차체경량화를 위한 반용융 단조기술의 적용

김낙수,윤종훈,임용택 한국소성가공학회 1999 고액공존성형 심포지엄 Vol.1999 No.10

역공학과 해석적 방법을 이용한 관재벌지시험에서의 관재물성치 결정

김낙수,김태준 대한기계학회 2003 大韓機械學會論文集A Vol.27 No.9

3차원 강소성 유한요소법을 이용한 링 로울링 공정의 해석

김낙수 대한기계학회 1990 大韓機械學會誌 Vol.30 No.3

3차원 강소성 유한요소법과 독특한 updating 방법으로 실험결과와 잘 일치하는 실용적인 프로그 램을 개발할 수 있었다. 몇 가지 해석결과의 예에서 알 수 있듯이 소재의 변형을 정확하게 예 측할 수 있고, 임의의 단면현상을 가진 로울에 대하여도 해석이 용이하였다. 링 로울링의 제작 공정을 3차원 강소성유한요소법으로 해석할 수 있고, 실험적으로 해석결과의 타당성을 결정지 음에 따라서, 링 로울링에 대한 연구결과는 보편적인 기대 이상으로 첨단산업분야에 기여할 수 있을 것으로 보여진다. 현재 링 로울링에 대한 국내에서의 관심은 비교적 적은 편이나, 항공우 주산업 분야중 부품제작분야 및 제반 기계공업분야 특히 소성성형가공 분야에서, 해석적 방법의 지속적인 개발 및 실험적 연구와 뒷받침은 궁극적으로 이 분야의 공정 및 소재 설계의 자동화 내지는 전산화로 이끌 것이며, 장차 이 분야를 국제적으로 주도해 나가고자 하는 데 필수적인 것으로 여겨진다.

Numerical analysis of internal flow and mixing performance in polymer extruder II: Twin screw element

김낙수,이재욱,김홍범 한국유변학회 2006 Korea-Australia rheology journal Vol.18 No.3

We analyzed the non-Newtonian and non-isothermal flow with Carreau-Yasuda viscosity model in co-rotating and counter-rotating twin screw extruder systems. The mixing performances with respect to the screw speed, the screw pitch, and the rotating direction have been investigated. The dynamics of mixing was studied numerically by tracking the motions of particles. The extent of mixing was characterized in terms of the deformation rate, the residence time distribution, and the average strain. The results showed that the high screw speed decreases the residence time but increases the deformation rate. Small screw pitch increases the residence time. It is concluded that the high screw speed increases the dispersive mixing performance, while the small screw pitch increases the distributive mixing performance. Co-rotating screw extruder has the better conveying performance and the distributive mixing performance than counter-rotating screw extruder with the same screw speed and pitch. Co-rotating screw extruder developed faster transport velocity and it is advantageous the flow characteristics to the mixing that transfers polymer melt from one barrel to the other barrel.

Numerical analysis of internal flow and mixing performance in polymer extruder I: Single screw element

김낙수,이재욱,김홍범 한국유변학회 2006 Korea-Australia rheology journal Vol.18 No.3

We analyzed the non-Newtonian and non-isothermal flow in a single screw extruder system and investigated the mixing performance with respect to the screw speed and the screw pitch. The viscosity of polymer melt was described with Carreau-Yasuda model. The mixing performance was computed numerically by tracking the motions of particles in the screw element system. The extent of mixing was characterized in terms of the deformation rate, the residence time distribution, and the strain. The results revealed that the high screw speed reduces the residence time but increases the deformation rate while the small screw pitch increases the residence time. It is concluded that the high screw speed increases the dispersive mixing performance and the small screw pitch increases the distributive mixing performance.

Optimum shape and process design of single rotor equipment for its mixing performance using finite volume method

김낙수,Jaeyeol Lee 한국유변학회 2009 Korea-Australia rheology journal Vol.21 No.4

We numerically analyzed flow characteristics of the polymer melt in the screw equipment using a proper modeling and investigated design parameters which have influence on the mixing performance as the capability of the screw equipment. We considered the non-Newtonian and non-isothermal flow in a single rotor equipment to investigate the mixing performance with respect to screw dimensions as shape parameter of the single rotor equipment and screw speed as process parameter. We used Bird-Carreau-Yasuda model as a viscous model of the polymer melt and the particle tracking method to investigate the mixing performance in the screw equipment and considered four mixing performance indexes: residence time distribution, deformation rate, total strain and particle standard deviation as a new mixing performance index. We compared these indexes to determine design parameters and object function. On basis of the analysis results, we carried out the optimal design by using the response surface method and design of experiments. In conclusion, the differences of results between the optimal value and numerical analysis are about 5.0%.

형단조 예비성형체 설계의 CAE

김낙수 대한기계학회 1992 大韓機械學會誌 Vol.32 No.6

형단조 제품의 예비성형체의 결정이 중요하며, 그 형상은 최종 제품의 설계 조건에 따라서 수 치적으로 결정될 수 있음을 알았다. 축대칭이나 평면 변형과 같은 2차원 해석이 필요한 제품의 경우에는 체계적인 방법으로 예비성형체의 모양을 결정할 수 있으며, 그 결과를 이용하여 일련의 단조 공정이 설계된다. 이러한 수치해석적 설계 방법은 단조에서 CNE의 근간이 되어 설계의 자동화에 직접적으로 기여할 수 있을 것이다. 이 분야에서 앞으로의 연구방향은 기존에 확립되어 있는 수치해석적 설계방법을 보편화하여 현장에서 사용하기 쉽도록 패키지화할 것과, 모형실험 또는 실제 공정을 통한 해석결과 및 설계를 검증할 것 등이다. 또한, 일반 3차원 형단조의 공정 해석도 활발하게 이루어져 복잡한 정밀 단조에 대한 설계 자동화도 연구되어야 할 것이다.

Minimizing the Axial Force and the Material Build-up in the Tube Flow Forming Process

김낙수,Kai Jin,김홍래 한국정밀공학회 2013 International Journal of Precision Engineering and Vol.14 No.2

An analysis method based on minimizing the axial force by the upper bound method was proposed to obtain the optimal attack angle of the roller in the flow forming process. And the method for minimizing axial force was verified effectively by FEM simulation. The axial force of the roller in the flow forming has an essential effect on producing material build-up and bulge ahead of the roller. The optimal attack angle should minimize the axial force of the roller and also avoid defects such as build-up or bulge effectively,improving the manufacturing accuracy and the surface quality of flow formed product. The possible defects like the material buildup and the spring back or the elastic recovery could be numerically simulated by the FEM. It was shown by the elastic-plastic FEM simulations that the attack angle resulting in the least magnitude of the axial force also resulted in the smallest amount of the material build-up. It is concluded that the simplified calculation of the attack angle is practically useful.

Optimal Design to Reduce the Maximum Load in Ring Rolling Process

김낙수,Kai Jin,김홍래 한국정밀공학회 2012 International Journal of Precision Engineering and Vol.13 No.10

Minimizing the maximum load on rolls in ring rolling process has been the most urgent demand in producing large rings made of high-strength material. With a view to meet the essential demand, the problem was solved by a novel process design, which respectively calculated the feed-rates of mandrel and axial rolls through optimum design. Based on the finite element simulation of ring rolling process by varying the feed-rates of the mandrel and axial rolls, an improved rolling schedule was established. The design of experiments via Taguchi method and the optimum design method such as Conjugate Gradient Method were used. The FE simulation was verified by comparison with experiment results. The optimized rolling schedule was suitable and reliable in the practical manufacture for both pure and radial-axial ring rolling process.

Study on Twisting and Bowing of Roll Formed Products Made of High Strength Steel

김낙수,Wan-gi Cha 한국정밀공학회 2013 International Journal of Precision Engineering and Vol. No.

Steel has been developed to have higher strength than ever before, especially for use of the lightweight structures of automobile. It needs to confirm spring back defects of cold roll forming of high strength steel, in which a sheet metal strip is gradually and successively bent into a desired profile. We developed a numerical analysis program based on the elastic-plastic finite element method to simulate roll forming of arbitrary cross sections. We applied augmented Lagrangian technique to solve contact problem between rolls and strip. Cross sections with different flange heights passing through three passes of roll stands have been experimented. The amounts of twisting and bowing occurred after roll forming were measured for both products made of mild steel and high strength steel, respectively. The performance of the developed FEA tool has been verified with measurements in terms of accuracy. The product of high strength steel showed more degrees of twisting and bowing than those of mild steel. We proposed a method to reduce the defects by compressing the web in thickness direction. It is confirmed using the verified FEA tool that the proposed method can reduce twisting and bowing of roll formed products significantly.