• Proceedings of the Korean Society of Precision Engineering Conference
• /
• 1994.10a
• /
• pp.156-160
• /
• 1994

Use of engineering ceramics has been increasing due to the outstanding physical and chemical properties. Conventional machining processes, however, are not applicable due to their hardness and brittleness. Laser cutting is a promising alternative for these ceramics. In this study, experimental data of CO $_{2}$ laser cutting of $Al_{2}$ $O_{3}$ and Si $_{3}$ N $_{4}$ are obtained to give a guide in the industry. Results of $Al_{2}$ $O_{3}$ cutting showed extreme weakness to thermal crack and it was found that pulsed beam has to be used for thick $Al_{2}$ $O_{3}$ specimen. Si $_{3}$ N $_{4}$ showed good results for both CW and pulsed beams. Using pulsed beam resulted narrower kerf width with increased surface roughness a nd reduced cutting speed. It was also found that a parameter call path energy is useful for representing minimum threshold value for possible cutting range with pulsed beam.

• Journal of the Korean Ceramic Society
• /
• v.29 no.10
• /
• pp.815-821
• /
• 1992

The batches having excess SiO2 to tetrasilicic mica KMg2.5 (Si4O10)F2 were melted at 1450℃. The fabricated samples were heat-treated for the nucleation and the crystallization. The crystallized samples were investigated on several properties. The tetrasilicic mica composition with excess 10 wt% SiO2 was successful both in glassifying and in crystallizing. The optimum temperatures for the nucleation and the crystallization were 680℃ and 1000-1100℃, respectively. The mica and the cristobalite crystallines were identified after heat-treatment. The properties of the samples processed appropriately were as follows, bulk density 2.64g/㎤, thermal expansion coefficient ∼80×10-7/℃, Vicker's hardness ∼105 Kgf/㎟, bending strength ∼666Kgf/㎟, dielectric constant ∼11.1, tan δ 2.5%, volume resistivity 2.35×107∼1.3×1011{{{{ OMEGA }}cm, surface roughness 6.984㎛.

• Transactions of the Korean Society of Mechanical Engineers
• /
• v.14 no.6
• /
• pp.1474-1486
• /
• 1990

The frictional characteristics of galvanized sheet steels(GA, EG, EGF, EGN) for automobiles were studied and compared with that of cold rolled sheet steel. A draw bead tester which simulates metal flow through a draw bead in stamping die face was used to measure coefficients of friction of galvanized sheet steels for four kinds of lubricants. Stamping formability of galvanized sheet steels for quarter outer panel was examined. The results show that stamping formability and friction characteristics were mainly influenced by the nature of zinc coating, surface roughness and micro hardness of coated layer, and proved to be very sensitive to the lubricant used.

• Korean Journal of Materials Research
• /
• v.16 no.2
• /
• pp.111-115
• /
• 2006

High-finned tubes have good thermal conductivity and have better cooling efficiency than plain tubes or low-fined tubes due to bigger air contact area. During high-fined tubes are manufactured by roll forming, the main technique is illustrated to optimizing primary material(copper pipe), optimized die matrix designing technique for roll forming, control manufacturing speed to develop productivity etc. In this study, a roll forming system was developed in oder to produce high-finned tube. Also a multi-step roll forming die was designed & built to produce high-finned tube that has over 10 mm fin height. And then, roll forming test using copper pipe was performed to produce high-finned tube. Roll forming process for producing highfinned tube was optimized by analyzing and adjusting misrostructure, hardness, and surface roughness of roll formed high-fined tube.

• Journal of Welding and Joining
• /
• v.5 no.3
• /
• pp.19-27
• /
• 1987

This paper presents the weldability for cold pressure but welding method in junction of dissimilar metals each other. Although the weldability between the same aluminium metal plate welding has been studied, the study of itthe rod of aluminium and coper has not fully been investigated. The purpose is to suggest the optimal conditions on the rod of those under above method. To obtain the optimal conditions, associated experiments were performed in a various welding parameters. Consequently, it was proved that the mechanical properties such as tensile strength, hardness and bending strength could be obtained excellent particularly under the welding conditions; pressure is $(32~39) {\times} 10^3/kg/cm^2$, time is beyond 70 seconds, stage is higher than fifth stage.

• Journal of the Korean Society for Precision Engineering
• /
• v.7 no.2
• /
• pp.105-112
• /
• 1990

Advanced ceramics have some excellent properities as the material for the mechanical component. It is, however, very difficult to grind ceramics with high efficiency because of their high strength, hardness and brittleness. In this paper, some experiments are carried out to find the basic grinding characteristic of advanced ceramics. Representative advanced ceramics, such as AL/sub 2/ O/sub 3/, ZrO/sub 2/, SiC and Si/sub 3/N/sub 4/and ground with diamond wheels. Special attention is paid to comparison between the conventional and creep feed grinding. Results obtained in this study provide some useful informations to attain the high efficiency grinding of advanced ceramics.

• Proceedings of the Korean Society of Precision Engineering Conference
• /
• 2004.10a
• /
• pp.537-542
• /
• 2004

Machinble Ceramics have some excellent properties as the material for the mechanical components. It is, however, very difficult to grind ceramics with high efficiency because of their high strength, hardness and brittleness. Lapping used diamond slurry and lapping by in-process electrolytic dressing is developed to solve this problem. On this paper, a comparative study of processing ability of lapping used diamond slurry and lapping by in-process electrolytic dressing.

• Proceedings of the Korean Society of Precision Engineering Conference
• /
• 2000.05a
• /
• pp.653-657
• /
• 2000

Machining performance in hard turning of hardened AISI M2 steel has been studied. Ceramic tools were used in the cutting tests without coolants and workpiece was prepared by heat treatment to increase its hardness up to Rc 60. Cutting state parameters such as cutting forces, temperature, and tool wear were measured in the experiments and effects of tool wear on cutting states were investigated.

• Journal of the Korean Society of Manufacturing Technology Engineers
• /
• v.20 no.3
• /
• pp.274-279
• /
• 2011

In this study, new abrasives that were composed of iron powder and carbon nanotube (CNT) particle were attempted to be abrasives for magnetic abrasive polishing. Because the CNT particles itself are very small ones with high hardness and magnetic strength, these properties are effective for magnetic abrasive polishing of nonmagnetic materials. As an experimental result for evaluating the machining characteristics in magnetic abrasive polishing, the CNT particles showed better performance than the conventional abrasives such as Fe and CBN powder.

• Korean Journal of Materials Research
• /
• v.12 no.1
• /
• pp.82-88
• /
• 2002

Chromium carbide films were deposited on high speed steels using a Cr_3C_2$ target by magnetron sputtering. Effects of the deposition parameters (power, Ar pressure and substrate temperature) on deposition rates and surface roughnesses of the films were investigated. The morphologies of those films were characterized by scanning electron microscopy and atomic force microscopy. The grain size of the samples deposited using dc-power is larger than that using equivalent rf-power. The hardness of the sample increases with increasing rf-power, whereas the elastic modulus nearly does not change with rf-power. The optimum sputter deposition conditions for chromium carbide on high speed steels in the corrosion resistance aspect were found to be the rf-power with small roughness.