Ni-Co 합금강의 기계적 특성에 대한 탄소함량의 영향

최병기(Byung-Ky Choi),장경천(Kyeung-Cheun Jang),최병희(Byung-Hui Choi),이기안(Kee-Ahn Lee) 한국생산제조학회 2006 한국생산제조학회지 Vol.15 No.5

This study was to evaluate the effect of carbon content on metallic change and fatigue characteristics with Fe-29%Ni-17%Co, low heat expansion alloy, widely using electronic components, precision machines, and sealing with glass and metal etc. The steels were fabricated with variation of carbon content, 0, 0.03, 0.06, 0.1, and 0.20% with VIM and tensile test and fatigue test were performed to achieve the above purpose. The more carbon content, the higher hardness value and yield strength. But elongation of 0.03%C, 0.06%C, and 0.10%C specimen decreased about 2.2%, 1.5% and 0.8% respectively more than that of the base metal. Especially the strength and elongation of 0.20%C specimen increased simultaneously about 14.4% and 7.5%. Fatigue life of 0.03%C specimen decreased but the more carbon content, the higher fatigue life over 0.06% carbon content more than that of base metal.

Ti 鎔接材의 機械的 特性 및 疲勞크랙 進展擧動에 關한 硏究

최병기(Byung-Ki Choi),장경천(Kyeung-Cheun Jang) 한국생산제조학회 2002 한국공작기계학회 춘계학술대회논문집 Vol.2002 No.4

Multi-Color Chip-LED용 어레이 렌즈 개발에 관한 연구

최병기(Byung-Ky Choi),장경천(Kyeung-cheun Jang),이동길(Dong-Gil Lee) 한국생산제조학회 2007 한국생산제조학회지 Vol.16 No.3

The purpose of this research is to enhance the luminance of the LED and to improve the implementation of color by mounting an array lens on the LED without special technology in process. The workmanship of key components considering the economical efficiency and the injection molding technology for high quality of the product are essential to achieve it. In this paper, the mold was computer-aided was designed and manufactured by CAM software(NX4) and high speed machining center. the applied final machining conditions were 3,000-5,000㎜/min feed speed, 15,000-25,000rpm and Φ0.3㎜ ball end-mill. And the Flow analysis was performed using the mold flow software(MPI) in order to get uniformity of resin. Injection conditions acquired by the flow analysis and the injection experiment are as follows. The cylinder temperature is 220-260℃, the mold temperature is 70-80℃, the injection time is about 1.2sec, the injection pressure and velocity is each 7.8-14.7㎫, and the injection velocity is 0.8-1.2m/sec.

GMA용접에서 유전자 알고리즘을 이용한 비드높이 예측 모델 개발에 관한 연구

손준식(Joon-Sik Son),김일수(Ill-Soo Kim),장경천(Kyeung-Cheun Jang),이동길(Dong-Gil Lee) 한국생산제조학회 2006 한국공작기계학회 춘계학술대회논문집 Vol.2006 No.-

Gas metal arc welding process has been chosen as a metal joining technique due to the wide range of usable applications, cheap consumables and easy handling. Three main indicators such as arc voltage, welding speed and welding current have a big influence in the quality welding. Since all these factors affect the quality of the welded joining parts, the effect of these parameters was investigated experimentally. In this paper, an attempt has been made to develop the predicted models (quadratic and cubic) for bead height using genetic algorithm. Performance of the developed models were proved to be compared to the regression equation.

임펠러 5축 가공시 가공성 평가

이기용(Ki-Yong Lee),박순섭(Sun-Sub Park),장경천(Kyeung-Cheun Jang),이호재(Ho-Jea Lee) 한국기계가공학회 2006 한국기계가공학회 춘추계학술대회 논문집 Vol.2006 No.-

Recently, according as request for parts of complex shape is increased, 5-axis machining has been studied actively. A impeller is a important part that is used at turbo engines of airplane and automobile, compressors, etc and it is representative part that 5-axis machining is necessary. In this research, to product a impeller using 5-axis cutting method, 5-axis machining center was evaluated in terms of its dynamic characteristics and thus cutting conditions were optimized. Also, in 5-axis cutting, cutting force signals were measured and analyzed. Finally cutting properties were invested to find optimum tool path for 5-axis cutting of an impeller.

등온선 반경을 통한 비드폭 예측에 관한 연구

손준식(Joon-Sik Son),전광석(Kwang-Suk Chon),김일수(Ill-Soo Kim),서주환(Joo-Hwan Seo),장경천(Kyeung-Cheun Jang) 한국생산제조학회 2005 한국공작기계학회 추계학술대회논문집 Vol.2005 No.-

The robotic CO₂ welding is widely employed in the fabrication industry for increasing productivity and enhancing product quality by its high processing speed, accuracy and repeatability. Reprogramming techniques have proved to be inadequate in taking into consideration of the component distortion due to heat imperfections during the welding process. Basically, the bead geometry plays an important role in determining the mechanical properties of the weld. So that it is very important to select the process variables for obtaining optimal bead geometry. However, it is difficult for the traditional identification methods to provide an accurate model because the optimized welding process is non-linear and time-dependent. In this paper, the possibilities of the Infrared camera in sensing and control of the bead geometry in the automated welding process are presented. Bead width and isotherm radii can be expressed in terms of process parameters using mathematical equations obtained by empirical analysis using infrared camera.

Ti 鎔接材의 機械的 特性 및 疲勞크랙 進展擧動에 關한 硏究

최병기,장경천,정장만 朝鮮大學校 機械技術硏究所 2001 機械技術硏究 Vol.4 No.2

Ti 용접재 시험편을 통하여 용접조건에 따른 기계적 성질 및 피로크랙 진전거동을 각각 비교·검토한 결과 다음과 같은 결론을 얻을 수 있었다. 동일한 용접조건에서 패스 수에 따라 4패스는 7패스와 비교하였을 경우 인장강도가 10%정도 높게 나타났고, 연신율은 30%종도 감소함을 알 수 있었다. 또한 실딩가스량이 많고, 용접 후 자연냉각 시간간격이 길수록 인장강도는 높게 나타났고, 연신율은 감소하였다. 충격 흡수에너지값은 4패스는 7패스에 비해 50%정도 감소하였으나, 실딩가스량이 많을수록 높게 나타났다. 또한 경도값은 패스 수가 적을수록 높게 나타났으며, 용접 후 자연냉각 시간간격에는 비슷하였으나 용접 후 자연냉각 시간간격이 적은 것은 조금 감소하였다. 초기크랙 진전속도는 Bond부, 용착부, HAZ, 온도영향부 순으로 느리게 나타났으나, 피로수명은 Bond부, HAZ부, 용착부, 온도영향부 순으로 높게 나타났다. The purpose of this thesis was to investigate the welding characteristics and the fatigue crack propagation behavior of titanium commonly using power station, aircraft and ship. The experimented material was TIG welded in order to look over the characteristics according to the notch position and compare with other materials. We compared and reviewed the fatigue crack propagation behavior of nonwelded base metal and welded specimens having different notch position to evaluate the fatigue crack propagation behavior by welding condition. The tensile strength and elongation of the 4 pass welded specimens was shown about 10% and 30% higher than those of the 7 pass welded specimens at the same welding conditions. Also, the more shield gas and the lower natural cooling time, the higher tensile strength but the lower elongation. The absorption energy of the 4 pass welded specimens, was decreased about 50% more than that of the 7 pass welded specimens, and the more shield gas, the higher impact absorption energy value. The higher hardness, the lower pass, but the natural cooling time almost had no relation to the hardness. The fatigue life was shown higher as following the order, boundary zone > HAZ > welding zone > base metal. Especially the fatigue life of boundary zone notched specimen was shown 700% higher than that of base metal.

SB41용접재의 피로크랙 진전거동에 관한 연구

최병기,장경천 한국공작기계학회 2002 한국생산제조학회지 Vol.11 No.2

SB41 material is welded automatically and is investigated some effects of the welding residual stress in the growth and propagation of fatigue crack, so as to study the fatigue behaviour in the welding residual stress field. The summarized results are as follows; 1) In case of the load amplitude is constant, as the stress ration is changing to 0.1, 0.33 and 0.5 the propagation life is constant but the growth life decreases. And than, when maximum load or minimum load is constant, as the stress ration increases the growth life and propagation life. 2) It was shown that the fatigue crack propagation ratio da/dN was almost constant regardless of the stress ration change at constant load amplitude and that the larger stress ratio, the slower was the fatigue crack propagation ratio. 3) The opening ratio U is influenced by K_max but it isn't only the function of K_max because data range is very large. 4) The fatigue life of the specimens on tensile compressive residual stress field was decreased and increased respectably more than that of the base metal.

18Ni 마르에이징강의 피로특성 및 유한요소해석

최병기,장경천 한국공작기계학회 2005 한국생산제조학회지 Vol.14 No.2

Recently the needs of high reliable substances of high strength and high ductility are gradually increased with the develoment of aerospace industry. The characteristics of maraging steel has high ductililty, formability, corrosion resistant and high temperature strength, and is easy to fabricate, weld and treat with heat, and maintain an invariable size even after heat treatment. The steels are furnished in the solution annealed condition and they achieve full properties through martensitic precipitation aging a relatively simple, low temperature heat treatment. As is true of the heat treating procedures, aging is a time/temperature dependent reaction. Therefore, the objective of this study was consideration of fatigue characteristics according as Nb(niobium) content and time/temperature of heat treatment change. Also the stress analysis, fatigue life, and stress intensity factor were compared with experiment results and FEA(finite element analysis) result. The maximum stresses of X, Y, and Z axis direction showed about 2.12×10²MPa, 4.40×10²MPa and 1.32×10²MPa respectively. The fatigue lives showed about 7% lower FEA result than experiment result showing almost invariable error every analyzed cycle. Stress intensity factor of the FEA result was lower about 3.5.10% than that of the experiment result showing that the longer fatigue crack length, the higher error. It considered that the cause for the difference was the modeled crack tip having always the same shape and condition regardless of the crack growth.

Ti 鎔接材의 機械的 特性 및 殘留應力의 分布에 關한 硏究

최병기,장경천,국중민,정장만,구남열 한국산업안전학회 2003 한국안전학회지 Vol.18 No.1

The objective of this paper was to investigate the welding characteristics according to the restraint condition, the pass number, and the shield gas quantity with titanium commonly using in power stations, aircrafts, ships, and so forth. The residual stress distribution was measured under restraint and nonrestraint welding conditions. The tensile strength and elongation of the 4 pass welded specimen were shown higher about 10% and 30% than those of the 7 pass welded specimen at the same welding conditions respectably. Also, the more shield gas quantity and the shorter natural cooling time, the higher tensile strength and the lower elongation.