• 한국산학기술학회논문지
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• 제17권4호
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• pp.718-725
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• 2016

본 논문에서는 대형 선박의 판형 열교환기 등에 널리 이용되고 있는 순 티타늄 판재의 소성변형을 유한요소해석하기 위한 기초 데이터로서 순 티타늄 판재의 유동곡선을 평가하였다. 순 티타늄 판재의 프레스 가공 시에 판재에는 국부적으로 큰 소성변형이 발생하고 있다. 그러나 기존의 단축 인장실험에서 얻을 수 있는 소성변형률이 낮아서 티타늄 판재의 가공공정 설계를 위한 유한요소해석의 정밀도를 떨어뜨리는 경우가 있다. 본 연구에서는 큰 소성변형률 까지 안정적으로 성형이 가능한 유압벌지실험을 수행하여 재료의 소성변형에서 가공경화특성을 나타내는 유동곡선으로써 진응력-진변형률 선도를 구하였고 그 결과를 인장실험 결과와 비교하였다. 순 티타늄 판재의 유압벌지실험에서 재료의 변형률은 3D 디지털 영상상관법을 이용한 ARAMIS 시스템으로 실시간 측정된다. 이 유압벌지실험으로부터는 소성 변형률이 0.65 이상 까지도 안정적으로 재료의 소성유동곡선을 얻을 수 있었으며 그 결과는 Kim-Tuan 이 문헌 17[Y.S. Kim, J.H. In, Korean Acadmia-Ind. Coop. Soc.,(be in print), 2016] 의 연구에서 제안한 가공경화식으로 잘 핏팅됨을 알 수 있었다.

• 한국소성가공학회:학술대회논문집
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• 한국소성가공학회 2003년도 춘계학술대회논문집
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• pp.291-294
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• 2003

Ball indentation tests have been used to estimate the mechanical properties of materials by some investigators. In this study, load-depth curves from ball indentation tests have been analysed using the geometric conditions of ball indentation. Series of numerical calculations and experimental results showed that those curves could be simplified by linear functions. After linearizing the indentation curves, the estimation process of the flow properties became straight forward and the scatter of results could be drastically reduced.

• 한국에너지공학회:학술대회논문집
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• 한국에너지공학회 2002년도 춘계 학술발표회 논문집
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• pp.219-222
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• 2002

석탄연소 순환유동층 연소로에서 석회석을 이용한 SO$_2$의 제거는 이미 기술적으로 입증된 방법이다. 연소로에 투입된 석회석은 식(1)과 같은 소성반응을 거친 후 CaO로 변화하며 식(2)와 같은 황화(sulfation)반응에 의해 SO$_2$를 흡수하여 CaSO$_4$ 형태로 변화한다.(중략)

• 소성∙가공
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• 제22권6호
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• pp.323-327
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• 2013

In this paper, the flow lines as a function of product design as well as the forging process design are explored using typical application examples. The prediction of flow lines using metal forming simulation technology is introduced along with their characterization. Experimental studies have shown that the metal flow lines have a strong influence on the structural rigidity of the final product. In this study we present several typical applications. One example is the case of severely cut metal flow lines during machining, especially in the region where periodic contacting forces are applied. Another example is the case of abnormal distortion of flow lines which can cause too much elongation or hot shortness due to viscous heating in the region of distortion. A third example is the case of a macrosegregation region which needs to be controlled so it is not adjacent to the region where the force is applied in the use of the final component. An example of weight reduction for an automobile component with improved flow lines is also introduced. These typical applications can provide process engineers with the insight in designing automobile or mechanical components as well as in designing the manufacturing methods to produce various parts.

• 한국소성가공학회:학술대회논문집
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• 한국소성가공학회 2008년도 추계학술대회 논문집
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• pp.410-413
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• 2008

In this study, we compare the mechanical properties of forged and machined bushings for an excavator track chain. The manufacturing process is explained in detail together with the procedure of making the specimens. The longitudinal tensile strength and elongation and the radial ring compression strength are measured for this comparison. It has been shown that the forged is much better than the machined with regard to both longitudinal tensile strength and radial ring compression strength but that both are the same in terms of longitudinal elongation.

• 한국정밀공학회:학술대회논문집
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• 한국정밀공학회 1996년도 춘계학술대회 논문집
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• pp.546-550
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• 1996

A fully automatic computer simulation technique of axisymmetric multi-stage compound forging processes was presented in this paper. A penalty rigid-viscoplastic finite element method was employed together with an improved looping method for automatically remeshing with quadrilateral finite-elements only. An application example of six-stage axisymmetric forging processes involving one cold and two hot forging processes, two piercing processes and a sizing process was given with emphasis on automatically tracing the metal flow lines through the whole simulation.

• 소성∙가공
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• 제29권6호
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• pp.316-322
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• 2020

The flow stress curve is usually determined via uniaxial tensile or simple compression test. However, the flow stress curve up to high strain cannot be obtained using these two tests. This study presents a simple method for obtaining the flow stress curve up to high strain via FE analysis, a simple compression test, and an indentation test. In order to draw the flow stress curve up to high strain, the indentation test was carried out with the pre-stained specimen using the simple compression test. The flow stress curve of Al6110 was evaluated up to high strain using the proposed method, and the result was compared with the flow stress curve of the uniaxial tensile test of the initial material.

• 소성∙가공
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• 제14권9호통권81호
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• pp.798-803
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• 2005

In this paper, the six sigma scheme together with the rigid-viscoplastic finite element method is employed to obtain the optimal metal flow lines of a hot forging according to the six sigma processes, i.e., five steps such as define, measure, analyze, improve and control. Each step is investigated in detail to meet customer's requirements through improvement of product quality. A forging simulator is used for analysis of the metal flow lines of the hot forging, manufactured by a hot press forging machine, under various conditions of major factors determined at each step. The analyzed results are examined in order to reveal the effects of major factors on the metal flow lines and the formed shapes. The effects are then used to find an optimal process and the optimal process with die is devised and tested. The comparison between the required metal flow lines and the experiments shows that the approach is effective for optimal process design in hot forging considering metal flow lines.

• 소성∙가공
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• 제18권8호
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• pp.640-645
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• 2009

Recently, boss and rib test based on backward extrusion process was proposed to quantitatively evaluate the interfacial friction condition in bulk forming process. In this test, the tube-shaped punch with hole pressurizes the workpiece so that the boss and rib are formed along the hole and outer surface of the punch. It was experimentally and numerically revealed that the height of boss is higher than that of the rib under the severe friction condition. This work is focused on the effect of the punch design and flow stress on deformation pattern in boss and rib test. From the boss and rib test simulations, it was found that there is slight variation in both the heights of boss and rib according to the length of punch land, nose radius, and face angle. However the hole diameter of the punch and the clearance between the punch and die have a significant influence on the calibration curves showing the heights of the boss and rib. In addition, the effect of flow stress on the calibration curves was investigated through FE simulations. It was found that there is no effect of strength coefficient of the workpiece on the calibration curves for estimation of friction condition. On the other hand, the strain-hardening exponent of the workpiece has a significant influence on the calibration curve.

• Korean Chemical Engineering Research
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• 제40권6호
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• pp.746-751
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• 2002

석탄 연소기술에서 타 연소로에 비해서 유동층 연소는 황산화물과 질소산화물 배출을 줄이는 기술이다. 석회석의 소성으로 생성되는 CaO에 의한 황산화물의 제거와 저온 연소와 공기 다단계 주입에 의한 NOx를 줄일 수 있다는 것이 유동층 연소로의 큰 장점이지만, 상대적으로 $N_2O$의 배출은 매우 높다. $N_2O$는 지구온난화 가스일 뿐만 아니라 성층권내의 오존층을 파괴하는 물질이기도 하다. CaO는 $N_2O$ 분해를 위한 촉매 물질로 알려져 있다. 본 연구는 CaO를 충진시킨 고정층 반응기에서 CaO에 의한 $N_2O$의 분해특성에 관하여 수행하였으며, 유동층 연소온도와 가스조성에서 온도변화에 대한 $N_2O$의 분해특성, CaO 충진량의 변화와 $CO_2$, NO, $O_2$ 농도변화에 따른 $N_2O$ 분해특성에 관하여 수행하였다. 또한 실험 결과로부터 CaO표면에서 $N_2O$분해반응에 대한 반응속도식을 나타낼 수 있었다. 결과로서 온도가 증가함에 따라 $N_2O$ 분해반응이 증가하였으며, $CO_2$의 농도를 변화시킬 경우 $CO_2$ 농도가 증가할수록 $N_2O$ 분해반응이 감소하였다. NO 존재시와 비교하였을 때 $N_2O$의 분해반응이 감소함을 알 수 있었다. 반응속도론적으로 해석한 결과 $CO_2$ 농도에 대한 $N_2O$ 분해반응의 반응속도식을 다음과 같이 나타내었다. 본 연구 결과 CaO는 $N_2O$분해 반응에서 좋은 촉매 기능을 지니고 있음을 알 수 있었다. $\frac{d[N_2O]}{dt}=\frac{3.86{\times}10^9{\exp}(-15841/R)K_{N_2O}[N_2O]}{(1+K_{N_2O}[N_2O]+K_{CO_2}[CO_2])}$