• Transactions of the Korean Society of Mechanical Engineers A
• /
• v.25 no.3
• /
• pp.399-407
• /
• 2001

The Surface, generated by end milling operation, is deteriorated by tool runout, vibration, friction, tool deflection, etc. Especially in cornering cut, surface accuracy is usually determined by varying cutting forces, which causes tool deflections. Cutting conditions like feed rate is usually kept constant during machining a part, which causes dimensional error in severe cutting. Cornering cut is a typical example of deterioration of surface accuracy when constant feed rate is applied. Therefore it becomes important to develop NC post processor module to determine optimal cutting conditions in various cutting situations. In this paper, cutting force is predicted in cornering cut with flat end mill and feed rate is determined by constraining constantly resultant force. Also some control characteristics of CNC machining center are evaluated.

• Journal of the Korean Society for Precision Engineering
• /
• v.28 no.12
• /
• pp.1341-1346
• /
• 2011

Currently, many researches are carried out for laser assisted machining, which is one of the important fields in materials difficult to process. However, a prediction of heat source is difficult because of moving heat source. In this paper, a thermal analysis of laser assisted machining of plate by change of heat source size is performed, and preheating temperature by adjusting the feed rate is controlled. It was recognized that the maximum preheating temperature increases according to the decrease in heat source size, and feed rate need to adjust as high speed. The results of this analysis can be used as a reference for preheating temperature prediction in laser assisted milling.

• Journal of the Korean Society of Food Science and Nutrition
• /
• v.33 no.1
• /
• pp.152-157
• /
• 2004

Physicochemical characteristics of rice milled by newly designed abrasive milling machine were studied. Crude protein and crude lipid contents were 7.81∼8.50% and 1.07∼0.95%, respectively, and they showed a tendency to decrease with milling times. However, they showed higher values than that of polished rice. Major fatty acids of crude lipid were palmitic acid, oleic acid, and linoleic acid. Whiteness of tested samples was higher than brown rice but lower than polished rice. The remain rate of rice germ of four pass-through and polished one time sample (FPS) was 39.33%, and it was higher than that of polished rice (4.00%). One thousand grain weight of samples over than three pass-through was significantly different from brown rice (p<0.05). FPS had smooth surface similar to polished rice and it showed some residual rice germ by scanning electron microscopy. Sensory evaluation showed that the taste of three pass-through rice, four pass-through rice, and FPS was not significantly different from polished rice, whereas their color, odor, texture, and overall acceptability had lower score than polished rice but higher than brown rice. Therefore, we estimate that rice ground over three pass-through by newly designed abrasive milling machine might be a good source having nutritive value.

• Journal of Powder Materials
• /
• v.16 no.5
• /
• pp.363-369
• /
• 2009

The amorphization process and the thermal properties of amorphous Ti$_{40}$Cu$_{40}$Ni$_{10}$Al$_{10}$ powder during milling by mechanical alloying were examined by X-ray diffractometry (XRD), differential scanning calorimetry (DSC), and transmission electron microscopy (TEM). The chemical composition of the samples was examined by an energy dispersive X-ray spectrometry (EDX) facility attached to the scanning electron microscope (SEM). The as-milled powders showed a broad peak (2$\theta$ = 42.4$^{\circ}$) with crystalline size of about 5.0 nm in the XRD patterns. The entire milling process could be divided into three different stages: agglomeration (0 < t$_m$ $\leq$ 3 h), disintegration (3 h < t$_m$ $\leq$ 20 h), and homogenization (20 h < t$_m$ $\leq$ 40 h) (t$_m$: milling time). In the DSC experiment, the peak temperature T$_p$ and crystallization temperature T$_x$ were 466.9$^{\circ}C$ and 444.3$^{\circ}C$, respectively, and the values of T$_p$, and T$_x$ increased with a heating rate (HR). The activation energies of crystallization for the as-milled powder was 291.5 kJ/mol for T$_p$.

• Journal of Hydrogen and New Energy
• /
• v.28 no.2
• /
• pp.137-143
• /
• 2017

In the present study, Ni and $TaF_5$ were chosen as additives to enhance the hydriding and dehydriding rates of Mg. A sample with a composition of 80 wt% Mg + 14 wt% Ni + 6 wt% $TaF_5$ (named $80Mg+14Ni+6TaF_5$) was prepared by high-energy ball milling in hydrogen. Its hydriding and dehydriding properties were then examined. At the fourth cycle, the activated sample absorbed 3.88 wt% H for 2.5 min, 4.74 wt% H for 5 min, and 5.75 wt% H for 60 min at 593 K under 12 bar $H_2$. $80Mg+14Ni+6TaF_5$ had an effective hydrogen-storage capacity (the quantity of hydrogen absorbed for 60 min) of about 5.8 wt%. The sample desorbed 1.42 wt% H for 5 min, 3.42 wt% H for 15 min, and 5.09 wt% H for 60 min at 593 K under 1.0 bar $H_2$. Line scanning results by EDS for $80Mg+14Ni+6TaF_5$ before and after cycling showed that the peaks of Ta and F appeared at different positions, indicating that the $TaF_5$ in $80Mg+14Ni+6TaF_5$ was decomposed.

• Journal of Powder Materials
• /
• v.27 no.1
• /
• pp.52-57
• /
• 2020

In this study, we report the microstructure and characterization of Ta₂₀Nb₂₀V₂₀W₂₀Ti₂₀ high-entropy alloy powders and sintered samples. The effects of milling time on the microstructure and mechanical properties were investigated in detail. Microstructure and structural characterization were performed by scanning electron microscopy and X-ray diffraction. The mechanical properties of the sintered samples were analyzed through a compressive test at room temperature with a strain rate of 1 × 10^-4 s^-1. The microstructure of sintered Ta₂₀Nb₂₀V₂₀W₂₀Ti₂₀ high-entropy alloy is composed of a BCC phase and a TiO phase. A better combination of compressive strength and strain was achieved by using prealloyed Ta₂₀Nb₂₀V₂₀W₂₀Ti₂₀ powder with low oxygen content. The results suggest that the oxide formed during the sintering process affects the mechanical properties of Ta₂₀Nb₂₀V₂₀W₂₀Ti₂₀ high-entropy alloys, which are related to the interfacial stability between the BCC matrix and TiO phase.

• Journal of Biosystems Engineering
• /
• v.3 no.2
• /
• pp.88-99
• /
• 1978

In this study, rice harvesting systems suitable to Korean situations and the optimum timing of these systems were determined, respectively, based on experimentally determined factors such as filed yield and the milling quantity and quality measured at various levels of the grain moisture content at harvest. Rice varieties used for the experiment were the AKIBARE (Japonica-type) and the SUWEON 251 (high yielding TONGIL sister-line variety), The harvesting systems studied by the experimental work of this study were traditional system with both the wet material and dry-material threshing system by use of binder with both the dry-material and wet-material threshings, and system by use of combine. Grain samples were taken from final products of the paddy rice harvested from the experiment a fields for each system to measure the recovery rates of the milled rice. The results may be summarized as follows; 1. The milling recovery rate of the AKIBARE variety had highest value within the range of the grain moisture at harvest, showing from 21 to 26 percent. The head-rice recovery for the same variety was a little greater in the wet-material threshing than in the dry-material threshing , higher values of which , were 20 to 25 percent , seen within the range of grain moisture at harvest regardless of the harvesting systems tested. 2. The milling recovery of the SUWEON 251 , when tested for different harvesting systems and harvesting grain moisture, did not show a statistically significant different. In contrast , head-rice recovery for the systems operated by the wet-material threshing was much greater than that by the -material threshing. The difference of the recoveries between these systems range from 2.6 to 4.7 percent. 3. An assessment of the optimum period of -harvest timing for each of the harve\ulcornersting systems tested were made bJ.sed on (a) the maximum total milled-rise yield and (b) the percentage reduction in the total milled-rice yield due to untimely harvest operations. The optimum period determined are: 23-19% for the ATD, AC, STD, SBW, STW systems, 25-21% for the ATW ani ABW systems, and 27-18% for the ABD, SBD, and SC systems, respectively.

• Elastomers and Composites
• /
• v.53 no.3
• /
• pp.158-167
• /
• 2018

In this study, in-situ trans-selective polymerization of isoprene was carried out using titanium-based Ziegler-Natta catalysts. The catalysts were prepared by high-energy ball milling. Individually Large-inner-diameter carbon nanotubes (CNTL), and hydroxylated carbon nanotubes (CNTOH), along with magnesium chloride ($MgCl_2$) were used as the carriers for the catalysts. The optimum ball-milling time for preparing the $CNT/MgCl_2/TiCl_4$ Ziegler-Natta catalysts was 4 h. The $CNTOH/MgCl_2/TiCl_4$ catalyst showed a higher efficiency than that of the $CNTL/MgCl_2/TiCl_4$ catalyst, based on the rate of polymerization. The effects of the CNT-filler type on the isoprene polymerization behaviors and polymer properties were investigated. The morphologies of the trans-1,4-polyisoprene (TPI)/CNT and TPI/CNTOH nanocomposites exhibited a tube-like shape, and the CNTL and CNTOH fillers were well dispersed in the TPI matrix. In addition, the thermal stability of TPI significantly increased upon the introduction of a small amount of both CNTL/CNTOH fillers (0.15 wt%), owing to the satisfactory dispersion of the CNTL/CNTOH in the TPI matrix.

• Design & Manufacturing
• /
• v.11 no.3
• /
• pp.19-24
• /
• 2017

In these days, increase requirement of TEM (Transmission Electro Microscope) in not only scientific field but also industrial field. Because TEM can measure inner-structure of specimen a variety of materials like metal, bio. etc. When use TEM, specimen should be thin about 50nm. So making for thin specimen, use Ion milling device that include specimen holder. The holder generally made of Aluminium Aluminium holder is worn away easily. For this reason, using time of ion milling with aluminum holder is too short. To solve the problem, we replace aluminium holer to molybdenum alloy holder. In this paper, we design molybdenum alloy holer for CAM and modify CAD modeling for effective machining process. So we array a specimen 3 by 4 and setup orientation for one-shot machining process. Next we make a CAM program for machining. we making a decision two machining strategy that chose condition of tool-path method, step-down, step-over. etc. And then conduct machining using CNC milling machining center. To make clear difference between case.1 and case.2, we fixed machining conditions like feed-rate, main spindle rpm, etc. After machining, we confirm the condition of workpiece and analysis the problems case by case. Finally, case.2 work piece that superior than case.1 cutting with WEDM because that method can not ant mechanical effect on workpiece.

• Transactions of the Korean Society of Mechanical Engineers A
• /
• v.37 no.1
• /
• pp.67-75
• /
• 2013

The flow stress of zircaloy-4 used in the spacer grid supporting a nuclear fuel rod was determined by the Johnson-Cook model, and model parameters were determined using reverse engineering. Parameters such as A, B, n and $\dot{\varepsilon}_0$ were determined by the tensile test result. To obtain the parameters C and m, a slot milling test and numerical simulation were performed. The objective functions were defined as the difference between the experimental and the simulation results, and then, the parameters were determined by minimizing the objective function. To verify the validity of the determined parameters, cross-verification for each case was conducted through a shearing test and simulation. The results tend to show agreement with the experimental results, such as the features of sheared edges and maximum punch force, with the correlation coefficients exceeding at least 0.97.