$ showed a good corrosion resistance.