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소성불안정조건을 이용한 FLSD의 관재액압성형에의 적용
허성찬(Seong-Chan Heo),김상우(Sang-Woo Kim),김정(Jeong Kim),강범수(Beom-Soo Kang) 대한기계학회 2005 대한기계학회 춘추학술대회 Vol.2005 No.5
During the tube hydroforming processes, failures such as buckling, necking, bursting, and etc. could occur because axial feeding and internal pressure is imposed simultaneously. The purpose of this research is to establish the necking criterion for prediction of forming limit. Especially, necking is closely related with the plastic instability criterion that is frequently used in prediction of forming limit for sheet metal. In this research, it is used that FLSD(Forming Limit Stress Diagram) using the application of the diagram to prediction of the necking phenomena in the tube hydroforming processes. The results of this investigation is available to estimate the failure of the material in tube hydroforming.
응력기반성형한계선도를 이용한 관재액압성형 부품의 성형한계 예측
허성찬(Seong-Chan Heo),김정(Jeong Kim),강범수(Beom-Soo Kang) 대한기계학회 2006 대한기계학회 춘추학술대회 Vol.2006 No.6
In tube hydroforming process, bursting is the most frequently occured failure mode among the major failures such as wrinkling, folding, buckling, bursting and so on. Forming limit diagram(FLD) is well known as a criteria for estimation of bursting failure in almost of sheet metal forming but it is dependent on strain path while stress based diagram is independent on it. Generally, tube hydroforming consists of three processes such as pre-bending, pre-forming, and hydroforming. It means that the strain paths of hydroformed materials are nonlinear. Therefore, forming limit stress diagram(FLSD) is more suitable to predict forming limit for hydroformed parts. In this study, FLSD is applied to estimate bursting failure for an engine cradle of an automobile part. Consequently, it is proved that application of FLSD to predict forming limit is available for tube hydroforming parts.
가변성형 공정에서 탄성 패드의 영향에 관한 수치적 연구
허성찬(Seong Chan Heo),서영호(Young Ho Seo),노학곤(Hak Gon Noh),구태완(Tae Wan Ku),강범수(Beom Soo Kang) 대한기계학회 2010 大韓機械學會論文集A Vol.34 No.5
가변성형공정에서는 형상 변형이 가능한 가변금형의 성형면을 고르게 형성하기 위하여 일반적으로 우레탄, 고무 등 같은 탄성체 패드를 가변금형과 소재 사이에 삽입하여 이용한다. 이에 본 연구에서는 이러한 탄성패드가 성형성에 미치는 영향에 대한 조사를 위하여 탄성체의 경도 및 두께를 주요 변수로 고려한 수치해석적 연구를 수행하였다. 탄성패드 소재로는 우레탄을 이용하였으며, 이의 물성 획득을 위한 압축시험을 수행하였고, 초탄성체 재료 모델로 가정하여 가변성형공정해석에 적용하였다. 탄성체의 경도와 두께의 변화에 따른 해석 결과로부터 성형 정확도를 조사하기 위하여 주방향의 단면형상을 비교하였으며, 목적형상에 대한 오차를 비교하였다. 이로부터 가변성형공정에 이용되는 탄성 패드가 적절히 선정되어야 함을 확인하였으며, 패드의 경도 및 두께 선정에 대한 기준을 제안하였다. In general, materials that can be used to form elastic pads, such as urethane and rubber, are often used in flexible forming processes by inserting the pads between a blank and flexible die for smoothing the forming surface that is formed by a reconfigurable die. In this study, the effects of the elastic pad on formability in the flexible forming process for sheet metals are investigated by performing numerical simulations. In the simulation, the hyperelastic material model is used, where the urethane elastic pads serve as elastic cushions. Case studies are carried out for elastic materials with different hardness values and thicknesses. The results are used to evaluate formability by comparing the configuration of the deformed blank and its major cross-sectional profiles. It is verified that the elastic pad used in the flexible forming process for sheet materials should be hard and that its thickness should be chosen appropriately.
허성찬(Seong Chan Heo),구태완(Tae Wan Ku),송우진(Woo Jin Song),김정(Jeong Kim),강범수(Beom Soo Kang) 대한기계학회 2010 大韓機械學會論文集A Vol.34 No.3
가변성형 공정에서 동일한 크기의 성형펀치 배열로 구성된 가변금형을 이용하는 경우 펀치의 크기가 일정하여 성형 가능한 곡률 반경이 제한되기 때문에 비교적 유연성이 낮다. 이에 본 연구에서는 가변금형의 유연성을 높이기 위하여 분할가변금형에 대한 개념을 제안하였다. 임의의 성형면을 형성하기 위하여 두 가지 크기의 펀치로 구성된 펀치 블록을 착안하였다. 상대적으로 큰 곡률 반경을 갖는 성형영역에 대해서는 크기가 큰 펀치 블록을 적용하였으며, 작은 곡률 반경을 갖는 성형영역에 대해서는 작은 크기의 펀치로 구성된 펀치 블록을 적용하였다. 해석적 연구를 토대로 성형된 제품의 단면 형상을 비교하였으며 이로부터 서로 다른 크기의 펀치 블록을 조합하여 구성한 분할가변금형을 이용한 판재의 성형공정이 비교적 복잡한 곡률 반경 분포를 갖는 곡면 가공에 적합함을 확인하였다. In general, the flexible forming die that has been used in the flexible forming process has the identical punch size; hence, its flexibility is relatively low because the range of allowable curvature radii is limited due to the uniform punch tip radius. Hence, a conceptual design of a sectional flexible die is presented for enhancing the flexibility of the forming process. Two punches of different sizes are used to configure the arbitrary forming surface. For a forming region with a relatively large curvature radius, a large punch array block is used; on the other hand, for the forming regions with small curvature radii, a small punch block is used. The cross-sectional profiles are compared with the target shape for evaluating the effectiveness of the process. Consequently, it is confirmed that the sectional flexible die can be used along with a combination of punch blocks of different sizes for manufacturing objective surfaces of complex shapes.
허성찬(Seong-Chan Heo),김정(Jeong Kim),강범수(Beom-Soo Kang) 대한기계학회 2007 대한기계학회 춘추학술대회 Vol.2007 No.5
Determination of loading conditions for tube hydroforming(THF) process that implies an amount of the increment in axial feeding and internal pressure for each step is one of the most important constituents at the process design level. On account of the fact that those design factors mentioned above are imposed simultaneously during the process, suitable loading conditions are required to obtain robust products without any failure such as buckling, necking, bursting and so on. In which, especially, bursting is well known as the most frequently occurred failure in general THF process. In this study, therefore, determination of the loading condition based on the adaptive method was carried out to obtain safe loading paths. In addition, forming limit curves are applied to evaluate the derived loading conditions by using the simulation results. Consequently, it is found that described method in this study for THF process design is useful and has a feasibility.
7톤급 연소기 챔버용 구리 개스킷의 체결하중 예측 및 구조 안정성 평가
허성찬(Seong-Chan Heo),유철성(Chul-Sung Ryu),최환석(Hwan-Seok Choi) 한국추진공학회 2012 한국추진공학회 학술대회논문집 Vol.2012 No.11
헤드부와 연소실부가 분리된 형태로 제작되는 7톤급 액체로켓 연소기 개발 시제의 기밀 조건에 대한 구조 안정성을 평가하였다. 기밀 소재로 이용된 구리 링의 소성변형을 고려하여 볼트 체결 하중을 예측하였다. 구리 소재를 강소성 재료로 가정한 성형해석을 수행하였으며 기밀을 위해 요구되는 볼트의 규격을 제안하였다. 산출된 볼트 체결 하중에 대한 연소기 체결부의 구조해석을 수행하여 구조 안정성을 확인하였다. Structural stability of a 7-tonf class thrust chamber which consists of separable mixing head and combustion chamber had been investigated for the metal-sealed condition using bolt clamp. A copper gasket was used as the sealing material and its plastic deformation behavior was considered. Bolt clamp load was estimated from the metal forming simulation of the clamp situation and the required bolt mechanical specification was proposed. Finally, numerical simulation of the assembled thrust chamber subjected to the bolt clamp load was conducted to verify the structural integrity of the combustion chamber.
서영호(Young-Ho Seo),허성찬(Seong-Chan Heo),구태완(Tae-Wan Ku),송우진(Woo-Jin Song),김정(Jeong Kim),강범수(Beom-Soo Kang) 한국소성가공학회 2011 한국소성가공학회 학술대회 논문집 Vol.2011 No.5
In this study, the dimple forming process was consider for dimple type heat exchanger to increase a heat exchange efficiency within Nuclear power plant. However, it is difficult to manufacture the rectangular tube with dimpled type structure because it experiences too much strain around the rectangular tube surface during the forming process. Accordingly, a numerical simulation for forming process of non-symmetric dimple shape on a thin sheet metal was carried out. Also, a theoretical forming limit curves were proposed as criteria of formability evaluation. It is found that the designed process has robustness and feasibility to safely manufacture the dimpled rectangular tube.
가변스트레치성형 설계변수와 성형오차에 대한 통계적 연구
서영호(Young-Ho Seo),허성찬(Seong-Chan Heo),김정(Jeong Kim),강범수(Beom-Soo Kang) 대한기계학회 2010 대한기계학회 춘추학술대회 Vol.2010 No.11
A flexible stretch forming process is an innovative manufacturing technology for sheet metal forming. It replaces the conventional solid dies with a set of height-adjustable discrete punches, called a flexible die. Then the flexible stretch forming process is useful in a small quantity batch production because of a various shape change of the flexible die. In this study, design parameters, which are punch size, objective curvature radius and elastic pad thickness, were quantitatively evaluated to find out its influence to formability of formed sheet plate using regression analysis. Forming simulations to obtain a shape error were planned and conducted by a three-way factorial design. Consequently, a regression equation was deducted and will use in flexible die design stage to estimate the shape error.
디젤 자동차용 딤플 사각 튜브형 EGR Cooler 의 열교환기 효율에 관한 연구
서영호(Young-Ho Seo),허성찬(Seong-Chan Heo),구태완(Tae-Wan Ku),송우진(Woo-Jin Song),김정(Jeong Kim),강범수(Beom-Soo Kang) 대한기계학회 2008 大韓機械學會論文集B Vol.32 No.10
In this study, the investigations on the dimpled type Exhaust Gas Recirculation (EGR) cooler have been focused on the high heat exchanger efficiency. To overcome low heat exchanger efficiency of general EGR cooler, the dimpled type EGR cooler was developed. It was ensured the improvement of the performance of the dimpled type EGR cooler related to the heat exchange based on a series of the experiment. These results were caused by the increase of thermal surface area in accordance with the dimple’s one. The estimation model of the heat exchanger efficiency using the Effectiveness-NTU method was also developed in order to verify the validity of experimental result. Also, the program for the estimation of the heat exchanger efficiency on the EGR cooler with regard to the dimpled tube shape was developed. Resultantly, it was confirmed that the dimpled type EGR cooler could be served better performance than the conventional one in view of the heat exchanger efficiency.