• Bulletin of the Korean Chemical Society
• /
• v.29 no.6
• /
• pp.1121-1124
• /
• 2008

A carbon composite was synthesized by mechanical mixing of ball-milled graphite and PVC powders, followed by pyrolysis reaction of PVC. Natural graphite ball milled under atmosphere of argon or air leads to a disordered structure. It appears that the electrochemical lithium intercalation reaction is dependent on the atmosphere in which the graphite is ball milled. The carbon composite obtained using air-milled graphite shows a high reversible capacity and high initial coulombic efficiency compared to argon-milled graphite. This is attributed to the enhanced thermal stability of a disordered structure in the air milled sample. For the one with air-milled graphite, the disordered structure is maintained during heat treatment, while argon-milled graphite is partially crystallized.

• Transactions of the Korean Society of Mechanical Engineers
• /
• v.17 no.8
• /
• pp.2001-2011
• /
• 1993

This study deals with the machining of sculptured surfaces on 5-axis CNC milling machine with end mill cutter. The study (I) has the following contents. In 5-axis CNC milling, CL-data consist of CC-data and cutter axis direction vector at the CC-point. Thus, in machining of the sculptured surface on 5-axis CNC milling machine, determination of the direction vector of the milling cutter is very important. The direction vector is obtained by the fact that bottom plane of the milling cutter must not interfere with the free-form surface being machined. The interference is checked by the z-map method which can be applied in all geometric types of the sculptured surfaces. After generating NC part programs from 5-axis post-processing algorithms, sculptured surfaces were machined with 5-axis CNC milling machine (CINCINNATI MILACRON, 20V-80). From these machining tests, it was shown that the machining of the free-form surfaces on 5-axis CNC milling machine with the end mill has smaller cusp heights and shorter cutting time than on 3-axis CNC milling machine with the ball-end mill. Thus, 5-axis CNC end milling was effective machining method for sculptured surfaces. The study (II) deals with the prediction of cusp height and the determination of tool path interval for the 5-axis machining of sculptured surfaces on the basis of study(I).

• Journal of Powder Materials
• /
• v.16 no.5
• /
• pp.316-325
• /
• 2009

Fe based (Fe$_{68.2}$C$_{5.9}$Si$_{3.5}$B$_{6.7}$P$_{9.6}$Cr$_{2.1}$Mo$_{2.0}$Al$_{2.0}$) amorphous powder, which is a composition of iron blast cast slag, were produced by a gas atomization process, and sequently mixed with ductile Cu powder by a mechanical ball milling process. The experiment results show that the as-prepared Fe amorphous powders less than 90 $\mu$m in size has a fully amorphous phase and its weight fraction was about 73.7%. The as-atomized amorphous Fe powders had a complete spherical shape with very clean surface. Differential scanning calorimetric results of the as-atomized Fe powders less than 90 $\mu$m showed that the glass transition, T$_g$, onset crystallization, T$_x$, and super-cooled liquid range $\Delta$T=T$_x$-T$_g$ were 512, 548 and 36$^{\circ}C$, respectively. Fe amorphous powders were mixed and deformed well with 10 wt.% Cu by using AGO-2 high energy ball mill under 500 rpm.

• Journal of Computational Design and Engineering
• /
• v.2 no.4
• /
• pp.233-247
• /
• 2015

In this paper, the cutting force calculation of ball-end mill processing was modeled mathematically. All derivations of cutting forces were directly based on the tangential, radial, and axial cutting force components. In the developed mathematical model of cutting forces, the relationship of average cutting force and the feed per flute was characterized as a linear function. The cutting force coefficient model was formulated by a function of average cutting force and other parameters such as cutter geometry, cutting conditions, and so on. An experimental method was proposed based on the stable milling condition to estimate the cutting force coefficients for ball-end mill. This method could be applied for each pair of tool and workpiece. The developed cutting force model has been successfully verified experimentally with very promising results.

• Proceedings of the Korean Powder Metallurgy Institute Conference
• /
• 2006.09a
• /
• pp.360-361
• /
• 2006

Nanostructured aluminum powders were obtained by means of planetary ball milling with methanol as the Process Control Agent (PCA). The behavior, during milling, was considered measuring the microhardness and grain size at different milling times. Bulk near-full density samples were sintered using the Spark Plasma Sintering technology with different schedules: temperature of $500^{\circ}C$ and $550^{\circ}C$, pressure of 30 MPa and 60 MPa and different modes of applying the pressure were changed in order to understand the behavior during sintering. All the samples retained their nanostructure with an increase of the grain size from about 46 up to 70-90 nm.

• Journal of the Korean Society for Heat Treatment
• /
• v.18 no.1
• /
• pp.29-40
• /
• 2005

Formation of nanocrystalline ferrite was investigated using milled powders obtained by planetary ball milling of chips, which were made by high speed mechanical cutting of a low carbon steel(0.15%C-1.1%Mn-0.01%Ti). After 4 hour milling the chips were changed to powders of $50{\mu}m$ in average size, and with increasing milling time the powders were refined to about $3{\mu}m$ for 128 hour and showed more equiaxed shapes. Nanocrystalline(nc) region appeared in the surfaces of powders milled for 1 hour, and the 4 hour milled powders were almost filled with nc region. Hardness of nc region was much higher than that of work-hardened(WH) region. With increasing milling time, ferrite and cementite in pearlite were severely deformed and lamellar spacing was decreased, and then cementites began to disappear after 4 hour milling due to dissolution into ferrite. Deformation bands formed in lightly work-hardened region showed large width and similar crystallographic orientations. Spacing of deformation bands was decreased with deformation and the layered microstructure consisting of narrow deformation bands subdivided into variously oriented small grains was formed by more deformation, and eventually this structure seemed to be evolved to the nc structure by further deformation. It is also conjectured the growth of nc ferrite grains occurred through the coalescence of nanocrystalline ferrites rather than the nucleation and growth of recrystallized grains.

• Transactions of the Korean hydrogen and new energy society
• /
• v.15 no.2
• /
• pp.98-107
• /
• 2004

Modified Ni/YSZ cermets for high temperature electrolysis were synthesized by dry or wet mechanical alloying methods. The Ni/YSZ composit particle was directly fabricated from the ball milling of Ni and YSZ powder or obtained from the reduction of NiO/YSZ particle after the ball milling of NiO and YSZ. In the case of the NiO/YSZ composite particle, the dry milling increased the average particle size whereas the wet milling decreased the size. The dry milling showed that fine YSZ particles were distributed over large Ni surfaces while Ni and YSZ particles similar in size were well mixed in the wet milling method. These features were the same in the Ni/YSZ composite particle prepared from Ni and YSZ powders. The electrical conductivity of the wet-milled Ni/YSZ cermet showed the highest value of $2{\times}10^2S/cm$ among the specimens and this value was increased to $1.4\times10^4S/cm$ after the sintering at $900^\circ{C}$ for 1 h.

• Bulletin of the Korean Chemical Society
• /
• v.29 no.2
• /
• pp.309-312
• /
• 2008

Two different anode composite materials comprising of Fe, Cu and Si prepared using high energy ball milling (HEBM) were explored for their capacity and cycling behaviors. Prepared powder composites in the ratio Cu:Fe:Si = 1:1:2.5 and 1:1:3.5 were characterized through X-Ray diffraction (XRD) and scanning electron microscope (SEM). Nevertheless, the XRD shows absence of any new alloy/compound formation upon ball milling, the elements present in Cu(1)Fe(1)Si(2.5)/Graphite composite along with insito generated Li2O demonstrate a superior anodic behavior and delivers a reversible capacity of 340 mAh/g with a high coulombic efficiency (98%). The higher silicon content Cu(1)Fe(1)Si(3.5) along with graphite could not sustain capacity with cycling possibly due to ineffective buffer action of the anode constituents.

• Transactions of the Korean Society of Mechanical Engineers A
• /
• v.33 no.4
• /
• pp.440-446
• /
• 2009

This paper was designed to fabricate the miniature spur gear with pitch circle of 2.25mm using extrusion process of a mechanically alloyed Al-78wt%Zn powder. The mechanical alloying of the powder particles were performed for ball milled times of 4h, 8h, 16 and 32h by the planetary ball milling. The mechanical properties of these alloyed powders, which were compacted and sintered-cylindrical preforms, were estimated using compression test. The results showed that the alloyed powder with average particle size of $10{\mu}m$ milled for 32h has the highest compressive(fractured) strength(288MPa). Extrusions of the miniature spur gear using the alloyed powder were carried out at different extrusion temperatures. Extrusion temperature of $300^{\circ}C$ provided the spur gear with the highest relative density and Vickers hardness and without any surface defects.

• Bulletin of the Korean Chemical Society
• /
• v.32 no.5
• /
• pp.1491-1494
• /
• 2011

Lithium vanadium phosphate, $Li_3V_2(PO_4)_3$ was prepared by a simple solid state route. It was found that making a fine powder of $Li_3V_2(PO_4)_3$ by the mechanical milling is very effective for increasing the insertion/extraction of lithium from $Li_3V_2(PO_4)_3$ structure. In charge/discharge test, the ball-milled $Li_3V_2(PO_4)_3$ sample exhibited a higher initial discharge capacity of 174 mAh/g in the voltage range of 3.0-4.8 V, compared with pure $Li_3V_2(PO_4)_3$ sample (152 mAh/g). Furthermore, the ball-milled $Li_3V_2(PO_4)_3$ presented not only higher cycle retention rate after 50 cycles, but also better rate capability compared with pure sample in the whole region (0.1-7 C).