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경계밀착좌표계를 이용한 ROD형 분무성형체의 열전달해석
이호인,윤종규,나형용,오규환,석현광,오동훈 대한금속재료학회(대한금속학회) 1998 대한금속·재료학회지 Vol.36 No.5
A coupled analysis of rod growth model using vector calculus and heat transfer model using boundary fitted coordinate has been formulated. Temperature profile in a spray formed rod of 2024 aluminum has been calculated by the proposed model. At initial stage of spray forming. the temperature of substrate and preform increases rapidly. And then temperature of the vertex point is kept as about 525℃ During the cooling stage after the spray farming steps, temperature of all points inside rod decrease and the cooling rate of surface is higher than that inside the rod.
이호인,나형용,오규환,석현광 대한금속재료학회(대한금속학회) 1997 대한금속·재료학회지 Vol.35 No.6
The effect of initial eccentric distance, substrate withdrawal velocity, spray angle and substrate shape on steady state behavior was studied, using 3 dimensional model of spray forming of rod by computer simulation. The mechanism to reach steady state at various conditions was analyzed through the growth velocity at vertex of rod, G_v. Above a critical eccentric distance, G_v, increased from the beginning of forming and reached steady state. Below a critical eccentric distance, G_v, decreased and reached steady state. Below a certain critical withdrawal velocity, the growth velocity of vertex reached steady state. .Above the critical value of withdrawal velocity, G_v, increased to critical value and decreased to zero growth velocity of vertex. The critical withdrawal velocity was the maximum velocity where spray axis coincide with vertex.
과공정 Al-Si 합금의 분무성형-압출에 따른 미세조직 변화
라형용,이호인,김상균,석현광,이재철,신돈수 대한금속재료학회(대한금속학회) 1998 대한금속·재료학회지 Vol.36 No.10
Microstructural evolutions of both Si particles and matrix grains of hypereutectic Al-Si alloy were investigated by calculating temperature profiles within the preform during spray forming. Based on calculations, the cooling rates were observed to be relatively higher both at the bottom and the top than the inner regions of the preform along the rotation axis of rod. Such trends in temperatures resulted in size variations of Si particles within the preform. The size of Si particles varies from 3㎛ to 13.5㎛ with distance from the surface to the inner of the preform along the rotation axis of rod. Larger Si particles observed from the inner regions of the preform were found to be poly-crystals having irregular surface boundaries. However, such Si particles were fractured after extrusion, indicating a possibile means for fabricating hypereutectic Al-Si alloys with fine Si particles. In addition, the methodology for predicting the matrix grain size in the presence of small Si particles was also demonstrated.