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유한요소법을 이용한 냉간 단조품의 연성 파괴 및 결함 분석에 대한 연구
정현철(H. C. Jung),김태호(T. H. Kim),최정묵(J. M. Choi),이영선(Y. S. Lee) 한국소성가공학회 2012 한국소성가공학회 학술대회 논문집 Vol.2012 No.5
In large plastic deformations, ductile fracture is a significant problem in metal forming processes. So many researches of ductile fracture have been studied to predict and to solve the failure of products. The chevron crack is one of the most representative defects on cold extrusion process. Therefore, it is important to identify the cause of central burst which is difficult to discover in production processes. The following studies were carried to determine internal defects of the drive shaft product occurred chevron cracks. In order to get critical damage value (CDV), the results of compression test using notched cylinder specimens are compared with that of FEM analysis. Also extrusion processes for products were analyzed by FEM to investigate the effect of CDV. After then the cause of the central burst and solutions are presented.
피라미드 형상의 PCM 코어 단위 셀의 압축 및 전단특성에 관한 해석적 연구
정현철(H. C. Jung),김상우(S. W. Kim),이영선(Y. S. Lee),강범수(B. S. Kang) 한국소성가공학회 2010 한국소성가공학회 학술대회 논문집 Vol.2010 No.5
A sandwich panel which is comprised of truss cores faced with solid face sheets is lightweight and multi-functional. So it is widely used to not only structural material but also heat transfer media in transportation field such as airplane, train and vessel. There are various core topologies such as pyramidal and tetrahedral truss, square honeycombs and kagome truss. The study focused on analytical approach to optimize compression and shear quality of the unit cell of PCM with pyramidal configuration. With various unit cell models which have the same core weight per unit area but different truss member angle, analytical solution for effective stress (σ, τ), peak stress (σpeak, τpeak) by yielding and buckling, relative density (Pc) and effective stiffness (E, G) have been computed and compared each other. With this approach, the most optimal core configuration was predicted. The result has become the efficient guidelines for the design of PCM core structure.
예비성형체의 형상과 잔류응력이 금형에 미치는 영향에 관한 연구
정현철(H. C. Jung),이영선(Y. S. Lee),김상우(S. W. Kim) 한국소성가공학회 2012 한국소성가공학회 학술대회 논문집 Vol.2012 No.5
Former forging processes by horizontal type press are widely used in mass production of automotive parts such as screws and bolts that require high speed and productivity. The multi-stage former forging enables continuous production because it can combine several processes divided individually into a sequential process by one die system. For continuous production, winded wires go through the rolling process for straightening and shear cutting process. Such pre-form and deformation history may affect the accuracy of product and die life. In this study, in order to investigate the effect of preform shape and residual stress on die stress, rolling and shear cutting process were analyzed by FEM. After then former forging process and die stress analysis were performed and the results were discussed.
정현철(H. C. Jung),이영선(Y. S. Lee),강범수(B. S. Kang) 한국소성가공학회 2011 한국소성가공학회 학술대회 논문집 Vol.2011 No.5
The high production rate and low material consumption are the best advantage of die forging process. Especially, many kinds of gears such as spline, bevel and spur gear which comprised automotive transmissions and differential gear component have been researched to manufacture with high mechanical properties. Despite many researches, helical gear is difficult to control the shape and to improve the accuracy of dimensions due to the helix angle. Also it couldn’t apply in real industrial field due to die failure by the high forming load and reduced tool life. In this paper, some die shapes for helical gear by cold extrusion process were proposed to improve the accuracy of dimensions and to increase tool life using FEM. The results of each condition such as the forming load and burr were compared to find the optimal condition and the effect on the different inlet angles of tooth shape. After then the die stress on changes in the shape of tooth from optimal inlet angle and mesh density was analyzed and compared by 1 st principle stress.
정현철(H. C. Jung),강범수(B. S. Kang),강성훈(S. H. Kang),이영선(Y. S. Lee) 한국소성가공학회 2011 한국소성가공학회 학술대회 논문집 Vol.2011 No.10
Many kinds of forged gears have been studied to improve mechanical properties of gear and dimensional accuracy under the elastic recovery and heat treatment process. At the result, many gears have been produced by cold forging such as spur, bevel and spline gear. However, cold forged helical gears have not been widely used due to difficulty of dimensional accuracy control. In the production of products using a cold forging process may affect the quality and accuracy due to high strain, residual stress and elastic deformation of the product. In this study, machined and forged products before and after heat-treated have been compared involute curve of tooth. And residual stress due to heat treatment was compared to analyze the effect of dimension variations.