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황현태,소상우,김종도,Hwang, Hyun-Tae,So, Sang-Woo,Kim, Jong-Do 한국재료학회 2011 한국재료학회지 Vol.21 No.7
Currently, there are two main issues regarding the development of core technologies in the automotive industry: the development of environmentally friendly vehicles and securing a high level of safety in the event of an accident. As part of the efforts to address these issues, research into alternative materials and new car body manufacturing and assembly technologies is necessary, and this has been carried out mainly by the automotive industries. Large press molds for producing car body parts are made of cast iron. With the increase of automobile production and various changes of design, the press forming process of car body parts has become more difficult. In the case of large press molds, high hardness and abrasive resistance are needed. To overcome these problems, we attempted to develop a combined heat treatment process consisting of local laser heat treatment followed by plasma nitriding, and evaluated the characteristics of the proposed heat treatment method. From the results of the experiments, it has been shown that the maximum surface hardness is 864 Hv by the laser heat treatment, 953 Hv by the plasma nitriding, and 1,094 Hv by the combined heat treatment. It is anticipated that the suggested combined heat treatment can be used to evaluate the durability of press mold.
High Power Diode Laser을 이용한 금형재료용 구상화 주철의 모서리부 표면처리
황현태,송현수,김종도,송무근,김영국,Hwang, Hyun-Tae,Song, Hyeon-Soo,Kim, Jung-Do,Song, Moo-Keun,Kim, Young-Kuk 한국재료학회 2009 한국재료학회지 Vol.19 No.9
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.
황현태 ( Hyun Tae Hwang ),소상우 ( Sang Woo So ),김종도 ( Jong Do Kim ) 한국열처리공학회 2011 熱處理工學會誌 Vol.24 No.4
Recently, from general machine parts and automobile parts using carbon steel to a mold, there has been efforts for improving durability and attrition resistance of these parts. Especially, heat treatment with laser which works fast and automatically can be used for the mass production with high quality. Moreover, local heat treatment can be used to handle with complex and precise parts. Accordingly, we analyzed hardening characteristics of carbon steel using the finite element method and compare the experimental results to have more reliability. We also proved the cause of thermal deformation with temperature and stress distribution by heat treatment. After these analysis and experimental, we found that each maximum hardness of the two tests was 728Hv and 700Hv, on condition of 1050℃ heating temperature, and 2mm/sec laser speed. We also found that difference of surface stress-distribution was occurred, and this makes deformation mode up after heat treatment.
고출력 다이오드 레이저를 이용한 프레스 전단금형의 경화특성
황현태 ( Hyun Tae Hwang ),소상우 ( Sang Woo So ),황재현 ( Jae Hyun Hwang ),김종도 ( Jong Do Kim ) 한국열처리공학회 2010 熱處理工學會誌 Vol.23 No.5
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.
과황산칼륨 (K2S2O8) 에 의한 비닐모노머의 중합반응에 관한 연구
황현태(Hyun Tae Hwang),정평진(Pyung Jin Chung) 한국화상학회 1995 한국화상학회지 Vol.1 No.1
This study concerns the homopolymerization and copolymerization of vinyl monomers (vinyl acetate, acrylonitrile, methyl acrylate, methyl methacrylate) by radical initiator potassium persulfate(K_2S_2O_2). In the comparison of reaction time there was no further reaction after one hour for homopolymerization. And neither did the adding initiator to monomer or vice versa nor did the change of the amount of initiator affect the reaction process. In case of copolymerization, the reactivities reduced in the usual order methyl methacrylate, methyl acrylate, acrylonitrile, vinyl acetate.