• Journal of the Korean Society for Precision Engineering
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• v.21 no.9
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• pp.41-47
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• 2004

As mechanical structures are minimized, the demand on micro dies and molds has increased. Machining complex 3D shapes requires fabrication procedures for preparing the electrodes. Micro electrical discharge milling using a simple shape electrode can produce 3D micro structure. In this paper the machining characteristics of micro electrical discharge milling according to depth of cut and capacitance are investigated. The machining time is diminished when simple tool-paths and algorithms for changing the feedrate are applied. But a distorted bottom shape and a tapered wall shape are inevitable after machining. The distorted bottom shape and the taper angle of wall are reduced by finish machining.

• Journal of the Korean Crystal Growth and Crystal Technology
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• v.16 no.3
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• pp.101-105
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• 2006

We fabricated the nano $TiN_x$ by making of reaction between titanium powder and $Si_3N_4$ during planetary milling. The $TiN_x$ powder was sintered by spark plasma sintering machine after mixing with 50 wt% of titanium powder, and the sintered body was heat-treated at $850^{\circ}C$ in order to investigate its hardness property at the elevated temperature. We analyzed crystal structure by XRD. We observed the peaks of $TiN_{0.26}$ and TiN after 10 hours milling, and we observed TiN peak mainly after 20 hours milling. The reacted particle size distribution was investigated by FE-SEM. Increase of milling time, the size of reacted particles was decreased and the $10{\sim}20nm$ size of $TiN_x$ on the surface of titanium and $TiN_x$ was observed after 20 hours milling. The micro-Vickers hardness of mixed sintered body was about $1050kgf/mm^2$.

• Korean Journal of Materials Research
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• v.11 no.12
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• pp.1020-1027
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• 2001

Powder type Ag system insert metals were manufactured by mechanical alloying method. Alloying method was the ball milling process using zirconia ball media, and all alloying variables were constant except the milling time. The milling times were selected 24, 48 and 72 hours. The insert metals made by milling method were observed using scanning electron microscope and x-ray analyses. And also, the evaluation of wettability and microstructures of the insert metals were conducted to investigate the characteristics of the brazed joint. The wettability of the insert metals made by milling of 48 hours, was the best condition. And the insert metals contained Cd shows good wettability, however, there was the oxides residue on the brazing test specimen. The microstructures of the manufactured and the commercial insert metals were almost same displaying the Cu- rich proeutectic and Ag-rich eutectic. Further, there were some porosities. The 48 hours alloyed insert metal was exhibited the most sound brazed joint without containing porosity due to the superior wettability and good alloying condition.

• KOREAN JOURNAL OF CROP SCIENCE
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• v.30 no.4
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• pp.381-387
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• 1985

Development and maturation of wheat were studied with reference to the quality of grain and milling properties. 1000-kernel weight and test weight increased as the wheat matured and as the orginal moisture decreased. The time of maturity was estimated 40 days after heading. Moisture content of wheat grain had a correlation coefficient of -0.877＊＊ with 1000-kernel weight, of -0.761＊＊ with test weight, and of 0.915＊＊ with pearling index. The milling data suggest that even in the early stages of maturing, the endosperm represented at large proportion of the grain. However, milling score was relatively constant at about 40 days. Break-Reduction flour ratio was a great difference between wheat varieties. 1000-kernel weight had a high significant correlation of +0.603＊＊ with milling yield, of -0.958＊＊ with ash content, and of +0.956＊＊ with milling score.

• Proceedings of the Korean Society of Precision Engineering Conference
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• 2005.06a
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• pp.1879-1882
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• 2005

Due to increase of demands on safety and convenience for automotive vehicle, the use of DC motor, such as power window, seat adjusting, pedal adjusting, sunroof, electric shift motor and so on, is increasing rapidly in the whole world. Worm gear is an important part to transmit torque to another gear in gear mechanism of automotive DC motor. But with current forming process, it has some problems in manufacturing and the quality. Also, the characteristics of automotive parts such as price and mass-production limit the quality improvement. Recently several methods are used in order to reduce a worm screw machining time and to maintain precision. In this paper, we introduce whirling tool machining and side milling cutter machining as effective manufacturing method of worm screw and study on the cutting force of side milling cutter and whirling tool in worm screw machining.

• Journal of Powder Materials
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• v.18 no.3
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• pp.256-261
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• 2011

In order to make a $Cu_2ZnSnSe_4$ (CZTSe) sputtering target sintered for solar cell application, synthesis of CZTSe compound by solid state reaction of Cu, Zn, Sn and Se mixed powders and effects of ball milling condition on sinterability such as ball size, combination of ball size, ball milling time and sintering temperature, was investigated. As a result of this research, sintering at $500^{\circ}C$ after ball milling using mixed balls of 1 mm and 3 mm for 72 hours was the optimum condition to synthesis near stoichiometric composition of $Cu_2ZnSnSe_4$ and to prepare sintered pellet with high density relatively.

• Tribology and Lubricants
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• v.33 no.6
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• pp.296-302
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• 2017

Ball milling of elemental powders in advance and using an induction heating system for intermetallic coatings are known to enhance the reactivity of combustion synthesis. In this work, the effects of simultaneously applying these two incentive methods on the properties of intermetallic coatings are studied. Ni-Al powder compacts ball-milled with three different ball-to-powder weight ratio mixtures are synthesized and coated on mild steel by combustion synthesis in an induction heating system. Consequently, similar to an electrical heating system, the positive effects of ball milling on the combustion synthesis are confirmed in the induction heating system. The enhancement in synthetic reactivity achieved by applying the two incentive methods at the same time is greater than that by applying each incentive method separately. In particular, the enhancement is remarkable at low reaction temperature. However, there are limitations to improving the reactivity by simultaneously applying the two incentive methods to the combustion synthesis, unlike the reaction temperature. The microstructure and hardness of the coating layer are both influenced by the ball-charging ratio employed in the ball-milling process.

• Journal of Powder Materials
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• v.6 no.2
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• pp.145-151
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• 1999

Nickel silicides ($Ni_5$Si$_2$, Ni$_2$Si and NiSi) have been synthesized by mechanical alloying (MA) of Ni-27.9at.9at%Si, Ni-33.3at% and Ni-50.0at% powder mixtures, respectively. From in situ thermal analysis, eash citical milling period for the formation of the three phases was observed to be 40.2, 34.9 and 57.5 min, at which there was a rapid increase in temperature. This indicates that rapid, self-propagating high-temperature synthesis (SHS) reactions were observed to produce the three phases during room-temperature high-energy ball milling of elemental powders. Each Ni silicide, Ni and Si, however, coexisted for an extended milling time even after the critical milling period. The powders mechanically alloyed after the critical period showed the rapid increase in microhardness. The Hv values were found to be higher than 1000kgf/mm$^2$. The formation of nickel silicides by mechanical alloying and the relevant reaction rates appeared to be influenced by the critical milling period and the heat of formation of the products involved ($Ni_5$Si$_2$$\rightarrow$-43.1kJ/mol.at., Ni$_2$Si$\rightarrow$-47.6kJ/mol.at., NiSi$\rightarrow$-42.4kJ/mol.at).

• Journal of Powder Materials
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• v.19 no.4
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• pp.310-316
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• 2012

Nanocrystalline $BaTiO_3$ powder could be synthesized by solid-state reaction using the mixture which was prepared by a high energy milling process in a bead mill for $BaCO_3$ and nanocrystalline $TiO_2$ powders mixture. Effect of the milling time on the powder characteristic of the synthesized $BaTiO_3$ powder was investigated. Nanocrystalline $BaTiO_3$ with a particle size of 50 nm was obtained at $800^{\circ}C$. High tetragonal $BaTiO_3$ powder with a tetragonality(=c/a) of 1.009 and a specific surface area of $7.6m^2/g$ was acquired after heat-treatment at $950^{\circ}C$ for 2 h. High energy ball milling was effective in decreasing the reaction temperature and increasing the tetragonality.

• Journal of the Korean Ceramic Society
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• v.46 no.2
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• pp.123-130
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• 2009

To understand the formation of core-shell structure in $BaTiO_3$ (BT) grains in multilayer ceramic capacitors, specimens were prepared with BT powders mixed with Y and Mg, and their microstructures were investigated with scanning electron microscopy, x-ray diffractometry, and transmission electron microscopy. Microstructural investigation showed that Y dissolved easily in BT lattice to a certain depth inside of the grain, whereas Mg tended to stay at grain boundaries rather than become incorporated into BT. It was considered that in case of Y and Mg addition in a proper ratio, Y could play a dominant role in the formation of shell leading to a slight dissolution of Mg in the shell. Next, the effects of ball-milling conditions on the core-shell formation were studied. As the ball-milling time increased, the milled powders did not show a significant change in size distribution but rather an increase of residual strain, which was attributed to the milling damage. The increase in milling damage facilitated the shell formation, leading to the increased shell portion in the core-shell grain.