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황세준(Sejoon Hwang),박원규(Warngyu Park) 한국자동차공학회 2007 한국자동차공학회 춘 추계 학술대회 논문집 Vol.- No.-
While stamping process, air may be trapped between die and blank and it builds up high pressure. This induces the imperfections on the blank surface and makes extreme high tonnage of punch required to reach home position. To prevent these problems, the air ventilation holes are drilled through the die. But, most of die makers drill air ventilation holes excessively on trial and error basis. The present work has developed a simplified mathematical formulation for computing the pressure of air pocket at given cross-sectional area of air ventilation holes and the pressure of air pocket was compared to commercial CFD code and experiments. The pressure was well agreed with the result of CFD code and experiments. The present work could also calculate the optimum cross-sectional area of the air ventilation hole not to exceed the prescribed maximum pressure of air pocket by using the Bisection method.
황세준(Sejoon Hwang),박원규(Warngyu Park),김철(Chul Kim),오세욱(Sewook Oh),조남영(Namyoung Cho) 한국유체기계학회 2006 유체기계 연구개발 발표회 논문집 Vol.- No.-
In sheet metal forming process using press and draw die some defect can be made because of the high pressure of air pocket between draw die and the product. The purpose of this study is to develop a program to decide an optimal combination of air vent hole size and number to prevent those defect on product. The air inside air pocket is considered as ideal gas and the compression and expansion is assumed as isentropic process. The mass flow is computed in two flow condition: unchocked and chocked condition. The present computation obtains required cross-sectional area of air vent hole for not exceeding the user specified pressure such as the pressure for yielding strength of the product or the pressure for unchocked flow. To validate the program the present results are compared with the results of other researchers and commercial CFD code.