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Yeong-Kwan Jo,유재현,Ki Yong Lee,Do Sik Shim,박상후 대한기계학회 2020 JOURNAL OF MECHANICAL SCIENCE AND TECHNOLOGY Vol.34 No.11
A practical method is proposed to control the direction of crack propagation and to generate a crack-growth-proof (CGP) zone on a metal plate using laser induced line patterns: heat treatment and cladding. To evaluate the effect on crack propagation by the line patterns, we fabricated and tested diverse line-pattern shapes on a thin SUS316 plate of 1 mm thickness, such as single vertical line; one, three, and five horizontal lines; one and three 45º-tilted lines; X-shaped lines; and rectangular box lines by both laser heat treatment and cladding process. For description of metallurgical change via the pattern and its effect on the crack growth, we did a microstructural analysis of the treated SUS316 specimen. For example, ultimate tensile stress (σ u ) and fracture strain changed according to the pattern shapes. A specimen treatiing a rectangular line pattern of 4×20 mm showed an increase of σ u to about 8.8 %, and fracture strain also increased by 10 % compared to that of a SUS316 plate. Through this work, we verified that the CGP zone could be controlled on a thin metal plate using the proposed method for protection of highly valuable mechanical parts mounted on it.
Yeong-Kwan Jo,Yeong-Wook Gil,Do Sik Shim,Young-Sik Pyun,박상후 한국정밀공학회 2021 International Journal of Precision Engineering and Vol.8 No.2
We propose an effective method to control the local hardness and morphology of a metal surface by tilting the incident angle of a horn during ultrasonic nanocrystal surface modification (UNSM). In this study, surface treatment using UNSM was performed on an S45C specimen and a parameter study was conducted for optimization. The process parameters were the feeding rate, static load, striking force, and processing angle ( Ф ). In particular, the Ф was analyzed by tilting the horn by 0°, 10°, 20°, 30°, 40°, and 45° to understand its effect on surface hardness and changes in the morphology. From fundamental experiments, some important phenomena were observed, such as grain-microstructure changes along the processing and thickness directions. Furthermore, to verify the practical usefulness of this study, a flat and a hemispherical specimen of S45C material were treated using UNSM with various values of Ф . A significant change in hardness (an increase from 2–45%) and a gradual hardness gradient on the tested specimens could be easily realized by the proposed method. Therefore, we believe that the method is effective for controlling the mechanical hardness of a metal surface.
레이저 기반 표면 열처리 및 클래딩을 이용한 SUS 316 판재 성형성 향상
조영관(Yeong-Kwan Jo),유재현(Jae-Hyun Yu),정호승(Ho-Seung Jeong),박상후(Sang-Hu Park) 한국기계가공학회 2020 한국기계가공학회지 Vol.19 No.2
We propose a practical method for increasing formability of a sheet metal plate using laser heat treatment (LHT) and cladding process. In this work, two kinds of process such as laser-induced heat treatment and cladding were utilized to evaluate the effect on formability of SUS316 sheets with different thickness of 1 and 3 mm. By using a vertically line-patterned tensile specimen that was LHTed or cladded on its surface, the process parameters of each surface treating method were studied and optimized. Through the basic test, we knew that the laser power of 900 W and scanning speed of 500 mm/min was the best condition for increase of formability. As the treatment results, ultimate tensile strength and elongation were increased as approximately 2.1 and 7.0%, respectively. To verify the usefulness of this work in industrial cases, we conducted a bulging test using with and without LHTed SUS316 sheet metal blanks. The results show that the bulging height of LHTed sheet was increased by 73% compared to that of the original one.
고온마모 특성 향상을 위한 클레딩 및 초음파나노표면개질 기술 개발
조영관(Yeong-Kwan Jo),최광덕(Kwang-Deok Choi),신동식(Dong-Sig Shin),서정(Jeong Suh),박상후(Sang-Hu Park) 대한용접·접합학회 2021 대한용접학회 특별강연 및 학술발표대회 개요집 Vol.2021 No.11
적층제조(Additive manufacturing, AM) 기반의 클레딩(Cladding) 기술은 일반적인 제조 공정들에 비해 다품종 소량 생산에 유리한 장점을 가진다. 또한 최근의 연구 방향은 적층 속도, 정밀도 향상, 대면적 적층 등을 구현하는데 집중되고 있다. 그리고 강도나 내마모성 등의 기계적 특성을 향상시키거나 다양한 소재에 대한 적층이 가능하도록 공정 개발을 진행하고 있다. 이를 통하여 그 응용분야가 지속적으로 확대 되어, 전기·전자, 건축, 자동차 및 항공·우주 산업 등에 광범위하게 활용되고 있다. 본 발표에서는 고온 내부식 및 내 산화성이 좋은 Inconel 718 소재의 고온 마모 특성을 개선하기 위한 클레딩 공정과 표면처리 공정을 소개하고자 한다. 분말을 이용한 DED 공정으로 1차적으로 적층을 한 뒤 표면에 Ultrasonic Nano-crystal Surface Modification(UNSM) 공정을 적용하여 표면의 내마모성을 향상시킨다. 표면의 경도는 약 23%의 향상을 나타내었고, 그리고 내마모성은 기존 대비 약 18%의 향상을 나타낸다.
조지민(Jo, Ji-Min),최민석(Choi, Min-Seok),한영규(Han, Young-Gyu),김영관(Kim, Yeong-Kwan) 강원대학교 산업기술연구소 2016 産業技術硏究 Vol.36 No.1
In this study, a series of experiment was carried to improve dewaterability of the sludge produced in a treatment plant, located in Hongcheon, Gangwondo, which has been treating municipal wastewater and livestock wastewater. Optimum sludge mixing ratio and the amount of sludge conditioner were determined. As sludge conditioners, alum and ferric salt were selected and tested. For the measurement of sludge dewaterability, capillary suction time(CST) and the specific resistance were measured, The specific resistance was detemined by running a series of Buchner Funnel Test. Mixing the two sludges at a 50:50 ratio with the addition of 20 mL alum gave the best results in terms of dewaterability. The moisture content decreased by 2% at this condition.