• 열처리공학회지
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• 제22권6호
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• pp.339-344
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• 2009

Recently, Laser surface treatment technologies have been used to improve wear charactenitics and fatigue resistance of metal molding. When the laser beam is irradiated on the surface and laser speed is appropriate, the laser focal position is rapidly heated and the thermal energy of surface penetrates the material after irradiation, finally imbuing it with a new mechanical characteristic by the process of self-quenching. This research estimates the material characteristic after efficient and functional surface treatment using HPDL, which is more efficient than the existing CW Nd:YAG laser heat source. To estimate this, microstructural changes and hardness characteristics of three parts (the surface treatment part, heat affect zone, and parental material) are observed with the change of laser beam speed and surface temperature. Moreover, the depth of the hardened area is observed with the change of the laser beam speed and temperature. From the results of the experiments, it has been shown that the maximum hardness is approximately 788Hv when the heat treatment temperature and the travel speed are $1150^{\circ}$ and 2 mm/sec, respectively.

• 한국재료학회지
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• 제14권11호
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• pp.795-801
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• 2004

The injection molded Fe sintered bodies were fabricated using two kinds of Fe powders haying 50 nm and $3\sim5{\mu}m$ in diameter. In the using of Fe powder having 50 nm in diameter, the comparatively dense bodies ($94\sim97\%$) were obtained even at low sintering temperature ($600\sim700^{\circ}C$), while in the sintered bodies ($1000^{\circ}C$) using $3\sim5{\mu}m$ Fe powder, their relative densities showed low values about $93\%$, although they were strongly depend on the sintering temperature and volume ratio of Fe powder and binder. In the sintered bodies using of 50 nm Fe powders, the volume shrinkage and grain size increased as the sintering temperature increased, but the values of hardness decreased. In the sample sintered at $650^{\circ}C$, the values of relative density, volume shrinkage and grain size were $96\%,\;37\%\;and\;0.97{\mu}n$, respectively and the minimum value of wear depth was obtained due to combination of fine grain and comparatively high density.

• 한국정밀공학회:학술대회논문집
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• 한국정밀공학회 2005년도 춘계학술대회 논문집
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• pp.199-202
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• 2005

High speed milling process is emerging as an important fabrication process benefits include the ability to fabricate micro and meso-scale parts out of a greater range of materials and with more varied geometry. It also enables the creation of micro and meso-scale molds for injection molding. Factors affecting surface roughness have not been studied in depth for this process. A series of experiments has been conducted in order to begin to characterize the factors affecting surface roughness and determine the range of attainable surface roughness values for the high speed milling process. It has previously been shown that run-out creates a greater problem for the dimensional accuracy of parts created by high speed milling process. And run-out also has a more significant effect on the surface quality of milled parts. The surface roughness traces reveal large peak to valley variations. This run-out is generated by spindle dynamics and tool geometry. In order to investigate the relationship between tool setting errors and surface roughness end tilted mills were used to cut aluminum samples. The results indicate that tool setting errors have significant effects on surface roughness and cutting forces.

• 한국정밀공학회:학술대회논문집
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• 한국정밀공학회 2006년도 춘계학술대회 논문집
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• pp.627-628
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• 2006

High speed milling process is emerging as an important fabrication process benefits include the ability to fabricate micro and meso-scale parts out of a greater range of materials and with more varied geometry. It also enables the creation of micro and meso-scale molds for injection molding. Factors affecting surface roughness have not been studied in depth for this process. A series of experiments has been conducted in order to begin to characterize the factors affecting surface roughness and determine the range of attainable surface roughness values for the high speed milling process. It has previously been shown that run-out creates a greater problem for the dimensional accuracy of pans created by high speed milling process. And run-out also has a more significant effect on the surface quality of milled parts. The surface roughness traces reveal large peak to valley variations. This run-out is generated by spindle dynamics and tool geometry. In order to investigate the relationship between tool alignment errors and surface roughness the scallop generating mechanism in the ball-end milling with tool alignement errors has been studied and simulated. The results indicate that tool alignment errors have no significant effects ell the dimension of scallops in for flat planes.

• Design & Manufacturing
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• 제16권4호
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• pp.17-23
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• 2022

Recently, several studies are being conducted to achieve a curvature of 180° or more for the edge of the display glass. The thermocompression molding process is applied to the manufacture of curved glass, and high hardness G5 graphite is used as the mold material to withstand the impact applied to the mold. G5 graphite has high hardness and strong brittleness, which makes tool wear and surface damage easy during machining. Therefore, the demand for diamond-coated tools with good mechanical properties is increasing in the G5 machining field. In this study, the optimal cutting conditions and machinability of a nanodiamond (NCD) coated ball end mill being developed by a tool manufacturer were analyzed and evaluated. For this purpose, the same test was performed on the microdiamond (MCD) coated ball end mill and compared together. In summary, the machinability of MCD and NCD coated tools showed better cutting performance at a cutting speed of 282 m/min, a feed rate of 1,400 mm/min, and a radial depth of cut of 0.08 to 0.1 mm.

• 대한공업교육학회지
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• 제31권2호
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• pp.350-363
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• 2006

최근 마이크로 엔드밀을 이용한 가공은 소형구조물이나 소형기계의 부품과 금형산업에서 양호한 표면 거칠기와 가공시간의 단축을 위해 고정도의 기술을 요구하고 있다. 마이크로 엔드밀을 이용한 가공에 있어서 가공조건은 절삭면의 표면거칠기에 커다란 영향을 미치게 된다. 따라서 본 연구에서는 마이크로 엔드밀을 이용하여 스테인리스 강(STS 304)의 표면을 가공하였고, 실험계획법에 의해 최적의 표면거칠기를 얻기 위한 가공조건에 대해 분산분석하였다. 본 연구를 통하여 마이크로 엔드밀에 의한 가공에서 가공조건은 절삭깊이, 스핀들의 회전수, 이송속도의 순서로 표면거칠기에 영향을 미치는 것을 알았다.

• 한국광학회지
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• 제11권2호
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• pp.73-79
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• 2000

사출성형법으로 제조된 $fheta$렌즈를 주사렌즈로 상요하는 Laser Scanning Unit의 주주사 및 부주사 방향의 빔경을 측정했다. 주주사 빔경의 경우 $62muextrm{m}$~ $68\mu\textrm{m}$로써 설계치와 유사한 성능을 보이지만 부주사 빔경의 경우 $78\mu\textrm{m}$~$115\mu\textrm{m}$로써 꽤 큰 빔경편차( $37\mu\textrm{m}$)를 나타내었다. 사출성형렌즈에서는 냉각.고화시 수축에 의한 형상오차와 불균일 냉각에 의한 내부왜곡(복굴절)이 발생하게 되는데, 이는 결국 파면수차(빔경확대)를 발생시키게 되고 결국 레이저프린터의 화상열화로 나타나게 된다. 본 논문에서는 부주사 빔경편차의 주요인을 밝혀내기 위해 복굴절(편광비) 및 $f\theta$렌즈의 비구면 형상을 측정하였다. 그리고 측정된 비구면 형상치를 CODE-V(미국 ORA사의 광학설계 프로그램)에 입력하여 부주사 상면만곡을 계산하고, 이와 설계 초점심도를 비교.분석함으로써 복굴절이 부주사 빔경편차의 주요인임을 알 수 있었다.

• 한국잡초학회지
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• 제12권1호
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• pp.8-15
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• 1992

방제(防除)하기 어렵고 우고화(優古化)가 원저(願著)하여 논 다년생(多年生) 잡초중(雜草中) 문제잡초(問題雜草)의 하나인 벗풀에 대하여 몇가지 환경변동(環境變動)에 따른 벗풀 지하경(地下莖)의 출아특성(出芽特性)을 구명(究明)하여 합리적(合理的)이고 효과적(效果的)인 방제체계(防除體系)의 확립(確立)을 위한 기초자료(基礎資料)를 제공(提供)하고자 일련(一聯)의 시험(試驗)을 수행(遂行)한 결과(結果)는 다음과 같다. l. 온도(溫度)의 차이(差異)에 따른 벗풀 지하경(地下莖)의 출아시험(出芽試驗) 결과(結果) 출아(出芽)는 본(本) 공시온도중(供試溫度中) 15-40$^{\circ}C$ 범위(範圍)에서 가능(可能)하였고, 출아온도(出芽溫度)은 25-35$^{\circ}C$로 판단(判斷)되었다. 15 및 20$^{\circ}C$에서 출아(出芽)는 각각(各各) 치상후(置床後) 56일(日) 및 12 일(日)만에 개시(開始)되었고, 치상(置床)한 지하경(地下莖) 모두의 출아소요일수(出芽所要日數)는 출아적온범위(出芽適溫範圍)에서 보다 길었다. 2. 야외(野外) 한냉사(寒冷絲) 처리(處理)에 의한 지하경(地下莖)의 출아소요일수(出芽所要日數)에 끼치는 차광(遮光)(광량(光量) 반응(反應)은 25-50% 차광(遮光)에서 짧았고 70%, 80% 및 노지(露地) (무차광(無遮光)에서는 큰 차이(差異)없이 걸었다. 3. 광질(光質)의 차이(差異)에 따른 벗풀 지하경(地下莖)의 출아(出芽)는 녹색(綠色), 적색(赤色) 및 황색광하(黃色光下)에서 치상(置床)한 지하경중(地下莖中) 일부(一部)가 출아(出芽)하지 못하고 사멸(死滅)되었다. 4. 토양산도(土壤酸度)의 차이(差異)에 따른 벗풀 지하경(地下莖)의 출아(出芽) 소요일수(所要日數)는 pH 6.0과 7.0에서 짧았고, pH 4.0, 5.0 및 8.0에서는 길었으며 일부(一部)는 출아(出芽)하지 못하고 사멸(死滅)되었다. 5. 벗풀 지하경(地下莖) 중량(重量)의 차이(差異)에 따른 출아소요일수(出芽所要日數)는 0.5 g 이상(以上)의 지하경(地下莖)이 0.5 g 미만(未滿)의 지하경(地下莖)보다 짧았다. 6. 담수심(湛水深)의 차이(差異)에 따른 지하경(地下莖)의 출아(出芽)를 보면 시험(試驗)한 0-20 cm 담수심(湛水深)에서 출아(出芽)되었다. 3 cm 및 5 cm 담수심(湛水深)에서 출아소요일수(出芽所要日數)가 짧은 것으로 나타났다 7. 재식심도(裁植深度)의 차이(差異)에 따른 지하경(地下莖)의 출아(出芽)를 보면 재식심도(裁植深度)가 얕을 수록 빠르고 출아소요일수(出芽所要日數)도 짧았다. 10 cm 재식심도(裁植深度)에서는 재식(裁植)한 9개체중(個體中) 1개체(個體)만 출아(出芽)되었고 그 이상(以上)의 깊은 재식심도(裁植深度)에서는 출아(出芽)되지 않았다.

• 소성∙가공
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• 제31권3호
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• pp.129-135
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• 2022

The purpose of this study was to quantitatively evaluate the influence of hardness of tool materials on wear resistance in the sheet metal forming process. Punches used in the wear test were made of STD-11 and K340 tool material, and the tempering temperature was set to 530℃ and 500℃, respectively, to control the hardness of the tool materials. The punches mimic the shape of stamping tool of automotive body component to reflect its plastic deformation, and are designed to concentrate wear on the curvature region of punches. Progressive die and coil sheet were used to save time, cost, and raw sheet materials. By quantitatively measuring the wear depth of the punches, the wear behavior and mechanism of the punches were investigated, and characteristics of hardness and wear resistance according to tool materials and tempering temperatures were evaluated. Testing results indicate that the punch made of K340 tool steel with higher hardness had better wear resistance than that of STD-11 tool steel, and the hardness and wear resistance of tool steel were significantly impacted by the tempering temperature.

• 한국재료학회지
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• 제19권9호
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• pp.457-461
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• 2009

Recently, metal molding has become essential not only for automobile parts, but also mass production, and has greatly influenced production costs as well as the quality of products. Its surface has been treated by carburizing, nitriding and induction hardening, but these existing treatments cause considerable deformation and increase the expense of postprocessing after treatment; furthermore, these treatments cannot be easily applied to parts that requiring the hardening of only a certain section. This is because the treatment cannot heat the material homogeneously, nor can it heat all of it. Laser surface treatment was developed to overcome these disadvantages, and, when the laser beam is irradiated on the surface and laser speed is appropriate, the laser focal position is rapidly heated and the thermal energy of surface penetrates the material after irradiation, finally imbuing it with a new mechanical characteristic by the process of self-quenching. This research estimates the material characteristic after efficient and functional surface treatment using HPDL, which is more efficient than the existing CW Nd:YAG laser heat source. To estimate this, microstructural changes and hardness characteristics of three parts (the surface treatment part, heat affect zone, and parental material) are observed with the change of laser beam speed and surface temperature. Moreover, the depth of the hardened area is observed with the change of the laser beam speed and temperature.