• The Korean Journal of Ceramics
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• 제5권2호
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• pp.119-124
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• 1999

Silicon nitride ceramics with highly oriented microstructure were prepared by tape casting a slurry containing 5 wt% of the silicon nitride whiskers. The whiskers were aligned in the casting direction and worked as seeds for the grain growth. The anisotropy was observed from the sintering shrinkage, Vickers indentation crack lengths, and XRD patterns. The cracks were much longer on the surface normal to the aligned grains than on the tape casting surface where the lateral cracks were also observed. The effect of sintering additives and the annealing treatment on the indentation crack length was examined. The sample with higher silica content had longer cracks than the one with lower silica content. The crack length anisotropy increased after annealing at 2123K.

• 한국주조공학회지
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• 제18권6호
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• pp.578-585
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• 1998

A multi-purpose code MAGMA was employed for mold design and process control in producing Al wheel by lowpressure die casting. Three-dimensional solid modeling was followed by mesh generation of casting and molds(top, bottom and side). The simulation of stability of casting cycle time, mold filling simulation with pressure variation from P1 to P2, solidification simulation by solidification time and feeding criteria, and temperature distribution of molds during processes were studied in this research. The thermal stability of molds was attained after 5 cycles when molds were preheated at $400^{\circ}C$. The pressure increase from P1 to P2 for mold filling was evaluated as slightly higher, and 6 seconds were taken for the mold filling. The cycle time was believed to be designed properly judged from the solidification time of casting and open/close time of molds.

• 한국정밀공학회:학술대회논문집
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• 한국정밀공학회 2000년도 추계학술대회 논문집
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• pp.902-905
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• 2000

As the manufacturing processes of automotive engine piston, gravity die-casting, squeeze casting, hot forging and powder forging process are generally used for the various specifications. As the semi-solid forming(SSF) is compared with conventional casting such as gravity die-casting and squeeze casting for the characteristics of its process, the product without inner defects such as gas porosity and segregation can be obtained and its microstructure is globular grain. In SSF process, the materials are heated up to the temperature between the solvus and liquidus line at which the materials exists in the form of liquid-solid mixture. In this time, Discussion is given about reheating process of row material and results are presented regarding accurate temperature and process variables controlling for right solid fractions.

• 한국주조공학회지
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• 제36권5호
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• pp.153-158
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• 2016

The lost foam casting process was used to fabricate Al-Si-Mg cast specimens, and the effects of the chemical composition and process variables on the tensile properties and the mold filling ability were investigated. Some porosity formation was observed in thick sections of the casting and better tensile properties were obtained for thin sections, presumably because of their lower porosity and the higher cooling rate. Tensile properties were not clearly enhanced by grain refining treatment with Ti; however, the elongation was significantly improved by Sr modification of the Al-Si-Mg alloy. The mold filling distance was generally proportional to the pouring temperature of the melt, and the distance was also increased by the addition of Ti.

• 대한치과기공학회지
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• 제41권4호
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• pp.255-262
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• 2019

Purpose: Recently, the production technology of dental prosthesis using 3D Printer workpeices has been developed. However, the lack of information on the work processes and casting techniques of materials for 3D printing casting is expected to require research. Therefore, in this study, we intend to cast a Dental DLP 3D Printer workpiece, which is being commercialized, to identify its appearance and internal clearance, and to observe its castability. Methods: Castability of the 3D Printer workpiece was evaluated. The specimen is prepared in a cylindrical shape and in a 1 mm thick coping shape. The control specimen is made of wax and the experimental specimen is made of resin using two types of 3D printers. After casting, the appearance of the casting body was observed and the internal clearance of the coping was measured. Results: RP1 and RP2, cylindrical specimens, were partially cast or fin. When coping-type specimens were measured before casting, the internal clearance of PE2 was more accurate than that of PC and PE1. When coping-type specimens were measured after casting, CE1 was the most accurate in occlusal clearance and CE2n was the most accurate in axial clearance. Conclusion: 1. Exterior observations of the casting body indicated casting defects and fins. 2. Internal clearance observations show that the occlusal clearance of the castings is larger after casting, and the axial clearance of the castings is smaller after casting. 3. It is judged that the RP2 specimen is more likely to be applied for casting than the RP1 specimen.

• 한국재료학회지
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• 제11권10호
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• pp.869-878
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• 2001

Alumina $(Al_2O_3)$ green bodies were fabricated by gel-casting using three kinds of alumina with different particle size (mean particle size: 4.6 $\mu\textrm{m}$, 0.32 $\mu\textrm{m}$, 10nm). The effects of particle size on gel-casting process and green microstructure were investigated. The optimum dispersion conditions using ammonium salt (D-3019) as dispersant were 0.2 wt% (4.63 $\mu\textrm{m}$), 0.5 wt% (0.32 $\mu\textrm{m}$), and 5.0 wt% (10 nm), in high solid loading. The optimum solid loading of each starting material for gel-casting was obtained as 59 vol% (4.63 $\mu\textrm{m}$), 57 vol% (0.32 $\mu\textrm{m}$), 15 vol% (10 nm), depending on particle size, indicating that nano-size particle (10 nm) represent lower solid loading as high specific surface area than those of other two starting materials. The drying at ambient conditions (humidity; $\thickapprox$90%) was performed more than 48hrs to enable ejection of the part from the mold and then at $120^{\circ}C$ for 2hrs in an air oven, showing no crack and flaw in the dried green bodies. The pore size and distribution of the gelcast green bodies showed the significant decrease with decreasing particle size. Green microstructure was dependent on the pore size and distribution due to the particle size, and on the deairing step. The green density maximum obtained was 58.9% (4.63 $\mu\textrm{m}$), 60% (0.32 $\mu\textrm{m}$), 47% (10 nm) theoretical density (TD), and the deairing step applied before gel-casting did not affect green density.

• 소성∙가공
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• 제17권1호
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• pp.5-8
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• 2008

As the semi-solid forming technology has a lot of advantages compared to the die casting, squeeze casting and hot/cold forging, it has been studied actively. This paper focuses on the thixoforging of the rheological materials fabricated by the spiral mechanical stirring equipment with A356 casting aluminum alloy and A6061 wrought aluminum alloy. Formability tests of rheological materials fabricated by spiral mechanical stirring were carried out and the microstructures of forged sample were observed. After thixoforging experiment, the heat-treated conditions of forged samples are investigated to improve the mechanical properties. These results are able to suggest the possibility of commercialization for rheological materials fabricated by spiral mechanical stirring.

• 한국주조공학회지
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• 제31권5호
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• pp.267-273
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• 2011

Erosion and thermal shock resistance of several refractory materials have been investigated, which are expected to be used as nozzles in a planar flow casting equipment for amorphous alloys. The test was conducted on five materials; graphite, boron nitride, fused silica, alumina and zirconia. Test specimens were preheated and dipped into the melt of carbon steel and amorphous alloys. Some test specimens were rotated to develop high erosion and to shorten the test periods. Fused silica and boron nitride specimens showed the excellent erosion and thermal shock resistance irrespective of the kind of melt and melting atmosphere.

• 한국주조공학회지
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• 제17권2호
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• pp.145-150
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• 1997

The striations parallel to the casting direction are the characteristic defects occurring during the unidirectional solidification of nonferrous metals such as pure Al and Sn. It has been known that the defects affect the recrystallization temperature as well as the mechanical and electrical properties of Al. However, it has not been still known about the effect of casting factors such as the casting speed, rod diameter of cast metals, and alloying elements on the occurrence of striations. In the present study, these casting factors affecting the occurrence of striation were investigated by adopting the quantitative examination of striations. Also, the relation between striation defects and feathery grain, which are very similar to the striation defects, was studied.

• 한국주조공학회지
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• 제14권5호
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• pp.464-470
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• 1994

The horizontal continuous casting method with the heated mold was applied to study the solidification structures of the pure Al and Al-0.5wt%Si and Al-1.0wt%Si alloy rods. The results could be summarized as follows: 1. The S/L interface structures of pure Al represented the hexagonal cells at the casting speed of 590 and 350mm/min, respectively. However, the hexagonal cells became irregular as the casting speed and(or) Si amount increased. 2. The striation increased as the Si amount and casting speed increased and was found to result from the occurrence of growth twin crystals by XRD analysis. 3. The striation did not affect the mechanical and electrical property of the drawn wire from the casted rod. This means the striation is not a serious defect which has to consider in the production of micro-sized fine wire in the drawing process.