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남찬희(C. H. Nam),이민철(M. C. Lee),손일헌(I. H. Son),전만수(M. S. Joun) 한국소성가공학회 2014 한국소성가공학회 학술대회 논문집 Vol.2014 No.10
In this paper, plastic deformation of tiny initial defects on initial material surfaces is simulated using finite element method. First, the difficulty of the simulation is discussed from standpoint of mesh generation and remeshing. 2D predictions are compared to 3D predictions to supply a proper model for engineering solutions. The reason of the difference between axi-symmetric defect, that is, a ring-type and a cone-type defect is discussed. Cone-type defect and its variants in upsetting are traced to reveal their similarity and/or hetereogeneity with ring-type defect which can be traced by axi-symmetric approach. Based on the predictions and their discussions, a proper 2D analysis model is proposed for revealing the effect of surface defect on the product quality.
성형하중과 소성유동선을 고려한 멀티홀 팬케이크형 제품의 열간밀폐형단조공정의 최적화 설계
남찬희(C. H. Nam),오도협(D. H. Oh),류효연(H. Y. Ryu),전만수(M. S. Joun) 한국소성가공학회 2014 한국소성가공학회 학술대회 논문집 Vol.2014 No.10
In this paper, finite-element based approach to optimized process design is applied to reduce forming load and increase metal flow lines in fabricating a difficult-to-forge product of pancake shape with multi-holes. The process design is characterized by the internal pockets or cavities between material and die during the entire process, which can reduce the magnitude of hydrostatic pressure at the final stroke, leading to decrease in forming load. It is found that the cavity can also contribute to improving the soundness of metal flow lines especially around the die corners where chronic badly-distorted metal flow lines occurs in pancake forging of complicated shapes. A rigid-thermoviscoplastic finite element method is employed to predict the plastic deformation during the process with high accuracy.
남찬희(C. H. Nam),진호태(H. T. Jin),손일헌(I. H. Son),전만수(M. S. Joun) 한국소성가공학회 2014 한국소성가공학회 학술대회 논문집 Vol.2014 No.10
In this paper, two-dimensional finite element approach of prediction the plastic deformation of tiny pinhole defects on the initial bloom surface, which were formed during continuous casting process of the base material of bloom. The initial pinhole shapes of which plastic deformations are to be traced are assumed V-shaped and U-shaped. Two different kinds of pass schedule of consecutive rolling stages are assumed to investigate the defect closing or lapping behaviors, i.e., one pass schedule of two forward rolling stages and another pass schedule of reverse rolling stage after forward rolling stage. The dimensions of the processes and the sizes of pinholes are also assumed to reflect the actual three-dimensional rolling processes. It has been shown that most plastic deformation occurs at the entry side and lapped or closed defects slightly open when they pass through the exit side. It is noteworthy that the reverse rolling decreases the lapped defect formed in the previous pass, implying that there exists an optimized pass schedule design to minimize the surface defect.
블룸 압연공정 중 외부 기공의 압착에 의한 열연코일 결함 길이의 근사적 예측
남찬희(C. H. Nam),엄재근(J. G. Eom),이민철(M. C. Lee),손일헌(I. H. Son),전만수(M. S. Joun) 한국소성가공학회 2015 한국소성가공학회 학술대회 논문집 Vol.2015 No.5
In this paper, three-dimensional finite element approach of predicting the plastic deformation of tiny pinhole defects on the initial bloom surface, which are supposed to be formed during continuous casting process of the base material of bloom. The initial pinhole shapes of which plastic deformations are to be traced are assumed U-shape, based on the observation of pinholes found in the literature. The surface defect closing phenomena are simulated until defects are almost closed and assumption of uniform contraction is utilized to estimate the surface line defect.
난성형 고형상비 열간단조에서 성형하중 감소 최소화 목적의 프리폼 최적화 설계
남찬희(C. H. Nam),오도협(D. H. Oh),엄재근(J. G. Eom),전만수(M. S. Joun) 한국소성가공학회 2014 한국소성가공학회 학술대회 논문집 Vol.2014 No.5
In this paper, finite-element based approach to optimized preform design is applied to reduce forming load in fabricating a difficult-to-forge product of pancake shape. A successful hot forging process with optimized preform or blocker is developed for a pancake-type forging with many holes. The process is characterized by the internal pockets or cavities between material and die which can reduce the magnitude of hydrostatic pressure at the final stroke. Since the hydrostatic pressure and/or forming load increases drastically after the material fills the internal cavities and the increased forming load or hydrostatic pressure may lead to die fracture, sound metal flows are very important for success of the process design especially for pancake-type forgings with complicated faces. A thermoviscoplastic finite element method is employed to predict the plastic deformation during the process with high accuracy.
남찬희(C. H. Nam),우정욱(J. W. Woo),이익균(I. K. Lee),이중규(J. K. Lee),전만수(M. S. Joun) 한국소성가공학회 2013 한국소성가공학회 학술대회 논문집 Vol.2013 No.10
In this paper, effect of tiny initial surface defects including roughness, indentation, or scratch on product quality in drawing is investigated using finite element method. The defect is assumed axisymmetric, which is defined by cylindrical defect region and tapered region connecting the defect region and normal region. Various conditions of initial surface defects are considered, including defect depth, defect slope and defect length. To describe the plastic deformation of defect in detail during simulation, a local remeshing capability is applied. Based on the finite element predictions, defect disappearance maps are given, It has found out that defect disappearance is dependent deeply on the defect depth and defect length coupled with the defect slope.
김민철(M. C. Kim),남찬희(C. H. Nam),남태현(T. H. Nam),강석순(S. S. Kang),전만수(M. S. Joun) 한국소성가공학회 2014 한국소성가공학회 학술대회 논문집 Vol.2014 No.5
In this paper, finite element analysis of die wear phenomenon in hot forging of a partially heated material for T-shape product is conducted using a rigid-thermoviscoplastic finite element method with an Archard wear model. The entire process including partial heating process and two hot forging stages is dealt with. The predictions are compared with experiments in terms of die wear in a qualitative manner. The comparison shows a good agreement between the predictions and experiments.
허브베어링 조립체의 조립을 위한 회전단조 공정의 해석 모델
최무호(M. H. Choi),김민철(M. C. Kim),남찬희(C. H. Nam),전만수(M. S. Joun) 한국소성가공학회 2013 한국소성가공학회 학술대회 논문집 Vol.2013 No.5
In this paper, a finite element model of the rotary forging process for assembling a hub bearing assembly is presented. The analysis model is composed of a section of material with two artificial planes of symmetry, which is to reduce computational time taken in simulating the holistic process. The predictions at the mid-plane of the analysis models of 30°, 60°, 90° are compared to reveal the validity of the presented analysis model. They are also compared with the experiments in terms of the deformed shape.