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보스-리브 시험 시 펀치 형상 및 마찰 조건데 따른 변형 양상에 대한 연구
윤여웅(Y. W. Yun),강성훈(S. H .Kang) 한국소성가공학회 2009 한국소성가공학회 학술대회 논문집 Vol.2009 No.10
Recently, boss and rib test based on backward extrusion process was proposed to quantitative 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 friction condition 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 heights of the boss and rib. In addition, the effect of flow stress was also investigated on the deformation pattern through FE simulations.
연성파괴에 기반한 다단 디프드로잉 및 아이어닝 공정에 의한 알루미늄 라이너 개발
윤여웅(Y. W. Yun),강성훈(S. H. Kang),윤춘기(C. K. Yun),이정환(J. H. Lee) 한국소성가공학회 2009 한국소성가공학회 학술대회 논문집 Vol.2009 No.10
In this work, finite element investigations were carried out to manufacture a seamless aluminum liner without crack generation using four-stage deep drawing followed by two-stage ironing process. In order to predict the crack generation during the liner manufacturing process, the Normalize Cockroft-Latham(NCL) which is one of ductile fracture criteria was adopted. In addition, the tensile tests were carried out to obtain the critical value of NCL by comparing the experimental and FE simulation results. From this, various case studies based on FE simulation were carried to obtain the optimum die designs which can prevent the crack generation during ironing processes. Finally, the aluminum liner was successfully made using obtained die designs so that requirements were met in terms of thickness and height of the liner.
강성훈(S. H. Kang),윤여웅(Y. W. Yun),이영선(Y. S. Lee) 한국소성가공학회 2009 한국소성가공학회 학술대회 논문집 Vol.2009 No.5
With the recent increase in the demand for the net-shape forming, numerical simulations are being commonly adopted to increase the efficiency and effectiveness of design of bulk metal forming processes. Proper consideration of tribological problems at the contact interface between the tool and workpiece is crucial in such simulations. In other words, lubrication and friction play important roles in meta forming by influencing the metal flow, forming load and die wear, In order to quantitatively estimate such friction condition or lubricant characteristic, the constant shear friction model is widely used for bulk deformation analyses. For this new friction testing method base on the forward or backward extrusion process is proposed to predict the shear friction factor in this work. In this method, the tube-shaped punch pressurizes the workpiece so that the heights at the center and outer of punch(or mandrel) become different according to the friction condition. That is, the height at the center of punch is higher than that at the outer of the punch when the friction condition at the contact interface is severe. From this founding, the proposed friction testing method can be applied to effectively evaluate the friction condition in bulk meta forming processes.