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플로우포밍 스플릿 공정 시 맨드릴의 응력 해석을 통한 파손 원인 분석
원권희,홍승우,박희수,이상철,홍성진,현승균,김상열 한국소성∙가공학회 2022 소성가공 : 한국소성가공학회지 Vol.31 No.6
The flow forming process consists of a split process, a divide process, and a forming process. The split process is a forming process in which rollers radially permeate a simple disc-shaped forging material and split it in both directions to form a top-bottom bidirectional cup. It is advantageous for post-processing to deepen the forming depth in the split process but this characteristic causes the failure near the edge of the mandrel during the actual process. The split process was analyzed using Rigid Plastic FEM, and the stress analysis of the mandrel was conducted to find the cause of the failure. It was found that the failure occurred due to fatigue accumulation damage caused by repeated residual stress.
스플라인 맨드릴 플로우포밍을 위한 롤러 가공 깊이 최적화 연구
홍승우,원권희,장형석,윤승민,현승균,김상열 대한기계학회 2023 大韓機械學會論文集A Vol.47 No.4
Flow forming is a metal forming method that forms a thick circular preform whose thickness and length are determined by its rotation and the two-dimensional motion of the rollers used. In this study, the optimal conditions for the forming depth for splined mandrel flow forming were obtained by the comparative analysis of actual forming data and analyzed data obtained from the flow forming process of a wet clutch housing of a transmission. It required a structure that can transmit a high torque and achieve mechanical reliability owing to the characteristics of agricultural tractors. The large forming load generated during the flow forming process acted as a major factor in the abrasion of the rollers and the mandrel. Moreover, an imbalance was caused by the difference between the loads of the three rollers, producing product defects. Therefore, the forming depth of the rollers was optimized as a variable using the finite element method to minimize the load applied to each roller and determine the balanced condition for the loads of the three rollers. The results of the forming depth analysis yielded forming depths of 4.2 mm, 2.4 mm, and 2.2 mm for the A, B, and C rollers, respectively. These results were confirmed by comparative verification with actual forming data. 플로우포밍은 프리폼의 회전과 롤러의 2차원 운동을 통해 두꺼운 원형 프리폼을 얇고 길게 성형하는 금속 가공법 중 하나이다. 본 연구는 농기계 트렉터의 특성상 높은 토크를 전달할 수 있는 구조와 기계적 신뢰성이 요구되는 변속기의 습식 클러치 하우징을 성형하는 플로우포밍 공정에서 실제 가공 데이터와 해석 데이터를 비교분석을 통하여 가공 깊이 최적 조건을 구하였다. 플로우포밍 공정 중 발생하는 큰 성형 하중은 롤러와 맨드릴의 마멸에 주 인자로 작용하며, 3개의 롤러의 하중 차이로 불균형이 발생하여 제품 결함의 원인이 된다. 따라서 맨드릴고 각 롤러에 작용 하중을 최소화시키고, 3개의 롤러의 부하를 균형 있는 조건을 찾기 위하여 유한요소법을 이용하여 롤러의 가공 깊이를 변수로 최적화하였다. 가공 깊이 해석 결과는 A 롤러 4.2 mm, B 롤러 2.4 mm, C 롤러 2.2 mm로 나타나며, 실제 성형공정 데이터와 비교검증을 통하여 확인하였다.
이상철(Sangchul Lee),현재호(Jaeho Hyun),홍승우(Seung-Woo Hong),원권희(Kwon Hee Won),박희수(Heesoo Park),현승균(Soongkeun Hyun),김상열(Sang-Yeol Kim) 한국생산제조학회 2022 한국생산제조학회지 Vol.31 No.1
Self-piercing rivets (SPR) are manufactured using multistage cold heading of a constant length of steel wire rods. This study attempted to design molds for tolerable loading to material and make the metal flow of the SPR lines parallel and without cusp. During this process, beyond the existing virtual experiment, which was limited to the plastic deformation of the SPR material, the analysis of the molds’ stress, elastic deformation, and wear were simultaneously performed. This study mainly aimed to mimic the multistage cold process of the heading machine for manufacturing SPR using DEFORM (commercial finite element method software) and minimize differences between with manufacturing sites. Furthermore, deviating from the existing mold development process (shape design with trial and error), the development efficiency was maximized by the reduction of both the mold development period and the mold cost. Finally, the hardness homogenization of the manufactured SPR with a tempering finished was verified.